Loxoconcha sesokoensis, Dung & Tsukagoshi, 2014

Dung, Le Doan & Tsukagoshi, Akira, 2014, Three new species of the genus Loxoconcha (Crustacea, Ostracoda, Podocopida) from the Okinawa Islands, southern Japan, Zootaxa 3796 (1), pp. 147-165 : 158-161

Loxoconcha sesokoensis sp. nov.

( Figs 10–13 )

Type series. All specimens were collected at the northwest coast of Sesoko-jima ( Fig. 1E ), Okinawa Islands, southern Japan on 27 May 2000. Holotype: SUM-CO-2167 (soft parts and one right valve of adult male; soft parts were mounted on a slide glass in the “Neo Sigaral” agent and carapace was on a card board with single hole). Paratypes: 5 males (SUM-CO-2168, 2171, 2173, 2174, 2177) and 7 females (SUM-CO-2165, 2166, 2169, 2170, 2172, 2175, 2176); also as for the dissected specimens, soft parts were enveloped on a slide glass in the “Neo Sigaral” as mounting agent and carapace was kept on a cardboard slide with single hole; other specimens, carapaces were preserved on a cardboard slice with single hole.

Etymology. After the type locality, Sesoko-jima Island.

Diagnosis. Carapace sub-rhomboid in lateral view, covered with distinct reticulations and sieve-type pore systems sparsely distributed. Number of pore canals 85 per valve. 4 adductor muscle scars in curved sub-vertical row, concave anteriorly. Valve with a gongylodont hingement with crenulations in the median element. Dorsal and ventral margins nearly parallel to each other, especially in male. On fifth and sixth limbs, plumose seta on the posterior margin of first podomere bearing several long setulae. In the male copulatory organ, distal lobe thin along distal margin and forming a long tip. Clasping apparatus large, thin and overlapping whole distal lobe with distal end forming a tip. Copulatory duct very short, fine and folded.

Description. Carapace ( Figs 10 , 11 ). Carapace showing strong sexual dimorphism; male more elongate and with straighter dorsal margin than female. Carapace surface covered with distinctive reticulations. Valves moderate in length, sub-rhomboid in lateral view. Right and left valves showing asymmetry in outline. Both valves slightly tapering toward posterior; greatest height at anterior-most fourth. Dorsal margin slightly convex. Ventral margin almost straight. Both margins nearly parallel to each other, especially in male. Anterior margin broadly rounded. Posterior margin somewhat narrowly rounded with slight caudal process. Marginal infold moderately developed. Most of the list present along the middle of the marginal infold in both valves. Vestibula weakly developed, especially in posterior area of valves ( Figs 10 ). Fused zone mostly as wide as infold ( Figs 10 ). All lateral pore canals of sieve-type, arranged sparsely with 85 pores per valve. Muscle scars ( Fig. 11I, L ): the smaller one round (from 2 frontal scars), a bigger one in curved shape; 2 mandibular scars; 4 adductor muscle scars in curved subvertical row, concave anteriorly. Hingement gongylodont with crenulations in median element except for third and eleventh teeth from posterior terminal tooth.

Antennula ( Fig. 12A ). Consisting of 5 articulated podomeres, length ratios from proximal to distal 25:18:8:15:12, width gradually narrowing in this order. First podomere stout without seta. Second podomere with 1 seta at the postero-distal end and setulae along proximal and distal part of the anterior margin. Third podomere with 1 seta antero-distally. Fourth podomere showing vestigium of segmentation as a ledge with 2 setae on both sides, 1 long seta postero-distally, and with 3 setae antero-distally. Fifth podomere slender, with 3 long setae and 1 short aesthetasc distally.

Antenna ( Fig. 12B ). Four articulated podomeres, length ratios from proximal to distal 14:7:20:1, width gradually narrowing in this order. First podomere stout bearing very long exopodite (=spinneret) at anterior distal end. Second podomere with 1 long seta postero-distally and bunch of long setulae along part of the anterior proximal margin. Third podomere with 2 setae at middle of anterior setiferous margin, 2 setae at medial suture making a ledge on the posterior margin, and 1 short seta at posterior distal end, and numerous setulae along posterior margin. Fourth podomere with 2 claws distally of sub-equal dimensions.

Mandibula ( Fig. 12C , C’). Five articulated podomeres. Coxa stout, consisting of teeth on medial edge and 1 long seta on anterior distal margin. Basis consisting of exopodite as a bunch of 4 plumose setae (one of those very short) and 1 seta on opposite distal end. First podomere of endopodite with 1 annulated seta antero-distally, 2 very long and 2 very short setae ventrally. Second podomere of endopodite with 6 annulated setae antero-distally, 2 setae of unequal length at postero-distal corner. Third podomere of endopodite bearing 4 long simple setae at distal end.

