Decaphyllus spinulodigitus, Komai & Rahayu, 2013

Komai, Tomoyuki & Rahayu, Dwi Listyo, 2013, Six New Species Of The Hermit Crab Genus Decaphyllus De Saint Laurent, 1968 (Crustacea: Decapoda: Anomura: Paguridae) From The Boholo Sea, The Philippines, And The Ryukyu Islands, Japan, Raffles Bulletin of Zoology 61 (2), pp. 589-620 : 610-614

Decaphyllus spinulodigitus , new species

( Figs. 17–19 )

Material examined. — Holotype: ovigerous female (sl 2.3 mm), PANGLAO 2004, stn T1 , Bolod , Panglao Island, 9°32.4'N, 123°47.3'E, 83–102 m, mud and many sponges, 30 May 2004, trawl, NMCR 39090.

Description. — Ten pairs of biserial phyllobranchiae (no pleurobranchs). Two very small arthrobranch gills above base of third maxilliped, anterior gill simple, posterior gill bilobed ( Fig. 17C ).

Shield ( Fig. 17A ) approximately as long as wide; anterior margin between rostral region and lateral projection slightly concave; anterolateral margins sloping; posterior margin roundly truncate; dorsal surface with anteromedian part poorly calcified, with several minute to short setae laterally. Rostrum broadly rounded. Lateral projections weakly developed, exceeding as far as rostral lobe, each with terminal spinule.

Ocular peduncle ( Fig. 17A ) about 0.7 times as long as shield, faintly constricted at midlength; dorsal surface with mesial row of long setae directed mesially and few setae laterally, and prominent tuft of moderately long setae at base of cornea; cornea not dilated, its width slightly less than 0.3 of length of ocular peduncle; basal part slightly inflated, its width greater than corneal width. Ocular acicle drawn out distally into acute spine, mesial margin with tuft of moderately short setae medially; separated basally slightly less than width of 1 acicle. Interocular lobe visible in dorsal view, anteriorly slightly concave.

Antennular peduncle ( Fig. 17A ) overreaching distal corneal margin by about 0.8 length of ultimate segment. Basal segment with prominent spine on lateral margin of statocyst lobe, mesial face unarmed. Penultimate and ultimate segments

unarmed, almost glabrous except for 1 thin minute seta at dorsomesial distal angle.

Antennal peduncle ( Fig. 17A ) slightly overreaching base of cornea of ocular peduncle. Fifth and fourth segments with few setae. Third segment with prominent spine on ventromesial distal margin. Second segment with dorsolateral distal angle strongly produced, terminating in bifid spine (lateral spine subterminal), dorsomesial distal angle with strong spine. First segment with small spine on ventrodistal margin; lateral surface unarmed. Antennal acicle slightly falling short of distal margin of fifth peduncular segment, reaching corneal base, terminating in small spine; mesial surface with row of sparse setae; lateral margin unarmed.Antennal flagellum with 2–4 short to moderately setae on distal margin of each article.

Third maxilliped with merus bearing strong dorsodistal spine; crista dentata on ischium consisting of 3 widely spaced, triangular teeth ( Fig. 17B ); basis with minute denticle distally on mesial surface. Exopod long, reaching nearly to distal margin of carpus.

