Vulcanocalliax arutyunovi Dworschak & Cunha, 2007, n.sp.

Vulcanocalliax arutyunovi n.sp.

(Figures 1–5, Table 1)

Material: Holotype NHMW 21927, ovigerous female (tl 55, cl 14.2, dissected), Atlantic Ocean, Gulf of Cádiz, Captain Arutyunov mud volcano, 35°39.805'N 07°19.997'W, 1339 m, TTR12 station AT399GR, 13 July 2002, RV Prof. Logachev, TV-guided grab. Allotype NHMW 21928, juvenile male (tl 18.5, cl 5.4), same locality as holotype, 35°39.740'N 07°19.942'W, 1327 m, TTR12 station AT393GR, 9 July 2002, RV Prof. Logachev, TV-guided grab.

Description of female holotype: Dorsally, carapace as long as abdominal somites 1 and 2 combined (Fig. 1 a, b). Frontal margin of carapace with narrow triangular acute rostrum, flanked by excavated shoulders forming anteriorly produced rounded prominences lateral to margins of eyestalks; rostrum extending to 0.3 times the visible length of eyestalks in dorsal view (Fig. 1 c, d). Lateral projections of carapace setose dorsally. Carapace lacking distinct dorsal oval and dorsal carina. A single median pit dorsally halfway between rostrum and distinct cervical groove, one pair of smaller pits anterior to cervical groove. Indistinct cardiac prominence bearing median pit in posterior fourth of carapace. Transverse sutures indistict to absent. Linea thalassinica strong, parallel to midline of carapace. Lateral surface of carapace finely tuberculate, ventral margin with short setae. Subantennular region of epistome bearing a few long setae.

Eyestalks (Fig. 1 e, f) dorsally flattened and depressed, slightly convex ventrally, keeled laterally, length 2.3 times width, in dorsal view reaching beyond basal antennal article; mesial surfaces flattened so eyestalks abutt closely at midline over entire length; lateral margin parallel to midline in proximal three quarters, tapering distally, no cornea or pigment detectable.

Antennular peduncle shorter than antennal peduncle (Figs. 1 d, 2a); basal article laterally inflated, with long setae dorsally near distal end; second article 0.76 times length of basal article with few dorsal setae near distal end, third article about 2 times length of second, with ventrolateral row of long, ventrally directed setae continued onto ventral ramus of flagellum; rami of flagellum about equal length, near 5 times length of third article of peduncle; dorsal ramus with few short setae, subterminal articles of dorsal ramus thicker than those of ventral ramus, bearing dense line of ventral aesthetascs (Fig. 2 a).

Antennal peduncle 1.2 times length of antennular peduncle (Fig. 2 b); basal article with ventrolaterally produced excretory pore; second article with deep, diagonal ventrolateral furrow, distally with field of long setae below ventrolateral suture; rounded, articulated dorsal scale at joint proximal to third article; third article elongate, same length as fourth or combined length of first two, fourth article narrower than third; flagellum sparsely setose, extending posteriorly to middle of pleonite 1.

Mandible (Fig. 2 c, d) with large, terminally setose, 3-segmented palp, third article of palp terminally rounded; incisor process thin, with minute teeth on cutting margin, mesial surface with lip giving rise to molar process proximal to incisor process.

First maxilla (Fig. 2 e) with endopodal palp long, narrow, terminal article deflected proximally at articulation; proximal endite setose on straight margin, terminally with field of thick simple setae; distal endite elongate, terminally truncate and armed with stiff simple setae.

Second maxilla (Fig. 2 f) with endopod narrowed at distal end, terminus directed mesially, first and second endites each longitudinally subdivided, exopod forming large, broad scaphognathite.

First maxilliped (Fig. 2 g) with endopod reduced; proximal endite triangular; distal endite elongate, lateral surface and all margins heavily setose, mesial surface concave; exopod triangular, no transverse suture; distal part broad, with long marginal setation at its mesial end, proximal part with field of mesially directed setae near mesial end; epipod large, broad, anterior end tapered, angular.

