Paracobanocythere vietnamensis Tanaka & Le

Tanaka, Hayato, Dung, Le Doan, Higashi, Ryouichi & Tsukagoshi, Akira, 2016, A new interstitial ostracod species of the genus Paracobanocythere from Vietnam, with mitochondrial CO 1 sequence data of three Asian species, ZooKeys 559, pp. 17-33 : 19-26

Taxon classification Animalia Podocopida Cobanocytheridae

Paracobanocythere vietnamensis Tanaka & Le sp. n.

Type series.

Holotype: adult male (NSMT-Cr 24314), right valve length 323 µm, height 107 µm, left valve length 337 µm, height 111 µm, soft parts mounted on a slide and valves preserved in a cardboard cell slide. Paratypes: 11 adult males (NSMT-Cr 24315-24325) and 9 adult females (NSMT-Cr 24326-24334). All specimens were collected by Hayato Tanaka on 21 November 2014.

Type locality.

The holotype specimen was collected from Dăm Ngoài Island, Phu Quoc Marine Protected Area in Phu Quoc Island, the southwest Vietnam, 9°59'42"N, 104°02'17"E (Fig. 1C); in an interstitial environment at 10 cm below the shoreline sand surface. The substrate consisted mainly of very coarse sand (median grain size is about 2 mm).

Diagnosis.

Carapace elongate in lateral view and depressed dorsoventrally. Anterior and posterior margins rounded. Carapace surface smooth but with small granular texture visible at high magnification. Sieve-type normal pores with recessed sieve plates and thick rims on carapace surface. Left hemipenis bearing one additional pincer-like structure and one hooked process.

Description of adult male.

Carapace (Figs 2 A–D, G–H, K, M–O; 3; 4). Length and height of left valves greater than those of right valve (Table 2). Carapace elongated in lateral view and depressed dorso-ventrally. In anterior view, carapace rounded triangular (Fig. 2K). Left valve slightly overlapping right valve along anterior and posterior margins. Anterior and posterior margin rounded in lateral view. Marginal infold broad along anterior margin and narrow in posterior area (Fig. 2C, D). Anterior vestibulum occupying most of area in marginal infold, containing five and six marginal pore canals in left and right valve, respectively (Fig. 3). In both valves a thick, irregular ridge runs diagonally upward across the anterior infold, and three short buttress-like ridges or wrinkles run anteriorly from the upper part of this ridge for additional strength. Adductor muscle scar pattern consisting of row of four elongate closely spaced scars and three frontal scars (Figs 2O; 3). Carapace surface with faint granular texture visible at high magnification, resulting from close-packed, tiny tubercules (Fig. 4A). Sieve type normal pores with recessed sieve plates and thick rims on carapace surface (Fig. 4). Pore systems with one bristle. Hingement adont type (Fig. 2M, N). Color translucent white; living individuals have brown granular patterns.

Antennula (Fig. 5A). Consists of six articulated podomeres, of which fourth and fifth are incompletely separated. First podomere bare. Second podomere about two and a half times as long as first podomere, with one long posterodistal seta and short setulae on distal end and eight coarser setulae on anterior margin. Third podomere same length as first podomere and bare. Fourth podomeres twice as long, with one long posterodistal seta. Fifth podomere almost as long, with three anterodistal setae of staggered lengths and one posterodistal seta. Sixth podomere long, slender, with three long anterodistal setae and long distal seta fused at its base with distal aesthetasc.

Antenna (Fig. 5B). Four articulated podomeres. First podomere (basis) bare and slightly triangular, tapering distally, with a long, thick, three-segmented exopodite (spinneret seta) reaching beyond distal claws. Second (first endopodial) podomere with one short seta on posterodistal end. Third podomere with one short and one medium anterodistal setae, one short posteromedial seta, and one short posterodistal seta. Fourth podomere with one long stout posterodistal seta and one curved stout distal claw.

Mandibula (Fig. 5C). Coxa with one short setulous seta on anterior margin. Coxal endite consisting of seven teeth, two short setae and one short claw-like seta. Palp consisting of four indistinct podomeres. Basis with one long setulous seta (exopodite) near proximal end and medium setulous seta on posterodistal end. First podomere of endo podite about one and a half times as long as basis, with one medium anterodistal seta and setulae on anterior margin. Second podomere half as long as first podomere, with two long and one medium setulous setae on middle of anterior margin, one medium mediodistal seta, and one medium posterodistal seta. Third podomere small, with four medium setae on distal end.

Maxillula (Fig. 5D). Thin branchial plate (exopodite) with ten plumose setae. Basal podomere with one palp (endopodite) and three endites. Palp consisting of two distinct podomeres: first podomere with five long setae on distal end; second podomere two-thirds as long as first podomere, with one long and one medium setae on distal end. Outer two endites with five setae, and posteriormost one with four setae.

