Callistocythere ventricostata Ruan & Hao, 1988

Ha, Tran Manh & Tsukagoshi, Akira, 2015, First records of interstitial leptocytherids (Crustacea, Ostracoda): two new species and a redescription of Callistocythere ventricostata Ruan & Hao, 1988 collected from the Okinawa Islands, southern Japan, Zootaxa 4006 (1), pp. 83-102 : 95-100

Callistocythere ventricostata Ruan & Hao, 1988

( Figs 11–15 )

Callistocythere ventricostata: Ruan & Hao 1988 , 320–321, pl. 56, figs 27–29.

Examined specimens. All specimens were collected from interstitial environments of the northwest coast of Sesoko Beach ( Fig. 1 C), the Okinawa Islands, Japan, 26°39'4.10"N, 127°51’27.00"E, on 16 May 2002 and 30 June 2014. 4 Males (SUM-CO-2359; SUM-CO-2360; SUM-CO-2361; SUM-CO-2362) and 3 females (SUM-CO–2363; SUM –CO-2364; SUM-CO-2365).

Diagnosis. Carapace outline elongated in lateral view and triangular in posterior margin. Surface covered with well-developed radially branched ridges on anterior half and clear polygon reticulation in posterior half and dorsal area. Strong ridges along ventral margin on anterior half, prominent ridge and few weak ridges along ventral margin. More than ten ring-like structure surrounding pore opening. Hingement of modified merodont type with smooth bar and smooth groove of median element in right and left valves, respectively. Male copulatory organ bearing thin and sharp triangular distal lobe, and 4 clasping apparatus of different shapes, copulatory duct simple, long and extending distally.

Redescription. Carapace ( Figs 11 , 13 ). Carapace outline elongated in lateral view, with triangular posterior margin. No conspicuous sexual dimorphism. Anterior margin evenly rounded downward. Dorsal margin almost straight and slightly arched at posterior half and sloping downward toward ventral margin. Ventral margin slightly curved at middle and sinuate. Carapace surface covered with clear polygonal reticulation, especially in posterior half and dorsal area. Shape of each reticulation pentagonal or hexagonal, and surrounding several pits. Some pores opening surrounded ring-like structure. Strong ridges running along ventral margin on anterior half, a prominent ridge and few weak ridges along ventral margin ( Fig. 12 C, H). Marginal infoldment developed, relatively broad along lower mid-anterior and posterior ventral margins and twisted in middle of ventral area. Vestibulum developed in anterior and posterior areas. Hingement ( Fig. 12 I, J) modified merodont type, very weak teeth on anterior and posterior elements, median element forming smooth bar in right valve and smooth groove in left valve, terminal teeth slightly crenulated in right valve and interlocking with corresponding sockets of left valve. Marginal pore canals ( Fig. 11 ) totalling about 22, bifurcated in anterior region and simple in posterior and ventral areas. Adductor muscle scars ( Fig. 13 G) consisting of 4 scars; elongated C shaped frontal scar in front of adductor scars; 2 divided small rounded mandibular scars in front of lowest adductor scar, fulcral point rounded. Snap structure ( Fig. 13 E, F) existing in middle ventral margin, right valve bearing knob interlocking with corresponding socket of left valve.

Antennula ( Fig. 14 A). Five articulated podomeres, length ratios from proximal to distal 15:14:4:8:5. First podomere stout without seta. Second podomere oblong, covered with numerous setulae along anterior distal margin, bearing two bunches of fine setulae, one located third from anterior proximal and anterior distal end, respectively. One long setulous seta at posterior distal end. Third podomere short sub-quadrangular, covered with numerous setulae along anterior margin, bearing 1 medium-length setulous seta at anterior distal corner. Fourth consisting of two fused podomeres and covered with numerous setulae along anterior margin, bearing 1 long and 1 medium-length setulous seta on middle of anterior margin, 1 setulous seta on middle of posterior margin, 1 short setulous, 2 very long, simple, slender setae, and 1 stout serrated claw at anterior distal end. Fifth podomere slender, bearing 1 long simple, slender and 1 short setae, 1 long aesthetasc seta, and 1 stout serrated claw at distal end.

Antenna ( Fig. 14 B). Four articulated podomeres, length ratios from proximal to distal 16:7:19:2, and width decreasing irregularly in this order. First podomere stout, adorned with numerous setulae along anterior and posterior margins and bearing very long, stout two-segmented (but almost fused) exopodite (= spinneret seta) at anterior distal end. Second podomere sub-quadrate, covered with numerous setulae along distal margin, 1 short setulous seta at posterior distal corner and bunch of setulae on anterior proximal end. Third podomere irregular oblong and slender, covered with numerous setulae along anterior margin of proximal half, 2 long, simple, slender setae at mid point of anterior margin, 1 setulous seta and 1 aesthetasc at mid-point of posterior margin, and 1 medium-length setulous seta at one fifth of length from posterior distal end. Fourth podomere very small and bearing two strong, sub-equal length claws.

Mandibula ( Fig. 14 C). Five articulated podomeres. Coxa stout and bearing developed teeth and about 3 aesthetasc-like setae on ventral margin. Basis sub-quadrangular, bearing 2 setulous setae on middle of ventral margin, and reduced exopodite as 1 plumose seta on dorsal margin. First podomere of endopodite oblong with 1 small, simple setae on middle margin of distal end and 2 long stout plumose setae (annulated at distal half) at ventro distal corner (lower ventro distal one only setulous along ventral margin). Second podomere of endopodite sub-pentagonal, bearing 3 medium-length setulous setae on middle of dorsal margin, 1 long, stout claw-like seta at anterior distal end, 1 short, simple and 1 medium -length, stout simple setae at anterior ventral corner. Third podomere of endopodite very small and sub-quadrangular, bearing 1 long, stout, simple claw-like seta, 2 mediumlength simple setae, and 1 small simple seta at distal end.

