Uruma, Naruse, Tohru, Fujita, Yoshihisa & Ng, Peter K. L., 2009

Naruse, Tohru, Fujita, Yoshihisa & Ng, Peter K. L., 2009, A new genus and new species of symbiotic crab (Crustacea: Brachyura: Pinnotheroidea) from Okinawa, Japan, Zootaxa 2053, pp. 59-68 : 60-62

publication ID	https://doi.org/ 10.5281/zenodo.186636
DOI	https://doi.org/10.5281/zenodo.6213435
persistent identifier	https://treatment.plazi.org/id/6655AE4D-5930-FFC3-62E6-FC11FEFBFCF5
treatment provided by	Plazi
scientific name	Uruma
status	gen. nov.

Treatment

Uruma n. gen.

Type species. Uruma ourana n. sp. by present designation.

Diagnosis. Carapace wide, trapezoidal; lateral, anterolateral margins cristate, but becoming poorly defined lateral to orbits. Front narrow, deflexed medially, deflexed part triangular in frontal view. Orbit oblique, mesial part of supraorbital margin placed more posteriorly than external orbital end; orbital margins entire, outer part granulated, infraorbital margin mesially terminated as sharp tooth. Epistome short, medially sunken. Eyes short, mobile, fully occupying orbit. Third maxillipeds covering about four-fifths of buccal cavern; ischium and merus distinctly separated by horizontal suture, ischium slightly longer than merus, palp (carpus, propodus, dactylus) attached to medial concave part of distal margin of merus, each segment of palp attached to distal end of proximal segment. Thoracic sternites 1/2 completely fused, sternite 1 tooth-like, directed dorsally at proximal end of buccal cavern; sternites 2/3 demarcated by deep groove; sternites 3/4 fused, lateral parts marked by very shallow depressions, pits; sternites 4–8 demarcated by narrow lateral grooves at outside of sternal cavity, grooves ending at lateral parts of sternal cavity; sternal cavity depressed medially, no clear longitudinal groove. Penis distinctly sternal, opening at anterior margin of sternite 8, adjacent to posterior margin of sternite 7. Cheliped merus with large transverse, triangular lobe on subdistal part of dorsal margin. P3 to P5 similar in shape, P4 longest; merus about two-thirds of respective carpus to dactylus length; carpus longer than propodus. P5 leg just reaching only proximal half of P4 merus; distal end of ischium, proximal end of merus each with single sharp tooth on flexor margin. All ambulatory legs with single pair of short, sharp claw on distoflexor angle of propodi; dactyli very short, claw-like. Male abdomen with all somites freely articulating, first somite widest, thoracic sternite 8 exposed when abdomen closed, third somite to telson forming triangular outline. G1 straight, slender, distally tapering, incurved. G2 very short.

Etymology. The new genus is named after the Ryukyuan word uruma (“Okinawa” or “Ryukyus”), which literally means “coral” (uru) and “island” (ma). The gender is neuter.

