Paguristes petalodactylus, Rahayu, 2007

Rahayu, Dwi Listyo, 2007, The hermit crabs Paguristes Dana, 1851 s. l. (Crustacea, Decapoda, Anomura, Diogenidae) from the western Indian Ocean, Zoosystema 29 (3), pp. 515-534 : 521-524

Paguristes petalodactylus n. sp.

( Figs 2 ; 3 )

TYPE MATERIAL. — Madagascar. Tuléar, coll. Thomassin, holotype, ♂ (5.7 mm) (MNHN-Pg 7741).

ETYMOLOGY. — From the Greek petalos, broad, and dactylos, alluding to the broad dactyls of the second and third pereopods.

TYPE LOCALITY. — Tuléar, Madagascar.

DISTRIBUTION. — Known only from Tuléar, Madagascar, depth unknown.

DESCRIPTION

Thirteen pairs of quadriserial gills; branchiostegites each with one spine on distal margin and few spinules on dorsal margin accompanied by few setae. Shield ( Fig. 2A ) 1.4 longer than broad, dorsal surface with few spinules laterally and sparse short setae. Rostrum acutely triangular, reaching half length of ocular acicles, terminating in small spinule. Lateral projections shorter than rostrum, triangular, each terminating in small spinule.

Ocular peduncles long, 0.8 shield length, moderately slender, dorsal surfaces each with row of sparse tufts of setae; corneal diameter 0.2 of peduncular length. Ocular acicles triangular, each terminating in acute spine, and with sparse setae on distal margin; separated by about basal width of one acicle.

Antennular peduncles when fully extended reaching middle of corneas; ultimate and penultimate segments unarmed, basal segment with small spinule on lateral face of statocyst lobe.

Antennal peduncles reaching 0.6 of ocular peduncles. Fifth segment with few scattered setae; fourth segment with small dorsodistal spine; third segment prominently produced ventrally, terminating in acute spine accompanied by moderately long, sparse setae; second segment with dorsolateral distal angle produced, terminating in bifid spine and with sparse setae, mesial margin with one spine; first segment unarmed. Antennal acicle overreaching distal margin of fifth peduncular segment, terminating in prominent bifid spine; three spines on dorsal surface mesially, two spines on lateral margin, sparse setae on dorsal and lateral faces not concealing armature. Antennal flagellum about same length as shield, article each with one or two short setae.

Chelipeds unequal and dissimilar, left ( Fig. 2B ) larger than right ( Fig. 2D ). Dactyl of left cheliped 1.5 longer than palm, somewhat subrectangular in shape (in dorsal view); dorsal surface with closelyspaced tuberculate spines, some corneous-tipped; dorsomesial margin delimited only proximally by row of corneous-tipped spines; mesial face ( Fig. 2C ) with irregular rows of tuberculate spines, some corneous-tipped, larger spines near dorsal margin, some spines accompanied by one or two short setae; ventral surface with few tufts of setae; cutting edge with moderately small calcareous teeth on proximal 0.7, corneous teeth distally, terminating in small corneous claw, no hiatus between dactyl and fixed finger. Palm approximately 0.6 length of carpus; dorsal surface with irregular rows of moderately small tuberculate spines, sometimes corneous-tipped, or accompanied by one or two short setae, becoming blunt and less dense proximally, but closelyspaced and densest on fixed finger; dorsomesial margin weakly delimited by row of slightly larger corneous-tipped spines; mesial face with irregular rows of tuberculate, corneous-tipped spines, some accompanied by one or two short setae; dorsolateral margin slightly delimited only distally by rows of moderately small corneous-tipped spines continuing onto lateral surface; ventral surface with rows of corneous-tipped spines and tuft of sparse short setae; cutting edge of fixed finger with row of moderately small calcareous teeth, terminating in small corneous claw. Carpus approximately half length of merus, row of moderately large, corneous-tipped spines on dorsomesial margin; dorsal surface with irregular rows of tuberculate spines, larger spines near dorsomesial margin, distal margin with row of small spines laterally; dorsolateral margin not delimited; mesial face with scattered tuberculate spines and sparse setae. Merus with large spine at dorsodistal margin and several smaller spines laterally; dorsal margin with subdistal transverse row of large spines continuing onto lateral face, remainder of dorsal margin with low protuberances; lateral face with few tubercles near ventral margin; ventrolateral and ventromesial margins each with row of spines; ventral surface with scattered tubercles and few tufts of setae.

Right cheliped ( Fig. 2D ) with dactyl 1.6 longer than palm, subrectangular in shape (in dorsal view); dorsomesial margin delimited by moderately large, corneous-tipped spines; dorsal surface with closelyspaced tuberculate, and sometimes corneous-tipped, spines; mesial face ( Fig. 2E ) with irregular rows of moderately large, corneous-tipped spines, each spine accompanied by one or two short setae. Palm approximately 0.6 length of carpus; dorsomesial margin with row of five prominent, corneoustipped spines, each accompanied by one or two short setae, dorsal surface with irregular rows of moderately small tuberculate, sometimes corneoustipped spines, becoming closely-spaced on moderately flattened dorsal surface of fixed finger. Carpus with 10 moderately large corneous-tipped spines on dorsomesial margin, sometimes accompanied by one or two short setae, dorsal surface with irregular row of small tuberculate spines, becoming less dense and obtuse tubercles near dorsolateral, distal margin with numerous small spines laterally. Merus with large spine at dorsodistal margin and several smaller spines laterally; dorsal margin with subdistal transverse row of large spines continuing to lateral face, remainder of dorsal margin with small spines; lateral face with few tubercles near ventral margin; ventrolateral and ventromesial margins each with row of spines.

