Enneophyllus ecarina, Komai, Tomoyuki, 2017

Komai, Tomoyuki, 2017, Enneophyllus ecarina, a new species of scaphopod shell dwelling hermit crab (Crustacea: Decapoda: Anomura: Paguridae) from deep-sea off the Ryukyu Islands, southern Japan, Zootaxa 4269 (4), pp. 593-600 : 594-599

Enneophyllus ecarina n. sp.

[New Japanese name: Hoso-tsutsu-yadokari] ( Figs 1–3 )

Material examined. Holotype: male (sl 1.64 mm), TRV “ Toyoshio-maru ”, 2005-4 cruise, stn 4, E of Amamiohshima Island, Ryukyu Islands, 28°08.44’N 129°31.01’E to 28°08.63’N 129°31.33’E, 348–353 m, mud, 24 May 2005, beam trawl, coll. T. Komai, CBM-ZC 13592.

Paratype: 1 female (sl 1.60 mm), TRV “Toyoshio-maru”, 2010-3 cruise, stn 5, SE of Amami-ohshima Island, 27°58.66’N 129°24.60’E to 27°59.08’N 129°24.98’E, 404–408 m, mud, 24 May 2010, beam trawl, coll. T. Komai, CBM-ZC 13593.

Description. Shield ( Fig. 1 A) approximately 1.5 times as long as wide; anterior margins between rostrum and lateral projections concave; anterolateral margins sloping; posterior margin truncate; dorsal surface almost glabrous, but with longitudinal row of sparse short setae laterally on each side. Rostrum strongly produced as roundly triangular lobe, deflected downward over inter-ocular lobe, and provided with small epirostral spine ( Fig. 1 B). Lateral projections broadly triangular, overreached by rostral lobe, with tiny marginal spine. Posterior carapace ( Fig. 1 A) entirely non-calcified, glabrous; lateral lobes very narrow; trace of short cardiac sulci discernible.

Ocular peduncles (including corneas) ( Fig. 1 A) 0.7 times as long as shield, stout, slightly compressed, slightly widened distally; dorsal surface with longitudinal row of few short setae; corneas slightly dilated, corneal width approximately 0.4 of peduncular length. Ocular acicles small, subtriangular, slightly bent, terminating in small submarginal spine; separated basally by basal width of 1 acicle.

Antennular peduncles ( Fig. 1 A), when fully extended, overreaching ocular peduncles by 0.8 length of ultimate article. Ultimate article with 1 long plumose seta and 1 shorter simple seta dorsodistally. Penultimate article short, with few short setae. Basal article with statocyst region strongly expanded laterally into dome-like lobe, with small spine on dorsolateral margin.

Antennal peduncles ( Fig. 1 A, C), slightly overreaching distal corneal margins. Articles 5 and 4 with few short setae. Article 3 unarmed on ventromesial distal angle. Article 2 with dorsolateral distal angle produced, not reaching midlength of article 3, terminating in acute simple spine and with 1 tiny subterminal spine on mesial margin; dorsomesial distal angle with prominent spine. Article 1 with tiny spine on lateral surface on distolateral margin; ventrolateral distal margin with 1 tiny spine. Antennal acicle reaching to distal end of peduncular article 4, nearly straight, terminating in acute spine and with few short setae obscuring terminal spine. Antennal flagellum not reaching tip of right chela, with 1 or 2 short (1 or 2 articles length) setae on each article.

Maxilliped 3 ( Fig. 1 D) endopod moderately stout. Basis with 1 minute denticle. Ischium with crista dentata consisting of row of 4 or 5 acute corneous-tipped teeth (proximal 2 teeth larger than other distal teeth); no accessory tooth. Merus and carpus unarmed. Exopod long, slightly overreaching distal end of carpus.

Chelipeds unequal, right appreciably larger. Male right cheliped ( Fig. 2 A–D) moderately elongate, chela not operculate, elongate subovate in general outline (2.1 times as long as wide); propodal-carpal articulation with slight degree of clockwise rotation. Dactylus 0.7 times as long as palm; dorsal surface nearly flat, dorsomesial margin delimited by distinct, faintly crenulate carina; mesial and ventral surfaces with scattered tufts of short setae; cutting edge with 2 blunt calcareous teeth in proximal two-thirds, minutely denticulate in distal one-third, terminating in small calcareous claw slightly overlapped by fixed finger. Palm subequal in length to carpus, 1.3 times as long as wide; dorsal surface gently convex, almost smooth, with few short setae proximally; dorsomesial margin not delimited, with minute spine near distal angle; dorsolateral margin also not delimited; mesial face with numerous long stiff setae often forming tufts; lateral face with tufts of long setae only ventrally; ventral surface slightly convex, with scattered setae. Carpus slightly shorter than merus; dorsomesial distal angle with small spine; dorsomesial margin with few low protuberances and tufts of long setae, all surfaces with sparse tufts of or individual setae (setae on ventral surface particularly long); ventromesial distal angle unarmed. Merus subtriangular; dorsodistal margin with minute spine; dorsal surface with row of very low protuberances and tufts of stiff setae; lateral surface almost glabrous, boundary between lateral and ventral faces rounded; mesial face with row of tufts of long setae adjacent to ventromesial margin, ventromesial margin armed with 1 small spine at distal angle; ventral surface oblique, visible in lateral view, with scattered long setae. Ischium unarmed on ventromesial margin. Coxa unarmed, with prominent tuft of setae on ventromesial margin.

