Loxoconcha santosi, 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 : 153-157

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.5083042
persistent identifier	https://treatment.plazi.org/id/A51A1114-FF8D-8364-C0CC-6F9B16B88C45
treatment provided by	Felipe
scientific name	Loxoconcha santosi
status	sp. nov.

Treatment

Loxoconcha santosi View in CoL sp. nov.

( Figs 6–9 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 )

Type series. All specimens were collected at estuary in Ada ( Fig. 1D View FIGURE 1 ), Okinawa Island, southern Japan, 26°44’30”N, 128°18’50”E on 21 March 1992. Holotype: SUM-CO-2151 (copulatory organs and both valves of adult male; copulatory organs were enveloped on a slide glass in the “Neo Sigaral” as mounting agent and carapaces were preserved on a cardboard slide with single hole). Paratypes: 7 males (SUM-CO-2154, 2156, 2157, 2160, 2161, 2162, 2163), 6 females (SUM-CO-2150, 2152, 2153, 2155, 2158, 2159) and one A-1 instar (SUM-CO- 2164); also as for the dissected specimens, soft parts were mounted on a slide glass in the “Neo Sigaral” agent and carapaces were on a cardboard slide with single hole; other specimens, carapaces were kept on a cardboard slide with single hole.

Etymology. In honour of Prof. Jorge Santos (University of Tromsø, Norway), who was the supervisor of the first author.

Diagnosis. Carapace rhomboid in lateral view, covered with distinct reticulations and sieve-type pore canals sparsely distributed. Number of pore systems 74 per valve. 4 adductor muscle scars in curved sub-vertical row, concave anteriorly, the second scar from bottom smaller than other three. Gongylodont hingement with strong crenulations in median element. Exopodite of mandible formed as a bunch of 3 long plumose setae and 1 very small degenerated seta. On the first podomere of fifth and sixth limbs, plumose seta at posterior margin bearing several long setulae. Seventh limb much longer and larger than fifth and sixth limbs. In the male, copulatory organ with large and thin distal lobe; clasping apparatus large, thin and overlapping partly the distal lobe and making large tip; copulatory duct fine, folded inside and short, about one fourth as long as length of capsule.

Description. Carapace ( Figs 6 View FIGURE 6 , 7 View FIGURE 7 ). Carapace showing prominent sexual dimorphism; male more elongate, with straighter dorsal margin and less compressed postero-ventral marginal area than in female. Surface covered with distinct reticulations and sieve-type pore canals sparsely distributed. Valves moderate in length, rhomboid in lateral view. Right and left valves showing asymmetry in outline. Both valves slightly tapering backward; greatest height at anterior first third. Dorsal margin very slightly convex. Ventral margin almost straight. Anterior margin broadly rounded. Posterior margin somewhat narrowly rounded, extremity at more than half of height, with slight caudal process. Marginal infold moderately developed. List present along middle of marginal infold in both valves. Vestibula weakly developed in anterior and posterior areas of valves ( Fig. 6 View FIGURE 6 ). Fused zone mostly as wide as infold ( Fig. 6 View FIGURE 6 ). All lateral pore systems sieve-type, with 74 pores per valve. Muscle scars ( Fig. 7I, L View FIGURE 7 ): the smaller one round (formed of 2 frontal scars), the larger one with curved shape, concave anteriorly; 2 mandibular scars of equal dimension; 4 adductor muscle scars in curved sub-vertical row, concave anteriorly, the second scar from bottom smaller than other three, especially in male. Hinge gongylodont with strong crenulations on median element.

Antennula ( Fig. 8A View FIGURE 8 ). Five articulated podomeres, length ratios from proximal to distal 20:16:7:14:17, width decreasing in this order. First podomere stout, without seta. Second podomere with 1 medium seta at posterior distal end and setulae along anterior margin. Third podomere with 1 short seta antero-distally. Fourth podomere showing vestigium of segmentation as a ledge with 1 seta, a median seta, and with 1 very long seta postero-distally, 3 setae antero-distally. Fifth podomere slender, with 3 long setae and 1 aesthetasc distally.

Antenna ( Fig. 8B View FIGURE 8 ). Four articulated podomeres, length ratios from proximal to distal 30:12:38:3, width decreasing gradually in this order. First podomere stout with very long exopodite (=spinneret) at anterior distal end. Second podomere with 1 long seta postero-distally and a bunch of long setulae along anterior proximal margin. Third podomere very long, with 2 setae on anterior margin, 2 setae and 1 aesthetasc on posterior ledge, 1 short seta at postero-distal end, and setulae along posterior margin. Fourth podomere very short and small with 2 distal claws of sub-equal length.