Remarks. Although Uruma n. gen. has an unusual physiognomy ( Fig. 1 View FIGURE 1 ), it shares a number of key characters with Aphanodactylus Tesch, 1918 . In both genera, the ischium and merus of the third maxillipeds are subquadrate, the palp of the third maxilliped is attached to a median concave part of the distal margin of the merus, with the propodus and dactylus of the palp connected to the distal end of the respective proximal segment ( Figs. 2 View FIGURE 2 b, 3b). Uruma n. gen. and Aphanodactylus also share diagnostic orbital characters: the orbital margins are entire, the infraorbital margins are terminated mesially as a sharp inner tooth, the external orbital corners are not connected to anterolateral margin of the carapace, and suborbital cristae are absent ( Figs. 2 View FIGURE 2 a, 3a). Furthermore, both genera have slender and straight G1s except for gently incurved distal tip, freely articulating male abdomens with almost straight lateral margins, and distally rounded telson being slightly longer than the sixth abdominal somite ( Fig. 4 View FIGURE 4 a, b). Both genera also share the characteristic, very short ambulatory dactyli ( Fig. 3 View FIGURE 3 e–g). Uruma n. gen. is distinct in that all ambulatory legs are almost subcheliform, the short dactylus being bracketed by strong claws at the distoflexor angle of the propodus. In preserved specimens, the dactylus can be folded proximally as far back as between the tips of a pair of distoflexor claws of the propodus. This structure is presumably to cling onto the host worm and/or its tube. On the other hand, the ambulatory dactyli of Aphanodactylus are short and not bracketed by claws (see Tesch 1918; Rathbun 1932; Edmondson 1962; Konishi & Noda 1999; Ng et al. 2009). In A. loimiae and one undescribed species of Aphanodactylus (Ng & Naruse, manuscript), there are 2–3 sharp claws on the distoflexor angle of the ambulatory propodus, which could be homologous with the claws of Uruma n. gen. but it is much less developed and not as prominent. Nevertheless, the form of the third maxillipeds, ambulatory legs and male abdomen suggest a relatively close relationship with Aphanodactylus . Gandoa (as Voeltzkowia ), with only one species, Gandoa zanzibarensis ( Lenz, 1905) , is very poorly known and represented by only one 5.0 by 8.0 female obtained from Zanzibar ( Fig. 5 View FIGURE 5 ; Lenz 1905: 364, pl. 47 figs. 9–9c). Compared to Uruma n. gen., Gandoa has a proportionately more rectangular carapace (trapezoidal in Uruma ), the orbits are incomplete, with supra- and infraorbital margins meeting far from tip of cornea (complete in Uruma ), the third maxilliped ischium is proportionately longer, and the ambulatory legs much shorter, with the short dactylus not bracketed by claws on the propodus (longer ambulatory legs with claws on propodus in Uruma ).

As discussed at length by Ng et al. (2008), Aphanodactylus and Gandoa may eventually be referred to their own family. Uruma n. gen. should also be placed in the same family. The phylogenetic relationships of these genera should then also be reappraised. For the moment, we tentatively assign Uruma n. gen. to the Pinnotheridae sensu lato.

Members of Sakaina (Pinnotherinae) most closely resemble Uruma n. gen. in their external appearance, especially in the transversely elongated carapace, long and stout P2–P4, and very short P5. Uruma n. gen., however, is readily distinguished from Sakaina by its general shape and the structure of the third maxillipeds, male abdomen, telson and G1. In Uruma n. gen. the merus and ischium of the third maxilliped are clearly articulated from each other and subrectangular in shape ( Figs. 2 View FIGURE 2 b, 3b), the lateral margins of the male abdomen and telson are gradually convergent distally, the telson is only slightly longer than sixth abdominal somite, the distal margin of the telson is rounded ( Fig. 4 View FIGURE 4 a) and the G1 is straight and slightly curved distally ( Fig. 4 View FIGURE 4 b). In Sakaina , however, the merus and ischium of the third maxilliped are fused and subtriangular in shape, the lateral margins of the male abdomen are abruptly narrowed from the third abdominal somite, the telson is about three times longer than the sixth abdominal somite, the distal margin of the telson is straight to strongly concave and the G1 is slender and L-shaped ( Sakai, 1936: Fig. 103a, c; 1969: Fig. 19; Serène, 1964: Fig. 22).

Species of Austinixa Heard & Manning, 1997, Glassella Campos & Wicksten, 1997 , Indopinnixa Manning & Morton, 1987 , Pinnixa White, 1846 , and Pseudopinnixa Ortmann, 1894 (all Pinnotherelinae) also have transversely elongated carapace and short P5. These pinnothereline genera, however, remarkably differ from Uruma n. gen. in that the ischium of the third maxilliped is distinctly smaller than the merus and the palp is often enlarged. The male abdomen and telson are also different (narrow subrectangular in Austinixa , e.g. Manning & Felder 1989: Figs. 2 View FIGURE 2 h, 3h, 5g, 7g, 9g, 10d, 12d; narrow abdomen with rounded wide telson in Indopinnixa , e.g. Davie 1992: Fig. 1 View FIGURE 1 F; Manning & Morton 1987: Fig. 1 View FIGURE 1 E; narrow to wide abdomen, including fused somites in some species of Pinnixa , e.g. Garth 1957: Figs. 3 View FIGURE 3 , 4 View FIGURE 4 E, 5E, 6E, 7E, 8E; Zmarzly 1992: Figs. 6G, 11E, 16C).