Gnathia kumejimensis, Ota, Yuzo, 2012

Ota, Yuzo, 2012, Gnathiidae from Kumejima Island in the Ryukyu Archipelago, southwestern Japan, with description of three new species (Crustacea: Isopoda) *, Zootaxa 3367, pp. 79-94 : 87-89

Gnathia kumejimensis n. sp.

New Japanese name: Kumejima-nokogiri-umikuwagata ( Figs. 6 , 7 )

Material examined. Holotype. Male 4.85 mm in total length (RUMF-ZC-1430), from Stn. Dredge 11 (triangular dredge), 26°22.806ʹN, 126°48.035ʹE – 26°22.670ʹN, 126°48.327ʹE, 68 m depth, off Kumejima Island, the Ryukyu Archipelago, southwestern Japan, 10 November 2009.

Paratypes. One male from the same site as the holotype (RUMF-ZC-1431). One male (RUMF-ZC-1432), from dead coral rubble or rock rubble, Stn. Trawl 45, 26°19.907ʹN, 126°43.191ʹE –26°20.056ʹN, 126°42.622ʹE, 67.5– 76 m depth, off Kumejima Island, 16 November 2009, beam trawl, towed by “Daisan-Emimaru”. One male (RUMF-ZC-1433), from rock rubble, Stn. Dredge 76, 26°19.672ʹN, 126°43.328ʹE – 26°19.698ʹN, 126°42.957ʹE, 93.2–101 m depth, off Kumejima Island, 19 Nov. 2009, triangular dredge, towed by “Daisan-Emimaru”.

Description. Male ( Figs. 6 , 7 ). Body 4.5–5.5 mm (4.78 ± 0.23 mm, n = 4). Cephalothorax ( Fig. 6 A–C). Cephalothorax almost rectangular, sparsely covered with setae. Dorsal sulcus narrow and shallow. Posterior margin concave. Frontal border concave with 3 setae on 2 superior frontolateral processes; frontal margin with 19 small tubercles. Mediofrontal process rounded with small round process on distal margin. Eyes with 55 ocelli in 8 horizontal rows. Paraocular ornamentation prominent, composed of several tubercles and long setae. Supraocular lobe not acute.

Pereon ( Fig. 6 A). Pereonite I slightly shorter than pereonite II, not fused, separated into 3 parts by posterior margin of cephalothorax. Pereonite II and III subequal in length and width, posterior margins almost straight. Pereonite IV with anterior constriction; median groove closed. Pereonite IV with areae laterales; semicircular parts visible. Pereonite VI as long as combined kength of pereonite IV and V. Pereonite VII not extending postero-lateral of pereonite VI, overlapping pleonite I.

Pleon ( Fig. 6 A). All pleonites sparsely covered with setae. Pleonites II–V subequal in length and width; epimera prominent.

Pleotelson ( Fig. 6 D). Width approximately 0.88 length. 3 pairs of setae bearing near lateral margin, central part, and apex. Lateral margins dentate, slightly concave at proximal third and convex at middle.

Mandible ( Fig. 6 B, C). Mandible approximately 0.8 times as long as cephalothorax; apex curved dorsomesially. Mandibular seta present on mid-dorsal surface near incisor. Dentate blade occupying approximately 0.4 times as long as mandible. Erisma prominent. Internal lobe visible in lateral view, remarkably elongated dorsally, extending incisor.

Antennula ( Fig. 6 E). 3 basal podomeres and 5 flagellar articles. Distal margins of basal podomeres I, II, III, and flagellar articles I and V bearing 3, 3, 1, 2, and 1 penicillate setae, respectively. Basal podomere III bearing 6 long setae on external margin. Flagellar articles III and IV each with 1 aesthetasc. Flagellar article V bearing 3 terminal setae.

Antenna ( Fig. 6 F). 4 basal podomeres and 7 flagellar articles. Basal podomeres III and IV bearing 1 and 5 penicillate setae on distal margins, respectively. Basal podomeres III and IV densely covered with long setae on distal margin and lateral margin, respectively. Flagellar articles I–VII with few setae on distal margins; article VII bearing 4 terminal setae.

Maxilliped ( Fig. 7 A). Endite reaching distal margin of palp article I. Palp articles I–IV bearing 4, 7, 5, and 7 plumose setae, respectively, on external margins; article IV bearing 4 simple terminal setae.

Pylopod ( Fig. 7 B). 3-articulate; 13 and 14 setae bearing near distal margin of article I and II, respectively. Article I elliptical with 3 areolae bearing 30 plumose setae on internal margin; 1 penicillate seta bearing near basis. Article II elliptical, fringed with fine setae; 12 setae near distal margin. Article III elliptical.

Pereopod II ( Fig. 7 C). Merus, carpus, and propodus inner margins covered with pectinate scales. Basis oblong, with 3 penicillate setae and 5 processes on outer margin. Ischium approximately 0.8 times as long as basis, becoming wider distally; setae bearing sparsely and 3 long setae near outer distal margin. Merus approximately 0.6 times as long as ischium; 4 setae on distal corner and 5 process on inner margin. Carpus three-fourth length of merus, bearing 1 spine, 3 setae, and 6 processes on inner margin. Propodus rectangular and 1.5 times as long as carpus; 2 spines on inner-middle and inner-distal margins and 1 penicillate seta on distal corner. Dactylus terminating in unguis.

Pleopod II ( Fig. 7 D). Protopod bearing coupling hook and 1 seta on distal corner; pectinate scales on inner margin. Both rami elliptic and same length; 8 and 9 plumose setae on endopod and exopod, respectively. Appendix masculina absent. Both rami of all pleopods same shapes, length, and same number of plumose setae.

Uropod ( Fig. 6 D). Both rami subequal in length, extending beyond apex of pleotelson. Longest seta on uropodal rami much longer than pleotelson. Exopod bearing 16 or 19 setae and 3 plumose setae laterally. Endopod bearing 3 or 4 setae and 5 or 6 plumose setae laterally. Dorsal surface of endopod bearing 3 penicillate setae.

Penes ( Fig. 7 F). Penes composed of 2 contiguous papillae and not prominent.

Etymology. The scientific name kumejimensis is derived from the island, Kumejima where the present new species was discovered.

Remarks. The present new species is most similar to Gnathia serrula Kensley, Schotte & Poore, 2009 , because of the following characters; frontal border is concave with mediofrontal process, pleotelson bears two pairs of long setae near the lateral margin and on the apex ( Kensley et al. 2009). This species, however, is distinguished from G. serrula by dorsally elongated internal lobe on the mandibles and a much larger number of setae on the ventral surface of pylopod (27 setae versus 8; Kensley et al. 2009).

Gnathia camuripenis Tanaka, 2004 , was also collected at the same locality of this expedition and similar in the whole shape to the present new species. Gnathia camuripenis , however, has prominent penes bent posteriorly on distal one-fourth length ( Tanaka 2004), rather than two contiguous papillae.

Figures

FIGURE 6. Gnathia kumejimensis n. sp., holotype, adult male (RUMF-ZC- 1430, total length, 4.85 mm): A, body, dorsal view; B, eye and frontal border, dorsal view; C, cephalothorax and pereonite I, lateral view (IL, internal lobe); D, pleotelson and uropods, dorsal view; E, left antennula, medial view; F, left antenna, medial view.

FIGURE 7. Gnathia kumejimensis n. sp., holotype, adult male (RUMF-ZC- 1430, total length, 4.85 mm): A, right maxilliped, ventral view; B, right pylopod, ventral view; C, right pereopod II, medial view; D, left pleopod II, ventral view; E, penes, ventral view.