Munidopsis exuta, Macpherson & Segonzac, 2005

Macpherson, Enrique & Segonzac, Michel, 2005, Species of the genus Munidopsis (Crustacea, Decapoda, Galatheidae) from the deep Atlantic Ocean, including cold-seep and hydrothermal vent areas, Zootaxa 1095 (1), pp. 1-60 : 22-25

Munidopsis exuta n. sp. ( Fig. 5 )

Munidopsis subsquamosa .—de Saint­Laurent, 1985: 475 (not M. subsquamosa Henderson, 1885 ) Munidopsis crassa .— Segonzac, 1992: 596 (not M. crassa Smith, 1885 ).

Material examined. Bay of Biscay, BIOGAS 5, Stn CV40 , 47º33’N, 09º02’W, 2860 m, 15.06.1974: 1 ovig. female 29.2 mm, 1 female 18.2 mm . Bay of Biscay , BIOGAS 6, Stn CP 10, 47º30’N, 09º04’W, 2878 m, 21.10.1974: 1 male 17.1 mm. Mid­Atlantic­Ridge, MAR vent site Snake Pit­Les Ruches, HYDROSNAKE, Stn HS 08, baited trap PT01, 23º22’N, 45º57’W, 3502 m, 26.06.1988: 1 ovig. female 34.7 mm. Mid­Atlantic­Ridge. MAR vent site Snake Pit­Elan. MAR93 , Dive 2617, 23°23' N, 44°56' W, 3500 m, 18.06.1993: 1 female 32.0 mm. Mid­Atlantic­Ridge. MAR vent site TAG. AMK47, Stn 4343, slurp gun 4, 26º08’N, 44º49’W, 3650 m, 26.06.2002: 1 ovig. female 39.5 mm, 1 female 31.6 mm .

Types. The ovigerous female of 34.7 mm from HYDROSNAKE, Stn HS08 (MNHN­ Ga 4621) has been selected as holotype, the other specimens are paratypes.

Etymology. From the Latin exutus, bared, naked, in reference to the absence of spines (except epigastric spines) on the carapace and abdomen.

Description. Carapace, exclusive of rostrum, longer than broad, moderately convex from side to side. Cervical groove distinct. Gastric region distinct, posterior part delimited by shallow groove; surface with pair of epigastric spines (2 or 3 additional small spines in one specimen), covered by scale­like rugosities much larger on posterior triangle than on remainder. Anterior branchial region also with scale­like rugosities, as illustrated. Rostrum broad at base, distally narrowed and upturned, weakly carinated dorsally, with fine rugosities, sometimes with 1–4 small lateral spines on each side; antennal spine absent. Oblique frontal margin leading to short anterolateral spine (first spine) directed straight forward, followed by 2 spines on anterior part of anterior branchial region, anterior (second spine) of these strong, directed anterolaterally, situated lateral to level of anterolateral spine, posterior (third spine) much smaller, followed by a few knobs and another small spine (fourth) bordering anterior and posterior branchial regions.

Thoracic sternites with a few arcuate setiferous ridges; third thoracic sternite posteriorly narrowed, anterior margin with acute submedian granules and small anterolateral spine on each side; fourth thoracic sternite subtriangular, anteriorly narrow elongate.

Abdomen smooth, with few granules on pleura; segments 2–4 each with 2 elevated transverse ridges; segment 6 bearing posterolateral lobes somewhat exceeding nearly straight transverse median margin. Telson composed of 8 plates; length­width ratio 0.78; midlateral plate convex on distolateral margin.

Eyes not movable; smoothly ovate cornea cupped within broad­based ocular peduncle; peduncle extended into strong but relatively short mesiodorsal spine directed upward at low angle; cornea relatively large, clearly wider than eyespine, and as wide as third article of antennal peduncle.

Basal article of antennule having dorsolateral spine much smaller than ventrolateral. Article 1 of antennal peduncle distomesially bearing flattish process rather straight laterally, somewhat convex mesially, distolateral spine well­developed; article 2 with strong distolateral spine.

Third maxillipeds with weak spination; ischium with distodorsal and distoventral spines, both small, latter in particular; mesial crest with 21–23 denticles. Flexor margin of merus with 5 small spines, extensor distal marginal spine small.

Chelipeds longer than carapace including rostrum. Merus nearly reaching end of rostrum, with 4 terminal spines (2 dorsal, 1 mesial, 1 lateral), a few small spines on dorsal sides, covered with scale­like elevated rugosities. Carpus with a few distal and mesial spines. Palm spineless, slightly longer than broad, with small granules along mesial margin. Fingers slightly longer than palm, distally spooned, prehensile edges crenulated; fixed finger moderately ridged along distal third of lateral margin.

