Order PATELLOGASTROPODA Lindberg, 1986

Diagnostic characters: 1) anteriorly pointed shell apex, 2) symmetrical protoconch, 3) shallow pallial cavity restricted to head region, 4) operculum absent in post-larval stage, 5) horseshoe-shaped shell muscle that is constricted into bundles and connected anteriorly by pallial muscle, 6) shell muscle penetrated by blood vessels from visceral sinus, 7) retractile pallial tentacles, 8) eyes within cephalic tentacles, 9) open eyes without vitreous body, 10) symmetrically paired osphradia of "wart-organ" type on pallial floor (absent in Lepetidae, Acmaeidae, and Neolepetopsidae), 11) ctenidium post-torsional left only (in Acmaeoi-dea), 12) ctenidium (if present) lacking skeletal rods, 13) hypobranchial gland absent, 14) secondary circumpallial gills (in Patelloidea and some lottiids), 15) single bilamellate, double-layered jaw, 16) anterior wings of jaw associated with inner lips, 17) posterior wings of jaw bound to odontophore, 18) licker well developed, 19) dorsal protractor muscles of odontophore present, 20) ventral approximator muscle of odon tophore cartilages two-layered, 21) transverse labial muscles present, 22) docoglossate (= stereoglossate) radula that is longitudinally inflexible on bending plane, 23) greatly reduced or completely lost central tooth, 24) lateral teeth with broad bases firmly fixed on basal plates (except Lepetidae and Neolepetopsidae), 25) mid-esophagus with lamellar folds, 26) simplification of stomach (loss of gastric shield and gastric caecum; reduction of sorting area), 27) single auricle, 28) rectum not passing through pericardium or ventricle, 29) muscular bulbous aorta within pericardium, 30) two unequal kidneys (smaller left and much larger right), 31) gonoduct extending from left side and connected to right kidney, 32) labial ganglia inter connected by labial commissure, and 33) statocysts on outer sides of pedal ganglia.

Included taxa: Patellina von Ihering, 1876, and Lepetopsina McLean, 1990.

Suborder PATELLINA von Ihering, 1876

Diagnostic characters: 1) radular teeth articulation absent, and 2) radula mineralized with magnetite.

Included taxa: Patelloidea Rafinesque, 1815; Lepetoidea Dall, 1869; and Acmaeoidea Forbes, 1850. Lindberg (1988 a, c) assumed paedomorphic trends within Patellogastropoda from Patellidae to Lottiidae: (i) reduction of body size, (ii) reduction in number of radular teeth, (iii) reduction in complexity of gut, and (iv) evolution of reproductive trait from K- to r-strategist. Similarly, the radular teeth show trends from thin complex to thick simple basal plates, and from broad to narrow marginal field (Lindberg, 1986 a).

Superfamily PATELLOIDEA Rafinesque, 1815

Diagnostic characters: 1) long circumpallial tentacles, 2) anterior pallial streaks present, 3) osphradia present, 4) 3 major odontophoral cartilages (anterior, anterolateral, and posterior pairs), 5) pluricuspid lateral teeth, 6) licker lamellate, 7) basal plates complexly sculptured, 8) marginal field of radula broad, 9) retractor muscles of subradular membrane ventrally fused, 10) median protractor muscles of subradular membrane asymmetrical, and 11) median tensor and retractor muscles of radular sac present.

Included taxa: Patellidae Rafinesque, 1815, and Nacellidae Thiele. 1891. Lindberg (1988 a) and Lind berg and Hedegaard (1996) considered an independent lineage for Patellidae within Patellogastropoda be cause of the absence of an outermost prismatic shell layer. However, a monophyletic relationship between Nacellidae and Acmaeoidea (Suborder Nacellina Lindberg, 1988) is not anatomically supported in this study, and therefore, the superfamily Patelloidea are here re-defined to include Patellidae and Nacellidae. Two families are united by many synapomorphies listed above.

Family Patellidae Rafinesque, 1815

Diagnostic characters: 1) 4-6 shell layers composed of crossed-foliated, crossed-lamellar and/or complex erossed-lamellar structures [= MacClintock's (1967) groups 6-10], 2) circumpallial gills continuous anteriorly, 3) anterior and lateral pallial streaks present, 4) radula formula 3-(1+2)-1/0-(2+1)-3, 5) at least 3 pairs (anterior+posterior+anterolateral) of odontophoral cartilages, 6) two pairs of long salivary ducts (in Patella), 7) gut configuration simple to complex, and 8) efferent pallial vessel left only.

Included taxa: Patella Linnaeus, 1758, and Helcion Montfort, 1810. The central tooth was reported as lost in British species of Patella (Jones et al., 1984) but it is clearly present in Japanese species (Sasaki et al., 1994).

Family Nacellidae Thiele, 1891

Diagnostic characters: 1) 4 shell layers (prismatic + foliated+myostracal +foliated) in Nacella [= MacClintock's (1967) group 11] or 5 shell layers (prismatic+foliated+crossed-lamellar+myostracal + foliated) in Cellana [= MacClintock's (1967) groups 12-14], 2) circumpallial gills interrupted anteriorly, 3) anterior pallial streak present, but lateral pallial streak absent, 4) radular formula 3-2-1-2-3, 5) labial carti lages in addition to 5 pairs (anterior + posterior + anterolateral+ventrolateral+posterodorsal) of odonto phoral cartilages, 6) single pair of long salivary ducts, 7) gut configuration complex, and 8) characteristic pathways of efferent pallial vessels entering pericardium from both right and left sides independently.

Included taxa: Cellana H. Adams, 1869, and Nacella Schumacher, 1817.

Superfamily LEPETOIDEA Dall, 1869

Family Lepetidae Dall, 1869

Diagnostic characters: 1) 5 shell layers (prismatic + foliated+crossed - lamellar + myostracal+crossed-lamellar) [= MacClintock's (1967) group 15], 2) circumpallial tentacles greatly reduced, 3) pallial streaks absent, 4) oral lappets present, 5) ctenidium and secondary gills absent, 6) osphradia and osphradial ganglia absent, 7) radular formula 2-0-1-0-2 with fusion of central and lateral into single complex, 8) basal plates absent, 9) 2 pairs (anterior and anterolateral) of odontophoral cartilages, 10) obliquely tubular salivary glands without duct, and 11) gut configuration complex.

Included taxa: Lepeta Gray, 1847; Bathylepeta Moskalev, 1977; lothia Forbes, 1849; Limalepeta Moskalev, 1977; Maoricrater Dell, 1956; Cryptobranchia Middendorff, 1851; Propilidium Forbes and Hanley, 1849; and Sagamilepeta Okutani, 1987 (Vaught, 1989). Genera are defined primarily on radular characters (Moskalev, 1977; Okutani, 1987). Anatomy of Lepeta, lothia and Propilidium was summarized by Angerer and Haszprunar (1996).

This family has been allocated to the superfamily Acmaeoidea together with Acmaeidae and Lottiidae (Lindberg, 1988 a; Lindberg and Hedegaard, 1996), but anatomical characters do not support their mono-phyly. Because pallial and radular characters (ctenidium, central tooth, and basal plates) support clear separation from "Acmaeidae plus Lottiidae," this family is here treated as independent superfamily.

Superfamily ACMAEOIDEA Forbes, 1850

Diagnostic characters: 1) short circumpallial tentacles, 2) pallial streaks absent, 3) ctenidium present, 4) radular formula typically 2/1/0-3-0-3-2/1/0,4) well-developed, simple basal plates, 5) simple licker, and 6) 2 pairs (anterior and anterolateral) of odontophoral cartilages.

Included taxa: Acmaeidae Forbes, 1850, and Lottiidae Gray, 1840.

Family Acmaeidae Forbes, 1850

Diagnostic characters: 1) 5 shell layers (prismatic+foliated+crossed-lamellar+myostracal+crossed- lamellar) in Acmaea and Pectinodonta (Lindberg and Hedegaard, 1996) [=MacClintock's (1967) group 15], 2) oral lappets present, 3) osphradium absent, 4) radular formula 0-3-0-3-0 (Acmaeinae) or 0-1-0-1-0 (Pecttnodontinae) with 3 basally fused cusps, 5) radula arranged in inverted-V configuration, 6) well-developed basal plates with anteriorly projected outer corner, 7) obliquely tubular salivary glands without ducts, and 8) gut configuration complex.

