Pagurus tenuilineatus, Rahayu, 2022

Rahayu, Dwi Listyo, 2022, Hermit crabs of Singapore (Crustacea: Decapoda: Anomura: Diogenidae, Paguridae), with description of two new species, Raffles Bulletin of Zoology 70, pp. 329-363 : 353-357

Pagurus tenuilineatus , new species

( Figs. 12 , 13 , 14D )

Material examined. Holotype, male 4.2 mm ( ZRC 2021.0254 ), st. IT81, Sister Island , 01°12.789′N 103°50.187′E, rocky reef, intertidal, 26 May 2013 . Paratypes, 1 male, 4.2 mm ( ZRC 2021.0255 ), st. IT65, Terumbu Semakau , 01°12.649′N 103°46.199′E, sandy, rocky submerged reef, 24 May 2013 ; 3 males, 2.8 mm, 3.2 mm, 4.2 mm, 2 ovigerous females, 3.5 mm, 4.2 mm ( ZRC 2021.0256 ), st. IT93, Pulau Jong , 1°12.901′N 103°47.194′E, intertidal, 28 May 2013 ; 2 ovigerous females, 2.2 mm, 2.5 mm, 1 female, 2.2 mm, 4 males, 1.8–2.7 mm ( MZB Cru 5226), st. SD177, Kusu Island , 01°13.314′N 103°51.640′E, dive, 16.4 m, 4 June 2013 ; 10 males, 2.4–3.3 mm ( ZRC 2021.0257 ), st. SD150, Kusu Island , 01°13.274′N 103°51.659′E, dive, 10.7 m, 1 June 2013 .

Other material. 3 males, 2 females, 16 specimens in shell ( MZB Cru 5227), st. TB91, 01°12.561′N 103°51.322′E, 46.1–72 m, 27 May 2013 ; 1 female (sl 1.6 mm), no locality, SS2689; 1 male, 1.3 mm ( ZRC 2021.0258 ), st. DR128, 01°12.889′N 103°52.460′E, 75.3−85.7 m, rocky bottom, 30 May 2013 ; 3 males, 1.3–1.8 mm ( ZRC 2021.0259 ), st. DR161 ; 2 males, 1.8 mm, 2.2 mm, 2 females, 2.5 mm, 2.9 mm ( ZRC 2021.0260 ), st. SD145, Pulau Hantu , 01°13.514′N 103°44.784′E, dive, 11.7 m, 1 June 2013 ; 2 males, 2.4 mm, 3.3 mm ( ZRC 2021.0261 ), st. SD150, Kusu Island , 01°13.274′N 103°51.659′E, dive, 10.7 m, 1 June 2013 ; 1 male, 2.0 mm ( MZB Cru 5228), st. DW58, east of Pulau Tekong , 01°25.064′N 104°04.992′E, 10.9–11.3 m, 22 October 2012 . Description. Shield ( Fig. 12A ) approximately as long as broad; anterior margins between rostrum and lateral projections gently concave; anterolateral margins sloping; posterior margin truncate; dorsal surface slightly convex transversely, with longitudinal row of tufts of moderately long setae on either side of midline; paragastric grooves faint. Rostrum obtusely triangular, exceeding as far as lateral projections. Lateral projections broadly triangular, with small marginal spine. Posterior carapace (not figured), measured along midline, distinctly shorter than shield; carapace lateral lobe moderately narrow, not calcified; cardiac sulci parallel, barely reaching to midlength of posterior carapace.

Ocular peduncle (including cornea) ( Fig. 12A ) relatively long, about 0.9 times as long as shield; slightly inflated basally; cornea slightly dilated, diameter about 0.2 times peduncular length; dorsal surface with longitudinal row of tufts of moderately short setae. Ocular acicles narrowly subtriangular, separated basally by width of less than one acicle, with minute marginal spine distally. Interocular lobe partially overhung by rostrum, medially concave.

Antennular peduncle ( Fig. 12A ), when fully extended, slightly overreaching distal corneal margin. Ultimate segment about 1.5 times as long as penultimate segment, slightly widened distally in lateral view. Basal segment with distolateral margin produced in sharply pointed lobe; statocyst lobe weakly inflated, with small spine medially; ventromesial distal angle not produced.

