Pagurixus Melin, 1939

Komai, Tomoyuki & Osawa, Masayuki, 2006, A review of the Pagurixus boninensis species group, with descriptions of six new species (Crustacea: Decapoda: Anomura: Paguridae), Zootaxa 1214 (1), pp. 1-107 : 6-7

Genus Pagurixus Melin, 1939

Pagurixus Melin, 1939: 37 .— McLaughlin & Haig, 1984: 122.—de Saint Laurent & McLaughlin, 2000: 184.— McLaughlin, 2003: 125. [Type species by monotypy: Eupagurus (Pagurixus) boninensis Melin, 1939 . Gender: Masculine. Established as a subgenus of Pagurus Fabricius, 1775 (as Eupagurus Brandt, 1851 )].

Diagnosis

Gills biserial, 11 pairs, including 1 pleurobranch above fourth pereopod (seventh thoracomere) and 2 arthrobranchs on each third maxilliped to fourth pereopods. Rostrum well­developed, triangular. Ocular acicles simple. Third maxilliped with 1 accessory tooth and well­developed crista dentata. Chelipeds markedly unequal, frequently exhibiting strong degree of sexual dimorphism; dorsal surface of right palm without prominent spines or covering of tufts of setae. Carpi of ambulatory legs unarmed or only with dorsodistal spine. Fourth pereopods semichelate, propodal rasp consisting of 1 row of corneous scales; preungual process absent. Coxae of male fifth pereopods dissimilar, right largest; right coxa with tuft of stiff setae directed toward left and occasionally with papilla­like sexual tube; left coxa usually with gonopore partially masked by short setae. Female with paired gonopores or single left gonopore. Eighth thoracic sternite composed of 2 contiguous, rounded lobes. Male with unpaired, unequally biramous left third to fifth pleopods; female with unpaired, unequally biramous left second to fifth pleopods, no paired first pleopods. Uropods markedly asymmetrical. Telson with faint or distinct transverse indentations; posterior lobes without fringe of long setae on lateral margins.

Remarks

The presence of two setal rows or series on the ventral surface of the ultimate segment of the antennular peduncle suggests monophyly of the Pagurixus boninensis group. This character appears to be unique within the Paguridae (unpublished data) and is a likely synapomorphy of the Pagurixus boninensis group. The Pagurixus boninensis group is further divided into two subgroups based on the presence or absence of a weak lateral ridge on one or both carpi of the chelipeds. The first subgroup (subgroup A), characterized by the presence of a weak lateral ridge, at least on the carpus of the left cheliped, includes P. laevimanus , P. maorus , P. nomurai , P. pulcher , P. tweediei , and P. concolor n. sp. The second group (subgroup B), characterized by the absence of the ridge, includes P. boninensis , P. festinus , P. brachydactylus n. sp., P. paulayi n. sp., P. pseliophorus n. sp., and P. ruber n. sp.

As discussed by McLaughlin & Haig (1984), marked sexual dimorphism is seen in the size and armament of the right cheliped in Pagurixus species. Variability in the development of the female gonopores was also discussed by McLaughlin & Haig (1984).

Owing to the strong sexual dimorphism, the following key is separated by sex. It is important to recognize that P. laevimanus , P. brachydactylu s n. sp. and P. paulayi n. sp. are not included in the key for females, as no female specimens of these species were available for study.