Included taxa: Members are allocated to two subfamilies (Marshall, 1985 b; Lindberg, 1986 b): (1) Acmaeinae Forbes, 1850 (Acmaea Eschscholtz, 1833), and (2) Pectinodontinae Pilsbry, 1891 (Pectinodonta Dall, 1882; Cerradonta Okutani, Tsuchida, and Fujikura, 1992; and Bathyacmaea Okutani, Tsuchida, and Fujikura, 1992). Niveotectura, that has been placed in Lottiidae, is anatomically more closely related to the members of this family in view of pallial character (absence of osphradium), gut morphology (salivary glands and complexly folded stomach), and a radula especially similar to Acmaea mitra (Habe, 1944).

Family Lottiidae Gray, 1840

Diagnostic characters: 1) osphradia present, 2) radular formula 0/1/2-3-0-3-2/1/0, 3) radular teeth in stepped configuration (except Rhodopetala and Erginus), 4) a pair of long salivary ducts, 5) stomach C- shaped, and 6) 4 intestinal loops.

Included taxa: Three subfamilies are defined mainly on the basis of shell structure and radular characters (MacClintock, 1967; Ponder and Creese, 1980; Lindberg, 1981 a, b, 1986 b, 1988 a, b, 1990; Lindberg and McLean, 1981; Lindberg and Vermeij, 1985; Sasaki and Okutani, 1993 a, b, 1994 a, b).

(1) Rhodopetalinae Lindberg, 1981 (Rhodopetala Dall, 1921): 1) shell composed of 5 layers (prismatic +foliated+crossed-lamellar+myostracal+complex crossed-lamellar) [=MacClintock's (1967) group 12], and 2) radular formula 0-3-0-3-0.

(2) Patelloidinae Chapman and Gabriel, 1923 (Patelloida Quoy and Gaimard, 1834 and Potamacmaea Peile, 1922): 1) shell consisting of 4 layers (prismatic+crossed-lamellar + my ostracal+crossed-lamellar) [= MacClintock's (1967) group 2], 2) radular formula 2-3-0-3-2, and 3) well-developed, spoon-like marginal teeth. Inclusion of Erginus Jeffreys, 1877 (=Problacmea Golikov and Kussakin, 1972) and Niveotectura Habe, 1944 within this subfamily is suggested by characters of shell structure but anatomically problematic.

(3) Lottiinae Gray, 1840: 1) fibrous structure present, 2) radular formula 0/1-3-0-3-0/1, and 3) marginal teeth vestigial, lost ontogenetically, or totally absent. Circumpallial secondary gills developed inde-pendently in some species of Lottia, Scurria, and Tectura within this subfamily (McLean and Lindberg, 1981; Lindberg, 1988 a: fig. 2). Based on a difference in shell structure, this subfamily can be divided into three groups: (i) Lotiiini (Lottia Gray, 1833; Tectura 1847; and Nipponacmea Sasaki and Okutani, 1993) with 5 shell layers (thin prismatic+thick fibrous+crossed-lamellar+myostracal+crossed-lamellar) [= MacClintock's (1967) group 1]; (ii) Scuriini (Scurria Gray, 1847 and Disscurria Lindberg, 1986) with 5 shell layers (thick prismatic+thin fibrous+crossed-lamellar+myostracal+crossed-lamellar) [= MacClintock's (1967) group 3]; and (iii) "Notoacmea -group" (e.g. Notoacmea, Iredale, 1915 and Atalacmea Iredale, 1915) with 6 shell layers (prismatic+fibrous+crossed-lamellar+crossed-lamellar+myostracal+crossed-lamellar) [= MacClintock's (1967) groups 4+5].

Suborder LEPETOPSINA McLean, 1990

Diagnostic characters: 1) articulation of radular teeth, and 2) non-mineralized radula.

Included taxa: Lepetopsoidea McLean, 1990

Superfamily LEPETOPSOIDEA McLean, 1990

Family Neolepetopsidae McLean, 1990

Diagnostic characters (based mainly on Eulepetopsis): 1) foliated structure present, 2) circumpallial tentacles short, 3) oral lappets present, 4) eyes absent, 5) anterior pallial streaks present, 6) ctenidium absent, 7) osphradium absent, 8) 3 pairs of odontophoral cartilages, 9) radular formula 2-(1+2)-1-(2+1)-2, 10) central tooth well-developed, 11) absence of basal plates in radula, 12) salivary glands present, 13) mid-esophagus not affected by torsion, 14) stomach C-shaped, and 15) 3 intestinal loops.

Included taxa: The extant members include three genera: Neolepetopsis McLean, 1990; Eulepetopsis McLean, 1990; and Paralepetopsis McLean, 1990. These limpets were previously called "hot-vent group-C" (Hickman, 1983) or "symmetrical limpets" (McLean, 1985 b). Anatomical descriptions were given by Fretter (1990) and McLean (1990 b).

Order VETIGASTROPODA Salvini-Plawen, 1980

Diagnostic characters: 1) columnar nacreous structure (except Lepetodriloidea, Fissurelloidea, Scis-surellidae, Tricoliinae, Phasianellinae, Halistylinae, and Skeneidae), 2) micropapillae on tentacles (except Pleurotomarioidea, Fissurelloidea and Lepetodriloidea), 3) epipodial tentacles, 4) epipodial sense organs, 5) ctenidial axes attached by afferent and efferent membranes to mantle skirt (except Pleurotomariidae and Haliotidae lacking afferent membrane), 6) ctenidial axes and lamellae both with skeletal rods, 7) bursicles on efferent side of ctenidial leaflets (except Mikadotrochus and Lepetodrilus), 8) osphradium(-a) on efferent ctenidial membrane, 9) paired hypobranchial glands, 10) fimbriate anterior edge of jaws (except some trochoids), 11) posterior depressor muscles of odontophore, 12) radular formula typically n-5-l-5-n, 13) posterior retractor muscles of radular sac present (except Anatoma and Lepetodrilus), 14) ramified salivary glands with longitudinal slit-like openings to buccal cavity (except Lepetodrilus), 15) salivary ducts absent, 16) expanded esophageal pouches with papillate glands, 17) spiral gastric caecum (reduced in limpet form), 18) rectum penetrating ventricle, 19) paired auricles, 20) two kidneys of different structure and function, 21) left kidney modified into papillary sac (degenerated in Fissurellidae), 22) gametes released through right kidney, 23) labial ganglia and commissure absent, 24) scalariform pedal cords, and 25) statocysts on anterodorsal sides of pedal ganglia.

Included taxa: Zeugobranchia von Ihering, 1876 (Pleurotomarioidea Swainson, 1840; Haliotioidea Rafi-nesque, 1815; Fissurelloidea Fleming, 1882; and Scissurelloidea Gray, 1847) and Trochoidea Rafinesque, 1815; Lepetodriloidea McLean, 1988; and Seguenzioidea Verrill, 1844.

Superfamily PLEUROTOMARIOIDEA Swainson, 1840

Family Pleurotomariidae Swainson, 1840

Diagnostic characters: 1) pallial tentacles absent, 2) papillate oral disk, 3) open eyes with vitreous body, 4) eye stalks absent, 5) cephalic lappets absent, 6) epipodial flaps with numerous epipodial sense organs, 7) tentacles non-papillate, 8) afferent ctenidial membrane absent, 9) bursicles present in Perotrochus (Hasz-prunar, 1987 c) but absent in Mikadotrochus, 10) accessory pair of hypobranchial glands present, 11) uncu-ticularized jaws, 12) radular formula (6-10+n+11-21)+(24-26+3-4)+1+(3-4+24-26)+(11-21+n+6-10) (Hickman, 1984 c), 13) asymmetrical arrangement of radular teeth (direction of skewness infras-pecifically variable), 14) asymmetrical central tooth, 15) smaller inner laterals and larger outer laterals ("lamellate teeth"), 16) three types of teeth in marginal field, i.e. sickle-shaped teeth, filament-ripped teeth (so-called bristle teeth representing "hystricoglossate" condition of Hyman, 1967), and paddle-shaped teeth (Hickman, 1984 c), 17) voluminous U-shaped stomach, 18) multispiral gastric caecum, 19) enlarged uro-genital papilla, and 20) visceral loop originating from cerebropleural connectives (not from pleural ganglia).

