Nematopagurus marianicus, Komai & Miller & Malay, 2022

Komai, Tomoyuki, Miller, Allison K. & Malay, Maria Celia D., 2022, Three new species of pagurid hermit crabs (Decapoda: Anomura: Paguroidea) from the Northern Mariana Islands, Micronesia, Zootaxa 5099 (5), pp. 563-585 : 570-576

Nematopagurus marianicus n. sp.

( Figs. 5–8 , 12B )

Material examined. Holotype. SIO-BIC C14523, male (sl 2.8 mm), Agrihan, no depth record, 17 June 2015, crab traps, field No. S 25722.4.

Paratypes. SIO-BIC C14238, 1 male (sl 2.9 mm), same data as holotype, field No. S 25722.2; SIO-BIC C14512, 1 male (sl 1.9 mm), station AKM-PAG-04, Pagan , 18.0865°N, 145.7652°E, 58–89 m, 20 June 2015, crab traps, field No. S 25713.1; SIO-BIC C14513, 2 males (sl 2.3, 2.3 mm; including DNA voucher), 2 ovigerous females (sl 2.1, 2.6 mm), same data as holotype; SIO-BIC C14517, 1 ovigerous female (sl 2.3 mm), Guguan, station AKM-GUG-05, 17.2912°N, 145.8371°E, 40–44 m, 23 June 2015, Buoy Guam (a kind of ring net), field No. S 25750.4; SIO-BIC C14518, 1 male (sl 2.8 mm), Guguan, station AKM-GUG-03, 17.6093°N, 145.8101°E, 48–84 m, 22 June 2015, crab traps, field No. S 25745.2; SIO-BIC C14519, 1 ovigerous female (sl 2.1 mm), same data as SIO-BIC C14518, field No. S 25745.3; SIO-BIC C14520, 3 males (sl 2.2, 2.5, 2.8 mm), 1 female (sl 1.9 mm), same data as SIO-BIC C14518, field No. S 25745.4; SIO-BIC C14522, 1 immature male (sl 1.7 mm), Pagan, 18.01°N, 145.04°E, 20 June 2015, ring nets for trapping crabs, field No. S25717 ; SIO-BIC C14524, 1 male (sl 2.3 mm), Pagan, depth not recorded, 17 June 2015, crab traps, field No. S 25722.3 .

Description. Gills biserial, 11 pairs.

Shield ( Fig. 5A ) approximately as long as wide, dorsal surface with longitudinal row of setae posterior to anterolateral projection on either side; anterior margin between rostral lobe and lateral projections weakly interrupted. Rostrum as broadly triangular or rounded rostral lobe, not quite reaching to level of lateral projections, unarmed, but with tuft of short setae on either side of midline. Lateral projections obtusely triangular, with or without submarginal spine. Lateral carapace lobe moderately broad.

Ocular peduncles ( Fig. 5A ) relatively stout, 0.8 length of shield, subcylindrical; dorsal surface tufts of short setae at corneal indentation; mesial surface with small, low setose protuberance proximal to corneal base; cornea substantially dilated, corneal width about half of peduncular length. Ocular acicles narrowly triangular, terminally bunt and with submarginal spine, separated widely. Interocular lobe fully exposed.

Antennular peduncles ( Fig. 5A ) slightly overreaching distal corneal margin by tip of ultimate article. Ultimate article without tuft of setae at distolateral margin, dorsal surface almost glabrous. Penultimate article unarmed. Basal article without spine laterally on statocyst lobe, ventrodistal angle not particularly produced.

Antennal peduncles ( Fig. 5A ) falling slightly short of distal corneal margin. Articles 3–5 unarmed but each with few tufts or individual stiff setae. Article 2 with dorsolateral distal angle produced beyond proximal margin of article 4, terminating in small spine and sometimes with additional subterminal spine, mesial and/or lateral margins with few tufts of setae; dorsomesial distal angle with small spine. Article 1 with ventrolateral margin prominently produced, unarmed. Antennal acicles reaching to or beyond midlength of peduncular article 5, terminating in small spine; dorsomesial margin with several tufts of stiff setae proximally and row of stiff setae in distal half. Antennal flagella long, far overreaching outstretched chelipeds; each article with one or two minute bristle-like setae, at least in distal half.

