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

publication ID	https://doi.org/ 10.11646/zootaxa.3796.1.7
publication LSID	lsid:zoobank.org:pub:100761B6-225E-48AF-97F4-8E3824348915
DOI	https://doi.org/10.5281/zenodo.4915143
persistent identifier	https://treatment.plazi.org/id/A51A1114-FF80-8360-C0CC-6AFE15388CCC
treatment provided by	Felipe
scientific name	Loxoconcha sesokoensis
status	sp. nov.

Treatment

Loxoconcha sesokoensis View in CoL sp. nov.

( Figs 10–13 View FIGURE 10 View FIGURE 11 View FIGURE 12 View FIGURE 13 )

Type series. All specimens were collected at the northwest coast of Sesoko-jima ( Fig. 1E View FIGURE 1 ), 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 View FIGURE 10 , 11 View FIGURE 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 View FIGURE 10 ). Fused zone mostly as wide as infold ( Figs 10 View FIGURE 10 ). All lateral pore canals of sieve-type, arranged sparsely with 85 pores per valve. Muscle scars ( Fig. 11I, L View FIGURE 11 ): 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 View FIGURE 12 ). 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 View FIGURE 12 ). 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 View FIGURE 12 , 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 View FIGURE 12 , 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 View FIGURE 12 ). 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 View FIGURE 12 ). 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 View FIGURE 12 ). 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 View FIGURE 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 View FIGURE 12 , H’). Y-shaped in general; consisting of pair of branches, with 16 fine setae on each distal margin.

Dimensions. See Table 1 View 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).