HOLOCENE OSTRACODS IN THE SOUTHERN BOSO PENINSULA
Paul M. Frydl
Mobil Oil Canada Ltd., Calgary, Canada
Systematic description
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Order Podocopida Sars, 1866 Superfamily Cypridacea Baird, 1845 Family Pontocyprididae G. W. Müller, 1894 Genus Argilloecia Sars, 1866 Argilloecia lunata n. sp. Pl. 8, figs. 3-7; text.fig.31f.
Etymology. —From "lunatus" [Latin, "bent into a crecsent"]. Type. —Holotype, UMUT-CA 15001, left valve, male (Pl. 8, fig. 6), obtained from sample no. 7, from coral bed at Koyatsu, West Coast Valley area, AL sub-biofacies. Diagnosis. —Species of the genus Argilloecia characterized by relatively broadly rounded posterior margin. Description. —Elongate in lateral outline, highest at the middle. Dorsal margin convex, ventral margin concave at anterior third. Anterior margin broadly rounded, posterior margin narrowly rounded, extremely at lower third. Sexual dimorphism moderate: in male, anterior margin obliquely truncated, meets dorsal margin with blunt cardinal angle, posterior margin more narrowly rounded. Dorsal outline elongate ellipsoid, anterior and posterior margins pointed, widest at the middle. Right valve larger than left, overlaps left valve at second anterior fifth and posterior two-fifths of length. Surface smooth, normal pores few, scattered. Inner lamella broad, line of concrescence runs parallel to the margins, coinciding with the inner margin in ventral area. Anterior and posterior vestibule large. Marginal pore canals simple, straight, numerous in anterior end, few in ventral part, moderately numerous in posterior end. Several false radial pore canals occur in posterior end. Muscle scar large, consisting of three anterior, two posterior closely set scars. Hinge adont. Dimensions. —Holotype, male LV; L, 0.54, H, 0.17; paratypes, female, LV, UMUT-CA 15002 (Pl. 8, fig. 3); L, 0.50, H, 0.18; male, LV, UMUT-CA 15003 (Pl. 8, fig. 4); L, 0.52, H, 0.19; female RV, UMUT-CA 15004 (Pl. 8, fig. 5); L, 0.55, H, 0,20; female RV, UMUT-CA 15005 (Pl. 8, fig. 7); L, 0.54, H, 0.19. Remarks. —This is the first species of the genus Argilloecia reported from Japan. Occurrence. —Common in LK biofacies and AL sub-biofacies, rare in AA, KN, K sub-biofacies and sample 162 of the SN biofacies. Absent in Tateyama Bay. Subgenus Propontocypris Sylvester-Bradley, 1947 Propontocypris (Propontocypris) sp. Text-fig. 32d.
Illustrated specimen. —A left valve, UMUT-CA 15042. Remarks. —Assigned to the genus Propontocypris on the basis of typical muscle scar, consisting of three inclined rows of 5 scars, elongated subtriangular outline, and simple marginal pore canals. Occurrence. —Rare in NL, AA sub-biofacies, and SN biofacies. Subfamily Paracypridinae Sars, 1923 Genus Paracypris Sars, 1866 Paracypris sp. Text-fig. 32e. Illustrated specimen . —A right valve, UMUT-CA 15006. Remarks. —The elongated, posteriorly tapering carapace, bifurcating marginal pore canals, and a muscle scar consisting of three anterior, two posterior and one upper scars characterize this species as belonging to the genus Paracypris. The species closely resembles Pontocypris? sp. 6, described by Maddocks (1966, p. 44, 45, figs. 32 J-Q) in outline, but differs in muscle scars and marginal pore canals. Occurrence. —Rare to common in LK biofacies and NK sub-biofacies, rare in A, SN biofacies and K sub-biofacies. Family Leptocytheridae Hanai, 1957 Genus Callistocythere Ruggieri, 1953 Callistocythere littoralis group Callistocythere numaensis n. sp. Pl. 9, figs. 1-3; text-fig. 31a.
