Patagurus, Anker, Arthur & Paulay, Gustav, 2013

Anker, Arthur & Paulay, Gustav, 2013, A remarkable new crab-like hermit crab (Decapoda: Paguridae) from French Polynesia, with comments on carcinization in the Anomura, Zootaxa 3722 (2), pp. 283-300 : 284-291

publication ID	https://doi.org/ 10.11646/zootaxa.3722.2.9
publication LSID	lsid:zoobank.org:pub:9D347B8C-0BCE-47A7-99DF-DBA9A38A4F44
DOI	https://doi.org/10.5281/zenodo.6154629
persistent identifier	https://treatment.plazi.org/id/C445540A-FFF4-1063-7AEB-FC877D36A46A
treatment provided by	Plazi
scientific name	Patagurus
status	gen. nov.

Treatment

Patagurus View in CoL gen. nov.

Diagnosis. Anterior carapace vaulted, well calcified, gastric region slightly elevated; rostrum subtriangular; lateral margins each developed into two relatively small, subacute lobes; cervical groove clearly delineated; posterior carapace lobes very prominent, laterally projecting; posterior carapace calcified except for a narrow, posterior, membranous band tucked under calcified portion; branchiostegite with two large and two small calcified plates. Ocular acicles vestigial. Third maxillipeds with well-developed crista dentata and one accessory tooth. Ambulatory (second and third) pereopods similar, slender, with elongate dactyli. Fourth pereopod with rasp comprised of a single row of long, slender spines. Fifth pereopod non-chelate, with no discernible rasp and very small dactylus. Thoracic sternites rigidly articulated through sternite VII. Males with elongate right sexual tube directed mesially, left sexual tube shorter and stouter than right tube, both calcified and with long tuft of setae distally. Pleon narrow, elongate, segmentation of anterior pleomeres not discernable (tergal plates not delineated), segmentation of fifth pleomere faintly discernible, sixth tergite clearly defined, but feebly calcified; male pleopods 2–5 absent. Uropods well developed, symmetrical. Telson subquadrate, entire, folded firmly against ventral surface of sixth pleomere; position of anus not determined. Female characters presently unknown.

Type species. Patagurus rex sp. nov., by present designation.

Etymology. The new genus is named after one of the world’s most eminent carcinologists, the late Dr. Patsy (Pat) A. McLaughlin (1932–2011). The generic name is a combination of McLaughlin’s preferred first name and the Greek word pagourus (a kind of crab), which was the origin for the nominal pagurid genus, Pagurus Fabricius, 1775 .

Remarks. The number of gills, one of the differentiating characters between Porcellanopagurus (11 pairs) and Solitariopagurus (10 pairs), could not be determined in Patapagurus, because penetration of the calcified branchiostegites would have resulted in serious damage to the branchial region of the single holotype specimen. The dorsal surface of the carapace of Patagurus ( Fig. 1 View FIGURE 1 C) is most similar to those of species of Porcellanopagurus ( Fig. 1 View FIGURE 1 A): they both generally have a pair of small lateral projections, two pairs of relatively small anterior carapace lobes, and a pair of more prominent posterior carapace lobes, which are posterior to, and clearly separated by, the cervical groove. However, the sclerotization of the posterior carapace is much more extensive in Patagurus , leaving only a narrow, posterior, membranous band. In contrast, Solitariopagurus ( Fig. 1 View FIGURE 1 B) has a pair of strong lateral projections, three pairs of anterior carapace lobes, and a pair of small posterior carapace lobes. The dorsal surface of the shield is unarmed in all species of Porcellanopagurus (e.g., Borradaile 1916; Martin et al. 2009; McLaughlin 2000), as well as in the type species of Solitariopagurus , S. profundus Türkay, 1986 . In the remaining three species of Solitariopagurus , the shield is armed with a row of large tubercles behind the anterior margin and occasionally also by a few smaller tubercles elsewhere (Poupin & McLaughlin 1996; McLaughlin 1997; McLaughlin 2000; Martin et al. 2009). Patagurus ( Fig. 1 View FIGURE 1 C) not only has the surface of the shield, but also the surfaces of the well-developed posterior carapace lobes covered with an abundance of tubercles of various sizes. Although the posterior carapace is well developed in all species of Porcellanopagurus , it is reduced in members of Solitariopagurus and presumably partly reduced and partly fused to the posterior lobes in the type species of Patagurus .

The thoracic sternites of Patagurus are quite similar to those of Solitariopagurus and both differ considerably from the sternites of Porcellanopagurus . In Patagurus and Solitariopagurus , sternites III through VII are broad and rigidly articulated, with sternite VII flexed dorsally at a right angle relative to sternite VI. Similarly, asymmetrically paired male sexual tubes are seen in Patagurus and in all four species of Solitariopagurus , but are lacking in all species of Porcellanopagurus . Although nothing is known about the female secondary sexual characters of Patagurus , females of Porcellanopagurus all have paired gonopores, whilst females of Solitariopagurus have only a single left gonopore. Propodal rasps are present on the fifth pereopod in Solitariopagurus , but are lost in Patagurus . Rasps on the fourth pereopod are modified to a single row of sharp, corneous spines in both genera, rather than well-developed as in most pagurids.