Chelipeds ( Fig. 18 ) slightly unequal in length, right slightly longer, appreciably stronger. Right cheliped ( Fig. 18A–D ) with chela elongate subovate in dorsal view, about 2.2 times longer than wide. Dactylus set at slightly oblique angle to palm ( Fig. 18C ), shorter than palm; dorsal surface mesially with several small spines or tubercles in proximal half; all surfaces with scattered moderately short to long setae, particularly numerous on mesial surface; cutting edge with row of moderately large, blunt calcareous teeth, terminating in tiny corneous claw. Palm subequal in length to carpus ( Fig.18A, C ); dorsomesial margin with row of 8 small spines, dorsal midline with row small spines decreasing in size and acuteness distally and not extending onto fixed finger, dorsolateral margin not delimited and with few minute tubercles, dorsal surface lateral to midline with scattered microscopic spinules; lateral and mesial surfaces with scattered short to long setae; ventral surface gently convex, smooth, with sparse setae. Fixed finger with row of blunt calcareous teeth on cutting edge, terminating in tiny corneous claw. Carpus ( Fig. 18A–C ) moderately widened distally, subequal in length to merus, 1.8 times longer than wide; dorsomesial margin with row of 4 moderately strong spines, dorsolateral surface with row of 4 moderately small spines and 1 proximal spinule; all surfaces with scattered short to long setae, subdistal transverse row of setae particularly prominent; ventrolateral distal angle with small spine, ventromesial distal angle unarmed. Merus ( Fig. 18A, B, D ) with 1 small spine on dorsodistal margin mesially; dorsal surface with sparse setae; lateral surface unarmed, ventrolateral margin with 1 small subdistal spine; mesial surface with small tubercle proximoventrally, ventromesial margin with 1 small subdistal spine; ventral surface unarmed. Ischium ( Fig. 18D ) with 2 widely spaced spinules on ventromesial margin; lateral surface with minute spine ventrodistally.

Left cheliped ( Fig. 18E–H ) with distinct hiatus between dactylus and fixed finger. Dactylus ( Fig 18G ) about 1.2 times longer than palm, gently curved; all surfaces unarmed, but with numerous short to long setae particularly on mesial surface; cutting edge microscopically denticulate, terminating in small corneous claw. Palm ( Fig. 18E–G ) about 0.6 length of carpus; dorsomesial margin without conspicuous spines, though few minute tubercles adjacent to dorsomesial margin; dorsal midline with row of spinules not extending onto fixed finger, dorsolateral margin not delimited and only with some minute tubercles; all surfaces with scattered short to long setae. Fixed finger with row of minute calcareous denticles on cutting edge, terminating in small corneous claw. Carpus ( Fig. 18E–G ) moderately widened distally, about 3.0 times longer than wide; dorsolateral margin with 2 moderately small spines in distal half, dorsomesial margin with 5 small to moderately strong spines; ventrolateral distal angle with spinule, distomesial angle unarmed; all surfaces with scattered setae. Merus ( Fig. 18E, F, H ) with sparse setae on dorsal surface; dorsodistal margin with small spine; lateral surface unarmed, ventrolateral margin with 2 widely spaced, small spines; mesial surface with spine-like tubercle proximoventrally, ventromesial margin with 2 widely spaced, small spines; ventral surface with tiny spine medially and scattered long setae. Ischium ( Fig. 18H ) with 2 widely spaced spinules on ventromesial margin, both directed forward; lateral surface with spinule distoventrally.

Ambulatory legs ( Fig. 19 ) overreaching tip of right cheliped. Dactyli ( Fig. 19A, B, D ) about 1.6 times longer than propodi, 11.7–14.6 times longer than broad, gently curved ventrally; all surfaces unarmed, but with numerous setae, particularly longer and stronger on dorsal margins. Propodi ( Fig. 19A, D ) unarmed, but with row of sparse setae on dorsal and ventral margins. Carpi each with dorsodistal spine (second; Fig. 19A ) or without dorsodistal spine (third; Fig. 19D ), and with 1 additional small spine located at proximal 0.4 (second; Fig. 19C ) or no additional spine (third; Fig. 19E ). Meri each with 2 small dorsal spines (distal-sided spine located slightly distal to midlength and another at proximal 0.2); dorsal and ventral margins with sparse long setae, latter armed with spinule at distal 0.4 (second, Fig. 19C ) or unarmed (third, Fig. 19E ). Ischium with distal spinule on ventral margin mesially (second, Fig. 19C ) or unarmed (third, Fig. 19E )

Fourth pereopods ( Fig. 17D ) non-chelate, with claw of dactylus entirely masked by tufts of short, dense setae; propodus roundly subquadrate, slightly wider than long, with numerous setae on dorsal margin and distal half of ventral margin; 3 minute corneous scales located distally on ventral margin. Fifth pereopods semichelate.

