Ezaxius ferachevali, De Matos-Pita, Susana S. & Ramil, Fran, 2015

De Matos-Pita, Susana S. & Ramil, Fran, 2015, Additions to thalassinidean fauna (Crustacea: Decapoda) off Mauritania (NW Africa) with the description of a new genus and a new species, Zootaxa 4020 (3), pp. 571-587 : 579-584

Ezaxius ferachevali n. sp.

( Figs. 2 A, B, 3A–M)

Type material. Holotype, MNCN 20.04/10091 hermaphrodite, TL/CL: 23.60/ 8.80 mm (right pereiopod 1 and left pereiopod 5 are missing, both pereiopod 4 detached), Expedition Maurit 0 911, Stn MUDR 08, 19°07´20″N, 16°50´31″W, 470 m, 13 November 2009; canyon area off Cape Timiris ( Mauritania); muddy coral rubble and shell debris, rock dredge.

Description. Carapace faintly pitted, laterally compressed, dorsally rounded; cervical groove distinct dorsally, visible laterally only over one-fourth of the distance to anterolateral margin; no discernible linea thalassinica; anterior margin with outer orbital angle rounded, evenly sloping posteriorly to a rounded anterolateral margin ( Figs. 3 A, 4B). Carapace ending midposteriorly as a median lobe separate from produced posterolateral margins; median lobe with a weak short, wide dorsal carina ( Figs. 3 B, 4A).

Rostrum triangular, as long as the antennular peduncle and with an upturned terminal tooth; slightly depressed below the level of gastric area; dorsal surface concave; lateral margins shortly produced posteriorly into gastric region as sharp ridges and armed with four pairs of symmetrically arranged teeth, five cut off and three regenerating, the third pair supraocular, the fourth on the short lateral carinae on anterior gastric region ( Figs. 3 A– B, 4A–B). Bristle setae are located between the rostral teeth.

Gastric region with median, submedian and lateral carinae; median smooth carina, thin in base of rostrum and wide in the middle of the gastric region, barely distinguishable near the cervical groove; submedian smooth carinae in the anterior gastric region, curving anteriorly to touch each other, forming a deep inverted U-shaped area slightly elevated from rostrum, each submedian carina bearing weakly defined and elevated indentation medially; lateral carinae short, with one tooth (posterior to the supraocular) and one posterior obscure tubercle each ( Figs. 3 B, 4A).

Eyes short, truncated distally and slightly angled anteroventrally, fused with carapace; cornea unpigmented ( Figs. 3 B, 4B). Antennular peduncle unarmed, reaching to rostral tip; length of article 1 twice that of articles 2 and 3 combined; article 3 about as long as article 2 ( Fig. 5 L). Antennal peduncle overreaching the antennular peduncle by the total length of the ultimate article; article 1 with ventral and lateral teeth; article 2 dorsodistally elongate forming a tooth-like tubular prolongation that reaches to the distal third of article 4, and with an acutely triangular ventral prolongation ( Fig. 5 M); antennal acicle unarmed, protruded straight forward and with the same shape and length of the dorsodistal tooth of article 2; article 3 with a pronounced ventrodistal tooth; article 4 about twice as long as article 5; antennal flagellum as long as the carapace (rostrum included). Maxilla 2 exopod posterior lobe (scaphognathite) with one long seta extending into branchial chamber. Maxilliped 3 pediform (ischium-merus length more than three times the merus width); coxa with a ventrodistal spine; ischium about twice as long as broad, inner crest with 11–12 similar denticles; merus about as long as ischium, armed with two sharp teeth subdistally on ventral margin, the distal-most more developed; carpus broadened distally, about half length of merus and about as long as propodus; dactylus about two-thirds the length of propodus; ischium, merus, carpus, propodus and dactylus ventral margin bearing pectinate setae obscured by simple setae; multiarticulate exopod hardly reaching proximal third of endopod carpus ( Fig. 5 F).