Included taxa: Entemnotrochus Fischer, 1885; Mikadotrochus Lindholm, 1927; and Perotrochus Fischer, 1885.

Superfamily HALIOTOIDEA Rafinesque, 1815

Family Haliotidae Rafinesque, 1815

Diagnostic characters: 1) shell with several holes, 2) three pallial tentacles, 3) open eyes with vitreous body, 4) eye stalks present, 5) cephalic lappets present, 6) enlarged right and thin left shell muscles, 7) circumpedal epipodial tentacles, 8) tentacles papillate, 9) afferent ctenidial membrane absent, 10) asymmetrical disposition of central tooth, 11) outermost lateral teeth not enlarged, 13) stomach U-shaped, 14) multis-piral gastric caecum, and 15) urogenital papilla not enlarged.

Included taxa: Haliotis Linnaeus, 1758, and thirteen subgenera (or genera) (Vaught, 1989).

Superfamily FISSURELLOIDEA Fleming, 1882

Diagnostic characters: 1) nacreous layer absent, 2) pallial tentacles absent, 3) cephalic lappets absent, 4) tentacles non-papillate, 5) hypobranchial gland lying around mantle-slit/hole area (or absent), 6) greatly reduced left kidney (but same histology as papillary sac of other Vetigastropoda; Andrews, 1985), 7) presence of anal gland (Haszprunar, 1989 a), and 8) gonoduct opening into right renopericardial duct, not directly into right kidney.

Included taxa: Fissurellidae Fleming, 1822, and Clypeosectidae McLean, 1989. Their diagnostic characters were given by McLean (1989 b) and Haszprunar (1989 a).

Family Fissurellidae Fleming, 1822

Diagnostic characters: 1) shell pores formed by canal structure (Reindl and Haszprunar, 1994, 1996), 2) mantle margin three-folded (Stasek and McWilliams, 1973) in contrast to the general gastropod two-folded scheme, 3) closed eyes, 4) eye stalks present, 5) unique hook-shaped termination of shell muscle present in Emarginulinae, but absent in Pissurellinae (e.g. MacClintock, 1963; McLean, 1984 a), 6) many triangular epipodial tentacles (vestigial in Macroschisma), 7) epipodial sense organs at ventral sides of epipodial tentacles, 8) radula strikingly asymmetrical (direction of skewness variable among genera; Hickman, 1981; Herbert and Kilburn, 1986), 9) asymmetrical attachment of teeth, 10) outer lateral teeth enlarged, 11) well-developed lateromarginal plates, 12) stomach pyriform, 13) gastric caecum short, crescent-shaped, and 14) pedal cord exposed on pedal musculature and connected by thick median commissure.

Included taxa: This family is often divided into two subfamilies based on characters of shell slit/hole, shell muscle, and radula (Thiele, 1929; McLean, 1984 a, b; McLean and Kilburn, 1986; Herbert and Kilburn, 1986). In other classifications, Diodorinae Wenz, 1938, is sometimes separated from Emarginulinae (e.g. Knight et.al., 1960). However, such a distinction is not justified, because no prominent difference is found at least in the following shell and radular characters.

(1) Emarginulinae Gray, 1834: 1) selenizone formed, 2) shell muscle with hook-shaped inward process, 3) central tooth rhomboidal, and 4) enlarged fifth laterals bicuspid.

(2) Fissurellinae Fleming, 1822: 1) selenizone absent, 2) shell muscle lacking inward process, 3) central tooth tapered at the tip, and 4) enlarged fifth laterals with four cusps.

Family Clypeosectidae McLean, 1989

Diagnostic characters: 1) shell muscle without hook-shaped process, 2) eyes absent, 3) epipodial tentacles 3 pairs in Clypeosectus and 4 pairs in Pseudorlmula, 4) radular formula n+(5-9)+1+(5-9)+n (laterals 6-9 pairs in Clypeosectus, 5 pairs in Pseudorimula), 5) radular teeth symmetrical, 6) outer lateral teeth not enlarged, 7) seminal vesicle present, 8) prostate present, 9) ciliated genital process at base of right cephalic tentacle and ciliated band along right neck present both in male and female of Clypeosectus, but absent in Pseudorimula, and 10) receptaculum seminis on right side present in female of Clypeosectus, but absent in Pseudorimula.

Included taxa: Clypeosectus McLean, 1989, and Pseudorimula McLean, 1989. Anatomical descriptions were given by Haszprunar (1989) and McLean (1989 b; 1992 c).

Superfamily SCISSURELLOIDEA Gray, 1847

Family Scissurellidae Gray, 1847

Diagnostic characters: 1) pallial tentacle present, 2) mantle edge papillate, 3) eye closed (or absent), 4) very short eye stalks, 5) cephalic lappets absent, 6) several pairs (usually 3-4) of epipodial tentacles: "single pair of separated epipodial sense organs (ESO) tentacles or several ESO-tentacles alone (Haszprunar, 1989 a)," 7) tentacles papillate or non-papillate, 8) two bi- or monopectinate ctenidia or single monopecti-nate ctenidium (Larocheinae), 9) radular formula n+(2-5)+1+(2-5)+n, 10) symmetrical radula, 11) central tooth with large broad base, 12) outer lateral teeth enlarged or not, 13) lateromarginal plate absent, and 14) short gastric caecum.

Included taxa: Anatomy has been described in Incisura lytteltonensis (fide Bourne, 1910), Anatoma crispata (fide Fretter and Graham, 1976), Anatoma yaroni (fide Herbert, 1986), and Anatoma sp. (this study). Diagnoses of subfamilies have been given by Herbert (1986), McLean (1989), and Marshall (1993 b).

(1) Larocheinae Finley, 1927 (Larochea Finlay, 1927, and Larocheopsis Marshall, 1993): 1) shell with-out anal slit or foramen; inner lip of shell enlarged to form brood chamber in females, 2) inoperculate, 3) right subpallial cavity utilized as brood pouch, 4) cephalic and epipodial tentacles non-papillate, 5) radular formula n-5-1-5-n, with fifth lateral enlarged, and 6) single left monopectinate ctenidium.

(2) Scissurellinae Gray, 1847 (Scissurella d'Orbigny, 1824; Incisura Hedley, 1904; and Sinezona Finlay, 1927): 1) shell with slit (in Scissurella and Insclsura) or foramen (in Sinezona), 2) radular formula n-5-1-5-n, with enlarged fifth lateral tooth, 3) cephalic and epipodial tentacles papillate, and 4) ctenidia bipectinate.

(3) Anatominae McLean, 1989 (Anatoma Woodward, 1859, and Sukashitrochus Habe and Kosuge, 1964): 1) shell with unclosed slit (in Anatoma) or closed forming foramen at maturity (in Sukashitrochus), 2) open umbilicus, 3) papillate cephalic and epipodial tentacles, 4) paired mono- or bipectinate ctenidia, and 5) radular formula n-5-1-5-n, with enlarged fifth lateral.

(4) Temnocinclinae McLean, 1989 (Temnocinclis McLean, 1989, and Temnozaga McLean, 1989); 1) nearly symmetrical subpatelliform, with long slit and selenizone, 2) multispiral operculum, 3) radular formula n-3-1-3-n, without enlarged outer lateral teeth, 4) paired monopectinate ctenidia, 5) non-papillate cephalic and epipodial tentacles, 6) 3 pairs (in Temnociclis) or 4 pairs (in Temnozaga) of epipodial tentacles, and 7) eyes absent.

(5) Sutilizoninae McLean, 1989 (Sutilizona McLean, 1989): 1) asymmetrical limpet form with long slit that is closed at maturity, 2) radular formula n-2 (-4?)-1-2 (-4?)-n, without enlarged outer lateral teeth, 3) paired monopectinate ctenidia, 4) one pair of posterior epipodial tentacles, 5) non-papillate cephalic and epipodial tentacles, and 6) eyes absent.

