Urothoe sibuensis AZMAN & MELVIN 2011

Type Locality: Pulau Sibu, Johor, Malaysia, South China Sea. (Azman & Melvin, 2011, p. 46-53, figs. 2a-2e.)

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, U. sibuensis differs in not having defining robust setae in propodus of gnathopods 1 – 2 (defining robust setae present in U. gelasina, U. gelasina ambigua, U. poucheti, U. varvarini), the antenna 2 significantly longer than antenna 1 (antenna subequal in length in U. bairdii, U. brevicornis, U. hesperiae, U. intermedia, U. marina), epimeron 3 smooth (epimeron 3 having distinct tooth in U. chosani, U. dentata, U. denticulata, U. marionis), presence of eyes (absence of eyes in U. abbreviata, U. latifrons, U.vemae), merus and carpus of pereopod 5 are both subequal in width (merus is wider than carpus of pereopod 5 in U. pulchella, U. spinidigitus), epimeron 2 having several plumose setae (epimeron 2 naked in U. elegans) and a less pronounced cephalic lobe (lateroventral cephalic corner of U. corsica produced and upturned).

The present species is especially close to U. spinidigitus Walker, 1904. It differs from U. spinidigitus by the absence of rostrum in the present species (small rostrum present in U. spinidigitus) and the absence of defi ning palmar spines in both gnathopods. The dactylus of pereopod 5 in Walker’s species bears 4 short and 4 long robust setae whereas U. 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 U. spinidigitus that has carpus twice as broad as merus.

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