Maxilliped 3 ( Fig. 5B, C ) endopod moderately slender. Carpus and merus unarmed. Ischium with well-developed crista dentata consisting of row of closely set, corneous-tipped teeth and with 1 well-developed accessory tooth located subdistally. Exopod reaching midlength of carpus.

Right cheliped ( Fig. 6A–D ) larger and slightly longer than left. Chela subovate in general outline, 2.2 times as long as wide. Dactylus 0.8 length of palm, bearing row of small spines on dorsomesial margin, not extending to tip; mesial face with several tufts of short to long simple setae and few spinules proximally. Palm subequal in length to carpus, with dorsomesial and dorsolateral marginal row of small spines, latter extending onto proximal half of fixed finger; dorsal surface with very weak median row of small spines, distinct as row only proximally, and with additional numerous small spines or spinules and short, distally curved setae, spines extending onto proximal half of fixed finger; mesial and lateral faces each with sparse tufts of simple setae, longer and more numerous on mesial and ventral faces; occlusal margin of fixed finger with row of 5 obtuse calcareous teeth and minute, fused corneous teeth in distal 0.2, terminating in small corneous claw. Carpus slightly widened distally, 1.8 times as long as distal width, with row of moderately large spines on dorsomesial margin and row of smaller spines on dorsal surface laterally, dorsodistal margin with 1 small spine; mesial and lateral faces each with numerous tufts of long simple setae, partially obscuring faces; ventrolateral distal margin armed with 1 small spine, ventromesial distal margin unarmed; gently convex ventral surface with scattered long setae. Merus dorsal surface with subdistal transverse ridge but otherwise smooth, almost glabrous; dorsodistal margin with 1 small spine mesially, obscured by row of moderately long setae; lateral surface with few, short transverse rows of minute setae, ventrolateral margin with 2 widely spaced spines in distal 0.3; mesial surface almost glabrous except for few tufts of short setae, ventromesial margin with 3 or 4 spines accompanied by few long setae; ventral surface with short, setose transverse ridges. Ischium unarmed.

Left cheliped ( Fig. 7A–D ) moderately slender, reaching level of base of dactylus of right cheliped. Chela elongate subovate in general outline, 2.6 times as long as wide. Dactylus with row of small spines on dorsomesial margin in proximal half. Dorsomesial and dorsolateral margins of palm each with row of spines, dorsal surface slightly elevated in midline and with row of moderately small spines, additional small spines and short setae scattered on dorsal surface, and median longitudinal row of spinules extending onto fixed finger; mesial and lateral faces each with few sparse tufts of short to long simple setae. Carpus with row of small spines on dorsomesial and dorsolateral margins, dorsodistal margin with 1 small median spine; lateral and mesial faces with sparse tufts or short vertical rows of long simple setae, partially obscuring faces (particularly on dorsal half of lateral face); ventral surface with few low protuberances and sparse tufts of long setae. Merus with transverse row of numerous setae on dorsodistal margin; dorsal surface glabrous; lateral face almost glabrous except for few tufts of setae adjacent to ventral margin, ventrolateral margin with 4 or 5 spines (distalmost one strongest); mesial face also almost glabrous with few tufts of short setae, ventromesial margin with 3 or 4 small spines accompanied with tufts of setae; ventral surface with short, setose transverse ridges. Ischium unarmed.