Superfamily TROCHOIDEA Rafinesque, 1815

Diagnostic characters: 1) cephalic lappets present, 2) open eyes on eye stalks, 3) inhalant (left) and ex-halant (right) neck lobes, 4) several (typically four) pairs of epipodial tentacles, 5) tentacles with sensory micropapillae, 6) right ctenidium absent, 7) transverse pallial vein present, 8) radular formula n-5-1-5-n (except some subfamilies, e.g. Trochaclidinae and Thysanodontinae), 9) protolateromarginal plates formed by extension of bases of innermost marginal teeth, 10) outer lateral teeth not greatly enlarged, 11) food collecting groove in marginal field, and 12) multispiral gastric caecum (except Broderipia).

Included taxa: Turbinidae Rafinesque, 1815; Trochidae Rafinesque, 1815; and Skeneidae Clark, 1851. Turbinidae and Trochidae are distinguished by (i) presence or absence of secondary cusps or attachment flap and (ii) length of growing edge of operculum (Hickman and McLean, 1990). Subgroups are classified by characters of snout (outer lip, pseudoproboscis), cephalic lappets, neck lobes, epipodium, epipodial tentacles, ctenidium (afferent and efferent membrane, bursicles, free tip), and radular morphology (base, attachment, shaft, cusp asymmetry, relative size to other teeth, and presence or absence of extension at base, etc.) (Hickman and McLean, 1990; Hickman, 1996).

Family Trochidae Rafinesque, 1815

Diagnostic characters: 1) growing edge of operculum long, and 2) secondary cusp or attachment flap on central tooth present.

Included taxa: 9 subfamilies in 4 informal groups: (1) "Liotiinae Adams and Adams, 1854+Angariinae Thiele, 1921," (2) "Moelleriinae Hickman and McLean, 1990+Colloniinae Cossmann, 1916," (3) "Prisogasterinae Hickman and McLean, 1990+Turbininae Rafinesque, 1815," and (4) "Gabrieloninae Hickman and McLean, 1990+Tricoliinae Woodring, 1928+Phasianellinae Swainson, 1840" (Hickman and McLean, 1990).

Family Turbinidae Rafinesque, 1815

Diagnostic characters: 1) growing edge of operculum short, and 2) secondary cusp or attachment flap on central tooth absent.

Included taxa: 10 subfamilies in 3 informal groups and 3 subfamilies of uncertain affinity: (1) "Tegulinae Kuroda, Habe, and Oyama, 1971 +Eucyclinae Koken, 1897 + Margaritinae Stoliczka, 1868," (2) "Trochinae Rafinesque, 1815+Stomatellinae Gray, 1840 + Calliostomatinae Thiele, 1924+Solariellinae Powell, 1951," (3) "Halistylinae Keen, 1958+Lirulariinae Hickman and McLean, 1990+Umboniinae Adams and Adams, 1854," and (4) Cataeginae McLean and Quinn, 1987, Trochaclidinae Thiele, 1928 (=Acremodontinae Marshall, 1983), and Thysanodontinae Marshall, 1988 (Hickman and McLean, 1990).

Family Skeneidae Clark, 1851

Diagnostic Characters: 1) non-pigmented trochiform shell lacking nacreous layer, 2) ctenidium monopectinate, 3) radular formula n+(2-6)+l+(2-6)+n, 4) simultaneous hermaphrodites, and 5) penis at right epipodium.

Included taxa: The family was reviewed by Hickman and McLean (1990) and redefined by War én (1991 a). Hickman and McLean (1990) classified it into four groups, viz. (1) Parviturbo-Haplocochlias group, (2) Austral microliotiform group, (3) Crosseola group, and (4) deep-water skeneiform group. Anatomical information for the family was given by Fretter and Graham (1977) and War én (1991 a).

This family includes exclusively small-sized animals, so that their character states are often unclearly defined because of difficulty of observation. Warén (1991 a) stated that some taxa currently included in this family are more similar in radular morphology to Turbinidae or Trochidae, but others to Seguenziidae.

Superfamily uncertain

Family Pendromidae Warén, 1991

Diagnostic characters: 1) teleoconch with net-type and axial or spiral sculpture, 2) radula absent, and 3) large receptaculum seminis on left side of pallial cavity in female.

Included taxa: Pendroma Dall, 1927, and Rugulina Palazzi, 1988. The family is anatomically of the archaeogastropod type but is different from other families in the absence of the radula (Warén, 1991 b). Conchologically they may be related to Skeneidae with a small trochoid shell.

Superfamily LEPETODRILOIDEA McLean, 1988

Diagnostic characters: 1) nacreous layer absent, 2) eyes and eye stalks absent, 3) tentacles non-papillate, 4) single left ctenidium that is bipectinate at anterior free tip but monopectinate posteriorly, 5) ctenidium without bursicles, 6) single left hypobranchial gland, 7) hypobranchial gland fused with ctenidium, 8) paired jaws with chitinous rods, 9) radular formula n-5-1-5-n, 10) inner lateral teeth aligned in V-shape configuration, 11) marginal teeth about 18 pairs (in Lepetodrilus) or 10 pairs (in Gorgoleptis), 12) outer lateral teeth not enlarged, 13) lateromarginal plates absent, 14) salivary glands absent, 15) glandular pouches of mid-esophagus greatly enlarged and overlapping posterior part of buccal mass, 16) esophageal wall papillate, 17) spiral gastric caecum absent, 18) intestine with anterior loop, 19) two auricles, 20) rectum passing through ventricle, 21) two kidneys of dissimilar histology, each linked to pericardium by renopericardial duct, 22) gonad discharging into right kidney, 23) gonochoristic, 24) cephalic penis present, 25) vas deferens functioning as seminal vesicle, 26) prostate present, 27) receptaculum seminis present, 28) ciliated genital groove in female, and 29) statocysts with numerous statoconia.

Included taxa: Lepetodrilidae McLean, 1988, and Gorgoleptidae McLean, 1988. Anatomical observations were made by McLean (1988) and Fretter (1988). The two families are distinguished by the following five anatomical criteria, 1) configuration of the shell muscles, 2) presence or absence of the operculum, 3) elaboration of the epipodial tentacles, and 4) structure and position of the penis. This group of limpets was formerly called "hot-vent group-B" (Hickman, 1983) or "dimorphic limpets" by McLean (1985 b).

Family Lepetodrilidae McLean, 1988

Diagnostic characters: 1) horseshoe-shaped shell muscle attachment, 2) operculum absent in adult, 3) three pairs of epipodial tentacles, one pair on anterolateral side of foot and two pairs posteriorly, 4) esophageal pouches enclosing radular sac, 5) postmedian retractor muscle of radular sac absent, and 6) penis with deep seminal groove near base of right cephalic tentacle (absent in Lepetodrilus schrolli Beck, 1993).

Included taxa: Lepetodrilus McLean, 1988.

Family Gorgoleptidae McLean, 1988

Diagnostic characters: 1) separate pair of shell muscle attachments, 2) multispiral operculum present in adult, 3) epipodial tentacles long, five on left and four on right, and 4) penis developed from left side of snout.

Included taxa: Gorgoleptis McLean, 1988.

Superfamily SEGUENZIOIDEA Verriill, 1884

Family Seguenziidae Verrill, 1884

Diagnostic Characters: 1) inhalant and exhalant pallial slits, 2) eyes and eye stalks absent, 3) cephalic lappets absent, 4) subocular peduncle on base of right cephalic tentacle (Quinn, 1983), 5) accessory cephalic process (Quinn, 1983), 6) neck lobes absent, 7) several pairs of epipodial tentacles, 8) micropapillae on cephalic and epipodial tentacles, 9) epipodial sense organ absent (Salvini-Plawen and Haszprunar, 1987) or present (Ponder and Lindberg, 1997), 10) monopectinate ctenidium, 11) ctenidium with skeletal rods and bursicles, 12) single left hypobranchial gland, 13) radula modified rhipidoglossate, with formula as (4-12) +1+1+1+(4-12) (Quinn, 1983), 14) radula diverticulum present, 15) esophagus with ventral mucous pockets (Salvini-Plawen and Haszprunar, 1987), 16) small crescent-shaped gastric caecum, 17) intestine with anterior loop, 18) intestine without penetrating ventricle (Quinn, 1983), 19) monotocardian heart (Ouinn, 1983), 20) paired kidneys, 21) true eonoduct discharging directly into pallial cavity (Haszprunar, 1988 b), 22) penis with ciliated sperm groove arising from right posterior neck region (Quinn, 1983), and 23) receptaculum seminis opening at left side ofpallial cavity.

