Atlantapseudes curvatus Esquete & Cunha, 2017, sp. nov.

Atlantapseudes curvatus sp. nov.

(Figs 2–6)

Atlantapseudes nigrichela Băcescu, 1978 [in part].

Material examined. Holotype: ♀ with marsupium, MNCN 20.04 /11185, 4.0 mm length, cruise 64PE253, station 64PE253_38C, NIOZ boxcore, 12.10.2006, Lazarillo de Tormes MV, 35°19.09'N, 6°46.40'W, 497 m depth. Paratypes: Gulf of Cadiz—Mud volcanoes. Meknes MV: St. TTR15_AT 581, 700 m, 1♀ (with marsupium) (DBUA 0002002.01). Yuma MV: St. TTR14_AT 524, 960 m, 1 ♀; St. TTR16_AT 605, 975 m 1 ♂ (DBUA0002003.01–02).

Gulf of Cadiz—Carbonate and coral mounds. Pen Duick Escarpment: St. 64PE237_5C, 533 m, 2 ♂♂ (DBUA 0002004.01).

Additional material: 4 ♀♀ (GANMNH TAN 032), W Portugal, 0 9.1972.

Etymology. From the Latin verb curvo, ‘ curve’, as masculine participle, referring to the lateral curved processes of the rostrum.

Diagnosis. Female with marsupium. With characteristics of the genus (as diagnosed by Santos & Hansknecht 2016). Cephalothorax with curved processes on both sides of the rostrum. Pereonite 1 posterolateral corners pointed; pereonites 2–3 with anterolateral apophyses and posterolateral corners pointed; pereonites 4–6 with anterolateral apophyses. Pleonites with ventral apophyses (not illustrated) and lateral pointed processes directed backwards. Antennule outer flagellum of 7–8 segments; inner flagellum of three segments. Antennal squama 2.7 times as long as third article. Maxilliped endite with three coupling hooks. Cheliped carpus with two ventral setae; chela fixed finger cutting edge without apophyses or teeth. Pereopod 6 propodus with subdistal setal row. Uropod exopod of six segments.

Description of ovigerous female paratype DBUA0002002.01. Body (Figure 2 A) 4.0 mm length, 5.0 times as long as broad. Cephalothorax about as long as broad, with lateral spines, eyelobes present, acute, rostrum pointed with lateral acute processes curved inwards on both sides. Pereon, pereonite 1 2.9 times as broad as long, with posterolateral corners pointed, not rounded; pereonites 2 and 3 with anterolateral apophyses and posterolateral corners pointed, pereonite 2 1.3 times as broad as long, pereonite 3 1.8 times as broad as long; pereonites 4–6 with anterolateral apophyses, respectively 1.0, 1.3 and 1.5 times as broad as long. Pleon 0.2 times as long as body, pleonites with ventral apophyses and lateral pointed processes directed backwards. Pleotelson 1.4 times as long as broad, distal margin tapering, with a pair of distal setae.

Antennule (Figure 2 B) peduncle article 1 4.0 times as long as broad, with one penicillate seta on outer margin; article 2 0.4 times as long as article 1, 2.7 times as long as broad, distal inner corner with one simple and two penicillate setae, distal outer corner with two simple and one penicillate setae; article 3 about as long as broad, with one short distal seta. Flagellum common article naked; inner flagellum of three segments, first segment with two setae, second segment with one seta, distal segment with three simple and one penicillate setae; outer flagellum of 7–8 segments, first segment 3.0 times as long as broad, naked, segments 2–5 about 1.5 times as long as broad, segment 6 about as segments 3–4, segment 7 0.2 times as long as segment 5, segments 2, 4, 6 and 7 with one aesthetasc, segments 2, 5 and 6 with terminal seta, segment 7 with three setae.

Antenna (Figure 2 C) peduncle article 1as long as wide, naked; article 2 2.6 times as long as broad, with one short seta on inner margin and one short seta on outer margin near squama insertion, squama 2.7 times as long as article 3, 9.2 times as long as broad, distally with one short seta and one long seta, longer than squama; peduncle article 3 about as long as broad, with one short seta on distal inner corner; article 4 0.8 times as long as article 1, with two penicillate setae; article 5 1.3 times as long as article 3, with three penicillate setae. Flagellum of six segments, segments 1–2 with one long seta each, segment 3 with one short seta, segment 4 with three simple and one penicillate setae, segment 5 with seta, distal segment with tuft of simple setae.