Pereopods 2 and 3 ( Fig. 8A–D ) generally similar in armature and ornamentation, third slightly longer. Dactyli slender (length 13 times of width in second, 14 times of width in third), 1.3 times as long as propodus in second, 1.8 in third; dorsal and ventral margins each with row of sparse setae, which are easily broken off; lateral faces with few short setae; mesial faces each with dorsal (arranged in single or double row, 14–20 in number) and ventral rows (arranged in single row, 6–10 in number) of moderately spaced small, slender corneous spines ( Fig. 8B, D ). Propodi 1.4–1.8 lengths of carpi; rounded dorsal surfaces each with row of sparse short, stiff setae; lateral and mesial faces smooth, glabrous; ventral surfaces glabrous, with 1 or 2 small corneous spines at ventrodistal margin ( Fig. 8B, D ). Carpi slightly more than 0.5 length of meri; dorsal surfaces each with dorsodistal and dorsoproximal spines and row of stiff setae; lateral, mesial and ventral faces almost glabrous. Meri each with dorsal row of tufts of setae (fewer in third), ventrolateral distal angle with small spine (second) or unarmed; ventral margins each with few small spines (second) or unarmed (third). Ischia each with few tufts of setae on dorsal and/or ventral surfaces.

Pereopods 4 semichelate ( Fig. 5D ); dactylus gently curved, terminating in long corneous claw, ventral margin with row of minute corneous spinules; propodal rasps each consisting of single row of corneous scales.

Pereopods 5 weakly semichelate. Male with elongate, soft sexual tube extruded from gonopore of right coxa ( Fig. 5E ); left with gonopore, but not protruded ( Fig. 5E ).

Sternite 6 anterior lobe ( Fig. 5F ) subcircular, anterior margin with row of short to moderately long setae. Sternite 8 ( Fig. 1E ) with pair of circular protuberances.

Pleon dextrally twisted. Male with unpaired left pleopods 3–5, pleopods 3 and 4 greatly unequally biramous, pleopod 5 uniramous. Female with paired and modified first pleopods typical of genus; unpaired left pleopods 2–5 unequally biramous.

Telson ( Fig. 5G, I ) divided into anterior and posterior portions by distinct lateral indentations; posterior lobes slightly asymmetrical, separated by moderately deep median cleft; terminal margins each with 2–6 principal spines and sometimes with additional spinules laterally.

Colouration in life. Fig. 12B . Shield generally pink; posterior carapace darker reddish. Ocular peduncles red, with dark ring basally; cornea brown-gray. Antennular and antennal peduncles red, antennal flagellum uniformly reddish translucent. Right chela mottled with red and pink, distal parts of fingers whitish; carpus with red and pink longitudinal stripes; merus also with alternate red and pink longitudinal stripes. Left cheliped similarly coloured to right cheliped. Ambulatory dactyli pink to violet, subdistally with red ring, distally white; propodi, carpi and meri with alternate red and pink longitudinal stripes (4 red stripes visible on respective article). Pereopods 4 and 5 also reddish. Pleon reddish, semi-translucent.

Variation. The setation on chelipeds in the small, immature male specimen (sl 1.7 mm; SIO-BIC C14522) is sparse compared with adult specimens, suggesting that the setation becomes denser with growth. Spination on the terminal margins of the telson is also variable, as figured ( Fig. 5G, I ).

Housing. Gastropod shells.

Etymology. Derived from the locality where the type specimens of the new species were collected.

Distribution. Presently known only from the Northern Mariana Islands, at depths of 40– 89 m.

Remarks. McLaughlin (2004b) reviewed species of Nematopagurus , recognizing 26 species, including five new species. Since then two new species have been described in the genus ( McLaughlin & Okuno 2010; Lima et al. 2019). Of the 28 presently recognized species, 26 occur in the Indo-West Pacific: N. longicornis A. Milne-Edwards & Bouvier, 1892 is restricted to the eastern Atlantic, and N. micheleae Lima, Tavares & de Mendonça, 2019 is known only from Trindade Island, off Espirito Santo, Brazil, southwestern Atlantic.

