Eutrichopagurus, Komai, Tomoyuki, 2015

Komai, Tomoyuki, 2015, A new genus and new species of Paguridae (Crustacea: Decapoda: Anomura) from shallow subtidal waters in Okinawa Island, the Ryukyu Islands, Japan, Zootaxa 3918 (2), pp. 250-260 : 251

Eutrichopagurus n. gen.

[New Japanese name: Shirakawa-yadokari-zoku]

Type species. Eutrichopagurus shirakawai n. sp. Gender: masculine.

Diagnosis. Eleven pairs of deeply quadriserial phyllobranchiate gills [including 2 pairs of arthrobranchs above bases of third maxillipeds to fourth pereopods and 1 pair of pleurobranch on seventh thoracomere (fourth pereopods)]. Rostrum acutely triangular. Ocular acicles elongate, simple. Third maxilliped with 2 accessory teeth and well developed crista dentata on ischium. Chelipeds unequal and dissimilar. Sixth thoracic sternite with subrectangular anterior lobe, unarmed. Fourth pereopods semichelate; propodal rasp consisting of 1 row of corneous scales; no preungual process. Female with single gonopore on coxa of left third pereopod; no paired first pleopods; second to fifth left pleopods unequally biramous. Telson with row of long setae on lateral margins of posterior lobes. Male unknown.

Composition. Monotypic.

Remarks. Except for the gill structure, Eutrichopagurus n. gen. is substantially similar to Trichopagurus . Shared diagnostic characters are: gills 11 pairs, including one pair of pleurobranchs on seventh thoracomere; third maxilliped with at least one accessory tooth and well-developed crista dentata on ischium; chelipeds distinctly unequal; female without right gonopore and first pleopods modified as gonopods; telson with prominent setae on lateral margin of each posterior lobe. In particular, the last character is not heretofore known for pagurid species other than the four species currently assigned to Trichopagurus ( Komai & Osawa 2005; Komai & Poupin 2012; Komai 2013). The new genus is immediately distinguished from Trichopagurus by the deeply quadriserial, rather than biserial, phyllobranchiate gills. Trichopagurus was originally diagnosed by the possession of 11 pairs of intermediate gills (de Saint Laurent 1970; = quadriserial phyllobranchiate as defined by McLaughlin & de Saint Laurent 1998), and this was followed by McLaughlin (2003). However, Komai & Osawa (2005) clarified that the gill structure of the type species of Trichopagurus , T. trichophthalmus (Forest, 1954) , was actually biserial as defined by de Saint Laurent & McLaughlin (1998). Other species assigned to Trichopagurus all have biserial phyllobranchiate gills ( Komai & Osawa 2005; Komai & Poupin 2012; Komai 2013). Furthermore, E. shirakawai n. sp. is characteristic in the reduced corneas, elongate ocular acicles, and microscopically granular surfaces of chelipeds and ambulatory legs, although these characters may be only of specific significance.

The new genus is the fifth of the pagurid genera characterized by the presence of 11 pairs of quadriserial phyllobranchiate gills and the lack of first pleopods modified as gonopods in females. The other four genera are: Cestopagurus , Pagurodes , Pseudopagurodes and Turleania . Gills are deeply quadriserial in Eutrichopagurus n. gen., Pagurodes and Turleania , while only distally quadriserial in Cestopagurus and Pseudopagurodes (in the latter genus, the gill structure is sometimes biserial according to species; McLaughlin & Rahayu 2007; Rahayu & Komai 2013). Furthermore, the absence of a female gonopore on the coxa of the left third pereopod also distinguishes Eutrichopagurus n. gen. from all the other four genera. The subequal chelipeds distinguish Pagurodes and Pseudopagurodes from Eutrichopagurus , Cestopagurus and Turleania . The lack of an accessory tooth and poorly developed crista dentata on the ischium of the third maxilliped sets Turleania apart from the other four genera.

Etymology. From the Greek prefix “eu” (= good or true), and the generic name Trichopagurus , to show that the new genus is similar to Trichopagurus , which was originally and incorrectly diagnosed as having trichobranchiate (= now quadriserial phyllobranchiate) gills. As noted above, the new genus is characterized by the possession of 11 pairs of quadriserial phyllobranchiate gills.