Paguropsis gigas, Lemaitre, Rafael, Rahayu, Dwi Listyo & Komai, Tomoyuki, 2018

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 : 51-59

Paguropsis gigas sp. n. Figs 15, 16, 17, 18A, Table 1

Type material.

Holotype: male 23.0 mm, South China Sea, NANHAI 2014, cruise OR 5, staDW 4105, 13°57.8902'N, 115°25.5073'E, 297-565 m, 3 Jan 2014 (NTOU A01445).

Paratype.

1 ovig female 20.5 mm, same sta data as holotype (NTOU A01446).

Description.

Shield (Figs 15A, 18A) subtriangular, ca. 1.3 times as long as broad; dorsal surface glabrous except for setae anterolaterally and transverse fringe of short setae on sloping anterior margins of gastric region; anterior margin between rostrum and lateral projections concave; lateral projections broadly triangular, each terminating in small spine; posterior margin roundly truncate; lateroventral distal angle produced into strong blunt spine adjacent to proximal margin of first antennal segment. Rostrum (Fig. 15A) acutely triangular, arched dorsally, strongly produced and extending to distal margin of ocular acicles; with distinct rounded dorsal longitudinal ridge having few short setae laterally, and ending in blunt subterminal spine. Branchiostegite unarmed except for 1 spine on dorsodistal angle of anterodorsal plate, and setose distal margin.

Ocular peduncles ca. 0.4 length of shield, constricted medially, glabrous except for dorsal longitudinal row of short setae; corneas strongly dilated, diameter 0.5 total peduncular length (including the cornea). Ocular acicles small, triangular, each terminating in blunt, setose distal spine directed anteriorly.

Antennular peduncles when fully extended overreaching distal margins of corneas by nearly full length of ultimate peduncular segment; ultimate and penultimate segments glabrous or at most with scattered short setae; basal segment with ventromesial tuft of setae distally; lateral face with distal subrectangular lobe, and setose lobe proximally.

Antennal peduncles overreaching distal corneal margins by ca. 0.2 length of ultimate segments. Fifth and fourth segments unarmed, nearly glabrous except for scattered short setae. Third segment with setose spine at ventrodistal angle. Second segment with dorsolateral distal angle produced, terminating in small simple or bifid spine; mesial margin rounded, setose, and small spine on dorsomesial angle. First segment unarmed except for moderately long setae on lateral face. Antennal acicle almost reaching distal margin of cornea, slender, nearly straight and terminating in sharp spine, with long setae dorsomesially and distally. Antennal flagellum reaching to midpoint of chelae, with few short setae less than one article in length.

Mouthparts not markedly different from those described for Paguropsis typica (see Fig. 4 A–F). Maxilliped 3 with exopod 4.0 times as long as broad.

Chelipeds (Figs 15B, 18A) subequal, similar in armature and setation; dorsal surfaces of chelae and carpi covered with dense tufts or short rows of long, bristle-like setae nearly obscuring armature below; ventral surfaces of palms with well-spaced tufts of long bristle-like setae, otherwise smooth except for few low tubercles or blunt spines ventrolaterally and ventromesially. Fingers with narrow hiatus proximally, forming spoon-like shape in ventral view when closed; each finger terminating in small curved corneous claw and subdistal blunt calcareous tooth ventral to claw, both claws and teeth interlocking when fingers closed; cutting edge of dactyl with terminal row of small, fused corneous teeth on distal one-third, and row of blunt calcareous teeth on proximal two-thirds and decreasing in size distally; cutting edge of fixed finger with row of blunt calcareous teeth decreasing in size distally. Dactyl 1.4-1.7 times as long as palm; dorsal surface convex, with numerous tufts of long bristle-like setae, and few small blunt spines or tubercles on rounded mesial surface; ventral surface with less dense tufts of bristle-like setae, lacking spines. Fixed finger with dorsal, lateral, and ventral surfaces similar to dactyl in armature. Palm ca. 0.7 times as long as carpus, dorsal surface convex, covered with numerous small blunt to sharp spines arranged in more or less longitudinal rows each with tufts of long setae; dorsomesial margin with 2-4 irregular rows of spines each with tufts of long setae; dorsolateral margin rounded, not delimited, with irregular rows of small tubercles or spines each with long setae. Carpus 0.5-0.6 times length of merus; dorsal and dorsolateral surfaces with well-spaced spines or short transverse rows of 2 or 3 small spines each bearing tufts of long setae, with longitudinal smooth area medially; dorsolateral margin rounded; dorsomesial margin with irregular rows of spines each bearing tufts of long setae; mesial surface with short transverse rows of bristle-like setae on dorsal half, otherwise smooth; ventral surface smooth, with fringe of long setae on ventrodistal margin. Merus subtriangular in cross-section, nearly as long as chela; dorsal margin with row of low protuberances each bearing transverse row of 2 or 3 small tubercles and bearing tuft of long setae; ventromesial and ventrolateral margins each with irregular row of spines with tufts of long setae; lateral and mesial surfaces with tufts of long and short setae; ventral margin smooth except for moderately dense bristle-like setae. Ischium with row of small spines on ventrolateral margin. Basis with ventromesial row of long setae. Coxa with short, weakly marked longitudinal fissure (Fig. 15C) near distal margin.

