Cobanocythere lata, Higashi, Ryouichi & Tsukagoshi, Akira, 2011

Higashi, Ryouichi & Tsukagoshi, Akira, 2011, Four new species of the interstitial family Cobanocytheridae (Crustacea: Ostracoda) from central Japan, Zootaxa 2924, pp. 33-56 : 40-45

Cobanocythere lata sp. nov.

( Figs 6 B, 7–10)

Type series. Holotype: adult male (SUM-CO-1959), right valve length 312 µm, height 103 µm, left valve length 321 µm, height 108 µm, appendages mounted on slide and valves preserved in a cardboard cell slide, Paratypes: 13 adult males (SUM-CO- 1960–1972) and 7 adult females (SUM-CO- 1973–1979). All illustrated specimens were collected from interstitial pore water at the type locality on April 16, 2010.

Type locality. Oiso, Oiso Town, Kanagawa Prefecture, Pacific coast of central Japan ( Fig. 1 B), 35°18'20"N, 139°18'33"E. Marine littoral beach; sediment composed of well-sorted clastic granule. Sampling depth approximately 5 cm.

Etymology. The Latin latus (wide) refers to the laterally extended carapace of this species.

Diagnosis. Female larger than male. Carapace extended laterally, and upside-down V shape in both anterior and posterior view. Smooth carapace surface. Anterior part of carapace sharply rounded and shallowly concaved on ventral margin in lateral view. Fifty-nine pore systems per valve. Seven and two marginal pores along anterior and posterior margins, respectively. One vein-like structure running forward on inner surface of ventral area of anterior marginal infold. Hingement of lophodont type. No rib behind adductor muscle scars. Spoon-shaped seta on postero-distal end of antennal endopodite. Male copulatory organ consisting of thin and triangular distal lobe, rounded tip of capsule, long projection on distal part of capsule and bended sharply copulatory duct.

Description. Carapace ( Figs. 7 , 8 ). Depressed dorso-ventrally and elongated. Upside-down V shaped outline in both of anterior and posterior views. External surface smooth. Anterior part protruded in dorsal view. Both anterior and posterior margins sharply rounded in lateral view. Ventral area flat and very shallowly concaved in anteroventral margin. All pore systems simple type and 59 per valve. Marginal infold broad in anterior area and narrow in posterior area. One vein-like structure running forward on inner surface of anterior marginal infold. Vestibula developed in anterior area and very narrow in posterior marginal infolds. Left valve slightly overlapping right valve along anterior and posterior margins. Hingement of lophodont type. Three adductor muscle scars in oblique row.

Antennula (Fig. 9A). Five articulated podomeres. First podomere bare. Second podomere twice as long as first podomere, with one long seta on outside of distal end and long setulae along anterior and outside margins. Third podomere as long as second podomere, with one medium seta on antero-distal end. Fourth podomere as long as third podomere, with one medium seta on antero-medial suture, two long and one medium setae on antero-distal end, one long medium seta on middle of posterior margin and one long seta on postero-distal end. Fifth podomere two-thirds as long as fourth podomere, with one long, one very long seta, and one pair of basally fused setae composed of slender and round-tipped setae on distal end.

Antenna (Fig. 9B). Four articulated podomeres. First podomere with two segmented spinneret (exopodite) on outside distal end. Second podomere half as long as first podomere, with one medium seta on postero-distal end and one medium thin seta on centre of outside. Third podomere three-halves as long as second podomere, with one long and one very short setae on antero-medial suture, one very short and round-tipped (aesthetasc) seta on middle of posterior margin and one short seta on postero-distal end. Fourth podomere two-fifths as long as third podomere, with claw on antero-distal end and one spoon-shaped seta on postero-distal end.

Mandibula (Fig. 9C1, C2). Coxa (Fig. 9C1) long, with one thick seta on antero-ventral part, two setae between first and second anterior coxal endites and one seta on postero-ventral part. Five coxal endites. Palp (Fig. 9C2) consisting of four articulated podomeres. First podomere (basis) with short process (exopodite) on middle outside of dorsal margin and one long setulous seta on ventro-distal end. Second podomere six-fifths as long as first podomere, with one long setulous seta on inside ventro-distal end. Third podomere two-thirds as long as second podomere, with three long setae on middle of dorsal margin, one relatively short and one thick setae on ventro-distal end and one medium and thick seta on outside distal end. Fourth podomere half as long as third podomere, with two medium setae on distal end.

Maxillula (Fig. 9D). Thin branchial plate (exopodite) with nine plumose setae. Basal podomere with one palp and three endites. Palp consisting of two indistinct podomeres: first podomere with three long and one short setae on dorso-distal end and one long seta on outside of distal end; second podomere half as long as first podomere, with two long setae on distal end. Endites: dorsally two with five setae; and ventrally one with four setae.

Fifth limb (Fig. 9E). Four articulated podomeres. First podomere with one short seta on antero-proximal part, one medium setulous seta on antero-distal end and very short seta on postero-proximal part. Second podomere four-thirds as long as first podomere, with one short seta on antero-distal end. Bare third podomere half as long as second podomere. Fourth podomere seven-fifths as long as second podomere, with stout distal claw.

Sixth limb (Fig. 9F, G). Remarkably reduced leg in male (Fig. 9F): three articulated podomeres; first podomere with one very short seta on antero-proximal part, one short seta on postero-proximal part and one medium seta on antero-distal end; second podomere as long as first podomere, with one medium seta on antero-distal end; third podomere half as long as second podomere, with short seta on distal end. Normal walking leg in female (Fig. 9G): four articulated podomeres; first podomere with one medium setulous seta on antero-distal end and one short seta on postero-proximal part; second podomere seven-fifths as long as first podomere, with medium seta on antero-distal end; third podomere two-fifths as long as second podomere; fourth podomere five-thirds as long as third podomere, with stout distal claw.