Etymology. —Named after the type locality of the Holocene coral-bearing sediments, village of Numa. Type. —Holotype, UMUT-CA 15007, right valve (Pl. 9, fig 1), obtained from sample no. 7, from the coral-bearing sediments in Koyatsu, West Coast Valley area. The sample belongs to the AL sub-biofacies. Diagnosis. —Species of the genus Callistocythere characterized by prominent sub-vertical ridge in the posterocentral area. Description. —Carapace oblong, reniform, highest at anterior cardinal angle. Dorsal margin gently convex upward, merges with obliquely rounded anterior margin. Anterior margin crenulated at lower half, ventral margin strongly concave at anterior third. Posterior margin meets dorsal margin at a distinct cardinal angle, gently rounded below. First anterior marginal ridge prominent, sinuous, running from the upper fifth of anterior margin to anterior sixth of ventral margin. Dorsal marginal ridge obscuring the dorsal margin, running from the eye tubercle to posterior fourth, where it bifurcates, one part joining the first posterior marginal ridge, the other running vertically to the posterocentral area. Posterior marginal ridge prominent, running from the posterior fourth of dorsal margin to the ventral sinuosity. First ventral margin starts at the ventral sinuosity and runs obliquely upwards to the posteroventral area, where it turns at a steep angle and continues to the central area. Second ventral marginal ridge running parallel to the ventral margin from anterior fourth to little past half, where it joins the first ventral ridge. Surface ornamented with coarse reticulation. Eye tubercle low, but large. Normal pores moderate in number, simple type, scattered. Inner lamella moderately wide, radial pore canals simple. Dimensions. —Holotype, RV; L, 0.43, H, 0.23; paratypes, LV, UMUT-CA 15008 (Pl. 9, fig. 2); L, 0.42, H.0.23; LV, UMUT-CA 15009 (Pl. 9, fig. 3); L, 0.45, H, 0.24. Remarks. —Development of the hingement and the short, unbranching radial pore canals seem to suggest that these are immature specimens; however, the width of the inner lamella indicates that the forms are adults. Occurrence. —Common in AL sub-biofacies, rare in KN and K sub-biofacies. Pl. 9, figs. 4-9; text-fig. 31b. Etymology. —Named after Tateyama City. Type. —Holotype, UMUT-CA 15010, left valve, female (Pl. 9, fig. 5), obtained from sample no. 57, from the village of Shiomi in the West Coast Valley area. The sediment is coarse sand and the sample belongs to the AA sub-biofacies. Diagnosis. —Species of the genus Callistocythere characterized by large depression developed between the first and second anterior marginal ridges, and reticulation of irregular outline. Description. —Carapace thick, oblong, subreniform, highest at anterior cardinal angle. Anterior margin broadly obliquely rounded, dorsal margin gently arched. Posterior margin truncated above, meets dorsal margin with a distinct cardinal angle in the left valve, merges with dorsal margin in the right valve. Ventral margin slightly concave at the middle. Surface sculptured with strong ridges and deep reticulation. First anterior ridge weak, runs from upper third of anterior margin to ventral sinuation. Second anterior ridge prominent, runs from anterior cardinal angle to lower third of anterior margin, where it joins the first anterior ridge. Third anterior ridge prominent, runs from anterior third of dorsal margin to anterior fifth of ventral margin, where it joins the first marginal ridge. Deep depression developed between the second and third marginal ridges and short, but very deep anteriorly oblique depression located behind the upper one third of the third marginal ridge. Dorsal marginal ridge strong, obscuring the dorsal margin, running from anterior third of the dorsal margin to the posterior fourth, where it merges with the second posterior marginal ridge. First posterior marginal ridge weak, running from posterodorsal cardinal angle to the ventral sinuation, obscures ventral margin behind the ventral sinuation. Second posterior marginal ridge very prominent, running from the posterior sixth of the dorsal margin, parallel to the posterior margin, and sloping obliquely downwards to the ventral sinuation. It runs parallel to the ventral margin and disappears a little anterior to the ventral sinuation. U-shaped depression present in dorsocentral area. Anterocentral and posterocentral area ornamented with deep reticulations, commonly separated by thin, low partitions into two or more compartments. Eye tubercle obscure. Inner lamella moderately wide along anterior and posteroventral margins, line of concrescence nearly coinciding with the inner margin. Anterior vetibule present but very narrow. Radial pore canals moderately numerous, repeatedly polyfurcate. Normal pores small, few, scattered. Muscle scars located slightly below the center. Four adductor scars in a vertical row, the highest subtriangular, the middle two elongated, horizontal, the lowest circular. Selvage prominent. Snap-knob present in the right valve, corresponding snap-pit in the left. Hingement of the Callistocythere littoralis type. Dimensions. —Holotype female LV; L, 0.55, H, 0.29; paratypes, male RV, UMUT-CA 15011 (Pl. 9, fig. 4); L, 0.54, H, 0.27; female LV, UMUT-CA 15012 (Pl. 9, fig. 6); L, 0.53, H, 0.26; female RV, UMUT-CA 15013 (Pl. 9, fig. 7); L, 0.58, H, 0.28; male LV, UMUT-CA 15043 (Pl. 9, fig. 8); L, 0.53, H, 0.28; female RV, UMUT-CA 15044 (Pl. 9, fig. 9); L, 0.53, H,0.28. Occurrence. —Rare to common in AA sub-biofacies, rare in AL and NL sub-biofacies. In Tateyama Bay, common to rare in DS biofacies. Subfamily Schizocytherinae Mandelstam, 1960 Tribe Paijenborchellini Deroo, 1966 Genus Neomonocertina Kingma, 1948 Neomonoceratina sp. Pl. 9, fig. 12. Illustrated specimen. —A left valve, UMUT-CA 15014. Remarks. —This species somewhat resembles Neomonocertatina japonica (Ishizaki, 1966) in carapace outline and surface ornamentation, but differs by possessing a dorsally located, downturned caudal process.