Second maxilliped (Fig. 2 h) with long endopod; merus straight, mesial surface concave, slightly thicker in proximal half than in distal, inferior margin with dense fringe of long, close-set setae; carpus short; propodus weakly arcuate, length 1.3 times width, less than 1/3 length of merus; dactylus short, about 1/2 length of propodus, tip with dense setae; exopod as long as endopodal merus and carpus combined, fringed marginally by long setae; epipod small, leaf-shaped, arthrobranch (not shown) greatly reduced.

Third maxilliped (Fig. 2 i, j) without exopod; endopod with long dense setation on mesial margin; endopodal ischium subrectangular, 1.5 times as long as broad, proximomesial lip rounded, mesial surface with medial longitudinally oriented elevation bearing well-defined curved row of 15 sharp teeth; merus subquadrate, as broad as long, mesial surface with setose elevation proximally; carpus strongly flexed in proximal third with setose lobe on inferior margin; propodus large, subrectangular, 1.2 times as long as broad; dactylus subtriangular, broad terminally, as long as broad, fringed with very dense field of close-set, stiff, serrated setae on broad terminal margin.

Branchial formula (Table 1) includes exopods and epipods as described for first, second and third maxillipeds above; branchiae limited to single arthrobranch on second maxilliped, pair of arthrobranchs on third maxilliped, and pair of arthrobranchs on each of the first through fourth pereopods (Fig. 3 e).

Left (presumably minor) cheliped (Fig. 3 c, d) strongly calcified; coxa with strong, posteriorly curved spine posteriomesially, simple epipod laterally; ischium stout, superior margin almost straight, inferior margin with spines increasing in size distally, length about 1.5 times distal breadth; merus stout, length about 2 times breadth at midlength, superior margin curved, inferior margin with two spines proximally, slightly undulated at midlength; carpus broad, broadest distally, inferior margin arcuate and keeled, terminating in rounded projection, superior margin slightly curved; propodus heavy, length (including fixed finger) about 1.6 times height, mesial surface of palm smooth; superior and inferior propodal margins slightly curved, tufts of setae on inner face below superior margin and above inferior margin; fixed finger thick, prehensile margin armed with triangular tooth proximally, proximal superior margin of tooth with denticles, distal margin with few tiny corneous teeth, terminating in rounded tip; weakly unarmed excavation below the tooth on mesial face; dactylus heavy, curved, line of several setose punctae on mesial side of superior margin, lateral face with several setose punctae along inferior border, cutting edge with few tiny corneous teeth, tip strongly curved posteriomesially.

Right (presumably major) cheliped apparently of same general shape as on left side, articles distal of ischium mutilated and distorted (Fig. 3 a, b), obviously in state of incompletely regeneration.

Second pereopod (Fig. 4 a) chelate, most of inferior margins of ischium and merus lined with evenly spaced long setae, similar setae restricted primarily to distal patches on inferior margin in carpus, inferior margin of propodus with similar setal patches, which are long proximally, progressively more reduced in length and stiffened distally, subterminally becoming dense patch of short, stiff bristles; prehensile margins of both fingers corneous, finely microserrate along straight edge over most of length, microserration terminating distally in corneous tips of fingers; superior margin of dactylus straight, with patches of stiff, arched bristles becoming increasingly reduced in length, close-set and more arched distally.

Third pereopod (Fig. 4 b) ischium short, 0.3 times length of merus; merus length about 2.5 times breadth, inferior margin weakly sinuous, with several tufts of setae; carpus broadly flared distally to produce strong inferior lobe, width there about 0.7 times length, inferior lobe terminally with field of long arched setae, diminishing in length toward articulation with propodus; propodus oval, 0.9 times as broad as long, inferior margin terminally with field of long arched setae diminishing in size distally along margin, becoming closeset shorter bristles at distal extreme, superior margin with tufts of arched setae, patterned tufts of thinner setae on lateral face of article; dactylus tear-shaped, length about 2.5 times width, terminating in narrow tip hooked toward lateral side, inferior margin sinuous, lateral face crossed by fields of short setae, longest near superior margin, with separate, dense field of slightly heavier short setae along lower extreme of lateral face and inferior margin.

