Urothoe sibuensis, Azman, B. A. R. & Melvin, C. W. H., 2011

Azman, B. A. R. & Melvin, C. W. H., 2011, Two new species of Urothoe (Crustacea, Amphipoda, Gammaridea) from the East Johor Islands Archipelago, Malaysia, ZooKeys 87, pp. 43-62 : 45-48

Urothoe sibuensis sp. n. Figs 2 A– 2E

Type material.

Holotype, male, 2.9 mm, UKMMZ-1394, seagrass area ( Halophila ovalis , Halodule uninervis , Cymadocea serrulata , Halophila spinulosa ) of Pulau Sibu, Johor, 2°13'55"N, 104°3'14"E, vertical haul plankton net (100 µm), 8 m, B.A.R. Azman, Melvin, C.W.H., Yoshida, T., 16 October 2008 (UKM I.D. 9047). Paratypes: 8 males, UKMMZ-1396, same station data.

Type locality.

Pulau Sibu, Johor, Malaysia, South China Sea.

Etymology.

This species is named after the type locality, Pulau Sibu, Johor.

Description.

Based on holotype male, 2.9 mm, UKMMZ-1394.

Headsubequal in length to pereonite 1 - 3 combined, rostrum absent, lateroventral cephalic lobe less pronounced. Eyes present, well-developed, elliptic shape and large, lateral cephalic lobe of eye advanced slightly forward. Antenna 1 shorter than antenna 2; peduncular article 1 slightly longer than article 2, provided with a band of setae on anterior margin; main flagellum with about 7 articles, distinctively shorter than peduncle; accessory flagellum biarticulate. Antenna 2 about as long as body length; peduncle article 4 about twice as broad as long; gland cone absent; peduncular article 4 with robust setae along anterior margin; peduncular article 4 about as long as peduncular article 5; calceoli present; flagellum with about 30 articles. Upper lip semicircular. Lower lip inner plate large, shoulders broad, mandibular process significantly winged outward. Maxilla 1 inner plate with one plumose setae apically; outer plate biarticulate, one setae and one plumose setae apically; palp with10 robust setae apically. Maxilla 2 inner and outer plate covered with pinnate and simple setae apically. Mandible with molar semicircular and not well-developed; incisors smooth. Maxilliped inner plate elongated, bearing two blunt robust setae; outer plate suboval, with about 8 robust setae; palp 4-articulate, first article subquadrate, second article the widest, strongly setose on the inner margin, third article subtriangular, with several long setae; fourth article small and slender.

PereonGnathopod 1 coxa subrectangular, narrow; basis elongate, posterior margin with several long and short setae; ischium subtriangular with several short setae along posterior margin; merus semicylindrical; carpus longer than propodus, about twice as broad as long, posterior margin densely setose; propodus slightly expanded distally; palm with several setae; dactylus large with setae at base. Gnathopod 2 coxa expanded ventrally; basis elongate with several long setae along posterior margin; ischium subtriangular with several long setae along posterior margin; merus subtriangular with rarely long and short setae present; carpus broad, longer than propodus, propodus subtriangular; dactylus similar to the dactylus of gnathopod 1.

Pereopod 3 - 4 almost homopodous except pereopod 3 slightly broader than pereopod 4. Pereopod 3 coxa slightly expanding ventrally, basis elongate with few long setae at distal end of posterior margin; ischium broader than long with few long setae; merus twice as long as carpus, posterior margin with dense setae and several plumose setae; carpus subquadrate, several setae, plumose setae and robust setae present; propodus narrow, armed with several robust setae along posterior margin; dactylus nodulate. Pereopod 4 coxa subtriangular; basis elongate, few long setae with a plumose setae; ischium rarely setose; merus elongate, setose at posterior margin; carpus covered with several robust setae, setae and plumose setae; propodus narrow, with several robust setae; dactylus nodulate. Pereopod 5 coxa bilobial; basis expanding backward, several setae in the notch of posterior margin, several plumose setae situated distally; ischium wider than long; merus wider than long provided with transverse rows of robust setae medially and distally, several long plumose setae distally; carpus subequal of length and width, provided with traverse rows of spines medially and distally, several long plumose setae distally; propodus provided with 3 traverse rows of robust setae ventrally and 2 transverse rows of robust setae posteriorly, several long plumose setae medially; dactylus nodulate. Pereopods 6 - 7 slender from basis to propodus except for dactylus of pereopod 6 nodulate whereas dactylus of pereopod 7 slender and smooth, basis rounded posteriorly.

PleonPleopods 1-3 peduncle distinctly longer than broad; biramous, multiarticulate. Uropod 1 peduncle with two rows of robust setae; rami subequal in length with long robust setae medially. Uropod 2 peduncle provided with several robust setae; rami subequal in length, outer ramus with a long robust setae medially and a distal setae. Uropod 3 well developed; both rami with long plumose setae; outer ramus 2 biarticulate; inner ramus shorter than outer ramus. Telson about 5/6 cleft; both lobes with robust setae apically and few setae medially and distally.

Remarks.

Urothoe sibuensis is very closely related to the ‘elegans’ group, defined by J.L. Barnard (1962), which included twenty other Urothoe species. This group of species is characterized by having similar gnathopods 1 - 2 with short and stout propodus expanded into poorly defined palms. Despite of that, detectable distinctions of morphological characters are found between the present species and the members of this group. As such, Urothoe sibuensis differs in not having defining robust setae in propodus of gnathopods 1 - 2 (defining robust setae present in Urothoe gelasina , Urothoe gelasina ambigua , Urothoe poucheti , Urothoe varvarini ), the antenna 2 significantly longer than antenna 1 (antenna subequal in length in Urothoe bairdii , Urothoe brevicornis , Urothoe hesperiae , Urothoe intermedia , Urothoe marina ), epimeron 3 smooth (epimeron 3 having distinct tooth in Urothoe chosani , Urothoe dentata , Urothoe denticulata , Urothoe marionis ), presence of eyes (absence of eyes in Urothoe abbreviata , Urothoe latifrons , Urothoe vemae ), merus and carpus of pereopod 5 are both subequal in width (merus is wider than carpus of pereopod 5 in Urothoe pulchella , Urothoe spinidigitus ), epimeron 2 having several plumose setae (epimeron 2 naked in Urothoe elegans ) and a less pronounced cephalic lobe (lateroventral cephalic corner of Urothoe corsica produced and upturned).

The present species is especially close to Urothoe spinidigitus Walker, 1904. It differs from Urothoe spinidigitus by the absence of rostrum in the present species (small rostrum present in Urothoe spinidigitus ) and the absence of defining palmar spines in both gnathopods. The dactylus of pereopod 5 in Walker’s species bears 4 short and 4 long robust setae whereas Urothoe sibuensis possesses a nodulate dactylus in its pereopod 5. The subequal merus and carpus of pereopod 5 in the present species clearly distinguish it from Urothoe spinidigitus that has carpus twice as broad as merus.

Distribution.

Malaysia. Johor, Pulau Sibu.