First walking leg slightly exceeding cheliped by half length of dactylus; dorsal crest of merus with row of small spines, lateral side with granules; carpus with row of spines along dorsal border, two granulate crests along lateral side and continued on to propodus, ventrolateral crest less conspicuous than dorsolateral; propodus nearly twice as long as dactylus, sometimes with spines on proximal half of dorsal margin; dactylus smoothly narrowed distally, ending in curved sharp spine, flexor margin slightly curving, bearing 13 or14 proximally diminishing low spines, ultimate spine rather remote from end of dactylus and much closer to penultimate. Meri of walking legs progressively shorter posteriorly.

Epipods on chelipeds, but absent on walking legs.

Eggs diameter: 2.6 mm.

Remarks. The new species belongs to the group of species having (usually) 2 epigastric spines, epipods on the chelipeds, the cornea distinctly broader than the eyespine, the fixed finger of the cheliped without a denticulate carina on the distolateral margin, the first walking leg overreaching end of the cheliped, the dactyli of the walking legs slightly curving on flexor margin, and the abdominal segment 6 with the posteromedian margin weakly convex, not produced. Munidopsis geyeri Pequegnat & Pequegnat, 1970 from the Caribbean Sea and South and Central Atlantic (see below) is the most similar species geographically and taxonomically, but it is readily differentiated by the following characters (see also Baba 2005):

– The rostrum is triangular with a marked dorsal carina in M. geyeri , whereas the

rostrum is clearly spiniform, without marked dorsal carina in the new species.

– The antennal spine is always present in M. geyeri , but absent in the new species.

– The eyespine is usually longer in M. geyeri than in the new species.

– The posterolateral lobes of the abdominal segment 6 do not reach the posterior median

margin in M. geyeri , whereas in M. exuta it distinctly overreaches that margin.

– The propodus of the walking legs is nearly as long as the dactylus in M. exuta , whereas

in M. geyeri the propodus is 1.3–1.4 times the length of dactylus.

M. exuta is also close to M. crassa (see above), but they can be differentiated by the shape of the distal margin of abdominal segment 6: weakly convex in the new species and strongly produced in M. crassa . Furthermore, M. exuta is characterized by the presence of two epigastric spines, the absence of antennal spine, the rostrum not triangular, and the dactyli of the walking legs slightly curving on the flexor margin, whereas M. crassa has some gastric spines, the antennal spine present, the rostrum moderately broadly triangular, and the dactyli of the walking legs clearly curving on the flexor margin.

Distribution and habitat. The species is only known from the northeast Atlantic at 2860–3502 m. This species occurs in both abyssal and hydrothermal vent environments. The BIOGAS specimens were collected in the Bay of Biscay, among actiniarians, polychaetes, brachiopods, molluscans and echinoderms. Two specimens were collected in the vent area of Snake Pit (HYDROSNAKE and MAR93 cruises). The HYDROSNAKE specimen was caught by a baited trap 100 m north of the site Les Ruches, together with the nephropid lobster Thymopides laurentae Segonzac & Macpherson , and the macrurid fish Coryphaenoides armatus (Hector) ( Segonzac & Macpherson 2003) . The MAR 93 specimen was collected from the site Elan, about 100 m west of Les Ruches, at the base of the active edifice, on sulfide rocks, among scattered sea anemones, chaetopterid tubeworms and alvinocaridid shrimps. The two specimens from the AMK47 cruise were collected at the base of an inactive chimney complex, among dead mytilid bivalves. An additional specimen (unfortunately lost) was collected during the cruise BRIDGE 1993, at the hydrothermal vent site Broken Spur site (dive Alvin 2625, 27.06.1993, 29°10’N, 43°10’W, 3056 m; E. Southward, Marine Biological Association of the U.K., Plymouth, personnal communication).

Figures

FIGURE 5. Munidopsis exuta n. sp., holotype, ovigerous female (34.7 mm), Mid­Atlantic Ridge, HYDROSNAKE, Stn HS08, MNHN­Ga 4621. A, carapace, dorsal. B, same, lateral. C, posterior part of sixth abdominal segment and telson. D, anterior part of sternal plastron. E, left antennule, antenna and ocular peduncle, ventral. F, endopod of right third maxilliped, lateral. G, right cheliped, lateral. H, right second pereiopod, lateral. I, dactylus of right second pereiopod, lateral. Scale: A–B, D–E, G. I = 5 mm, C, F, H = 2 mm.