Occurrence. —One specimen was found in sample 61 and one in sample 114, both from the Chikura area. Subfamily Hemicytherinae Puri, 1953 Tribe Hemicytherini Puri, 1953 Genus Hemicythere Sars, 1925 Hemicythere sp. Pl. 9, fig. 15. Illustrated specimen. —A right valve, UMUT-CA 15015. Remarks. —This species somewhat resembles Hemicythere? miii (Ishizaki, 1969) but differs by absence of ridges, and surface ornamentation, consisting of fine reticulation in the marginal areas and punctation in the central area. Occurrence. —One valve was found in sample 162, belonging to the SN biofacies. Genus Awila Pokorný, 1955 Awila sp. A Pl. 9, figs. 10, 11. Illustrated specimens. —A right valve, UMUT-CA 15016; a left valve, UMUT-CA 15017. Remraks. —This species strongly resembles Aurila cymba (Brady, 1869) in lateral and posterior outline and ornamentation. It. differs by the absence of dorsal, dorsoposterior ridge. Occurrence. —Abundant in AL sub-biofacies. Common in AA, KN sub-biofacies and SN biofacies, sample 61 and some samples of NL sub-biofacies. In Tateyaroa Bay, common in SFS and Z biofacies, rare in some samples of CBM and IR biofacies. Pl. 9, figs. 13, 14. Illustrated specimens. —A right valve, UMUT-CA 15018; a left valve, UMUT-CA 15019. Remarks. —This species resembles Awila sp. A, but in posterior view Awila sp. Bis oval in outline, while Awila sp. A is subtriangular. It further differs in possessing dorsal ridge ending in a tubercle in dorsoposterior area, while the ventral ridge is not as strongly developed as in Awila sp. A. Aurila sp. B might be a sexual dimorph of Aurila sp. A but even though the two forms commonly occur together their abundance is inversely proportional. Further, the differences in dorsal and ventral ridges become more prominent in immature forms. Occurrence. —Abundant to common in A biofacies. Common in LK, LP, N, SN, and KS biofacies. In Tateyama Bay, common in some samples of the SFS, CBM, DM, IR, and Z biofacies. Rare live specimens found in samples 15 and 27 of the CBM and IR biofacies. Subfamily Trachyleberidinae Sylvester-Bradley, 1948 Tribe Trachyleberidini Sylvester-Bradley, 1948 Genus Trachyleberis Brady, 1898 Trachyleberis straba n. sp. Pl. 8, figs. 1, 2; Pl. 9, figs. 16-18; text-fig. 31e. Etymology. —From "strabus" [Latin, "squinting"] Type. —Holotype, UMUT-CA 15020, left valve, female (Pl. 9, fig. 18), obtained from sample no. 107, from Tomoe River area near the village of Kotsuka. Sediment is silty sand, and the sample belongs to the KN biofacies. Diagnosis. —Species of the genus Trachyleberis distinguished by the presence of a snapknob and absence of eye tubercle. Description. —Carapace thick, rather small for the genus. In lateral view elongate, subtrapezoidal, tapering toward posterior end. Highest at anterior cardinal angle. Anterior margin broadly rounded. Dorsal margin straight, ventral margin slightly sinuate at the middle. Posterior margin truncated, meets dorsal and ventral margins at a distinct angle. Anterior, ventral, and posterior margins ornamented with spines and tubercles. Carapace ornamented with tubercles, normal pore canals few, mostly located at the top of tubercles. Anterior marginal ridge prominent, arising from area below anterior cardinal angle and running parallel to anterior margin to the upper half, where it disappears abruptly. A short, slightly sinuous ridges runs vertically from the anterior cardinal angle to a little below the beginning of the anterior marginal ridge. Marginal infold narrow, line of concrescence coincides with inner margin; no vestibule. Radial pore canals narrow, slightly curved, numerous in anterior and posterior ends. Hingement holamphidont, central bar crenulate. Muscle scars situated in subcentral depression and composed of a V-shaped frontal scar and four horizontally elongated muscle scars in a vertical row. Sexual dimorphism distinct, males longer and lower than females. Remarks. —Even