Antennal peduncle ( Fig. 12A ) overreaching distal corneal margins by 0.3 length of fifth segment. Fifth segment with few setae laterally. Fourth and third segments unarmed, with several tufts of long stiff setae mesially. Second segment with dorsolateral distal angle not reaching midlength of fourth segment, with 3 to 5 spinules distomesially; dorsomesial distal angle with small spine; mesial and lateral faces with short to long stiff setae. First segment with subterminal spinule on lateral face. Antennal acicle not reaching base of cornea, gently arcuate, terminating in small spine obscured by long stiff setae; dorsomesial margin with several tufts of long stiff setae. Antennal flagellum about 4 times as long as shield; each article with 1 or 2 minute setae on distal margin.

Mouthparts not dissected. Third maxilliped moderately slender; dactyl slightly shorter than propodus; carpus, merus unarmed; ischium with crista dentata consisting of narrowly spaced, moderately large, subacute corneous teeth, and with 1 moderately strong accessory tooth; basis-ischium fusion incomplete; basis with 2 or 3 denticles on mesial margin; exopod reaching distal margin of merus.

Chelipeds unequal. Right cheliped larger but not necessarily longer than left ( Fig. 13A, B, D, E ); chela about 2 times as long as greatest width at base of dactyl, generally suboval in outline in dorsal view. Dactyl subequal in length to palm and slightly overlapped by fixed finger; dorsal surface with sparse, short setae and prominent median row of broad-based, closely set spines; dorsomesial margin with double row of closely set, moderately large spines, decreasing in size distally; space between dorsal midline and dorsomesial margin smooth; ventral surface with scattered tufts of moderately short stiff setae; cutting edge with row of broad calcareous teeth and adjacent row of tufts of stiff setae, terminating in large calcareous claw. Palm slightly shorter than carpus; dorsomesial margin delimited by single row of moderately large, stout spines ( Fig. 13A, D ); dorsal surface convex, with numerous, small, scattered tubercles and tuft of short setae; dorsolateral margin delimited by small spines extending onto fixed finger, decreasing in size distally; fixed finger dorsal surface slightly depressed and with scattered tubercles, cutting edge with row of moderately large calcareous teeth, terminating in large calcareous claw; mesial face with scattered, very low, minute to small protuberances and sparse very short setae; lateral surface with scattered tufts of short stiff setae; ventral surface gently convex, with scattered tufts of short and long setae. Carpus slightly shorter than merus; dorsodistal margin with row of small spines, dorsomesial margin delimited by row of large spines accompanied by tufts of long stiff setae, dorsal surface with tufts of short to long stiff setae; dorsolateral margin delimited by row of small tubercles obscured by long setae; lateral face nearly glabrous except for some tufts of setae; mesial face ( Fig. 13B, E ) with few sparse long setae, ventromesial margin produced into flattened, wing-like crest in both sexes ( Fig. 13A, D ), edge of crest unarmed or with small tubercles in female ( Fig. 13D ); ventral surface with few tufts of setae. Merus with 1 prominent spine on dorsodistal margin; dorsal surface glabrous; lateral surface nearly glabrous except for few tufts of short setae, ventromesial margin produced in flattened, wing-like crest in males, edge of crest with tiny tubercles distally, strong spine proximally ( Fig. 13B ), in females no wing-like crest developed, but with row of spines and one prominent spine proximally ( Fig. 13E ); ventral surface with some low, blister-like protuberances and tufts of moderately long setae. Ischium with tufts of short setae on all surfaces.

Left cheliped ( Fig. 13C, F ) slenderer than right, moderately compressed laterally. Chela elongate subovate in dorsal view, 3.2 times longer than greatest width at base of dactyl. Dactyl about 2.7 times as long as palm, nearly straight with ventrally curved tip; dorsomesial margin with double row of strong spines on proximal 0.7, distal 0.3 smooth; dorsomesial margin and surfaces with tufts of long setae; cutting edge with row of minute, subacute calcareous denticles in proximal 0.4 and row of minute, closely set corneous teeth in distal 0.6, terminating in small corneous claw. Palm about half length of carpus; dorsomesial margin with row of spines, dorsal surface with double row of spines adjacent to dorsomesial margin, extending onto articulation with dactyl, remaining surface with scattered small tubercles; dorsolateral margin with row of spines extending onto tip of fixed finger; fixed finger dorsal surface with longitudinal row of moderately large spines extending along cutting edge, remaining dorsal surface with scattered tubercles; cutting edge bearing row of minute calcareous denticles terminating in moderately large corneous claw; moderately broad hiatus between dactyl and fixed finger. All surfaces with tufts of long setae. Carpus subequal in length to merus; dorsodistal margin with several strong spines; dorsomesial margin with row of moderately large spines; dorsal surface with few tubercles and sparse setae; dorsolateral margin with row of small spines and tufts of short setae; mesial and lateral surface with tufts of short and long setae; ventrolateral margin with row of small spines. Merus with prominent spine on dorsodistal margin; dorsal surface with sparse short stiff setae; lateral and mesial surfaces nearly glabrous except for row of tufts of stiff setae adjacent to dorsal margin and few similar tufts near ventral margin; ventrolateral margin with row of slender, sharp spines and long stiff setae; ventromesial margin with row spines, 2 larger spines proximally. Female left cheliped same as male.

