Paguropsis Henderson, 1888

Lemaitre, Rafael, Rahayu, Dwi Listyo & Komai, Tomoyuki, 2018, A revision of " blanket-hermit crabs " of the genus Paguropsis Henderson, 1888, with the description of a new genus and five new species (Crustacea, Anomura, Diogenidae), ZooKeys 752, pp. 17-97 : 20-22

Genus Paguropsis Henderson, 1888

Paguropsis Henderson, 1888: 98 (type species by monotypy: Paguropsis typica Henderson, 1888, gender feminine); Stebbing, 1893: 169; Alcock, 1905: 27; Gordan, 1956: 325; McLaughlin and Lemaitre, 1997: 112 (phylogeny); McLaughlin, 2003: 114 (key); McLaughlin et al., 2010: 23; McLaughlin, 2015: 153, fig. 6.3D.

Chlaenopagurus Alcock, 1899: 113 (type species by monotypy: Chlaenopagurus andersoni Alcock, 1899, gender masculine).

Diagnosis.

Thirteen pairs of quadriserial gills [no pleurobranchs on thoracomere VIII (last)], gills consisting of series of twin lamellae each ending on distolateral and distomesial angles in filamentous or stub-like extensions (e.g., Fig. 3A). Shield well calcified, subtriangular or subrectangular; dorsal surface somewhat vaulted; lateral projections broadly triangular, each terminating in small spine. Rostrum prominent and projecting anteriorly, subtriangular, arched and dorsally ridged. Branchiostegite with dorsal margin (e.g., Fig. 2B, D) divided into two calcified plates: one anterodorsal plate poorly delimited ventrally, and one small, subtriangular median plate with distinct central pit. Posterior carapace (e.g., Fig. 2A, C) with well calcified posteromedian plate, and well calcified lateral lobe on each side adjacent to shield. Ocular peduncles short, approx. half as long as shield; corneas dilated (diameter typically half or slightly more than length of ocular peduncle, including cornea); ocular acicles relatively small, subtriangular, armed with small dorsodistal spine. Antennal peduncles distinctly exceeding distal margins of corneas; acicles long, reaching to level of corneas. Mouthparts: maxillule with well- developed and strongly recurved external lobe of endopod; maxilliped 1 with exopodal flagellum, endopodite medially bent at nearly right angle, with distinctly developed epipod; maxilliped 3 ischium with well-developed crista dentata, lacking accessory tooth, exopod slender, 4 or more times as long as broad. Epistome unarmed. Chelipeds symmetrical or nearly so, subequal in size, armed with moderately dense to dense setation and numerous well-spaced small spines or tubercles; coxae each with ventral surface having an uncalcified median longitudinal fissure starting on distal margin and incompletely covering length of ventral surface. Pereopods 2 and 3 long; dactyl of pereopods 3 distinctly longer than dactyl of pereopod 2. Sternite XI (between pereopods 3; e.g., Fig. 5B, D) narrow, separating coxae of pereopods 3 by distinctly less than half length of one coxa (typically 0.2 to 0.3 length of one coxa); anterior lobe flat or slightly concave, posterior lobes broad, arched and forming arrowhead shape with apex directed anteriorly. Pereopod 4 chelate, extending to subdorsal position to manipulate carcinoecium (e.g., Fig. 1A, 2A, C), lacking rasp-like surfaces; dactyl with cutting edge armed with row of small corneous spines; fixed finger with sharp spines on cutting edge arranged like bear claw; coxae (e.g., Fig. 5B, D) with anteroventral margin sharply delimited, keel-like. Sternite XII (between pereopods 4; e.g., Fig. 5B, D) broad, ridge-like, weakly divided medially, with fringe of setae. Pereopod 5 chelate, with weakly-developed propodal rasp. Pleon curling under but not dextrally or sinistrally twisted; pleonal somite 1 not fused to last thoracic somite, with partly calcified tergite and pleura. Male with well-developed paired gonopods 1 and 2, and reduced (uniramous or biramous) pleopod 3-5 on left or right side (occasionally lacking pleopod 5), or altogether lacking pleopods 3-5. Female with paired gonopores; with paired uniramous pleopods 1 modified as gonopods (Fig. 7D); left or right side of pleon with well-developed biramous unpaired pleopods 2-4 (ovigerous) and reduced biramous or uniramous unpaired pleopod 5 (not ovigerous, occasionally absent); brood pouch large (e.g., Figs 1C, 3C), covering pleopods 2-4 and entire egg mass. Uropods and telson symmetrical; exopods long, slender; endopod small, curved. Telson subquadrate or subrectangular, lacking or with obscure lateral indentations; posterior margin weakly divided into broadly rounded lobes.