though this species strongly resembles Trachyleberis scabrocuneata in shape and ornamentation, the absence of an eye tubercle is remarkable. This is perhaps the only blind species of the genus. Dimensions. —Holotyps, female LV; L, 0.69, H, 0.40; paratypes, female RV, UMUT-CA 15021 (Pl. 9, fig. 17); L, 0.69, H, 0.39; male LV, UMUT-CA 15022 (Pl. 9, fig. 16); L, 0.77, H,0.41. Occurrence. —Rare to common in K and KN sub-biofacies. Genus Bythoceratina Hornibrook, 1952 Bythoceratina sp. Remarks. —This species resembles Bythoceratina sp. A described by Ishizaki (1968). It differs from Bythoceratina hanaii by near absence of median sulcus, lack of reticulation and less protruding, more broadly rounded posterodorsal margin. Only immature specimens were found. Occurrence. —Rare in SN and N biofacies. Suobfamily Cytherurinae G. W. Müller, 1894 Genus Semicytherura Wagner, 1957 Semicytherwa sabula n. sp. Pl. 8, figs. 8-14, 16, 17; text-fig. 31d. Etymology. —From "sabulum" [Latin, "coarse sand"]. Type. —Holotype, UMUT-CA 15023, female carapace (Pl. 8, fig. 10), obtained from sample T10 taken in the Tateyama Bay at depth of about 10 m. Sediment was coarse to medium sand, and the sample belongs to the SCS biofacies. Diagnosis. —Species of Semicytherura distinguished by its outline and surface ornamentation consisting of wrinkles in the anteroventral area. Description. —Carapace small, thin, sexual dimorphism pronounced. Female: Valves slightly asymmetrical, right valve higher than left. Valves reniform in lateral view, greatest height at the middle. Anterior margin broadly rounded, posterior margin more narrowly rounded, extremity at lower third. In right valve posterior margin slightly concave at upper half, meeting the dorsal margin at a distinct cardinal angle. In the left valve posterior margin merges with dorsal margin. Ventral margin gently concave at the middle. In dorsal view, carapace oblong oval, anterior pointed, posterior widely rounded, widest at the middle. Left valve overlaps the right at the anterior and posterior one-sixth; right valve overlaps left at the central two-thirds. Male: Carapace elongated subrectangular in lateral view. Dorsal margin very gently archped, meets anterior margin with a distinct cardinal angle in left valve and merges with anterior margin in right valve. Anterior margin broadly rounded. Ventral margin gently concave at the middle. Posterior margin broadly rounded in left valve, more narrowly rounded in right valve. Extremity at slightly below middle. Posterior margin slightly concave in upper half in right valve, meeting dorsal margin at a small cardinal angle. In the left valve posterior margin merges with dorsal margin. In dorsal view, oblong, anterior narrowly pointed, posterior bluntly pointed, slightly compressed at middle, widest at posterior fourth. Surface smooth except at anteroventral and posteroventral area, where it is sculptured with weak, wrinklelike, sinuous ridges parallel to margins. Normal pores few, scattered. Infold and fused zone moderately wide: one-tenth length anteriorly, four-fifteenth length posteriorly in female, two-fifths in male. Radial pore canals moderate in number, mostly unbranched, often curved. False radial pore canals also present. Adductor muscle scars four in vertical row; frontal scars could not be observed. Hingement lophodont of Cytherwa type. Dimensions. —Holotype female carapace; L, 0.33, W, 0.10; paratypes, female LV, UMUT-CA 15024 (Pl. 8, fig. 8); L, 0.33, H, 0.16; male carapace, UMUT-CA 15025 (Pl. 8, fig, 9); L, 0.33, W, 0.09; female RV, UMUT-CA 15026 (Pl. 8, fig. 11); L, 0.33, H, 0.15; male RV, UMUT-CA 15027 (Pl. 8, fig. 12); L, 0.32, H, 0.13; male RV, UMUT-CA 15028 (Pl. 8, fig. 13); L, 0.31, H, 0.13; male carapace, UMUT-CA 15029 (Pl. 8, fig. 14); L, 0.33, H, 0.12; female RV, UMUT-CA 15040; L, 0.31, H, 0.15; female LV, UMUT-CA 15041; L, 0,35, H, 0.15. Occurrence. —Live specimens abundant in SCS