Pereopods 2 and 3 (Fig. 16 A–D) similar in armature and setation, distinctly dissimilar in length, with pereopod 2 shorter than pereopod 3 (particularly dactyls). Dactyls ca. 1.4 (pereopod 2) or 1.8 (pereopod 3) times as long as propodi; nearly straight except for slightly incurved distal portion, terminating in sharp corneous claw; lateral and mesial faces with shallow longitudinal concavity; all surfaces covered with tufts of bristle-like setae often arranged in oblique rows; ventromesial margin with distal row of minute corneous spinules (pereopod 2) or lacking armature (pereopod 3) except for setae. Propodi 1.4 (pereopod 2) or 1.2 (pereopod 3) times as long as carpi; dorsolateral and ventrolateral surfaces with tufts or rows of tufts of long bristle-like setae; mesial face with scattered setae. Carpi unarmed except for scattered setae laterally and mesially, tufts of short setae dorsally, and distolateral fringe of long setae. Meri with fringe of long setae on ventral margins; ventral margin of merus of pereopod 2 with row of small blunt spines hidden by setae. Ischia unarmed except scattered setae on lateral face of pereopod 2. Coxae with ventromesial margin sparsely setose; coxae of pereopods 3 (Fig. 15C) narrowly separated by 0.2 ventral length of 1 coxa. Sternite XI (Fig. 15C) having anterior lobe flat or weakly concave; posterior lobes each with transverse fringe of setae.

Pereopod 4 (Figs 15D, 17A) with chela as long as or slightly shorter than carpus, ca. 2.2 times as long as high. Dactyl and fixed finger leaving wide gap when closed, each terminating in sharp, inwardly curved corneous claws crossing when closed. Dactyl strongly curved, dorsal margin with row of short setae; cutting edge with ventrolateral distal row of 4 or 5 small corneous-tipped spines (in addition to corneous claw). Fixed finger curving inward, cutting edge with 4 strong corneous-tipped spines (in addition to corneous claw) arranged like bear claw; lateral face usually with 1-4 minute scale-like corneous spines near base of finger. Palm straight, broad, ca. 1.6 times as long as high, lateral face weakly concave medially; dorsal face with long simple setae in addition to prominent dense patch of thin capsulate setae arranged in oblique fringes and occupying oval area from dorsal margin to midlength of lateral face; ventral margin with sparse tufts of short setae continuing on fixed finger. Carpus unarmed except for long setae on dorsal margin, and short oblique fringes of thin capsulate setae on dorsodistal angle of lateral face, and scattered short setae ventrally. Merus 0.5 or 0.6 times as long as meri of pereopod 2 and pereopod 3, respectively. Sternite XII with fringe of long dense setae (Fig. 15C).

Pereopod 5 (Fig. 17B) with chela as long as carpus and 0.7 times as long as merus, with long, brush-like setae on dorsal and ventral surfaces; merus and carpus each with dorsal and ventral row of long setae. Dactyl with rasp on ventral face. Propodal rasp consisting of minute, ovate scales, occupying 0.2 length of propodus. Ischium with setae dorsally and ventrally. Coxa with fringe of long bristle-like setae on rounded ventromesial distal angle.

Male gonopod 1 with inferior lamella armed on distal margin with posterior row of slender, semitransparent hook-like spines, and 2-4 anterior irregular rows of small, straight or slightly curved corneous spines. Gonopod 2 with distal segment strongly twisted distally, densely setose. In only known male, left side with biramous, reduced pleopods 3 and 4, and uniramous vestigial pleopod 5; right side with uniramous vestigial pleopod 3 and lacking pleopods 4 and 5.

Female (only one specimen known) with unpaired left pleopods 2-4 well developed, lacking pleopod 5. Brood pouch large, subquadrate, distal margin strongly scalloped and fringed with setae.

