Rayllianassa Komai & Tachikawa, 2008

Komai, Tomoyuki, Fujita, Yoshihisa & Maenosono, Tadafumi, 2014, Additional record of Rayllianassa amboinensis (de Man, 1888) from Japan, and description of a new species from Okinawa Island, Ryukyu Islands (Crustacea: Decapoda: Axiidea: Callianassidae), Zootaxa 3835 (4), pp. 549-563 : 550-551

Genus Rayllianassa Komai & Tachikawa, 2008

Rayllianassa Komai & Tachikawa, 2008: 42 . Notiax .— Sakai 2011: 381 (part).

Emended diagnosis. Carapace with rostrum obsolete to broadly triangular, never spiniform; dorsal oval present ( R. amboinensis ) or absent ( R. rudisulcus n. sp.) (see “ Remarks ” below); linea thalassinica extending nearly to posterolateral margin. Second pleomere subequal in length to sixth pleomere; third to fifth pleomeres each with lateral tufts of setae. Telson trapezoidal. Eyestalk slightly flattened dorsoventrally, with distomesial lobe beyond cornea; cornea subterminal and lateral. Third maxilliped with merus-ischium broadly operculiform; merus with distal margin somewhat projecting beyond articulation with carpus; propodus and dactylus slender, digitiform. Paired arthrobranchs above bases of third maxilliped to fourth pereopod. Chelipeds (first pereopods) slightly unequal and dissimilar, merus of major cheliped without conspicuous process or spine on ventral margin; carpus of minor cheliped much deeper than long. Propodus of third pereopod subcircular, proximoventral angle not heelshaped. Fifth pereopod chelate. Male with first pleopod greatly reduced to minute, rudimentary bud; second pleopod very small, consisting of protopod, rudimentary exopod and small endopod, without appendices interna and masculina. Female with uniramous first pleopod and biramous second pleopod. Third to fifth pleopods relatively narrowly foliaceous; peduncles meeting with rounded margins; appendices internae longer than wide, digitiform, projecting beyond mesial margins of endopods. Uropodal exopod with small dorsal plate bearing thick assemblage of stiff setae distally; endopod not widened distally.

Remarks. The genus Rayllianassa was established by Komai & Tachikawa (2008) to accommodate Callianassa amboinensis de Man, 1888. Sakai (2011) placed Rayllianassa in the synonymy of Notiax without consideration of characters discussed by Komai & Tachikawa (2008). Callianassa amboinensis differs from Callianassa brachyophthalma A. Milne-Edwards, 1870 , the type species of Notiax , in several key characters ( Manning & Felder 1991), as follows: (1) rostrum broadly triangular to obsolescent in C. amboinensis , but spiniform in C. brachyophthalma ; (2) major cheliped merus devoid of hook-like process on ventral margin in C. amboinensis , whereas bearing a strong hook-like proximal process on ventral margin in C. brachyophthalma ; (3) chelipeds similar in general structure though slightly unequal in length in C. amboinensis , rather than strongly dissimilar in C. brachyophthalma ; (4) male first pleopod greatly reduced to rudimentary, papilla-like bud in C. amboinensis , whereas uniramous and biarticulate in C. brachyophthalma ; (5) appendices internae on third to fifth pleopods distinctly longer than wide, digitiform, and distinctly projecting beyond mesial margins of endopod in C. amboinensis , rather than stubby and slightly projecting beyond mesial margins of endopods in C. brachyophthalma . Furthermore, Tudge et al. (2000) estimated that C. amboinensis represents an early-derived lineage within Callianassinae , not closely related to C. brachyophthalma . We thus reinstate herein Rayllianassa as a valid genus.

Biffarius Manning & Felder, 1991 is also similar to Rayllianassa . Nevertheless, the presence of a prominent hook-like process on the merus of the major cheliped, the absence of the male second pleopod and the stubby appendices internae on the third to fifth pleopods will distinguish Biffarius from Rayllianassa .

The generic diagnosis of Rayllianassa is emended to accommodate the new species, R. rudisulcus n. sp. Most important point is the development of a dorsal oval of the carapace, although, in general, the character is considered to be of generic importance in the taxonomy of Callianassidae (cf. Manning & Felder 1991; Poore 1994; Sakai 1999, 2011). The dorsal oval was defined as “an area bounded by the cervical groove, and delimited anteriorly by a transverse groove behind the rostrum” ( Schmitt 1935; Dworschak et al. 2012). The current usage of “dorsal oval” in decapod literature, however, is rather loose, and the presence of a deep cervical groove alone has sometimes been regarded as a condition that “a dorsal oval is developed” (e.g., Sakai 1999, 2005; Lin et al. 2007b; Komai & Tachikawa 2008; Anker 2010). In many callianassine taxa, however, the transverse groove or depression behind the rostrum is faint or even absent (e.g., Sakai 2002; Komai & Tachikawa 2008; Komai & Fujiwara 2012). In R. amboinensis , it is regarded that the dorsal oval is present, because an area bounded by the deep cervical groove and a very shallow transverse groove behind the rostrum is recognizable. In contrast, in R. rudisulcus n. sp., the cervical groove is merely suture-like (no incision is seen in the lateral view), and there is no transverse groove or depression behind the rostrum; as such, it can be said that a dorsal oval is not defined. In spite of the difference in the structure of the dorsum of the carapace, however, the new species is closely similar to R. amboinensis in other diagnostic characters, e.g., the non-spiniform rostrum, the broadly operculiform third maxilliped, the structure of chelipeds and third to fifth pleopods, and digitiform appendices internae on the third to fifth pleopod. Reevaluation of the homology of the dorsal oval in Callianassidae based on phylogeny would be necessary.