Seventh limb (Fig. 9H). Four articulated podomeres. First podomere with one short seta on antero-proximal part, one medium setulous seta on antero-distal end and one short seta on postero-proximal part. Second podomere four-thirds as long as first podomere, with one medium setulous seta on antero-distal end and setulae distally along two-thirds of anterior margin. Third podomere two-fifths as long as second podomere, with setulae along anterior, posterior and distal margins. Fourth podomere four-thirds as long as third podomere, with one stout distal claw and setulae distally along half of anterior and distal margin.

Male brush-shaped organ (Fig. 9I). Consisting of two branches and each branch with about 10 setae on distal margin.

FIGURE 9. Appendages of Cobanocythere lata sp. nov. A–E, Holotype (SUM-CO-1959); F, H and I, Paratype (SUM-CO- 1960); G, Paratype (SUM-CO-1973). A, antennula; B, antenna; C1, coxa of mandibula; C2, palp of mandibula; D, maxillula; E, fifth limb; F, sixth limb of male; G, sixth limb of female; H, seventh limb; I, brush-shaped organ. Scale bar indicates 50 µm.

Male copulatory organ ( Fig. 10 A, B). Capsule trapezoidal. Tip of capsule (Tc) rounded. Long claw-like projection (Cp) on distal part of capsule. Distal lobe (Dl) thin and sharply round-tipped triangular: left Dl shorter than right. Copulatory duct (Cd) about one-third as long as capsule, bended sharply on distally one-fourth. Caudal part of female ( Fig. 6 B). Genitalia consisting of strongly sclerotised projection and rounded framework, each component connected to ovum by duct. Caudal rami near genitalia, with two setae on anterior and posterior parts, respectively. Caudal process with one spine on distal end, surrounded by thin setulae. Eye. Absent.

Dimensions. See Table 2.

Length (µm) Height (µm)

Mean Observed range N Mean Observed range N Male Right valve 315 299–326 7 103 98–107 7

Left valve 321 310–333 7 113 107–123 7 Female Right valve 386 376–399 5 129 123–133 5

Left valve 395 382–409 5 144 138–147 5 Occurrence. So far known only from type locality.

Remarks. This new species resembles Cobanocythere guttaeformis Gottwald, 1983 in the shape of carapace and most of features of the appendages. The laterally extended shape of carapace especially, is shared with C. lata sp. nov., and C. guttaeformis . Moreover, the absence of rib behind adductor muscle scars is a common feature between them. The proportion of podomeres of each appendage is almost the same, except that the ratio of length of the third podomere of mandibular palp of C. lata sp. nov. (approximately two-thirds length of the second podomere) is larger than C. guttaeformis (approximately half length of the second podomere). Cobanocythere lata sp. nov., and C. guttaeformis should be put together as “ guttaeformis group”, owing to their morphological similarities. Although the structure of the male copulatory organ of C. guttaeformis was not shown in its original description in Gottwald (1983), C. lata sp. nov., can be distinguished from C. guttaeformis by the following features: straight row of adductor muscle scars; an extremely short and round-tipped seta on the middle of the posterior margin of antennal third podomere; a spoon-like seta on distal end of antennal endopodite; relatively slim seventh limb and oval-shaped tip of sclerotised projection of the female genitalia.

The fossil species C. pulchra is also similar to C. lata sp. nov. in its carapace characters. Cobanocythere lata sp. nov. can be distinguished from C. pulchra by the following features of carapace: no hollow at median part of ventro-lateral region and more sharply rounded posterior part than C. pulchra .

Figures

FIGURE 1. Study area. A, map of Japan; B, sampling sites.

FIGURE 6. Caudal part of female. A, Cobanocythere ikeyai sp. nov., ventral view (Paratype, SUM-CO- 1956); B, Cobanocythere lata sp. nov., ventral view (Paratype, SUM-CO- 1974). Scale bars indicate 50 µm.

FIGURE 7. Carapaces of Cobanocythere lata sp. nov. A – K, male specimens: A and B, Paratype (SUM-CO- 1962); C, I and J, Paratype (SUM-CO- 1963); D and K, Paratype (SUM-CO- 1964); E, Paratype (SUM-CO- 1965); F, Paratype (SUM-CO- 1966); G, Paratype (SUM-CO- 1967); H, Paratype (SUM-CO- 1968). A, left external lateral view; B, right external lateral view; C, internal view of left valve; D, internal view of right valve; E, dorsal view; F, ventral view; G, anterior view; H, posterior view; I, adductor muscle scars of left valve; J, hingement of left valve; K, hingement of right valve. L – O, female specimens: L and M, Paratype (SUM-CO- 1975); N and O, Paratype (SUM-CO- 1976). L, left external view; M, right external view; N, internal view of left valve; O, internal valve of right valve. Scale bar indicates 200 μm for A – H and L – O, 50 µm for I, and 100 µm for J and K, respectively.

FIGURE 8. Carapaces of Cobanocythere lata sp. nov. A and B, Holotype (SUM-CO- 1959). A, left external view; B, right external view. Each of the carapace structures are transmitted images. Scale bar indicates 200 µm.

FIGURE 10. Male copulatory organs of Cobanocythere lata sp. nov. A and B, Holotype (SUM-CO- 1959). A, internal view of right organ; B, internal view of left organ. Copulatory ducts are shaded. Abbreviation: Tc, tip of capsule; Cp, claw-like projection; Dl, Distal lobe. Scale bar indicates 50 µm.