Mouthparts. Labrum (Figure 3 A) naked. Left mandible (Figure 3 B, C) molar distally setulose, with several teeth; incisor with four denticles; setal row consisting of eight bi- and multifurcate setae; lacinia mobilis with three denticles; mandibular palp first article twice as long as broad, with short seta, second article six times as long as broad with row of three setae, third article with seven distal and one subdistal setae. Right mandible (Figure 3 D–F) as left, but without lacinia mobilis, setal row of consisting of six bi- and multifurcate setae, palp second article with five unequal setae. Labium (Figure 3 G) naked, palps with setules and three terminal spines. Maxillule (Figure 3 H) outer endite margins setulose, with nine terminal spines and one pair of subterminal setae; inner endite with marginal setules and four terminal spines; palp (Figure 3 I) of biarticulate, subequal in length, distal article with two long setae. Maxilla (Figure 3 J) outer margin with few denticles; outer lobe of movable endite with two outer and four inner plumose setae; inner lobe of movable endite with five plumose setae; outer lobe of fixed endite with four simple and four bifurcate setae; inner lobe of fixed endite with row of setae arising from a peduncle, in front of one plumose setae and three longer simple setae.

Maxilliped (Figure 3 K) basis naked; palp article 1 with one inner and one outer seta, article 2 with row of inner setae and two outer setae, article 3 with inner row of setae, article 4 with a row of distal setae; (Figure 3 L) endite with three coupling hooks, inner margin with three plumose setae, distal margin with setules, four bifurcate and three pointed spines. Epignath (Figure 3 M) with one long seta.

Cheliped (Figure 4 A) basis naked, about twice as long as broad, with ventral curved spiniform process. Merus naked, 2.3 times as long as broad, with ventral spiniform process. Carpus 2.5 times as long as broad, with two ventral setae. Chela 1.8 times as long as carpus, propodus fixed finger with three ventral setae, cutting edge regularly curved with no invagination or denticle, with spinules, dorsal edge perpendicular to ventral; dactylus dorsal margin invaginated near insertion with propodus, with one pair of dorsal setae, cutting edge with spinules; unguis 0.4 times as long as dactylus.

Pereopod 1 (Figure 4 B) coxa with anterior spiniform process (not illustrated); basis 2.3 times as long as broad, with one dorsal and one ventral seta. Ischium with ventral seta. Merus twice as long as broad, ventral margin with five setae, ventrodistal corner with spine and seta, dorsodistal corner with spine and two setae. Carpus about as long as merus, ventral margin with eight setae and subdistal stout spine, dorsal margin with five setae and dorsodistal spine. Propodus 1.6 times as long as broad about half length of carpus; ventral margin with five spines and one seta, dorsal margin with two spines and three setae, distal margin with two simple and one serrated setae. Dactylus and unguis together about as long as propodus; dactylus with ventral spinules; unguis 0.5 times as long as dactylus.

Pereopod 2 (Figure 4 C) coxa naked (not illustrated); basis cylindrical, 5.3 times as long as broad, with ventrodistal seta. Ischium with ventrodistal seta. Merus 2.9 times as long as broad, dorsodistal corner with four setae, ventral margin with row of six setae. Carpus 0.7 times as long as merus, ventral margin with five setae, ventrodistal corner with two spines, dorsal margin with six setae. Propodus about as long as carpus, ventral margin with five setae and three spines, dorsal margin with five setae. Dactylus and unguis slender, together about as long as propodus, dactylus with one dorsal and one ventral setules, unguis 0.7 times as long as dactylus.

Pereopod 3 (Figure 4 D) coxa naked; basis naked, with dorsodistal spiniform process. Ischium with pair of ventral short setae. Merus 2.8 times as long as broad, with dorsodistal seta, ventral margin with three spines. Carpus 0.8 times as long as carpus, dorsal margin with three setae, ventral margin with three setae and one subdistal spine. Propodus 0.8 times as long as carpus, with two dorsodistal setae, ventral margin with four setae and two spines. Dactylus and unguis slender, together 1.1 times as long as propodus, unguis 0.8 times as long as propodus.

Pereopod 4 (Figure 5 A) coxa naked; basis 5.0 times as long as broad, with one penicillate simple seta on dorsal margin and one ventrally. Ischium with ventral seta. Merus 0.3 times as long as basis, with dorsodistal seta and pair of ventrodistal spines. Carpus 1.2 times as long as merus, with mid-ventral spine followed by five pairs of spines, increasing in length toward propodus insertion. Propodus 0.8 times as long as carpus, ventral margin with one short and one long spine, dorsal margin with one mid-distal penicillate seta, distal margin with two spines and a tuft of five setae. Dactylus and unguis together 0.7 times as long as propodus, unguis about as long as dactylus.