Mandibula ( Fig. 8C View FIGURE 8 , C’). Five articulated podomeres. Coxa stout, with teeth on medial edge and 1 medium seta on anterior distal margin. Basis bearing exopodite as bunch of 4 setae (3 long plumose setae and 1 very small reduced seta) and 1 seta at ventral distal end. First podomere of endopodite with 1 annulated seta antero-distally, 2 very long and 2 short setae ventrally. Second podomere of endopodite with 5 annulated setae antero-distally, 2 short setae of unequal length ventrally. Third podomere of endopodite with 4 simple setae, 2 long and 2 short setae.

Maxillula ( Fig. 8D View FIGURE 8 , D’). Thin branchial plate bearing 16 long plumose setae. Basal podomere bearing a palp and 3 endites; palp with 4 long setulous annulated setae antero-distally, 1 seta ventro-distally, 1 strong claw and 2 stout setae on distal end; 3 endites bearing 6, 5, and 5 setae, respectively; especially the most ventral seta of 3rd endite bearing long setulae arranged in a cluster and terminating in a club-like process.

Fifth limb ( Fig. 8E View FIGURE 8 ). Four articulated podomeres, length ratios from proximal to distal 29:24:11:14. First podomere with 2 setulous setae along anterior margin, 2 short setulous setae at anterior distal end, and 1 setulous seta in the middle of posterior margin bearing several long setulae. Second podomere with 1 simple short seta on anterior distal corner, and setulae along anterior margin. Third podomere with short setulae along anterior margin. Fourth podomere bearing 1 long and stout distal claw and setulae along anterior margin.

Sixth limb ( Fig. 8F View FIGURE 8 ). Consisting of 4 articulated podomeres, length ratios from proximal to distal 34:30:13:16. First podomere bearing 2 setulous setae along anterior margin, 1 setulous seta at anterior distal end, and 1 long setulous seta with some long setulae at posterior margin. Second podomere with 1 long seta on anterior distal end, and setulae along anterior margin. Third podomere with very short setulae along anterior margin. Fourth podomere with 1 long and stout distal claw and setulae along anterior margin.

Seventh limb ( Fig. 8G View FIGURE 8 ). Much larger and longer than fifth and sixth limbs. Consists of 4 articulated podomeres, length ratios from proximal to distal 35:29:14:20. First podomere with 2 setulous setae in middle of anterior margin, 1 short setulous seta at anterior distal end, and 1 setulous seta at first fifth from proximal end of posterior margin. Second podomere with 1 long seta on anterior distal corner, and setulae along anterior margin. Third podomere with very short setulae along anterior margin. Fourth podomere with 1 long, and stout distal claw and setulae along anterior margin.

Male copulatory organ ( Fig. 9 View FIGURE 9 ). Sub-circular shape in general. Basal part relatively large, with a blunt triangular shape. Distal lobe large, and thin with a triangular shape. Clasping apparatus thin and large, overlapping partly distal lobe with distal end extending posteriorly and forming a large tip. Copulatory duct fine, folded inside and short, about one fourth as long as length of capsule.

Brush-shaped organ ( Fig. 8H View FIGURE 8 , H’). Three-pronged fork shape in general; consisting of pair of branches, with about 23 fine setae on each distal margin.

Dimensions. See Table 1 View TABLE 1 .

Remarks. The carapace outline and appendage morphology of Loxoconcha santosi sp. nov. are similar to those of L. uranouchiensis , but the former can be clearly distinguished from the latter by some features of the male copulatory organ (see Okubo 1980), and small differences which are found on the fifth, and sixth limbs and the maxillula. The general shape of the male copulatory organ is significantly different between the two species. The distal lobe of L. santosi sp. nov. has a triangular shape, whereas that of L. uranouchiensis has a sub quadrangularlike shape, with small process at anterior end. In the new species, there are several long setulae on the plumose seta on the posterior margin of first podomere of fifth and sixth limbs. In the maxillula, the most ventral seta of the 3rd endite of new species bears long setulae arranged in a cluster and terminating in a club-like process.

The carapace outline, appendage morphology, and pore system of Loxoconcha santosi sp. nov. resemble those of L. noharai sp. nov. One difference between the two species is found in the general shape and structure of the male copulatory organ. Additionally, the exopodite of the mandible of L. noharai sp. nov. consists of a bunch of 4 long plumose setae, while that of L. santosi sp. nov. is composed of a bunch of 3 long plumose setae and 1 very small reduced seta. Unlike in L. noharai sp. nov., the seventh limb in L. santosi sp. nov. is much larger and longer than the fifth and sixth limbs.