Xestoleberis natuvuensis Chand & Kamiya, 2016, n. sp.

Xestoleberis natuvuensis n. sp.

Type series. Holotype: male UMUT RA32543 (Figs. 7 A–B’, G, K, 11E, I1–I3). Paratypes: females: UMUT RA32545 (Fig. 7 C–F’, H–J), UMUT RA32546 (Fig. 2 I–J), UMUT RA32547 (Fig. 7 L), UMUT RA32548 (Fig. 11 F, H), UMUT RA32549 (Fig. 11 G). All type material was collected from the type locality. The holotype and paratypes are deposited at the University Museum, University of Tokyo, Japan. Valves on paleontological paper/ cavity slides and soft parts mounted on glass slides. Additional paratypes preserved in 70% ethanol: two females UMUT RA32544.

Type locality. A flat and very fine sand to muddy beach coast in front of Natuvu Village in the east of Savusavu Bay, Vanua Levu Island (P4, Fig. 1, Table 1); habitat: a green filamentous alga.

Etymology. Specimens of this species were collected from the fringing reef flat in front of Natuvu village/area.

Diagnosis. Widely rounded posterior and anterior ends of carapace; wider posterior than anterior. Anterior and ventral edges of valves lined with numerous simple marginal pores. Coloration in living specimens transparent with opaque patches. BO short segment with numerous fine terminating setae. Ejaculatory ducts arranged in Oshapes with hook-like projections exiting outwards. Furca reduced to two short setae.

Description. Carapace ovate and strongly inflated (Figs. 2 I-J, 10E– I3). Maximum valve length range: 465 µm–521 µm, maximum valve height range: 255 µm–280 µm (Table 2). Maximum height at mid-length. Dorsal margin convex, indentation on ventral margin; about one third of way from anterior end. Wide anterior and narrow posterior vestibula. Merodont hinge. Normal sieve pores scattered over carapace; those lining anterior and anteroventral edges of carapace slightly more recessed. Scar pattern: posterior row of four elongated adductor scars, and U-shaped anterior scar.

An1 with six podomeres; first two big, wide and rectangular, third–sixth small and quadrate (Fig. 7 A–A’). One medial seta at junction of second and third podomeres, third podomere with one dorsal apical seta, fourth and fifth podomeres with two dorsal apical setae, terminating setae of sixth podomere: one stout with pointed tip, one slender and round tipped, one whip-like, and two fine. An2 with one ventral apical seta on first podomere of endopodite, two dorsal and ventral (one hirsute seta) medial setae and one hirsute stout ventral apical seta on second endopodite podomere (Fig. 7 B–B’). Slight serration on one terminating claw. Md coxa with eight pointed teeth and three fine setae. (Fig. 7 C–E). Palp with four podomeres: second podomere with one dorsal and one ventral apical setae, two medial setae at junction of second and third podomere, third podomere with five dorsal and one ventral apical setae, one medial seta at junction of third and fourth podomeres, three stout terminating setae. Exopodite with at least two long setuled setae. Mx with two segmented palp; first segment with three distal dorsal-apical setae and second segment with three terminating setae (Fig. 7 F–F’). Branchial plate with 14–16 setuled setae. BO is symmetrical; short segment with numerous fine terminating setae (Fig. 7 G).

Basal setal formula for L5 1+1:2:1 and L6 and L7 1+1:1:1 (Fig. 7 H–J). Knee setae of legs hirsute. Second podomeres of L5 and L6 with one hirsute dorsal apical seta each. Terminating claws of L5, L6 and L7 stout, straight and slightly curved. Hp with asymmetrical, wide, rounded to sub-rounded distal processes; one with wide end other with tapered end (Fig. 7 K). Proximal ends of capsules rounded and proximal support structure T-shaped. Furca two short setae (one slightly shorter than other) on short base.

Distribution. Xestoleberis natuvuensis n. sp. appears to have a restricted distribution; only collected from Natuvu Village coast (type locality above). Apart from the above-mentioned habitat (green filamentous alga), high counts of this species were also collected from a green calcareous alga, Halimeda macroloba and a short brown alga, Padina sp.

Remarks. Xestoleberis natuvuensis n. sp. is similar to Xestoleberis sp. D reported from Solomon Islands (Fig. 4, Nos. 22, 25, Pl. 2, 26–29, Titterton & Whatley 2005). However, both species differ in the shape of the frontal muscle scar; X. sp. D has a trefoil scar while in X. sp. D, X. natuvuensis n. sp. has a U-shaped scar.