Female right cheliped generally similar to that of male, but less elongate and less setose. Chela ( Fig. 2 E) 1.4 times as long as wide. Palm with small spines arranged in double row on distal half of dorsomesial margin, otherwise unarmed.

Left cheliped ( Fig. 3 A–D) reaching level of base of dactylus of right cheliped; propodal-carpal articulation without torsion. Chela somewhat dorsoventrally flattened, 3 times as long as wide. Dactylus unarmed but with scattered setae, longer and more numerous ventrally; cutting edge with row of small corneous teeth, terminating in small corneous claw. Palm 0.65 length of carpus; several tufts of long setae on rounded dorsomesial margin, dorsal surface smooth, with scattered tufts of short to long setae, dorsolateral margin also rounded, including fixed finger; mesial face with several tufts of long setae; ventral surface slightly convex, also with tufts of long setae. Cutting edge of fixed finger jagged row of very small calcareous teeth, terminating in very small corneous claw. Carpus subequal in length to merus, slightly widened distally; dorsomesial distal angle with small but conspicuous spine; dorsal surface mesially with several tufts of long setae, and laterally with tufts of shorter setae, without conspicuous armature; lateral face with row of tufts setae on along midline, distolateral angle produced but unarmed; mesial face with several tufts of long setae in distal half; ventral surface gently convex, with some tufts of long setae. Merus subtriangular; dorsal margin with row of tufts of moderately long setae, distal margin with 1 small spine; lateral face almost glabrous, boundary between lateral and ventral surfaces bluntly delimited, oblique ventral surface visible in lateral view; mesial face with tufts of setae adjacent to ventromesial margin, small spine at ventromesial distal angle. Ischium unarmed on ventromesial margin or surfaces. Coxa similar to that of right.

Pereopods 2 and 3 ( Fig. 3 E, F) not overreaching outstretched right cheliped, strongly compressed laterally; generally similar from left to right. Dactyli ( Fig. 3 G, H) 1.3 (second) or 1.6 (third) times as long as propodi, in dorsal view generally straight, in lateral view slightly curved ventrally; terminating in long corneous claws; dorsal margins each with row of widely-spaced long, bristle-like setae; lateral faces each with few moderately long setae adjacent to ventral margin; mesial faces with sparse short setae along midline and margins; ventral margins each with 2 or 3 widely-spaced slender spiniform setae. Propodi each with 1 small spiniform seta on ventrodistal margin mesially; dorsal and ventral margins each with widely spaced tufts or individual setae; lateral and mesial faces glabrous. Carpi each with small dorsodistal spine, dorsal margin otherwise unarmed, with few long setae. Meri with sparse tufts of setae on dorsal margins (setae more numerous in second than in third); lateral and mesial faces glabrous; ventral margins unarmed, with sparse long setae. Ischia unarmed. Coxae of third each with large gonopore in female ( Fig. 1 M).

Pereopods 4 ( Fig. 1 F) weakly semichelate, without conspicuous ventrodistal projection on propodus. Dactylus short, terminating in blunt, curved corneous claw; no preungual process. Propodal rasp consisting of single row of 5 or 6 scales. Carpus unarmed. Merus with tufts of long setae at dorsodistal margin.

Pereopods 5 chelate. Left coxa of male ( Fig. 1 H) with long, basally stout sexual tube directed exteriorly and curved dorsally across pleon from left to right; terminus of sexual tube ( Fig. 1 I) blunt, with few very short setae. Right coxa ( Fig. 1 H) without sexual tube, only with small gonopore partially obscured by row of short setae.

Thoracic sternite 6 ( Fig. 1 G) with very small, subtrapezoidal anterior lobe, bearing some setae on slightly concave anterior margin; posterior lobe enlarged, separated by deep median groove. Thoracic sternite 8 ( Fig. 1 H) very narrow, with tuft of setae on distal margin.

Pleon ( Fig. 1 J) greatly elongate, exceeding 2.5 times of carapace length, straight; membranous, trace of tergites discernible when stained with methylene blue; tergites 3 and 4 widely divided transversely, each small, oval in shape; tergite 5 subquadrate, not divided; tergite 6 ( Fig. 1 K) well calcified, longer than wide, divided into two parts by distinct transverse groove; posterior margin slightly tri-lobed. Male with unpaired left pleopods 3–5, all unequally biramous. Female with unpaired left pleopods 2–5, pleopod 2 subequally biramous, pleopods 3–5 unequally biramous; no pleopods 1. Uropods symmetrical ( Fig. 1 K).