Male brush-shaped organ (Fig. 5E). Consisting of two branches (right and left) each with 16 setae on distal margin.

Fifth limb (Fig. 6A). Four articulated podomeres; two distal podomeres and claw somewhat thickened. First podomere with one medium setulous anterodistal seta, one long setulous posteroproximal seta and setulae along both margins. Second podomere five-fourths as long as first podomere, with one short anterodistal seta. Third podomere bare and half length of second podomere. Fourth podomere same length as third podomere with rows of setulae on anterior surface and one stout distal claw.

Sixth limb (Fig. 6B). Three podomeres, of which two are flimsy and weakly developed. First podomere with one medium setulous seta on middle of anterior margin and one long setulous seta on middle of posterior margin. Second podomere two-thirds as long as first podomere, posterior margin flabby, with one long setulous seta on antero-distal end. Basal part of third podomere same length as second podomere, with flabby elongated sheet distally and two weakly developed long branches.

Seventh limb (Fig. 6C).Four articulated podomeres, all very large. First podomere with one short setulous seta on antero-distal end, one medium setulous seta on near postero-proximal part, and setulae along anterior margin. Second podomere five-fourths as long as first podomere, with one short seta and row of setulae on antero-distal end. Third podomere one-third as long as second podomere, with rows of setulae on anterior surface and distal margin. Fourth podomere same length as third podomere, with rows of setulae on anterior surface and distal margin, with one stout, club-shaped distal claw with rows of setulae on middle part, near distal part, and around distal end.

Male copulatory organ (Fig. 7). Copulatory duct very long, more than length of capsule. Tip of capsule (Tc) and distal lobe (Dl) asymmetric in right and left hemipenes. Right hemipenis (Fig. 7A): Tc almost square distal part with rounded corner; Dl finger-shaped, bending ventrally at half. Left hemipenis (Fig. 7B): Tc slender, bending ventrally near the tip; Dl acute-angle triangular, curving ventrally at half; additional pincer-like structure (Ps) and hooked process (Hp) exist. Both hemipenes bearing one long and two short setae on ventral margin (vestigial furca).

Eye. Present.

Description of adult female.

Carapace (Fig. 2E, F, I, J, L). Both left and right valve of female slightly greater than valves of male (Table 2, Fig. 9). In dorsal view, width of carapace slightly greater than that of male (Fig. 2I, J). Anterior and posterior margins more tapered rather than those of male (Fig. 2E, F).

Sixth limb (Fig. 6D). Four articulated podomeres with slender, more normal proportions than the male limb. First podomere with one medium setulous anterodistal seta and one medium setulous posteroproximal seta. Second podomere four-thirds as long as first podomere, with one short anterodistal seta. Third podomere bare and half as long as first podomere. Fourth podomere same length as third podomere, with row of setulae on anterior distal surface, with one tapering distal claw.

Posterior part of body and female genitalia (Fig. 8). Sclerotized framework of paired genital openings trapezoidal in shape. Spermathecal duct very long, connecting with genital opening and receptaculum seminis. Two setulose setae (vestigial caudal rami) situated near each genital opening. Five rows of tiny setulae on abdominal end.

Dimensions.

See Table 2 and Fig. 9.

Occurrence.

So far known only from type locality.

Etymology.

Named in recognition of this being the first record of Paracobanocythere from Vietnam.

Remarks.

Paracobanocythere grandis and other three species including Paracobanocythere vietnamensis sp. n. are easily distinguishable by the length of carapace (Table 3). While Paracobanocythere grandis has an exceptionally large carapace (approximately 500 µm) for this genus ( Higashi and Tsukagoshi 2011), those of the other three species are relatively smaller (roughly 300 µm) ( Gottwald 1983, Higashi and Tsukagoshi 2011). Furthermore, the female carapace larger than that of the male in Paracobanocythere grandis , and that is opposite to the status in the other three species (Table 3). The carapace shape as well as appendage morphologies including chaetotaxy and the number of podomeres, of Paracobanocythere vietnamensis sp. n. are quite similar to those in Paracobanocythere hawaiiensis and Paracobanocythere watanabei (Table 3). One slight difference is found in the chetotaxy of the sixth limb of male, i.e., the first podomere lacks the one short seta on antero-distal end, which is present in Paracobanocythere hawaiiensis and Paracobanocythere watanabei but absent in Paracobanocythere vietnamensis sp. n. Moreover, the faintly granular texture of carapace surface of Paracobanocythere vietnamensis sp. n. has never been reported from Paracobanocythere hawaiiensis and Paracobanocythere watanabei . As for the morphology of the male coplatory organ, the new species can be easily distinguished from these two species. Specifically, the left hemipenis of Paracobanocythere vietnamensis sp. n. possesses Ps and Hp, whereas these structures are not observed in the original description of either of the two other species (Table 3).