Psammogammarus barrerai, Ortiz & Winfield & Ardisson, 2017

Ortiz, Manuel, Winfield, Ignacio & Ardisson, Pedro-Luis, 2017, A new deep-sea Psammogammarus species (Crustacea: Amphipoda: Eriopisidae) from the continental slope of the SE Gulf of Mexico, Journal of Natural History 52 (1 - 2), pp. 13-28 : 15-25

Genus Psammogammarus Karaman, 1955

Psammogammarus barrerai sp. nov.

( Figures 2–8 )

Type material

Holotype. adult male ( CNCR33891 ), 7 mm (measured from base of rostrum to base of telson), sampling station 81_33 (O/C, Xcambó-4), 19.9993°N, 93.0004°W, 1317 m in depth, 21 September 2009; collector Teresa Herrera-Dorantes.

Diagnosis

Head with cephalic lobe and anteroventral notch present. Body long and unpigmented. Accessory flagellum 2-articulated. Coxa 1 pointed forward. Gnathopod 1 palmar margin oblique; palmar angle with five setae; dactylus curved, fixing palm. Gnathopod 2 palmar margin oblique, seven short, one simple long, and one robust oblique setae; one long and six short robust setae on posterior margin. Basis of pereopod 7 forming a wide serrated posterior lobe. Epimeral plate 2 with six long setae. Epimeral plate 3 with four robust setae. Uropod 3, 0.4× as long as total length of body. Telson notch 0.6× body length; distal coupling spines (retinacula) on pleopod 1 peduncle ‘W’ shaped.

Description

Adult male, based on holotype, 7.0 mm ( CNCR33891 ) .

Body ( Figure 2 ) elongate, slender, unpigmented. Head as long as pereonal segments 1 and 2 combined; eyeless; lacking rostrum; lateral lobe rounded; cephalic notch present ( Figure 3 (a)).

Antenna 1 ( Figure 2 ), 2.2× length of antenna 2; article 1 as long as 2 and 3 combined; one distoventral robust seta; accessory flagellum 2-articulated; basal 2× as

long as distal; flagellum 20-articulated. Antenna 2 ( Figures 2 and 3 (a)), article 4 as long as 5; flagellum 4-articulated, article 1, 2× as long as 2–4 combined; gland cone not reaching middle of third peduncle article.

Mouthpart bundle; lower lip ( Figure 3 (b)) with distinct well-developed inner lobes, outer lobes with four small distal extensions on each tip, mandible lobe present. Upper lip ( Figure 4 (b)) ovoid, 2× wider than long, few minute setae on lower margin. Maxilla 1 ( Figure 3 (c)), outer lobe with five trifid long setae; palp 2-articulated, distal article 2× as long as basal, with four robust and one simple distal setae; inner lobe ovoidal, 2× wider than outer, 12 long narrow setae. Maxilla 2 ( Figure 3 (d)), outer lobe as wide as inner, 11 distal setae; inner lobe with 13 distal setae, a row of 11 facial setae. Mandibles ( Figure 4 (c,d)), molar well developed, triturative; palp 3-articulated, article 3, 1.5× longer than 2, with three setae on basal inner margin, and 10 distal and subdistal simple setae; article 2 with three setae on inner margin; article 1, 0.5× length of article 2, naked; left mandible ( Figure 4 (c)) with 4- cuspidate incisor; lacinia mobilis 4-cuspidate; 10 racker spines; right mandible ( Figure 4 (d)) with 4-cuspidate incisor; lacinia mobilis 4-cuspidate (two big and two small cuspidate), nine racker spines. Maxilliped ( Figure 4 (a)), outer lobe expanded distally, covered with 10–12 marginal setae; inner lobe with seven simple and three odonthoid distal setae; four robust setae on inner margin; palp 4-articulated; article 2, 1.2× longer than 3, 10–14 setae on inner margin; article 3 expanded distally to form, together with the long and curved dactylus, a rudimentary ‘chelate’ distal structure, a long distal seta; dactylus with nail.