Uropodal exopods (Fig. 17C) slender, broadly curved, terminating in strong spine, anterior margin with fringe of long setae and row of well-spaced corneous-tipped spines; endopods short, strongly curved, anterior margin with long setae and 1 or 2 irregular rows of corneous-tipped spines; protopods with strong, ventrally curved proximal spine.

Telson (Fig. 17C) slightly subrectangular, broader than long; posterior lobes obscurely divided medially, terminal margins unarmed except for fringe of long setae.

Genetic data.

See Table 1.

Color

(Fig. 18A). Shield light orange except for white anterior margins. Ocular peduncles orange dorsally except for white near cornea and proximally, otherwise white; corneas black; ocular acicles light orange except for white distal spine and margins. Antennules orange, flagella of similar but darker color than peduncle. Antennal peduncles with fifth segment light orange on dorsal and lateral surfaces, otherwise white; acicle with tinge of light orange distally; flagella light orange. Chelipeds with yellow bristle-like setae; chelae very light orange to cream; meri and carpi orange except for white spines and tubercles, and white portion of ventrolateral and ventromesial distal margins of meri. Pereopods 2 and 3 generally orange except for white on proximal margins of ischia, distal margins of meri, carpi and propodi, and distal 0.3 of dactyls; meri each also with small white patch proximally on lateral faces. Pereopods 4 and 5 orange.

Etymology.

The specific epithet is from the Latin gigas, meaning giant, used as a noun in apposition, and in reference to the large size attained by individuals of this new species.

Distribution.

Western Pacific: known so far only from the South China Sea. Depth: 297 to 565 m.

Habitat and symbiont.

Found with indeterminate species of acontiate anemone (see “Remarks” under genus).

Variations.

With only two specimens known, no variations can be evaluated.

Affinities.

Paguropsis gigas sp. n. shares with P. lacinia sp. n. the presence of a prominent patch of dense, capsulate setae on the dorsolateral face and dorsal margin of the palm of the chelae of pereopod 4. The shape and arrangement of the setae on the patch, however, is quite different in both species. In P. gigas sp. n., the capsulate setae are relatively short and arranged in a series of oblique fringes that occupy and oval area from the dorsal margin to midlength of the lateral face of the palm (Figs 15D, 17A). In P. lacinia sp. n., the capsulate setae are narrow and long, not arranged in rows, and occupy only one-third of the lateral surface of the palm (Figs 21B, C, 22F). The ultrastructure of these setae has not been studied, but they appear to be hollow and filled with a light brown fluid (at least in preserved specimens). The function, if any, of these setae is unknown, although conceivably they could be used for feeding or grooming. The presence of this unusual patch in these two species might suggest a close phylogenetic relationship. However, in other morphological characters these two species differ substantially, and thus the presence in both of a patch appears to reflect homoplasy. The two species differ also as follows: growth patterns, with specimens of P. gigas sp. n. reaching a much larger size than those of P. lacinia sp. n.; stronger spination of chelipeds, and denser setation of chelipeds and pereopods 2 and 3 in P. gigas sp. n. than in P. lacinia sp. n.; dactyls more robust and wider in P. gigas sp. n. than in P. lacinia sp. n., 7-9 times as long as broad in the former vs. 10-16 times as long as broad in the latter; and once again, as in other species of Paguropsis , drastically different coloration patterns (Fig. 18A, B).

Remarks.

Among the species discussed in this revision, Paguropsis gigas sp. n. and P. andersoni are similar in that they grow to the largest size, the former reaching a shield length of 23.0 mm, the latter to a shield length of 20.6 mm. Morphologically they are also generally similar, both having strong, dense spination and bristle-like setation on the chelipeds, and numerous tufts of bristle-like setae on pereopods 2 and 3. The lateral surfaces of the dactyls of pereopods 2 and 3 are concave in both species, although only moderately so and along the proximal half or more of the segment in P. gigas sp. n., whereas the concavity is strongly marked along the proximal one-third in P. andersoni . Despite these similarities, P. gigas sp. n. differs markedly from P. andersoni , the former having a prominent dense patch of thin capsulate setae arranged in oblique fringes on the dorsal margin and dorsolateral face of the palm of the chelate pereopod 4, whereas in the latter there is no patch of setae and only a fringe of long setae on the dorsal margin of the palm. Furthermore, in P. gigas sp. n. the palm of pereopod 4 is often more noticeably lateromesially flattened than in P. andersoni , although there is some variation in this character in both species. The coloration of the ocular peduncles, chelipeds, and pereopods is also clearly different in these two species (compare Figs 8C, 18A).