Fourth pereopod (Fig. 4 c) not subchelate, inferodistal corner of propodus rounded without evidence of fixed finger; dense setation on lateral surface of both propodus and tear-shaped dactylus divided into upper and lower fields, setae thicker in lower fields of propodus, especially on and near inferior margin, proximally field of thick, serrate setae near articulation with dactylus.

Fifth pereopod (Fig. 4 d) minutely chelate, opposable surfaces of propodus and minute dactylus excavate, spooned, terminally rounded, forming beak-like chela obscured by dense fields of setation on distal 1/2 of propodus and superior surface of dactylus.

Abdomen long (Fig. 1 a, b); dorsal length ratio (along midline) of first to sixth abdominal somites: 1.0: 1.14: 0.71: 0.75: 0.71: 0.75. First somite slightly narrowed anteriorly, pleuron triangular with acute triangular projections anterolaterallly and straight ventral margin. Second somite with straight anterior margin, posterior margin expanded posterolaterally, with one setal tuft near the posterior margin, ventral and posterior margin bearing setae. Third to fifth somites each distinctly shorter than second somite, posterior margins expanded posterolaterally; pleura each with row of plumose setae midlaterally and simple setae on posteroventral margin. Sixth somite trapezoid in dorsal view, narrowed posteriorly, ventral margin of pleurite with short setae, posterior margin with tuft of long setae on each side, another on posterolateral margin.

First female pleopod uniramous (Fig. 4 e), composed of two articles, total length 2/3 that of second pleopod, proximal article half as long as distal article, few long setae distally on posterior face, distally on mesial face one field of strong ovigerous setae terminally surrounded by a branched structure connecting via a funiculus to a single embryo; terminal article strongly curved posteriorly, with few long setae on mesial and lateral margins.

Second female pleopod biramous, with appendix interna (Fig. 4 f); dense setation largely restricted to distal lobe of basipod, lateral margin of exopod, and mesial margin of endopod; bearing small appendix interna with cincinnuli; four fields of ovigerous setae on posterior face, one on anterior face.

Third to fifth pleopod pairs (Fig. 4 g) forming large, posteriorly cupped fans when cross-linked by hooked setae of appendices internae on opposed margins of endopods; endopod of each triangular. Appendices internae stubby, movably articulated to mesial margin of endopod. Third pleopod with four fields of ovigerous setae on posterior surface. Total of 30 embryos on pleopods, 2.2–2.7 mm in diameter.

Telson (Figs. 1 h) about 1.2 times as long as broad, broadest proximally, narrowing distally, posterolateral margin rounded, with few short simple setae, dorsal surface with one tuft of long, dorsally directed setae and two low tubercles at 1/4 length.

Uropod with endopod oval, 1.7 times as long as broad (Fig. 1 b, g), overreaching telson, posterolateral and posterior margins with few simple setae, dorsal surface convex with indistinct longitudinal carina; exopod oval, 2 times as long as broad, posterior margin of anterodorsal plate strongly curved and descending to distal margin, anterior part of plate depressed, distal edge of plate lined with short, thick spiniform setae and simple setae, posterodistal margin of exopod with few simple setae.

Description of male allotype: Body and appendages generally similar to that of female holotype (Fig. 5 a) with the following exceptions:

Carapace smooth laterally.

Major and minor chelipeds in male allotype slightly unequal in size, similar in shape between the right and the left (Fig. 5 b–e), both with sharp triangular tooth on cutting edge of fixed finger; merus of major cheliped with one proximal ventral spine, that of minor with 2 spines; major cheliped with ischium and merus as long, merus 1.13 times the height, carpus 1.15 times the height and length, and propodus (including fixed finger) 1.2 times the height and 1.11 times the length of these articles in the minor cheliped, dactylus more curved in major than in minor cheliped.