Included taxa: According to the classification of Marshall (1991), this taxon consists of 20 genera in 3 subfamilies, (1) Asthelysinae Marshall, 1991, (2) Seguenziinae Verrill, 1884 (including tribes Seguenziini Veriill, 1884, and Fluxinellini Marshall, 1991), and (3) Guttulinae Goryachev, 1987. Marshall (1991) assumed the evolutionary pathways from Asthelysinae to Seguenziini through Pluxinellini. If this assumption is accepted, there are some consistent "trends" in character evolution. (i) Central and lateral teeth become thinner and more flexible, (ii) Marginal teeth become more slender, (iii) Number of radular teeth is reduced from up to about 20 pairs (Fluxinellini) to up to about 7 pairs (Seguenziini). (iv) Deep notches areelaborated in shell aperture.

"Vent Taxa"=Peltospiroidea+Neomphaloidea

Superfamily PELTOSPIROIDEA McLean, 1989

Family Peltospiridae McLean, 1989

Diagnostic characters (based mainly on Rhynchopelta): 1) snout tapered (except in Hirtopelta), 2) eyes absent, 3) epipodial tentacles not long, 4) tentacles non-papillate, 5) single left bipectinate ctenidium, 6) skeletal rods present (except Melanodrymia), 7) osphradium along left shell muscle, 8) hypobranchial gland absent, 9) paired jaws, 10) radular formula n-4-l-4-n, 11) single pair of cartilages, 12) sac-like salivary glands without ducts, 13) enlarged esophageal pouches, 14) single left auricle, 15) auricle lacking filter chambers, 16) ventricle not penetrated by rectum, 17) left and right kidneys, 18) nephridial gland in diverticulum of left kidney, 19) right renopericardial canal present in both sexes, 20) left renopericardial canal found only in female, 21) gonopericardial duct absent, 22) gonad with glandular pallial gonoduct, 23) gonoduct urogenital in female, but separated from right kidney in male, 24) seminal vesicle and prostate in male, 25) cephalic penis absent, 26) receptacular duct in female, 27) sperm-ingesting epithelium in ovary, and 28) fertilization within ovary.

Included taxa: Melanodrymia Hickman, 1984; Depressigyra, Pachydermia, and Lirapex, all Warén and Bouchet.1989; Echlnopelta, Peltospira, Nodopelta, Rhynchopelta, and Hirtopelta, all McLean, 1989 a; Ctenopelta, Planorbidella, and Helicrenion, all Warén and Bouchet,1993. Solutigyra Warén and Bouchet, 1989 was originally described as a member of this family but transferred to Skeneidae based on the similarities to Xyloskenea Marshall, 1988 in radula and to Leptogyropsis Marshall, 1988 in soft parts and protoconch (Warén and Bouchet, 1993). The internal anatomy of Rhynchopelta, Peltospira, Nodopelta, Echinopelta, and Hirtopelta was described in detail by Fretter (1989). Some additional information was given by McLean (1989 a) and Warén and Bouchet (1989, 1993). These taxa were previously called "hotvent group-A" (Hickman, 1983) or "taper-snout limpets" (McLean, 1985 b).

Melanodrymia is represented by M. aurantiaca Hickman 1984 and M. brightae Warén and Bouchet, 1993. Hickman (1984 b) tentatively placed this genus in Trochoidea. Haszprunar (1989 b) described the anatomy of the species, and Warén and Bouchet (1989) documented additional anatomical information and revealed its higher-level taxonomic position, Diagnostic characters of genus Melanodrymia are given as follows: 1) several epipodial tentacles, 2) skeletal rods absent, 3) sensory pockets on ctenidial lamellae, 4) jaw absent, 5) single left kidney, 6) cephalic tentacles ciliated and used as copulatory organ, 7) ciliated seminal groove present, 8) receptaculum seminis on the left side, and 9) statocysts bearing single statolith.

Superfamily NEOMPHALOIDEA McLean, 1981

Diagnostic characters: 1) eyes absent, 2) tentacles non-papillate, 3) single left ctenidium bipectinate, 4) afferent ctenidial membrane absent or very short, 5) skeletal rods present, 6) bursicles absent, 7) radular formula n-4-l-4-n, 8) single left auricle, 9) ventricle not penetrated by rectum, 10) left kidney only, 11) gonad with glandular gonoducts, 12) left cephalic tentacle of male used as penis, and 13) open or closed sperm groove in male.

Included taxa: Neomphalidae McLean, 1981 and Cyathermiidae McLean, 1990

Family Neomphalidae McLean, 1981

Diagnostic characters (based mainly on Neomphalus): 1) shell penetrated by microtubules (Batten, 1984 b), 2) neck long, 3) epipodial tentacles along posterior side of foot, 4 to 9 on right and 5 or 6 on left (in Neomphalus), or up to 20 in number (in Symmetromphalus), 4) paired jaws, 5) central and lateral teeth non-serrated, 6) single pair of odontophoral cartilages, 7) salivary gland absent, 8) overlap of esophageal pouches on buccal mass, 9) nephridial gland present at anterior right side of kidney, 10) gonopericardial duct present in female, 11) male gonoduct with prostate, 12) open seminal groove in left cephalic tentacle, 13) cirri at tip of penis (as in Cyathermiidae) absent, 14) fertilization chamber in proximal part of oviduct, 15) receptaculum seminis unconnected to oviduct, and 16) statocysts containing single statolith.

Included taxa: Neomphalus McLean, 1981, and Symmetromphalus McLean, 1990. Anatomical description was given by McLean (1981), Fretter etal. (1981), McLean (1990 a) and Beck (1992 a). Two genera differ in the following characters: 1) operculum absent (in Neomphalus), or present in adult (in Symmetromphalus), 2) shell muscle crescent-shaped (in Neomphalus), or symmetrically paired (in Symmetromphalus), and 3) food groove present (in Neomphalus), or absent (in Symmetromphalus).

Family Cyathermiidae McLean, 1990

Diagnostic characters: Cyathermiidae are separated from Neomphalidae by the following characters (McLean 1990 b): 1) neck short, 2) serration of central and lateral teeth, 3) enlargement of central tooth, 4) closed sperm groove running in left cephalic tentacle, and 5) two cirri at tip of cephalic tentacles.

Included taxa: The family was proposed for coiled neomphaloids and consists of two genera: Cyathermia Waren and Bouchet, 1989, and Lacunoides Waren and Bouchet, 1989. Soft parts of Cyathermia were described by Warén and Bouchet (1989).

"COCCULINIFORMIA" Haszprunar, 1987

Diagnostic characters: 1) ciliated epipodial tentacles, 2) epipodial sense organ absent, 3) pseudoplicate gill (in Cocculinoidea) or secondary subpallial leaflets (in Lepetelloidea), 4) osphradium left only, 5) secondary respiratory organs at right innervated by osphradial ganglion at left side of pallial roof, 6) modified rhipidoglossate radula, 7) alimentary tract variously modified, 8) gastric caecum absent, 9) single left auricle, 10) pericardium connected only with left kidney, 11) right and left kidneys present (in Lepetelloidea), or left only (in Cocculinoidea), 12) hermaphroditic (except in gonochoristic Choristellidae), 13) copulatory organ at right side, and 14) open seminal groove (except closed duct in Pseudococculina and Notocrater; Haszprunar, 1988 d).