Second and third pereopods ( Fig. 3 A-D) with broad dactyls, second broader than third. Dactyls approximately twice length of propodi; dorsal margins each with row of corneous-tipped spines (second) or row of protuberances (third), all with long setae, not concealing armature; ventral margins each with row of 24 or 25 (second) or 20-25 (third) corneous spines and moderately long setae; mesial faces of second flattened, only slightly on third, each with three or four irregular rows of tiny corneous spines, larger corneous spines on third, and short, shallow longitudinal sulcus proximally; lateral faces each with rows of tufts of sparse, short setae and shallow, short longitudinal sulcus proximally. Propodi each with row of prominent corneous-tipped spines (second) and smaller spines (third) on dorsal margin, accompanied by tufts of setae; mesial faces of second slightly flattened, each with irregular rows of spinules, accompanied by two or three short setae, mesial face of third weakly convex with few tuft of short setae; lateral surfaces each with three rows of tuft of sparse, short setae; ventral margins each row of spinules and setae, barely visible on lateral face. Carpi each with row of prominent spines on dorsal margin, second row of smaller spines near dorsal margin on second pereopod, each accompanied by short setae; lateral faces each with longitudinal sulcus. Meri each with row of protuberances and short setae on dorsal margin, longer and denser setae on ventral margin, ventromesial margins each with row of small spines; ventrolateral margin with row of small spine (second), or unarmed (third). Fourth pereopods ( Fig. 3E ) each with preungual process at base of dactylar claw, no spines on distal margins of carpi.

Male first pleopods ( Fig. 3F, G ) each with single row of small hook-like corneous spines on distal margin of inferior lamella; external lobe as long as inferior lamella, internal lobe short, with marginal setae. Second pleopods ( Fig. 3H ) with basal segment and endopod glabrous, appendix masculina with moderately long setae. Female unknown.

Telson ( Fig. 3I ) with moderately deep lateral incisions; median cleft small, shallow; posterior lobes almost symmetrical, terminal and lateral margins unarmed, each with row of long setae.

REMARKS

The species of Paguristes s.l. are known to have considerable intraspecific variability in morphological characters, therefore a suite of characters is needed to differentiate closely related species ( McLaughlin 2004). Although only one specimen of P. petalodactylus n. sp. is available in this study, a combination of characters distinguish this new species from other species of the genus that have unequal chelipeds and unarmed telson, such as P. alcocki McLaughlin & Rahayu, 2005 , P. arostratus Rahayu, 2005 , P. balanophilus Alcock, 1905 , P. brachyrostris Rahayu, 2006 , P. calvus Alcock, 1905 , Paguristes sp. (new species to be described by McLaughlin in press), P. frontalis H. Milne Edwards, 1936 , P. kimberleyensis Morgan & Forest, 1991 , P. lewinsohni McLaughlin & Rahayu, 2005 , P. purpureantennatus Morgan, 1987 , and P. seminudus Stimpson, 1858 . This combination of characters includes broad and flattened dactyls on the second and third pereopods, subrectangular dactyls of the chelipeds, which are covered by small corneous-tipped spines on the mesial faces, and symmetrical lobes of the telson.

The apparently most closely related species is P. lewinsohni . These two species are quite similar in general appearance of the shield and cephalic appendages. The differences are in the shape of the dactyls of the chelipeds, which are subtriangular, and the small spines on the mesial faces that are arranged in two irregular rows partially concealed by tufts of moderately short setae with one or two low protuberances ventrally in P. lewinsohni . Furthermore, the ventral margins of the dactyls of the second and third pereopods of P.petalodactylus n. sp. have 20-25 corneous spines, while in P. lewinsohni only 14-20 corneous spines are present. The armature of mesial faces of propodi of the second and third pereopods is also different. In P. lewinsohni a scute-like ridge is developed ventrally, whereas in P. petalodactylus n. sp. there are only simple spinules or protuberances. There is a difference also in the shape of the telson, which is appreciably asymmetrical in P. lewinsohni . Additionally, P. petalodactylus n. sp. has simple ocular acicles, whereas in P. lewinsohni the ocular acicles have two or three spines on distal margin.

This new species also is superficially similar to Paguristes sp. (new species to be described by McLaughlin in press) in having a subrectangular right cheliped. However, both chelipeds of P. petalodactylus n. sp. are subrectangular while in Paguristes sp. only the right cheliped is rectangular, furthermore the mesial face of dactyl of the cheliped is covered with small tubercles in the new species, while in Paguristes sp. it is armed with one row of spines. The setation is denser in Paguristes sp. obscuring some armament of the cheliped and pereopods while in the new species the setation is sparse.

Figures

FIG. 2. — Paguristes petalodactylus n. sp., holotype, ♂, 5.7 mm: A, shield and cephalic appendages; B, left cheliped, dorsal view; C, dactyl of left cheliped, mesial face; D, right cheliped, dorsal view; E, dactyl of right cheliped, mesial face. Setae omitted. Scale bars: 1 mm.

FIG. 3. — Paguristes petalodactylus n. sp., holotype,♂, 5.7 mm:A, left third pereopod, lateral view;B, same,mesial view;C, left second pereopod,lateral view;D, same,mesial view;E, left fourth pereopod,lateral view; F, male first pleopod,external view;G, same,internal view; H, male second pleopod, external view; I, telson, dorsal view. Setae omitted. Scale bars: 1 mm.