Telson ( Fig. 1 L) with posterior lobes symmetrical, each outer angle produced and terminating in strong spine, terminal margins strongly oblique, each armed with minute spine proximally; lateral indentations faint.

Coloration in preservative. No distinct markings seen on appendages. Calcified integument of carapace, ocular peduncles and chelipeds slightly iridescent.

Distribution. Known only from off Amami-ohshima Island, Ryukyu Islands; at depths of 340– 408 m.

Habitat. The two specimens of E. ecarina n. sp. were found to inhabit scaphopod shells, like the holotype of E. spinirostris (cf. McLaughlin 1997).

Remarks. Notable variation is seen in the armature of the right palm between male and female. In the male holotype, the palm is unarmed on the dorsal surface (except for one minute spine near the dorsomesial distal angle), whereas there are small spines arranged in irregular double row along the dorsomesial margin in the female paratype. The reduction of the armature of the right palm in males is known in several members of Paguridae (e.g., McLaughlin 1997; Komai 1999, 2010; Komai & Osawa 2006; Komai & Takeda 2005; McLaughlin & Rahayu 2008), and thus the difference seen in this new species could also be attributed to sexual dimorphism.

Although the new species is confidently assigned to Enneophyllus , it is immediately distinguished from the type species of the genus, E. spinirostris , in the different structure of the right chela. In E. ecarina n. sp., the right chela is not operculiform with rounded dorsolateral and dorsomesial margins of the palm; dorsal surface of the palm is evenly convex; and the dorsomesial margin of the dactylus is delimited with a weak carina. In contrast, in E. spinirostris , the right palm is operculiform with the distal half of the dorsomesial margin of the right palm is strongly elevated into a prominent, acute crest; the dorsolateral margin is not delimited in the proximal third, but produced as an obliquely elevated crest distally and extending to the fixed finger; the palmer dorsal surface is weakly concave on the fixed finger; and the dorsomesial margin of the dactylus is drawn out into subacute obliquely elevated ridge ( McLaughlin 1997). Other potential characters include the armature of the ambulatory dactyli and of the ambulatory meri. The ambulatory dactyli bear fewer ventral spiniform setae in E. ecarina n. sp. (two or three versus five or six). The meri of the pereopods 2 are unarmed on the ventral margin in the new species, while being armed with a small spine in E. spinirostris .

Within Paguridae , the use of scaphopod shells for housing is also seen in some species of Pylopagurus A. Milne-Edwards & Bouvier, 1891 , some species of Lophopagurus McLaughlin, 1981 , Orthopagurus minimus ( Holmes, 1900) , Pagurus imafukui McLaughlin & Konishi, 1994 , and two species of Dentalopagurus McLaughlin, 2007 ( Schmitt 1921; McLaughlin & Konishi 1994; de Saint Laurent & McLaughlin 2000; McLaughlin & Lemaitre 2001; McLaughlin 2007; Osawa & Chan 2008; Lemaitre & Tavares 2015). Overall morphological disparity among these taxa clearly suggests that the habitat preference and similar straight, elongate pleon with symmetrical telson and uropods are results of convergence ( Zhadan 1999).

Etymology. The specific epithet “ ecarina ”, meaning “non-carinate”, refers to the non-operculiform right chela with rounded, non-carinate dorsolateral and dorsomesial margins in the new species.

Figures

FIGURE 1. Enneophyllus ecarina n. sp. A – L, holotype, male (sl 1.64 mm), CBM-ZC 13592; M, paratype, female (sl 1.60 mm), CBM-ZC 13593. A, carapace, cephalic appendages and left sexual tube, dorsal view; B, rostrum and left ocular acicle, dorsolateral view; C, left antennal peduncle, ventral view; D, left maxilliped 3, lateral view; E, same, ischium and basis, ventral view; F, left pereopod 4, lateral view; G, sternal lobe of thoracic sternite 6 (pereopods 3); H, sternal lobes of thoracic sternites 7 and 8 and coxae of pereopods 5; I, tip of left sexual tube; J, carapace and pleon, dorsal view; K, tergum of pleomere 6 and uropods, dorsal view; L, telson, outer view; M, coxae of pereopods 3 and sternal lobe of thoracic sternite 6.

FIGURE 2. Enneophyllus ecarina n. sp. A – D, holotype, male (sl 1.64 mm), CBM-ZC 13592; E, paratype, female (sl 1.60 mm), CBM-ZC 13593. A, right cheliped, mesial view; B, same, lateral view; C, right chela, dorsal view; D, carpus of right cheliped, dorsal view; E. right chela, dorsal view.

FIGURE 3. Enneophyllus ecarina n. sp., holotype, male (sl 1.64 mm), CBM-ZC 13592. A, left chela, dorsal view; B, carpus of left cheliped, dorsal view; C, left cheliped, mesial view; D, same, lateral view; E, right pereopod 2, lateral view; F. left pereopod 3, lateral view; G, H, dactyli of right pereopod 2 and left pereopod 3, respectively.