Included taxa: According to the phylogenetic classification of Haszprunar (1988 c), "Cocculiniformia" are divided into two basic phyletic lines, Cocculinoidea Thiele, 1909 and Lepetelloidea Thiele, 1908. Their relationship is summarized as follows: (i) Cocculinoidea and Lepetelloidea are distinguished by division of shell muscle, types of secondary gill, paired or unpaired kidney, and contents of statocysts. (ii) Within Lepetelloidea, Lepetellidae, Pyropeltidae, and Psudococculinidae have single gonoduct, and gonopore connected with excretory opening. (iii) Addisoniidae and Choristellidae share gill leaflets with proximal glandular zone and skeletal rods, reduction of stomach (also with Cocculinellidae), and gonoduct free from excretory opening (also with Osteopeltidae and Cocculinellidae). (iv) The above-mentioned two groups of Lepetelloidea form a single lineage linked by Osteopeltidae and Cocculinellidae.

Superfamily COCCULINOIDEA Thiele, 1909

Diagnostic characters: 1) shell muscle divided into bundles, 2) pseudoplicate gill, 3) subpallial glands (except Cocculina and Coccocreter; Haszprunar, 1987 a), 4) paired jaws, 5) single pair of radular cartilages, 6) central radular tooth vestigial or absent, 7) ventricle not penetrated by rectum, 8) single left kidney, 9) hermaphroditic gonad with fused ovary and testis, 10) single glandular gonoduct, 11) gonopore independent of kidney opening, 12) copulatory organ from right neck, 13) receptaculum seminis present, and 14) statocysts with single statolith.

Included taxa: Cocculinidae Dall, 1882, and Bathysciadiidae Dautzenberg and Fischer, 1900 (Haszprunar, 1988 c).

Family Cocculinidae Dall, 1882

Diagnostic characters: 1) oral lappet present, 2) bristles around mouth, 3) eyes modified to basitentacular gland, 4) one pair of posterior epipodial tentacles (except Coccopigya lacking tentacles; Haszprunar, 1987 a), 5) osphradium present, 6) left hypobranchial gland present, 7) anterior levator muscle absent, 8) radula n-4-l/0-4-n, 9) fourth lateral teeth enlarged, 10) salivary glands absent, 11) esophagus with pouches, 12) stomach with gastric shield, 13) single mid-gut gland opening, 14) three intestinal loops, and 15) one or two receptaculum seminis with separate ducts.

Included taxa: Cocculina Dall, 1882; Paracocculina Haszprunar, 1987; Coccocrater Haszprunar, 1987; Coccopigya Marshall, 1986; Fedikovella Moskalev, 1976; and Teuthirostria Moskalev, 1976. Anatomical descriptions and diagnoses were given by Haszprunar (1987 a).

Family Bathysciadiidae Dautzenberg and Fischer, 1900

Diagnosti characters: l)eys absent, 2) radular formula 1-3-1-3-1 (in Bathysciadium) 1-3-0-3-1 (in Bonus), 3) salivary glands present, 4) esophageal glands enlarged, 5) stomach with gastric shield, 6) midgut gland absent, and 7) short intestine.

Included taxa: Bathysciadium Dautzenberg and Fischer, 1900; Bathypelta Moskalev, 1971; and Bonus Moskalev, 1973 (Moskalev, 1973; Haszprunar, 1988 c). Anatomical information on pallial, gonopericardial, and alimentary system was given by Haszprunar (1988 c).

Superfamily LEPETELLOIDEA Thiele, 1908

Diagnostic characters: 1) undivided horseshoe-shaped shell muscle or single columellar muscle (in Choristellidae), 2) secondary gill-leaflets in right pallial and/or subpallial cavities, 3) sensory pocket in gill leaflets present (in Lepetellidae, Pyropeltidae, and Pseudococculinidae), or absent (in Osteopeltidae, Cocculinellidae, Addisoniidae, and Choristellidae), 4) proximal glandular area in gill leaflets absent, or present (in Addisoniidae and Choristellidae), 5) skeletal rods within efferent axis absent, or present (in Addisoniidae and Choristellidae), 6) hypobranchial gland absent, 7) subpallial glands absent, 8) well-developed central tooth, 9) salivary glands present (except Lepetellidae), 10) ventricle penetrated by rectum (except in Addisoniidae and Choristellidae), 11) two kidneys (smaller left kidney connected with pericardium; larger right kidney isolated without renopericardial duct), 12) right kidney ramified into branches (except simple kidney in Lepetellidae), 13) hermaphroditic (except gonochoristic Choristellidae), 14) testis and ovary clearly separated (ventral testis and dorsal ovary), 15) gonoducts simply ciliated without glands, 16) vas deferens and oviduct fused into common genital duct (in Lepetellidae, Pyropeltidae, and Pseudococculinidae), or separated (in Osteopeltidae, Cocculinellidae, and Addisoniidae), 17) right kidney openingandgonopore fused into urogenital opening (in Lepetellidae, Pyropeltidae, and Pseudococculinidae) or separated (in Osteopeltidae, Cocculinellidae, Addisoniidae, and Choristellidae), 18) right cephalic tentacle used as copulatory organ, and 19) statocysts with several or many statocones.

Included taxa: 8 families are included in this Superfamily: Lepetellidae Dall, 1882; Pyropeltidae McLean and Haszprunar, 1987; Pseudococculinidae Hickman, 1983; Osteopeltidae Marshall, 1987; Bathyphytophilidae Moskalev, 1978; Cocculinellidae Moskalev, 1971; Addisoniidae Dall, 1882; and Choristellidae Bouchet and Warén, 1979 (Haszprunar, 1988 c).

Family Lepetellidae Dall, 1882

Diagnostic characters: 1) oral lappets absent, 2) unpaired papilla on posterior end of foot (Dantart and Luque, 1994), 3) jaws absent, 4) one pair of odontophoral cartilages, 5) radular formula 3-1-3 (Dantart and Luque, 1994), 6) salivary glands absent, 7) greatly enlarged esophageal pouches, 8) stomach without gastric shield, 9) several openings of digestive gland into stomach, and 10) short intestine.

Included taxa: Lepetella Verrill, 1880; Tectisumen Finlay, 1927; and Tecticrater Dell, 1956 (Haszprunar, 1988 c). Anatomical information on pallial cavity, gonopericardial system, and alimentary tract was given by Haszprunar (1988 c).

Family Pyropeltidae McLean and Haszprunar, 1987

Diagnostic characters: 1) oral lappets absent, 2) eyes absent, 3) one pair of posterior epipodial tentacles, 4) osphradium present, 5) paired jaws with tooth-like elements, 6) two pairs of odontophoral cartilages, 7) radular formula n-5-1-5-n, 8) esophageal pouches present, 9) stomach with gastric shield, 10) paired midgut glands, and 11) several intestinal loops.

Included taxa: The family consists only of a single genus, Pyropelta McLean and Haszprunar, 1987 (McLean and Haszprunar, 1987; McLean, 1992 b).

Family Pseudococculinidae Hickman, 1983

Diagnostic characters: 1) sensory papillae on mantle edge, 2) oral lappets present, 3) eyes present or absent, 4) one pair of posterior epipodial tentacles, 5) osphradium absent, 6) paired jaws, 7) two pairs of odontophoral cartilages, 8) radular formula n-5-l-5-n, 9) esophagus with pouches, 10) stomach with gastric shield, 11) single mid-gut gland, and 12) several intestinal loops.

Included taxa: Two subfamilies, (1) Pseudococculininae Hickman, 1983 (Pseudococculina Schepman, 1908; Bandabyssia Moskalev, 1976; Kurilabyssia Moskalev, 1976; Mesopelex Marshall, 1986; Notocrater Finlay, 1927; and Tentaoculus Moskalev, 1976) and (2) Caymanabyssinae Marshall, 1985 (Caymanabyssia Moskalev, 1976; Amphiplica Haszprunar, 1988; Colotrachelus Marshall, 1986; Copulabyssia Haszprunar, 1988; and Yaquinabyssia Haszprunar, 1988). Anatomical descriptions and diagnoses were given by Haszprunar (1988 d).