Left pereiopod 1 coxa armed with a distoventral spine. Basis unarmed. Ischium with 3 irregularly spaced denticles on ventral margin. Merus about twice as long as the maximum broad, armed with a subterminal tooth on dorsal margin and with 4 sharp teeth increasing in size distally on ventral margin, a few setae on distoventral and dorsal margins. Carpus dorsal length about half length of merus, unarmed, scattered groups of setae on dorsal margin and lateral surface. Chela about 2.5 times as long as broad, with tufts of setae mostly arranged longitudinally on the lateral surface, more abundant on dactylus; dorsal and ventral margins also furnished with tufts of setae ( Fig. 5 G). Palm slightly longer than wide; lateral surface with a subventral crest strongly demarcate proximally, with teeth joined at base and saw-like, becoming less evident in the fixed finger; three irregular subterminal teeth below articulation with dactylus; mesial surface with two subventral tubercles distally, and five subdorsal, regularly spaced and decreasing in size (the distal subterminal, the second cut off). Propodus cutting edge with eight teeth in the proximal three-fourths decreasing in size distally, lateral surface with dentate carina on ventral margin, mesial surface with three median proximal teeth. Dactylus longer than palm, lateral surface with a median carina proximally, cutting edge armed with a proximal blunt tooth followed by a concave gap and five other blunt teeth decreasing in size distally. Distal fourth of both propodus cutting edge and dactylus are unarmed and crossing when chela is closed. Right pereiopod 1 is missing.

Pereiopod 2 chelate, unarmed except by two dorsal spines on coxa, the distal one more acute, inner margins of the chelae furnished with spiniform setae; carpus about half length of merus, and about two-thirds as long as the chela; fingers slightly longer than the palm; dense row of long setae on propodus and carpus lower margins, some scarce setae distally on merus lower margins, tufts of setae on dactylus, propodus and carpus dorsal margins ( Fig. 5 H).

Pereiopod 3 simple, unarmed except for two dorsomesial spines on coxa; coxae with genital pore; carpus about half length of merus and slightly longer than propodus; propodus elongate, about four times longer than wide, furnished with seven stout spiniform setae on ventrolateral margin, and sparse tufts of long setae on dorsal and ventral margins; dactylus tip corneus, with two short and stout spiniform setae on lateral surface and tufts of setae on dorsal and ventral margins.

Pereiopod 4 simple, unarmed except for one dorsomesial short blunt spine on a short and cylindrical coxa; carpus about half length of merus and two-thirds as long as propodus ( Fig. 5 I); propodus elongate, ventrolateral margin with a longitudinal row of 7–8 stout spiniform setae, some of which accompanied by a supplementary spiniform seta as an interrupted second longitudinal row ( Fig. 5 J), ventrodistally furnished with pectinate setae ( Fig. 5 K), some sparse tufts of simple setae along dorsal margins and some single setae along ventral margin; dactylus corneus tipped and with four short, stout spiniform setae on lateral surface decreasing proximally in size ( Fig. 5 J), some tufts of simple setae on dorsal and ventral margins.

Right pereiopod 5 unarmed, with scattered tufts of setae on dorsal margins and lateral surfaces; coxa ventrodistally produced, with genital opening; carpus slightly longer than half of merus and as long as half of propodus; propodus mesial surface with an oblique row of pectinate setae in the distal two-fifths, ventrodistal margin produced; dactylus corneus tipped and one-fifth of propodus length. Left pereiopod 5 is missing.

Exopod on maxillipeds 1–3; single epipod on maxillipeds 1–3 and pereiopods 1–4. Single podobranchia on maxilliped 2, and double on maxilliped 3 and pereiopods 1–3; single arthrobranchia on maxilliped 3 and double on pereiopods 1–4; pleurobranchia absent.

Pleomeres smooth, unarmed and with sparse setae either single or coupled; mid-dorsal length of somites 2–6 subequal, slightly decreasing distally; weakly developed carina between terga and pleura on somites 2–5; somite 1 slightly longer than half of dorsal length of the second somite and with pleura acutely angled posteroventrally; pleura on somite 2 the widest, ventrally truncated, broadly rounded on lateroanterior and lateroposterior margins; pleura lateroanterior margin on somites 3–5 broadly rounded, declining backward to a rounded angle at lateroposterior margin; pleura on somite 6 rounded ( Fig. 5 A).