Female with unpaired left gonopore.

Anterior lobe of thoracic sternite 6 (third pereopods, Fig. 17E ) subsemicircular, slightly skewed to left, bearing numerous long setae anteriorly. Sternite of thoracic sternite 8 (fifth pereopods) in female transversely subovate, with setae along anterior margin.

Telson ( Fig. 17F ) with shallow median cleft; terminal margin with prominently produced, spinose left exterior angle separated from non-produced, minutely pointed right exterior angle, and with 1 spinule on either side of median cleft; lateral margins apparently not chitinous.

Male unknown.

Colouration. — In preservative. No distinct markings seen on body and appendages. Chelipeds and ambulatory legs with iridescence, particularly strong on chelipeds.

Distribution. — Known only from Panglao Island, the Philippines, 83– 102 m.

Remarks. — Although only a single ovigerous female is available, this new species is safely assigned to Decaphyllus by the unarmed but setose dactyli of the ambulatory legs, the non-chelate fourth pereopod, the entire eighth thoracic sternite and the characteristic shape of the telson. The setation of the ocular peduncle also supports the generic assignment.

The presence of several small spines or tubercles on the dorsal surface of the dactylus of the right cheliped and the relatively long antennular peduncle of Decaphyllus spinulodigitus , new species, suggests a close relationship with D. similis ; however, there are some morphological differences of diagnostic significance between the two taxa (de Saint Laurent, 1968b). The strongly produced dorsolateral distal angle of the second segment of the antennal peduncle terminates in a clearly bifid spine in D. spinulodigitus , rather than terminating into a simply acuminate spine in D. similis . The basal segment of the antennular peduncle is unarmed on the mesial face in D. spinulodigitus , but it is armed with a small spine on the mesial face in D. similis . The antennal acicle does not reach the distal margin of the fifth segment of the antennal peduncle in D. spinulodigitus , rather than slightly overreaching it in D. similis . The armature of the right cheliped is weaker in D. spinulodigitus than in D. similis . For example, the dorsomedian row on the palm consists of small spines or tubercles decreasing in the size and acuteness distally in D. spinulodigitus , whereas it is composed of numerous conspicuous spines not weakened distally in D. similis . The merus of the second pereopod bears a small spine on the ventral margin, located slightly distal to the midlength in D. spinulodigitus , but such a spine is absent in D. similis .

Etymology. — From the combination of the Latin spinuloso (spinulose) and digitus (finger), in reference to the dactyli of the right cheliped bearing several spinules on the dorsal surface. Used as a noun in apposition.

Figures

Fig. 17. Decaphyllus spinulodigitus, new species, holotype, ovigerous female (sl 2.3 mm), PANGLAO 2004, stn T1, NMCR 39090. A, shield and cephalic appendages, dorsal view; B, ischium of left third maxilliped, ventral view; C, arthrobranchs on left third maxilliped; D, distal three segments of left fourth pereopod; E, sixth thoracic sternite, ventral view; F, telson, dorsal view. Scale bars = 1 mm (A), 0.5 mm (B, D–F), 0.25 mm (C).

Fig. 18. Decaphyllus spinulodigitus, new species, holotype, ovigerous female (sl 2.3 mm), PANGLAO 2004, stn T1, NMCR 39090. A, right cheliped, mesial view; B, same, lateral view; C, same, chela and carpus, dorsal view; D, same, merus, dorsal view; E, left cheliped, mesial view; F, same, lateral view; G, same, chela and carpus, dorsal view; H, same, merus, dorsal view. Setae omitted except for E. Scale bar = 1.0 mm.

Fig. 19. Decaphyllus spinulodigitus, new species, holotype, ovigerous female (sl 2.3 mm), PANGLAO 2004, stn T1, NMCR 39090.A, right second pereopod, lateral view; B, same, dactylus, mesial view (only mesial setae shown); C, same, carpus to ischium, mesial view (setae omitted); D, left third pereopod, lateral view; E, same, carpus and merus, mesial view (setae omitted). Scale bars = 1.0 mm.