biofacies of Tateyama Bay. Subfamily Loxoconchinae, Sars, 1925 Genus Loxoconcha Sars, 1866 Loxoconcha sp. Pl. 9, figs. 19, 20. Illustrated specimens. —A right valve, UMUT-CA 15030; a left valve, UMUT-CA 15031. Remarks. —A species of Loxoconcha characterized by somewhat converging dorsal and ventral margins and surface ornamented with fine reticulation. Only immature specimens were found. Occurrence. —Abundant in sample 61 and common in sample 76, both from Chikura area. Common to rare in KS, N, and LP biofacies.In Tateyama Bay one specimen was found in sample 13 of the DS biofacies. Genus Nipponocythere Ishizaki, 1971 Nipponocythere hastata n. sp. Pl. 8, fig. 15, 18-20; text-fig. 31c. Etymology. —From "hastatus" [Latin, "spear-shaped"]. Type. —Holotype, UMUT-CA 15032, right valve, female, (Pl. 8, fig. 19), obtained from sample no. 7 from the coral-bearing sediment in Koyatsu, West Coast Valley area. The sample belongs to the AL sub-biofacies. Diagnosis. —Species of the genus Nipponocythere distinguished by strong sinuation of the ventral margin. Description. —Carapace rather flat, in lateral view elongate subtrapezoidal in outline, highest at anterior cardinal angle. Anterior margin broadly, evenly rounded, dorsal margin straight, ventral margin concave slightly anterior to middle. Posterior end obliquely truncated, narrowly rounded at lower third. Longest at lower third. Sexual dimorphism present, male lower and longer than female. Surface smooth in anterior, ventral and posterior areas, closely punctate in the central and dorsal areas. Inner lamella wide anteriorly, narrower ventrally and posteriorly. Line of concrescence parallel to outer, subparallel to inner margin. Vestibule moderate anteriorly, small posteriorly. Radial pore canals few, evenly spaced, straight. False radial pore canals present. Normal pores of simple type with a low lip, moderately numerous, scattered. Muscle scar consisting of a row of four elongate adductor scars and one inclined reniform anterior scar. Hingement Loxoconchinae gongylodont. In the right valve, anterior tooth is surrounded dorsally by a crescent-shaped extension of the median groove. Median groove narrow, smooth; first posterior tooth small, second large. Dimensions. —Holotype female RV; L, 0.43, H, 0.20; paratypes, female LV, UMUT-CA 15033 (Pl. 8, fig. 15); L, 0,43, H, 0.20; female RV, UMUT-CA 15034 (Pl. 8, fig. 18); L, 0.41, H,0.20. Occurrence. —Rare to common in AL aub-biofacies and LK biofacies, rare in AA subbiofacies. Absent in Tateyama Bay. Subfamily Paradoxostomatinae Brady and Norman, 1889 Genus Paradoxostoma Fisher, 1855 Paradoxostoma sp. 1 Text-fig. 32a. Illustrated specimen. —A left valve, UMUT-CA 15036. Remarks. —Species of the genus Paradoxostoma characterized by prominent caudal projection at the lower third of the posterior margin. Occurrence. —Rare to common in A biofacies. In Tateyama Bay one specimen found in sample 18 (SCS). Text-fig. 32c. Illustrated specimen. —A right valve, UMUT-CA 15037. Remarks. —The present species resembles Paradoxostoma lunatum illustrated by Okubo (1976), but differs in more narrowly rounded anterior and posterior margins. Occurrence. —One specimen was found in sample 60 and one in sample 61. Text-fig. 32b. Illustrated specimen. —A right valve, UMUT-CA 15038. Remarks. —This species resembles Paradoxostoma convexum illustrated by Okubo (1977), but differs in more sharply angulated dorsal margin and slightly concave posterodorsal margin. Occurrence. —Rare in LK, SN and A biofacies. Cytherois? sp. Text-fig. 32f. Illustrated specimen. —A right valve, UMUT-CA 15039. Remarks. —This species somewhat resembles Cytherois zosterae Schornikov, but differs in the much more acutely rounded anterior and posterior margins. Occurrence. —Rare to common in A biofacies, rare in LK and SN biofacies. In Tateyama Bay common in sample 7 of the CBM biofacies.
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