Male gonopore mesially on coxa of fifth pereopod. First pleopod of male (Fig. 5 f) vestigial, consisting of two articles, not yet fully developed.

Second pleopod of male (Fig. 5 g) biramous, with appendix interna on endopod; setae on mesial and lateral margins of both endopod and exopod, endopod shorter than exopod.

Etymology: The species is named after the late Alexander B. Arutyunov, former captain of RV Prof. Logachev, whose name also graces the type locality, the mud volcano "Captain Arutyunov" in the Gulf of Cádiz.

Colour (from notes and colour photographs of specimens taken immediately after sampling): Pale white.

Ecology: The specimens were found in two grab samples collected from the outer rim of the crater where sediments were mud breccia with a smooth surface. The callianassids were accompanied by over 40 other benthic species, among them abundant siboglinid polychaetes and desmosomatid isopods, several other aselotte isopods, and varied species of small molluscs. Other samples collected in the more disturbed and active central areas of the crater did not yield any callianassid specimens.

Distribution: Known only from the type locality; North Atlantic, Gulf of Cádiz, Captain Arutyunov mud volcano, 1327–1339 m, in mud breccia with smooth surface.

Remarks: Vulcanocalliax arutyunovi n.gen. n.sp. is most closely related to Bathycalliax geomar (see remarks above). Both species have one unique character among the Callianassidae, the presence of epipods on Mxp3 and P1 to P4. Epipods are found in some other thalassinidean families, e.g. the Laomediidae and the Axiidae. In these cases, however, they are much more differentiated, showing anterior and posterior lobes as well as podobranchs in variable numbers. In Vulcanocalliax arutyunovi n.gen. n.sp. as well as in Bathycalliax geomar (SMF 23866, 23867), the epipods are rather simple (see Fig. 3 e). Sakai & Türkay (1999: table 1) mentioned an epipod and a podobranch for Mxp 2 in Bathycalliax geomar. Investigation of the type material, however, showed that this appendage has also a well-developed arthrobranch.

It should be noted that only the male holotype of B. geomar (SMF 23866) has Plp1 as described and figured by Sakai & Türkay (1999: 208, fig. 1). The male paratype (SMF 23867) lacks any signs of Plp1. This specimen shows numerous stalked ellipsoid bodies (0.78 0.36 mm) attached ventrally to the cuticle between the coxae of P5 and on abdominal somites 1 to 6. These are most probably externae of a rhizocephalan cirriped of the family Thompsoniidae Høeg & Rybakov, 1992. Between the externae are numerous scars of externae that dropped off. Such scars occur also in the holotype (SMF 23866).

Another unique character of Vulcanocalliax arutyunovi n.gen. n.sp. is the anterolateral projections of the first abdominal somite (Fig. 1 a, b). Such anterolateral projections are present in other thalassindean familes, e.g. Laomediidae and Axiidae. In those families, however, the lobes ride on posterolateral carapace ridges (see Poore, 1994). A posterolateral lobe of the carapace with ridges is missing in the new species. The anterolateral projections of the first abdominal somite in Vulcanocalliax are therefore not considered to be homologous with those in the Laomediidae and Axiidae.

Remarkable is also the large size and low number of embryos in the new species. With only 30 embryos, 2.2 to 2.7 mm in diameter, these are the fewest in number and the largest ever reported for Callianassidae (see summaries in Pezzuto, 1998 and Corsetti & Strasser, 2003). Large and few embryos generally indicate an abbreviated larval development typical for restricted and specialised habitats (Rabalais & Gore, 1985).

The attachment system of the embryos is also unique. Their big size allows only a single embryo to be attached to a dense patch of thick setae (see Fig. 4 e). In other callianassids, several small eggs are usually attached to a single seta via an investment coat and funiculi (P.C.Dworschak, pers. obs., see also Saigusa et al., 2002)