In species of Porcellanopagurus and Solitariopagurus , even in the largest specimens examined (McLaughlin 2000; de Saint Laurent & McLaughlin 2000), the right cheliped was not shorter than the left, as is the case in the male of the type species of Patagurus .

The number and type of gills and several important female characters remain unknown for Patagurus . Therefore, and in the absence of a more complete phylogenetic data for the family Paguridae , speculations of the phylogenetic relationship of Patagurus with Porcellanopagurus and Solitariopagurus would be premature. Porcellanopagurus , Solitariopagurus and Patagurus share numerous synapomorphies and appear to form a morphologically distinctive clade. However, the phylogenetic position of this clade within the large and heterogeneous family Paguridae remains poorly understood. There is at least an indication of some affinity of Porcellanopagurus and Solitariopagurus to several other pagurid genera characterized by a more or less calcified posterior carapace, reduced abdomen and absence of pleopods in males, especially Ostraconotus (McLaughlin & Lemaitre 1997) (see Discussion). Porcellanopagurus was included in recent phylogenetic analysis of anomurans (Schnabel et al. 2011, Bracken-Grissom et al. 2013) and recovered well within the Paguridae , sister to a clade comprised of several northern temperate Paguridae and representative king crabs.

Patagurus rex sp. nov. ( Figs. 1 View FIGURE 1 C, 2–6)

Type material. Holotype male (sl 5.1 mm), UF 23548, French Polynesia, Society Islands, Moorea, R/V Alis sta. DW 3471, 149.9167 °W, 17.4833°S, Warén dredge, depth 400 m, mud and rocks, some shells, leg. G. Paulay et al., 21 October 2009.

Description. Shield ( Figs. 1 View FIGURE 1 C, 2A) considerably wider than long; anterior margins between rostrum and lateral projections broad, each with slight median protrusion; lateral projections ( Fig. 2 View FIGURE 2 B) widely separated, moderately developed, subacute. Rostrum subtriangular, prominently drawn out into appreciably narrower tip with a middorsal ridge. Anterolateral margins of shield developed as subrectangular protrusions with relatively small first and second anterior carapace lobes ( Fig. 2 View FIGURE 2 A). Posterior carapace lobes extremely developed, sclerotized, subtriangular, each with dentate anterior margin; a narrow membranous portion, completely concealed in dorsal view, remaining near posterior margin of carapace. Dorsal surface of carapace with abundant tubercles and ridges of various sizes and shapes as illustrated ( Figs. 2 View FIGURE 2 A, B, 4A). Branchiostegite with two large and two small calcified plates ( Fig. 4 View FIGURE 4 E). Ocular peduncles about 0.2 shield length, each distinctly swollen in proximal half; corneas approximately half peduncular length. Ocular acicles very small, hidden in dorsal view by proximally broadened margins of rostrum.

Antennular peduncle ( Figs. 2 View FIGURE 2 B, C) considerably longer than antennal peduncle, overreaching distal corneal margin by more than full length of ultimate segment, unarmed, but with several long setae on distodorsal margin of ultimate segment (omitted from Fig. 2 View FIGURE 2 C). Antennal peduncle ( Figs. 2 View FIGURE 2 B, D) overreaching distal corneal margin by at least full length of ultimate segment, but considerably shorter than antennular peduncle; epistomial plate and first peduncular segment unarmed and lacking setae; second segment with dorsolateral distal angle produced, unarmed and terminally subacute; third through fifth segments each with few short setae; antennal acicle reaching to distal margin of fourth peduncular segment, unarmed, terminally blunt.

Mouthparts not removed. Third maxilliped with basis armed with subdistal tooth on mesial surface; ischium with well-developed crista dentata and one accessory tooth ( Fig. 2 View FIGURE 2 E); merus, carpus, propodus and dactylus unarmed.

Thoracic sternite III prominently produced anteriorly into two triangular, subacute lobes, each with distinctly elevated, oblique ridge ( Fig. 4 View FIGURE 4 C, D). Sternite IV roundly subrectangular, unequally divided into anterior and posterior portions by broad suture; posterior portion rigidly articulated with sternite V ( Fig. 4 View FIGURE 4 D). Sternite VI narrow, rigidly articulated with sternite VII at ~90° angle, latter extending dorsad. Sternite VIII narrow, anterodorsal to sternite VII, separated from latter by membranous area.