Distribution.

Subtropical to tropical Indo-West Pacific. Depth: 30 to 1125 m.

Habitat and symbionts.

Several cnidarian names have been reported in the literature as symbionts of what has been presumed to be P. typica , including: Epizoanthus paguropsidis [e.g., Boas (1926), Schäfer et al. (1983, as E. paguropsides ), Ates (2003), Williams and McDermott (2004)]; Mammillifera sp. [e.g., Alcock (1905), Balss (1924, 1927), Ross (1983)]; Actinia equina [e.g., Williams and McDermott (2004)]. There is considerable taxonomic confusion on these cnidarian names. The name E. paguropsidis is considered a nomen nudum apparently introduced by Boas (1926), and attributed to Ates (2003, as per WoRMS Editorial Board 2018). Schäfer et al.'s (1983) study identified the host of the cnidarian as P. typica , but that host is shown herein to actually apply to a species of Parapaguridae . Mammillifera is currently a subjective junior synonym of Zoanthus . Given the discovery of several species previously confounded under P. typica as well several new species, and the general unavailability of hermit crab materials that go along with reports of cnidarian symbionts, it is impossible to ascer tain the identity of the cnidarian as well as to which species of Paguropsis or the new genus described herein. Those symbiont names apply to the Zoanthidea (often called Zoantharia ), and those associated with hermit crabs that are typically assigned in the literature to colonial species of the genus Epizoanthus , (JD Reimer, pers. comm.; see Fig. 1D). However, the symbionts found with species of Paguropsis are actually indeterminate species of acontiate anemones which belong to the Actiniaria (DG Fautin, pers. comm.), and are herein reported as such.

Type species.

Paguropsis typica Henderson, 1888, by monotypy. Gender: feminine.

Species included.

In addition to the type species, P. typica , the genus includes: P. andersoni (Alcock, 1899), and three new species described herein.

Remarks.

Henderson (1888) considered Paguropsis and its only species at that time, P. typica , to be unique among hermit crabs based on the peculiar subdorsal position of pereopods 4 and 5 adapted to manipulate the symbiont zoanthid, the presence on the left or right side of the pleopods, and the straight pleon. Alcock (1905) considered his monotypic genus Chlaenopagurus Alcock, 1899 to be a junior synonym of Paguropsis , although he provided no explanation for that taxonomic action. Alcock (1905) suggested that Paguropsis was closely related to Paguristes Dana, 1851, but differed in the former having stout eyestalk, a non-coiled pleon, symmetrical tail fan (uropods and telson), chelate pereopod 4, and indifferent position (left or right side) of the pleopods. The taxonomy or morphology of Paguropsis has not been discussed or revised since that early time, although Boas (1926) did study in detail the morphology of P. typica relative to its symbiotic zoanthid.

During this study, several important characters previously overlooked or not sufficiently discussed have been added to the diagnosis of Paguropsis . Among these are the shapes of mouthparts (maxillule external lobe of endopod, and maxilliped 3 exopod); presence on posterior carapace of a well delimited calcified lateral lobe (e.g., Fig. 2A) fused to shield; on the branchiostegite (e.g., Fig. 2B, D), presence of a well calcified median plate with a central pit adjacent to the cervical groove, and an anterodorsal plate; presence on ventral surface of coxae of chelipeds of a longitudinal, uncalcified fissure (e.g., Fig. 5B, D); shape of thoracic sternites XI and XII (between pereopods 3 and 4 respectively; e.g., Fig. 5B, D); development of a full chela lacking rasp on pereopod 4, and distinct, bear-like claw armature of fixed finger; and sharply delimited anteroventral margin of coxae of pereopods 4 (e.g., Fig. 5B, D). Furthermore, coloration has been found to be unique for each of the species (Figs 8, 18A, B, 28 A–D).