Nematopagurus marianicus n.sp. resembles N.gardineri Alcock, 1905 (junior synonyms: N.holthuisi McLaughlin & Hogarth, 1998 ; N. pilosus Komai, 1999 ) and N. lewinsohni Türkay, 1986 . Shared characters are: dactylus of right cheliped armed with several spines on dorsal surface; dorsal surfaces of palms of chelae armed with generally even covering of pointed spines over entire surface, but devoid of drop-like sensory structures. Nematopagurus marianicus n. sp. is distinguished from N. gardineri by the following particulars: the cornea is distinctly dilated, of which the width is about half of the ocular peduncle length in N. marianicus n. sp. ( Fig. 5A ), whereas it is not particularly dilated, of which the width is 0.3–0.4 in N. gardineri (cf. McLaughlin 2004b: fig. 23a); the carpus of the left cheliped bears a dense covering of long iridescent setae on the upper part of the lateral face in N. marianicus n. sp. ( Fig. 7B, D ), while there is no such setal field on the left cheliped carpus in N. gardineri (cf. McLaughlin 2004b: fig. 23b, c; see also Komai 1999: figs. 16E, 18E, as N. pilosus ); and the dactyli of the pereopods 2 and 3 are more elongate and slender in N. marianicus than in N. gardineri ( Fig. 8A–D versus McLaughlin 2004b: fig. 23d, e).

Nematopagurus marianicus n. sp. is easily differentiated from N. lewinsohni by the lack of a row of bristlelike setae on the dorsal surface of each ambulatory dactylus ( Fig. 8A–D ), which is present in the latter species ( McLaughlin 2004b: fig. 22c). The carpus of the left cheliped lacks a dense setal field on the lateral face in N. lewinsohni (cf. McLaughlin 2004b: 210, fig. 22b), which is present in N. marianicus n. sp., as mentioned above.

Figures

FIGURE 1. Catapagurus tenuilamina n. sp., holotype, SIO-BIC C14512, male (sl 2.7 mm).A, shield and cephalic appendages, dorsal view; B, distal two peduncular articles and flagella of left antennule, lateral view; C, left maxilliped 3, lateral view; D, same, basis and ischium, ventral view; E, coxae of chelipeds, ventral view; F, dactylus, propodus and carpus of left pereopod 4, lateral view; G, coxae of pereopods 5 and thoracic sternite 8, ventral view; H, distal part of right sexual tube, crossing dorsal surface of anterior part of pleon; I, thoracic sternite 6, ventral view; J, telson, dorsal view.

FIGURE 5. Nematopagurus marianicus n. sp.: A–G, holotype, SIO-BIC C14523, male (sl 2.8 mm); H, I, paratype, SIO-BIC C14513, female (sl 2.1 mm). A, shield and cephalic appendages, dorsal view; B, left maxilliped 3, lateral view; C, same, basis and ischium, ventral view; D, left pereopod 4, lateral view; E, coxae of pereopods 5 and thoracic sternite 8, ventral view; F, thoracic sternite 6, ventral view; G, I, telson, dorsal view; H, paired pleopods 1, ventral view.

FIGURE 6. Nematopagurus marianicus n. sp., holotype, SIO-BIC C14523, male (sl 2.8 mm). A, right cheliped, mesial view; B, same, lateral view; C, same, chela, dorsal view (setae omitted); D, same, carpus, dorsal view (setae omitted).

FIGURE 7. Nematopagurus marianicus n. sp., holotype, SIO-BIC C14523, male (sl 2.8 mm).A, left cheliped, mesial view; B, same, lateral view; C, same, chela, dorsal view (setae omitted); D, same, carpus, dorsal view.

FIGURE 8. Nematopagurus marianicus n. sp., holotype, SIO-BIC C14523, male (sl 2.8 mm).A, right pereopod 2, lateral view; B, same, carpus, mesial view; C, same, dactylus and distal part of propodus, mesial view; D, left pereopod 3, lateral view; E, same, dactylus and distal part of propodus, mesial view.

FIGURE 12. A, Catapagurus tenuilamina n. sp., holotype, SIO-BIC C14512, male (sl 2.7 mm)., habitus in lateral view, showing living colouration; B, Nematopagurus marianicus n. sp., paratypes, 3 males (sl 2.2, 2.5, 2.8 mm), 1 female (sl 1.9 mm), SIO-BIC C14520, showing living colouration.