Maxillula ( Fig. 12D , D’). Thin branchial plate with 16 long plumose setae. Basal podomere bearing palp and 3 endites; palp with 4 setulous annulated antero-distal setae, 1 ventral seta, 1 strong claw and 2 stout setae on distal end; 3 endites bearing 5, 6, and 5 setae of unequal length, respectively; especially most ventral seta of 3rd endite bearing long setules arranged in a cluster and terminating in a club-like process.

Fifth limb ( Fig. 12E ). Four articulated podomeres, length ratios from proximal to distal 33:25:12:18. First podomere with 2 setulous setae along anterior margin, 2 setulous setae at anterior distal end, and 1 setulous seta with several long setulae in middle of posterior margin. Second podomere with 1 simple seta on anterior distal corner, and setulae along anterior margin. Third podomere with short setulae along anterior margin. Fourth podomere with 1 long, stout distal claw and setulae along anterior margin.

Sixth limb ( Fig. 12F ). Four articulated podomeres, length ratios from proximal to distal 18:15:7:10. First podomere with 2 long setulous setae along anterior margin, 1 setulous seta at anterior distal end, and 1 long, branched, setulous seta in middle of posterior margin. Second podomere with 1 long simple seta on anterior distal corner, and setulae along anterior margin. Third podomere with short setulae along anterior margin. Fourth podomere bearing 1 long, stout distal claw and short setulae along anterior margin.

Seventh limb ( Fig. 12G ). Four articulated podomeres, length ratios from proximal to distal 26:21:9:14. First podomere consisting of 2 setulous setae along anterior margin, 1 setulous seta at anterior distal end, and 1 setulous seta at proximal end of posterior margin. Second podomere with 1 long simple seta on anterior distal corner, and short setulae along anterior margin. Third podomere with short setulae along anterior margin. Fourth podomere with 1 long, stout distal claw and setulae along anterior margin.

Male copulatory organ ( Figs 13 ). General shape oval. Basal part relatively large, triangular. Thin distal lobe triangular. Clasping apparatus triangular, thin and large, overlapping whole distal lobe with distal end forming a tip. Copulatory duct very short, fine and folded.

Brush-shaped organ ( Fig. 12H , H’). Y-shaped in general; consisting of pair of branches, with 16 fine setae on each distal margin.

Dimensions. See Table 1 .

Remarks. Loxoconcha sesokoensis sp. nov. is the first species of this genus studied inhabiting coral reefs in Japan and adjacent seas. The somewhat oval carapace outline, the shape of the male copulatory organ, and the chaetotaxy of the mandibula and the maxillula of Loxoconcha sesokoensis sp. nov., are clearly different from those of other Loxoconcha species living in Japan and adjacent areas as shown by Ishizaki (1968), Okubo (1980), Nakao & Tsukagoshi (2002) and Ozawa (2013).

Figures

FIGURE 1. Maps showing location of the study area. A. map of Japan B. map of the Okinawa Islands C–E. sampling sites of Loxoconcha noharai sp. nov., L. santosi sp. nov. and L. sesokoensis sp. nov., respectively.

FIGURE 10. Carapace of Loxoconcha sesokoensis sp. nov. A. female right valve in internal lateral view (SUM-CO-2165, paratype) B. female left valve in internal lateral view (SUM-CO-2166, paratype). Scale: 200 µm.

FIGURE 11. Carapace morphology of Loxoconcha sesokoensis sp. nov. A. male right valve in external lateral view (SUM- CO-2167, holotype) B. male left valve in external lateral view (SUM-CO-2168, paratype) C. male carapace in dorsal view (SUM-CO-2169, paratype) D. female right valve in external lateral view (SUM-CO-2170, paratype) E. female left valve in external lateral view (SUM-CO-2171, paratype) F. female carapace in dorsal view (SUM-CO-2172, paratype) G. male left valve in internal lateral view (SUM-CO-2173, paratype) H. male right valve in internal lateral view (SUM-CO-2174, paratype) I. muscle scars of male right valve (SUM-CO-2174, paratype) J. female left valve in internal lateral view (SUM-CO-2175, paratype) K. female right valve in internal lateral view (SUM-CO-2176, paratype) L. muscle scars of female right valve (SUM- CO-2176, paratype) M & N. anterior and posterior elements of hingement on male right valve (SUM-CO-2174, paratype). Scale: 200 µm for A–H, J, K, 60 µm for I, L, M, N.

FIGURE 12. Loxoconcha sesokoensis sp. nov. A, C, D. Male (SUM-CO-2177, paratype) B, E–H. male (SUM-CO-2167, holotype). A. antennula B. antenna C. mandibula D. maxillula E. fifth limb F. sixth limb G. seventh limb H. brush-shaped organ C’, D’, H’, enlarged details of C, D, H, respectively. Scale: 100 µm for A–H, 50 µm for C’ D’ H’.

FIGURE 13. Loxoconcha sesokoensis sp. nov., holotype, male (LO2060). A. right copulatory organ B. left copulatory organ. Abbreviation: Ca, clasping apparatus, Cd, copulatory duct, Dl, distal lobe. Scale: 100 µm.