Pleopod 1 uniramous, unsegmented and distally spatulate ( Fig. 5 D); pleopods 2–5 alike, slender, biramous, endopods with appendix interna in their proximal third ( Fig. 5 C); pleopod 2 without appendix masculina ( Fig. 5 E).

Uropod exopod outer margin with submarginal ventral spinules barely visible dorsally in the distal third, movable tooth at posterodistal angle, just at the beginning of a clearly defined transverse suture dorsally furnished with 9–10 spinules; unarmed dorsal longitudinal midrib. Uropod endopod ovate, outer lateral margin with subventral spinules visible dorsally in the distal third and one distal apparent tooth; dorsal midrib with distal subterminal spine ( Fig. 5 B).

Telson about twice as long as wide, slightly convergent toward a rounded posterior margin without median spine; lateral margin bearing proximal lobe with spine, followed distally by two teeth each accompanied by a movable spine; half anterior dorsal surface with two short divergent carinae ending in a spine; scattered tufts of setae on dorsal surface ( Fig. 5 A).

Reproductive strategy. Hermaphrodite, our specimen shows clear male and female genital openings but no appendix masculina. No further details are available.

Remarks. The present species closely resembles Eiconaxius borradailei Bouvier, 1905 , especially because of the unarmed submedian horseshoe-shaped carinae on the anterior gastric region, the strongly protruded prolongation of the second antennal peduncle and the morphology of the pleomere pleurae (see Bouvier 1925: Pl. 7: figs. 8, 7 and Pl. 9: fig. 4, respectively). The genus Eiconaxius was described as having a weak median carina only on the rostrum, with submedian carinae converging anteriorly to join the median carina ( Poore & Collins 2009). However, E. borradailei was described by Bouvier (1925: 465, Pl. 7, fig 8, Pl. 9, fig. 4) with a rostral median carina extending away from the union of submedian carinae and thickening until barely discernible before reaching the cervical groove, which concurs completely with our specimen. Moreover, other characters in the genus Eiconaxius , such as the presence of pleurobranchiae and posteromedian tooth on telson posterior margin (vs both absent in E. ferachevali ) and the absence of uropodal exopod transverse suture and postcervical carina (vs both present in E. ferachevali ), keep our species separate from the genus Eiconaxius and, accordingly, from E. borradailei .

Habitat. The specimen was found on muddy coral rubble and shell debris at 470 m depth.

Type locality. Off Cape Timiris area, Mauritania (19°07´20″N, 16°50´31″W), 470 m depth.

Etymology. The species name derived from fer à cheval, the French expression for horseshoe, with reference to the horseshoe-shaped anterior gastric region.

Figures

FIGURE 2. Trypaea oblonga (Le Loeuff & Intès, 1974) n. comb. Male MU 215: A) Left pleopod 4; B) Left pleopod 4 appendix interna detail. Female MUDR 26: C) Left pleopod 1; D) Left pleopod 2, mesial view. Scale bars: A, 2 mm; B, 0.2 mm; C, D, 1 mm.

FIGURE 3. Ezaxius ferachevali n. gen. n. sp., holotype: A) Entire animal, left view; B) Carapace, dorsal view. Scale bars: A, 5 mm; B, 1 mm

FIGURE 5. Ezaxius ferachevali n. gen. n. sp., holotype: A) Telson, dorsal view; B) Left uropod, dorsal view; C) Pleopod 3 left; D) Pleopod 1 left, mesial view; E) Pleopod 2 left, mesial view; F) Maxilliped 3 right, lateral view; G) Pereiopod 1 left, lateral view; H) Pereiopod 2 left, lateral view; I) Pereiopod 4 right, mesial view; J) Pereiopod 4 right, propodus and dactylus, lateral view; K) Pectinate setae, P 4 distoventral propodus; L) Right antennula, dorsolateral view; M) Left antenna, lateral view. Scale bars: F, G, H, I, 2 mm; A, B, C, D, E, J, L, M, 1 mm; K, 0.2 mm.