Family Osteopeltidae Marshall, 1987

Diagnostic characters: 1) oral lappets absent, 2) eyes present, 3) single pair of epipodial lappets, 4) sensory pocket absent in gill leaflets, 5) osphradium absent, 6) paired jaws, 7) single pair of odontophoral cartilages, 8) radulae similar to those of Pseudococculinidae, 9) narrow anterior esophagus without pouches, 10) stomach with gastric shield, 11) paired mid-gut glands, and 12) short intestine.

Included taxa: Osteopelta Marshall, 1987, only. This genus was defined as cocculiniform limpets with pseudococculinid-like shell and radula with an addisoniid-like animal (Marshall, 1987; Haszprunar, 1988 c, e).

Family Bathyphytophilidae Moskalev, 1978

Diagnostic characters: 1) outer lateral teeth enlarged, 2) filamentous marginal teeth, and 3) one pair of marginal plates present.

Included taxa: Two genera (Bathyphytophilus Moskalev, 1978, and Aenigmabonus Moskalev, 1978) were assigned to this family (Moskalev, 1978), but their anatomy and taxonomic relationships have not been clearly understood (Haszprunar, 1988 c).

Family Cocculinellidae Moskalev, 1971

Diagnostic characters: 1) oral lappets absent, 2) eyes absent, 3) epipodial tentacles absent, 4) reduction of gill into two ciliary spots, 5) osphradium present, 6) jaws absent, 7) radular formula 7-1-1-1-7 (Marshall, 1983 c), 8) 2 paired and 2 unpaired odontophoral cartilages, 9) narrow anterior esophagus without pouches, 10) stomach reduced with vestigial gastric shield, 11) unpaired mid-gut gland, and 12) intestine enlarged.

Included taxa: Cocculinella Thiele, 1909. The anatomy was described for Cocculinella minutissima by Haszprunar (1988 e).

Family Addisoniidae Dall, 1882

Diagnostic characters (based mainly on Addisonia): 1) oral lappets absent, 2) eyes absent, 3) epipodial tentacles absent, 4) single left osphradium present, 5) jaws absent, 6) two pairs of odontophoral cartilages, 7) radular formula 7-1-7, 8) narrow anterior esophagus without pouches, 9) stomach completely reduced, 10) paired mid-gut glands, 11) intestine forming pseudostomach, and 12) receptaculum seminis present.

Included taxa: The family consists of two subfamilies, (1) Addissoninae Dall, 1882 (Addisonia Dall, 1882), and (2) Helicopeltinae Marshall, 1996 (Helicopelta Marshall, 1996). Details on shell, external and internal anatomy, radula, and life habit were described by Hickman (1983), McLean (1985 a), Haszprunar (1987 b), Dantartand Luque (1994), and Marshall (1996).

Family Choristellidae Bouchet and Warén, 1979

Diagnostic characters: 1) operculum present, 2) oral lappet present, 3) eyes absent, 4) one to two suboptic tentacles posterior to right cephalic tentacle, 5) several epipodial tentacles (up to 4 pairs), 6) osphradium 0present, 7) jaws fused dorsally, 8) two pairs of odontophoral cartilages, 9) radular formula 5-1-5, 10) anterior esophagus without pouches, 11) stomach completely reduced, 12) single opening of mid-gut glands, 13) intestine forming pseudostomach, 14) gonochoristic, and 15) receptaculum seminis present.

Included taxa: Choristella Bush, 1897, and Bichoristes McLean, 1992. Systematics reviewed by McLean (1992 a). The anatomy was described by Haszprunar (1992).

Order NERITOPSINA Cox and Knight, 1960

Diagnostic characters: 1) protoconch multispiral or globular, 2) inside of upper whorls resorbed, 3) closed eyes with vitreous body, 4) visceral mass without spiral coiling (true columella absent), 5) ctenidium lacking skeletal rod, 6) right hypobranchial gland present (absent in some members), 7) osphradium left only (absent in terrestrial forms), 8) osphradium with ciliated zones, 9) three (anterior, posterior, and median) pairs of odontophoral cartilages, 10) dorsal levator muscles of odontophore present, 11) tensor muscles of anterior cartilages present, 12) radular formula typically n-(1+3)-1/0-(3+1)-n, 13) salivary glands absent, 14) esophageal glands septate and separated posteriorly from mid-esophagus, 15) gastric caecum small, crescent-shaped, 16) ventricle penetrated by rectum (except Helcinoidea and Hydrocenoidea), 17) single left kidney composed of glandular and non-glandular parts (Little, 1972), 18) pallial gonoduct developed within anterior pallial vein, 19) gonopericardial canal absent, 20) prostate present in male gonoduct, 21) female gonoduct monaulic, diaulic, or triaulic, 22) bursa copulatrix or spermatophore sac present, 23) receptaculum seminis present, 24) internal fertilization, 25) egg-capsules produced, 26) labial commissure present, without labial ganglia, 27) one-side origin of visceral loop from right side, 28) supraesophageal part of visceral loop reduced or absent, and 29) pleural comissure present.

Included taxa: Neritoidea Rafinesque, 1815; Titiscanioidea Bergh, 1890; Hydrocenoidea Troschel, 1856; and Helcinoidea Thompson, 1980.

Superfamily NERITOIDEA Rafinesque, 1815

Diagnostic characters: 1) oral lappets present, 2) sublingual glands evaginated from sublingual pouch, 3) median levator muscles of odontophore present, 4) two auricles (right auricle functional but vestigial), 5) cephalic penis originating from inner side of right cephalic tentacle, 6) spermatophore in male and spermatophore sac in female, 7) female gonoduct typically diaulic, and 8) capsule and albumen glands in female.

Included taxa: Neritopsidae Gray, 1847; Neritidae Rafinesque, 1815; Phenacolepadidae Thiele, 1929; and Shinkailepadidae Okutani, Saito, and Hashimoto, 1989.

Family Neritopsidae Gray, 1847

Diagnostic characters: 1) calcified operculum with strong inner projection, and 2) radular formula n-(l +3)-0-(3+l)-n (three pairs of slender laterals and enlarged fourth teeth) (Baker, 1923; Warén and Bouchet, 1993: fig. 3 D).

Included taxa: Extant members are represented only by a single genus, Neritopsis Grateloup, 1932, which includes Indo-Pacific N. radula (Linnaeus. 1758) surviving from the Eocene (Batten, 1984 a) and the recently discovered western Atlantic species, N. atlantica Sarasua, 1973 (Rosenberg, 1992). Details of anatomy are unknown.

Family Neritidae Rafinesque, 1815

Diagnostic characters: 1) calcified operculum with interior apohysis, 2) paired attachments of columellar muscles (divided into bundles in Nerlta), 3) right hypobranchial gland present (absent in Neritina and Theodoxus; Fretter, 1965), 4) vestigial gill on right side (in Nerita), 5) radular formula n-(1+3)-0/1-(3+1)-n, 6) "annex gland" of Lessen (1899) in male, and 7) crystal sac in female organ (except Neritilinae).

Included taxa: The family is divided into 4 subfamilies based on characters of radula and reproductive organ (Baker, 1923; Andrews, 1937; Knight et al, 1960; Stramühlner, 1976, 1983; Komatsu, 1986).

(1) Neritinae Rafinesque, 1815 (Nerita Linnaeus, 1758; Neritina Lamarck, 1816; Neritodryas von Martens, 1869; and Theodoxus Montfort, 1810); 1) radular formula n-(1+3)-1-(3+1)-n, 2) first lateral stransversely elongated, 3) fourth teeth transversely thickened with indistinct denticles on shield-shaped cusp, 4) many marginals of similar form, 5) basal gland present in male, 6) cephalic penis present, 7) female gonoduct diaulic without enigmatic duct, and 8) crystal sac present in female.

(2) Septariinae Golikov and Starobogatov, 1975 (Septaria Férussac, 1807): 1) limpet-shape, 2) semiinternal operculum, 3) radular formula n-(1+3)-1-(3+1)-n, 4) teeth morphology similar to that of Neritinae, 5) basal gland absent, 6) cephalic penis present, 7) female gonoduct triaulic with enigmatic duct, and 8) crystal sac present.