Maxillula ( Fig. 14 D, E). Thin branchial plate bearing 14 long plumose setae and 2 short simple setae. Basal podomere bearing palp and 3 endites; palp consisting of two podomeres, proximal one with 1 stout simple setae on distal end, distal one with 1 simple and 1 claw-like seta. Three endites (masticatory lobes) possessing 3, 3, 4 simple setae at distal end, respectively.

Fifth limb ( Fig. 14 F). Four articulated podomeres, length ratios from proximal to distal 12:8:6:6. First podomere bearing 1 setulous seta on middle of anterior margin, 2 setulous setae at anterior distal corner, 1 setulous seta at one fourth of length from posterior proximal end. Second podomere covered by short setulae along anterior margin and bearing 1 setulous seta at anterior distal end. Third podomere covered with numerous setulae along anterior margin and bearing no seta. Fourth podomere covered with numerous setulae along anterior margin and bearing strong terminal claw with serrations arranged in 1 row along anterior margin near tip.

Sixth limb ( Fig. 14 G). Four articulated podomeres, length ratios from proximal to distal 15:8:6:6. First podomere bearing 1 setulous setae on middle of anterior margin, 1 short setulous seta at anterior distal corner, 1 setulous seta at one fourth of length from posterior proximal end. Second podomere covered with numerous setulae along anterior margin and bearing 1 setulous seta at anterior distal end. Third podomere covered by short setulae along anterior margin and bearing no seta. Fourth podomere covered with numerous setulae along anterior margin and bearing strong terminal claw with serrations arranged in 1 row along anterior margin near tip.

Seventh limb ( Fig. 14 H). Four articulated podomeres, length ratios from proximal to distal 15:11:7:7. First podomere bearing 1 setulous setae on middle of anterior margin, 1 short setulous seta at anterior distal corner, 1 setulous seta at posterior proximal end. Second podomere covered with numerous setulae along anterior margin and bearing 1 setulous seta at anterior distal end. Third podomere without seta, covered with numerous setulae along anterior margin. Fourth podomere covered with numerous setulae along anterior margin and bearing strong terminal claw with serrations arranged in 1 row along anterior margin at tip.

Male copulatory organ ( Fig. 15 ). General outline of capsule sub-elliptical, left and right hemi-penes almost symmetrical, thin and sharp triangular distal lobe. Four clasping apparatus of different shape; proximal most one stout and forming hook-like tip, second one widely spread lamella and overlapped by third one with tongue shape, distal most one broad lamella with thumb like tip. Copulatory duct simple, long and extending distally.

Dimension. See Table 1 .

Remarks. Callistocythere ventricostata Ruan & Hao, 1988 is similar to Callistocythere minor ; the differences between the two species are that the shell of C. ventricostata is low and elongate, and its surface is broad and flat with reticulate ornamentation. No brush-shaped organ has been observed in any of the examined specimens. This species is distributed from the shoreline to the sub-tidal level in areas dominated by coarse sand (particle size range from 1.4–1.7 mm) to depths from 5–15 cm below the surface of the sediment.

Figures

FIGURE 1. Maps showing the location of the study area. A, map of Japan; B, map of the Okinawa Islands; C, sampling site of this study (Sesoko Beach).

FIGURE 11. Callistocythere ventricostata Ruan & Hao, 1988. Internal view of male carapace. A, left valve; B, right valve (SUM-CO- 2359). Scale 50 µm.

FIGURE 12. Carapace of Callistocythere ventricostata Ruan & Hao, 1988 (SEM images). A, B, external lateral view of male right and left valve, respectively (SUM-CO- 2359); C, D, external lateral view of female right and left valve, respectively (SUM-CO- 2363); E, F, internal lateral view of female left and right valve, respectively (SUM-CO- 2364); G, complete male carapace in dorsal view (SUM-CO- 2360); H, complete male carapace in ventral view (SUM-CO- 2361); I, J. hingement of female left and right valve, respectively (SUM-CO- 2364); Scale, 50 µm.

FIGURE 13. Callistocythere ventricostata Ruan & Hao, 1988 (SEM images) female (SUM-CO- 2364); A, B, anterior and posterior socket of hingement on left valve, respectively; C, D, anterior and posterior teeth of hingement on right valve, respectively; E, F, snap structure in ventral view; G, scars of female right valve. Scale: 10 µm (A – D) and 20 µm (E – G).

FIGURE 14. Callistocythere ventricostata Ruan & Hao, 1988. A. antennula; B. antenna; C, mandibula with endopodite pedometers figured at higher magnification; D, maxillula palp; E, branchial plate of maxillula; F, fifth limb; G, sixth limb; H, seventh limb. A, D, E, female (SUM-CO- 2365); C, male (SUM-CO- 2362); B, F, G, H, male (SUM-CO- 2359); Scale: 20 µm and 10 µm for three endopodites of C.

FIGURE 15. Male copulatory organ of Callistocythere ventricostata Ruan & Hao, 1988 (SUM – CO – 2359). A, B, right and left copulatory organ, respectively. Abbreviations: ca, clasping apparatus; cd, copulatory duct; dl, distal lobe. Scale 50 µm.