P2 and P3 ( Fig. 12B, C ) stout, right P2 slightly overreaching tip of extended right cheliped. Dactyls 0.9‒1.0 times as long as propodi, 4.3–4.6 times longer than broad, in dorsal view nearly straight, in lateral view slightly curving ventrally; dorsal and ventral margins each with row of tufts of short to moderately long setae, ventral margins each with row of 5‒6 moderately large corneous spines increasing in size distally. Propodi slightly narrowing distally; dorsal surfaces unarmed but with row of long stiff setae; lateral and mesial surfaces with few tufts of long stiff setae; ventral surfaces with few tufts of long stiff setae. Carpi each with small dorsodistal spine; with row of tufts of long stiff setae on dorsal margin; lateral surface convex, with row of tufts of long stiff setae along midline. Meri each with row of tufts of long stiff setae on dorsal surface; lateral surface almost smooth, with few tufts of long stiff setae distally; ventral surface unarmed but with row of tufts of short to long stiff setae, ventrodistal lateral margin unarmed. Ischia unarmed but with tufts of setae on dorsal and ventral margins.

P4 semichelate, left ( Fig. 12D ) slightly larger than right ( Fig. 12E ). Dactyls slightly curved ventrally, terminating in small corneous claw; each with row of minute, closely spaced corneous teeth on ventral margin; no preungual process. Propodal rasp consisting of 1 row of corneous scales. All segments with dorsal and/or ventral tufts of long stiff setae.

Anterior lobe of sternite of third pereopod ( Fig. 12F ) subrectangular, ventral surface with tufts of setae medially. Male with 3 unequally uniramous pleopods. Female second to fifth pleopods greatly unequally biramous with much elongate exopods; length third> second> fourth> fifth.

Telson ( Fig. 12G ) with distinct lateral indentations; posterior lobes strongly produced, rounded, unequal, median cleft shallow; each terminal margin with row of numerous slender spines interspersed by spinules, not extending onto lateral margin.

Colour in life. Shield mottled with light brown and white, with dark brown patches on anterolateral and dorsodistal surface. Ocular peduncle whitish proximally; narrow brown ring at base of cornea and broad brown patch proximally; cornea dark brown. Antennular peduncle generally blue, distal part of penultimate segment and flagella orange. Antennal peduncle generally white; second and fourth segments each with three dark brown longitudinal stripes on dorsal surface, fifth segment with dark brown stripe on lateral and mesial margin; flagellum with brown stripe along lateral and mesial margin of each article, white on articulation of each segment. Right cheliped mottled with light brown and white in general, with large dark brown patches and stripes; mesial surfaces of carpus and merus with irregular patterns of dark brown on white background. Left cheliped with thin brown lines on white background on chela, carpus, and merus. Ambulatory legs with thin dark brown stripes on propodi, carpi, meri, and ischia; dactyls each with one dark brown median stripe and two broad light brown bands (one subdistal and one proximal); propodi, carpi, and meri each with three dark brown stripes on lateral surface, with broad light brown band medially. Dark brown stripes on chelipeds and ambulatory legs usually reaching ends of segments ( Fig. 14E ).

Distribution. At present known only from Singapore; 0–85 m, on reef, sandy and rocky bottom.

Etymology. The name is derived from Latin tenuis, meaning slender, and linea, meaning stripes, alluding to the narrow stripes on the chelipeds and pereopods, used as a noun in apposition.