(3) Smaragdiinae Baker, 1923 (Smaragdia Issel, 1869; Magadis Melville and Standen, 1899; and Pisulina Nevill, 1869): 1) radular formula n-(1+3)-1-(3+1)-n, 2) first laterals not enlongated, 3) fourth laterals transversely prominent with a few distinct denticles, and 4) several pairs of marginals with innermost teeth differentiated, 5) cephalic penis present, and 6) crystal sac present.

(4) Neritiliinae Baker, 1923 (Neritilia von Martens, 1879, and Septariellina Bequaert and Clench, 1936); 1) radular formula n-(1+3)-0-(3+1)-n, 2) first laterals elongated, 3) fourth laterals enlarged and obliquely aligned with saw-like denticles, 4) many marginals of similar form, 5) cephalic penis absent, 6) female gonoduct monaulic, and 7) crystal sac absent.

Bathynerita Clarke, 1989 in uncertain subfamilial position was reported from hydrocarbon seeps south of Luisiana, 540-722 m (Warén and Bouchet, 1993).

Family Phenacolepadidae Thiele, 1929

Diagnostic characters: 1) corneous operculum with vestigial apohysis embedded in foot in Phenacolepas (Fretter, 1984 a), but absent in Cinnalepeta, 2) mantle margin with numerous papilla, 3) cephalic lappets absent, 4) epipodial papillae absent, 5) hypobranchial gland absent, 6) radular formula n-(1+3)-1-(3+1)-n (first laterals transversely elongated with sharp cusps; fourth laterals longitudinally elongated, and marginals with comb-like cusps), 7) erythrocytes present, 8) finger-shaped cephalic penis, 9) female gonoduct diaulic, 10) spermatophore sac and receptaculum seminis present, and 11) crystal sac absent.

Included taxa: Phenacolepas Pilsbry, 1891 with 3 subgenera (or genera: Amapileus Iredale, 1929; Cinnalepeta Iredale, 1929; and Zacalantica Iredale, 1921) and Plesiothyreus Cossmann, 1888 (Vaught, 1989). The anatomy of Phenacolepas omanensis was described by Fretter (1984 a).

Family Shinkailepadidae Okutani, Saito, and Hashimoto, 1989

Diagnostic characters: 1) internal operculum consisting of anterior calcareous and posterior corneous layers, 2) mantle margin with numerous papillae, 3) cephalic lappets absent in Shinkallepas (Okutani et al., 1989: fig. 10) but present in Olgasolaris (Beck, 1992 b: pl. 5, fig. 5), 4) epipodial papillae present posteriorly, 5) radular formula n-(1+3)-1-(3+1)-n (n=ca. 80 in Shinkailepas tufari, 70 in Olgasolaris tollmanni; Beck, 1992 b), 6) cephalic penis present, 7) female gonoduct diaulic, and 8) spermatophore sac, receptaculum seminis, and crystal sac absent (Beck, 1992 b: fig. 4).

Included taxa: Two deep-sea genera, Shinkailepas Okutani, Saito, and Hashimoto, 1989, and Olgasolaris Beck, 1992. Anatomical descriptions was given by Okutani et al. (1989) and Beck (1992 b). Beck (1992 b) synonymized this family with Phenacolepadidae, but these two families differ in the morphology of operculum, the presence or absence of epipodial papillae, and the structure of female gonoduct.

Superfamily TITISCANIOIDEA Bergh, 1890

Family Titiscaniidae Bergh, 1890

Diagnostic characters: 1) shell absent, 2) bipectinate ctenidium present, 3) radular formula n-3-0-3-n (first laterals small, second laterals slightly enlarged, third laterals enlarged; Saito and Tsuchiya, 1990), 4) two auricles, 5) ventricle penetrated by rectum, 6) vas deferens not coiled, 7) accessory gland absent in prostate, 8) ciliated groove on right side of head, 9) cephalic penis absent, 10) female gonoduct diaulic with spermatophore sac, 11) oviduct with albumen and capsule glands, 12) receptaculum seminis present, and 13) crystal sac absent.

Included taxon: Monotypic genus Titiscania Bergh, 1890, represented by Titiscania limacina Bergh, 1890 (=? T. shinkishihatdii Is. Taki, 1955) distributed from the Philippines to Baja California (Bergh, 1890; Taki, 1955; Keen, 1971; Saito and Tsuchiya, 1990). Anatomical descriptions were given by Bergh (1890) and Houston (1990).

Superfamily HYDROCENOIDEA Troschel, 1856

Family Hydrocenidae Troschel, 1856

Diagnostic characters: 1) calcified operculum with interior apohysis, 2) ctenidium absent and replaced by "lung," 3) single columellar muscle, 4) jaws absent, 5) salivary glands absent, 6) central and lateral radular teeth reduced, 7) single left auricle, 8) ventricle not penetrated by rectum, 9) prostate gland in two portions, 10) cephalic penis absent, 11) female gonoduct monaulic, and 12) receptaculum seminis present.

Included taxa: Hydrocena Pfeiffer, 1847; Georissa Blanford, 1864; and Lapidaria Kang, 1986 (Vaught, 1989). Anatomy of Hydrocena cattaroensis was described by Thiele (1910).

Superfamily HELICINOIDEA Thompson, 1980

Diagnostic characters: 1) non-operculate (in Ceresidae and Proserpinidae) or operculate (calcified operculum without apohysis in Helcinidae), 2) gill absent and replaced by "lung," 3) osphradium absent, 4) hypobranchial gland discharging into mantle cavity via hypobranchial duct, 5) radular formula n-(1+3)-1-(3+1)-n, 6) ventricle not penetrated by rectum, 7) cephalic penis absent, 8) female gonoduct diaulic or triaulic, 9) spermatophores absent, 10) "provaginal sac" (Thompson, 1980) always present in female, and 11) "V-organ" and accessory sperm sac (Thompson, 1980) in female.

Included taxa: Ceresidae Thompson, 1980; Proserpinidae Gray, 1847; and Helcinidae Férussac, 1882 (fide Thompson, 1980).

Family Ceresidae Thompson, 1980

Diagnostic characters: 1) operculum absent, 2) foot "holopod" (without mucous groove), 3) heart with two functional, nearly equal-sized auricles, 4) prostate not divided into upper and lower divisions, 5) provaginal sac absent in males, and 6) crystalline gland absent on pallial oviduct.

Included taxa: Ceres Gray, 1856; Archecharax Thompson, 1980; Linidiella Jousseaume, 1889; Proserpinella Bland, 1865; and Staffola Dall, 1905 (Thompson, 1980).

Family Proserpinidae Gray, 1847

Diagnostic characters: 1) operculum absent, 2) foot "aulacopod" (side of foot demarcated by mucus groove as in Pulmonata), 3) single left auricle, 4) prostate divided into prostate-I and -II, 5) vestigial provaginal sac present within prostate-I, and 6) crystalline gland present at base of pallia] oviduct.

Included taxa: Proserpina Sowerby, 1839 (Thompson, 1980).

Family Helcinidae Férussac, 1882

Diagnostic characters: 1) operculum present, 2) foot "holopod" (without mucus groove), 3) single left auricle (paired in Hendersonia; Thompson, 1980), 4) prostate divided inio prostate-I and -II, 5) provaginal sac absent in male, and 6) crystalline gland absent.

Included taxa: 28 genera (Vaught, 1989) in 3 subfamilies, (1) Helcinnae Férussac, 1882, (2) Hendersoniinae Baker, 1926, and (3) Vianinae Baker, 1922 (Thompson, 1980). Anatomy of some genera was described by Bourne (1911) and Thompson (1980). According to Thompson (1980), several "evolutionary trends" seem to occur in this family: 1) modification of operculum from paucispiral to concentric, 2) increasing complexity of shell sculpture, 3) reduction and loss of right auricle, 4) increase in lengths of pallial gonoduct and hypobranchial duct, 5) simplification and elongation of female primary oviduct, 6) shift of accessory sperm sacs on pedicel, 7) reduction of cusps on radular teeth, 8) fourth lateral ("D-lateral") teeth changing from comb-shaped to T-shaped, and 9) reduction in structural complexity of accessory plate of fourth lateral teeth ("E-lateral"). Presence of the operculum is only discrete character to distinguish this family from others.