Right cheliped much larger and more robust than left cheliped, but slightly shorter in overall length; propodocarpal articulation perpendicular to main axis of cheliped, without pronounced rotation ( Fig. 4 View FIGURE 4 B, 5B). Chela ( Fig. 3 View FIGURE 3 C, 4B) approximately as long as carpus; dorsal surface convex, smooth, drawn out mesially and laterally into thin margins; ventral surface of palm and dactylus with scattered fine setae; dactylus approximately 0.6 length of palm, unarmed, with rounded margins, some scattered setae present; cutting edges of dactylus and fixed finger calcareous, each with two low teeth, proximal larger than distal; fingers proximally gaping when closed; fingertips with small corneous point. Carpus ( Fig. 3 View FIGURE 3 A, B) approximately as long as merus, trapezoidal, with dorsomesial and dorsolateral margins each elevated into low, unarmed crest, dorsal surface elevated in midline and with median row of tubercles, forming a distinctly rounded ridge distally; ventral surface with scattered, moderately long setae. Merus roundly triangular; lateral surface minutely granular; ventromesial and ventrolateral margins each with row of spinulose tubercles, ventral surface with some larger tubercles, smaller granules and fine setae. Ischium with faint rugosities or granules mesially, remaining surface unarmed.

Left cheliped elongate, slender; dactylus and fixed finger distinctly arched ventrally. Chela shorter than carpus; dorsal surface unarmed, slightly convex, with rounded margins; ventral surface with numerous tufts of moderately long setae on palm and especially on fixed finger; cutting edge of fixed finger with row of small corneous teeth; dactylus more than twice length of palm, unarmed, with tufts of moderately long setae; margins rounded; cutting edge with row of minute corneous teeth ( Fig. 3 View FIGURE 3 D–F). Carpus approximately equal to merus length; dorsomesial and dorsolateral margins each elevated into unarmed crest; dorsal surface elevated in midline and armed with row of subacute spiniform tubercles; lateral face minutely granular; ventral surface with scattered small tubercles and moderately long setae. Merus roundly triangular; lateral surface minutely granular; ventral surface with irregular row of spinulose tubercles adjacent to lateral margin, some tubercles and fine setae present on ventral surface and mesially. Ischium unarmed.

Ambulatory legs (second and third pereopods) similar in shape and length ( Figs. 2 View FIGURE 2 F, 5). Dactyli slightly shorter than propodi, each with sparse, moderately long setae dorsally and one corneous spinule adjacent to terminal corneous unguis; mesial and lateral faces with few shorter, scattered setae; ventral margins each with row of 11 or 12 corneous spines ( Fig. 2 View FIGURE 2 G). Propodi approximately 1.5 length of carpi, unarmed, with scattered setae. Carpi short, slightly less than 0.5 lengths of meri; unarmed, with few scattered setae. Meri unarmed except for minute protuberances on ventral margin. Ischia unarmed; lengths of ischium of second and third pereopods similar.

Fourth pereopod ( Fig. 2 View FIGURE 2 H) with dactylus and propodus bearing scattered setae; dactylus somewhat sickle-shaped, about as long as propodus, covered with minute tubercles ( Fig. 2 View FIGURE 2 I); propodal rasp consisting of single row of five, long corneous spines; carpus and merus unarmed, each with few setae. Fifth pereopod ( Fig. 2 View FIGURE 2 J) with very small dactylus obscured by terminal tufts of long setae originating from propodus, without rasp. Coxae of male fifth pereopods each with well-developed sexual tube, right longer and more slender, both densely setose distally ( Fig. 2 View FIGURE 2 K).

Male pleon markedly reduced ( Figs. 4 View FIGURE 4 D, 5C, E), lacking pleopods 2–5. Uropods symmetrical; endopod and exopod each with ovate rasp of corneous scales, exopodal rasps larger than endopodal rasps ( Fig. 3 View FIGURE 3 G). Telson subquadrate, with trace of lateral indentation; dorsal surface proximally with median depression; posterior margin entire, unarmed ( Fig. 3 View FIGURE 3 H).

Female unknown.

Color in life. Calcified portions of carapace hyaline-whitish with scattered tints of orange and pink; tip of rostrum and first and second anterior carapace lobes darker orange; ocular peduncles white; antennular and antennal peduncles and flagella orange; ventral cephalothorax pale orangish-white; chelipeds bright orange dorsally, lighter orange ventrally; ambulatory legs with orange dactyli, propodi and carpi each reddish-orange with white band at distal margin, meri reddish-orange, each with irregular splotches of white ( Figs. 5 View FIGURE 5 , 6 View FIGURE 6 ).

Etymology. Referring to the extraordinary albeit superficial resemblance of this new species to some king crabs ( rex = king in Latin).

Distribution. Presently known only from the type locality off Moorea, Society Islands, French Polynesia.

Habitat. Mud and rocks bottom at a depth of 400 m.

Biological notes. The hermit crab was covering its miniature abdomen with a valve of the mytilid bivalve, Gregariella sp. ( Figs. 4 View FIGURE 4 C, 6A, B).