Remarks. The characters of this new species correspond with the Pagurus anachoretus group as defined by Forest & Ngoc-Ho (1992) and McLaughlin & Forest (1999). Among the species in this group, P. tenuilineatus , new species, belongs to the group which have wing-like projection on mesial face of the carpus and merus of the right cheliped, i.e., P. boriaustraliensis , P. gordonae ( Forest, 1956b) , P. hedleyi , P. kulkarnii , P. liochele ( Barnard, 1947) , P. pitagsaleei , and P. sticticus McLaughlin, 2007b . The presence of a row of moderately large spines on the dorsal surface of the fixed finger of the left cheliped, extending along cutting edge but not reaching the distal part of the finger, separates this new species from its congeners. Furthermore, differences between congeners are also observed on the proportion of the dactyl and palm of the left cheliped. In P. tenuilineatus , new species, the dactyl of the left cheliped (2.7 times as long as palm) is much longer than that of P. boriaustraliensis and P. pitagsaleei (1.5 times as long as palm), P. gordonae (almost as long as palm), P. liochele (1.3–2 times as long as palm), P. kulkarnii (2.5 times as long as palm), and P. sticticus (1.8 times as long as palm), whereas in P. hedleyi the left cheliped has a much longer dactyl (3.3 times as long as palm).

Although living colouration of the species in the anachoretus group is quite specific, with colour pattern usually consisting of patches and longitudinal stripes of pigment that cover part or all of the segment of the chelipeds and ambulatory legs ( McLaughlin & Forest, 1999), the position and colour pigmentation of the stripes and patches are different from one species to another. The colouration for P. hedleyi , P. kulkarnii , P. pitagsaleei , and P. tenuilineatus has been described above and differences can be seen in Fig. 14 . Forest (1956b) described the colour of P. gordonae as follows: shield, ocular and atennal peduncles are greenish grey with brown longitudinal patches, antennnular peduncle with large brown band on penultimate segment, ultimate segment brown on distal half; antennal flagella alternately brown and white; chelipeds greenish brown, carpi and meri with irregular longitudinal stripes; ambulatory legs with irregular brown stripes on half proximal of each segment, half distal orange without any stripes. McLaughlin & Forest (1999: 322) cited the colour of P. liochele after Barnard (1950) as follows: ocular peduncle sienna at base, distal half cobalt, with narrow dark sienna ring immediately adjacent to black cornea, meral segment of left and right chelipeds with cobalt band border with sienna, and distal margin dark sienna; granules on dorsal surface of palm white on pale sienna ground, sienna longitudinal stripes on dactyl and fixed finger; proximal halves of meral segment of second and third pereopods sienna, distal halves pale, longitudinal sienna stripes on carpi and dactyls and dorsally on proximal halves of propodi, distal halves of propodi yellowish, passing into cobalt apically. Pagurus boriaustraliensis shield is cream or pale brown with dark brown mottling, ocular peduncle cream with black or reddish black short longitudinal stripes distally and proximally, chelipeds cream brownish with dark brown line, ambulatory legs with longitudinal brown stripes, and with brown band around midline ( Morgan, 1990). The colouration in life of P. sticticus is not known, but in preservative the ambulatory legs have orange spots and patches on each segment ( McLaughlin, 2007b).

Figures

Fig. 12. Pagurus tenuilineatus, new species. Holotype, male, 4.4 mm (ZRC 2021.0254). A, shield and cephalic appendages; B, left P2; C, left P3; D, left P4; E, right P4; F, anterior lobe of sternite of third pereopods; G, telson. B–E, lateral view. Scale = 1 mm.

Fig. 13. A–C, Pagurus tenuilineatus, new species. Holotype, male, 4.4 mm (ZRC 2021.0254); D–F, paratype, ovigerous female, 4.2 mm (ZRC 2021.0256). A, D, chela and carpus of right cheliped, dorsolateral view; B, E, chela, carpus and merus of right cheliped, mesial view; C, chela and carpus of left cheliped, dorsolateral view; F, chela, carpus and merus of left cheliped, mesial view. Scale = 1 mm.

Fig. 14. A, Pagurus hedleyi (Grant & McCulloch, 1906), male, not measured and sexed, st. SD25, St John’s Island, 01°12.882′N 103°50.952′E, 22 May 2013; B, Pagurus kulkarnii Sankoli, 1962, ovigerous female, 4.2 mm (ZRC 2021.0253); C, D, Pagurus pitagsaleei McLaughlin, 2002a, C, male, not collected, st. SD25, St John’s Island, 01°12.882′N 103°50.952′E, 22 May 2013; D, male, 4.9 mm (ZRC 2021.0239); E, Pagurus tenuilineatus, new species, paratype, male, 4.2 mm (ZRC 2021.0255); F, Spiropagurus spiriger (De Haan, 1849), ovigerous female, not collected, Johor Strait.