Pereopod 5 (Figure 5 B) coxa neked; basis with one dorsal and one ventral penicillate seta. Ischium naked. Merus 3.3 times as long as broad, dorsodistal corner with seta, ventrodistal corner with one seta and one spine. Carpus cylindrical, 1.4 times as long as merus, ventral margin with five spines, dorsodistal corner with one spine. Propodus 0.7 times as long as carpus, dorsodistal corner with pair of simple setae, ventral margin with four ventral spines, one longer. Dactylus and unguis together 0.8 times as long as propodus, unguis 0.7 times as long as dactylus.

Pereopod 6 (Figure 5 C) coxa naked; basis dorsal margin with one simple and two penicillate setae, ventral margin with one penicillate seta. Ischium with ventral seta. Merus 2.0 times as long as broad, with one dorsodistal and one ventrodistal setae. Carpus 1.3 times as long as broad, with dorsodistal seta, ventral margin with two setae and one dorsodistal spine. Propodus 0.7 times as long as carpus, dorsal margin with mid-distal seta, and with two long spines and one seta distally; proximal ventral margin with a pair of spines, one more than twice as long as other, subdistally with six setules and one short spine. Dactylus and unguis together 0.9 times as long as propodus; propodus with dorsal setule, unguis 0.6 times as long as dactylus.

Uropod (Figure 2 A) protopod 0.4 times as long as telson, with distal seta. Endopod incomplete in all specimens; first segment about as long as broad, naked, rest of segments elongate, some of them with distal seta. Exopod of six segments; first segment about as long as broad, rest of segments elongate, segments 3, and 5 with one distal seta, segment 6 with two distal setae.

Distinctions of young male. Cheliped (Figure 6 A) carpus dorsal margin with seta; propodus dorsal margin rounded, fixed finger with seven (two ventral) setae.

Remarks. Atlantapseudes curvatus sp. nov. differs from the other species of the genus known from the study area, Atlantapseudes nigrichela, (both the original description type material examined here and the description of the material from the GoC by Błażewicz-Paszkowycz et al. 2011) in the following characters: presence of lateral curved processes on both sides of the rostrum (absent in A. nigrichela), presence posterolateral apophyses on pereonites 1–3 (absent in A. nigrichela), presence of three coupling hooks on maxilliped endite (four in the type material, two in the material from the GoC) and presence of setal row in pereopod 6 propodus (absent in A. nigrichela).

Remarkably, the rostrum of A. curvatus is like that of some of the male specimens illustrated by Băcescu (1978) when describing A. nigrichela. Nevertheless, according to his description, there is no sexual dimorphism in the species, which differs from our specimens by the above-mentioned characters.

Atlantapseudes curvatus is most like Atlantapseudes cynaea Bamber, 2007 from the bathyal slope off New Caledonia in the number of segments of the antennule and antenna flagella, the length of the squama, and the presence of a row of setae on the propodus of pereopod 6. Nevertheless, it can be readily distinguished because of the shape of the rostrum, with rounded smooth shoulders in the latter and the lack of apophyses on pereonites 1 and 2. Furthermore, it has two coupling hooks on maxilliped endite, and four setae on maxillule palp.

Atlantapseudes curvatus can be readily distinguished from A. brasiliensis Santos & Hansknecht, 2007, from Brazil, A. madagascariensis Santos & Hansknecht, 2007, from Madagascar, and A. lindae Meyer & Heard, 1989 from the Gulf of Mexico because of the shape of the rostrum and the posterior border of the female chela being perpendicular to the anterior border.

The absence of marked sexual dimorphism (e.g., cheliped differentiated, presence of pleopods in male) indicates immaturity of the males, as suggested by Meyer & Heard (1989) when mentioning the original description of A. nigrichela.

Distribution and Ecology. The species occurred at depths of 497–700 m, in the Moroccan margin slope. In the crater of Meknès MV, the sample in which A. curvatus was found consisted of mud breccia and H2S and included chemotrophic species such as frenulate worms of the genus Siboglinum and Solemyidae bivalves. The maximum depth at which the species was recovered was 960 m at Yuma MV. One ovigerous female specimen came from Pen Duick Escarpment in a site with no evidence of fluid seepage.