Gnathopod 1 ( Figure 5 (a)), coxa 1 pointed ahead, a tiny seta near anteroventral corner; basis 1.2× as long as ischium and merus combined, four long and three short setae on posterior margin; ischium 0.8× as long as merus, posterior margin covered with three short setae on posterior margin; merus forming a discrete posterior lobe, covered posteriorly with one long and one short setae, followed by a cover of very tiny setae; carpus 1.3× as long as propodus, one anterodistal setae and seven on distal half of posterior margin; propodus subtriangular, palmar margin oblique, palmar angle with five setae; dactylus curved, fixing palm. Gnathopod 2 ( Figure 5 (b)), coxa rounded, naked; basis as long as propodus, two short setae on basal half on anterior margin, posterior margin with six very long and two short setae on posterior margin; ischium with two posterior setae; merus with one posterior setae; carpus 0.3× as long as propodus, three long setae on posterodistal angle, and two short setae on anterior margin; propodus with one large and one short anterodistal setae, palmar margin oblique; with seven short, one simple long, and one robust oblique setae; posterior margin with one strong, eight short robust setae, and a tuft of four long setae, backward; dactylus long, tapering distally.

Pereopod 3 ( Figure 6 (a)), coxa rounded, devoid of setae; basis with seven setae on posterior margin, as long as ischium, merus and carpus combined; ischium with one short seta; merus with one antero- and another postero-distal setae; carpus with three long and one short setae on posterior margin, one short anterodistal seta; propodus 1.2× as long as carpus, three long setae on posterior margin and two submarginal setae on distal half, one short seta midway on anterior margin and another long anterodistal; dactylus 0.5× as long as propodus. Pereopod 4 ( Figure 6 (b)), coxa ovoidal, naked; basis as long as merus and carpus combined, five setae on posterior margin; ischium with one short seta in posterior margin; merus with two short setae on distal half of posterior margin, one posterodistal seta; carpus as long as propodus, three long setae on posterior margin, another distal long seta; dactylus 0.5× as long as propodus. Pereopod 5 ( Figure 6 (c)), coxa bilobed, naked; basis as long as merus and carpus combined, tapering distally, with seven robust setae in anterior margin, and four setae in posterior margin; ischium with two setae on anterior margin; merus 1.3× as long as carpus, two short and one long setae in anterior margin, one robust seta in posterior margin, and another distal; carpus as long as propodus, three setae in anterior margin, six robust and three simple setae distally; propodus with two robust and one simple setae on anterior margin, five long and one short setae, distally; dactylus 0.5× as long as propodus. Pereopod 6 ( Figure 6 (d)), coxa subrounded, one minute process in anterior and another in posterior margins; basis 1.7× as long as broad, anterior margin straight with seven setae, posterior margin convex, with seven short and one distal long robust setae; ischium with one posterodistal robust seta; merus 1.2× as long as carpus, anterior margin with four robust setae, the more distal the longer, posterior margin with one short basal seta and three pairs of equidistant setae, gradually longer distally; carpus as long as propodus, five submarginal robust setae, and other one subdistal and two distal; propodus with four robust setae in anterior, and three in posterior margins, one long and three short robust setae distally, another lateral subdistal robust seta; dactylus 0.7× as long as propodus.

Pereopod 7 ( Figure 7 (a)), coxa subrectangular; basis ovoid, 1.4× as long as broad, anterior margin slightly serrated, nine equidistant setae in each serration, two robust setae, convex distally, serrated posterior margin, with 10 setae settled in each serration; ischium devoid of setae; carpus as long as ischium and merus combined; merus with two long and two short robust setae in anterior margin, three long and three short in posterior margin; carpus as long as propodus, three long and two short robust setae in anterior margin, with one short seta midway in posterior margin, and two long distal setae settled distally, in a small posterior lobe; propodus with one midway posterior seta, two long and one short robust distal setae, a pair of robust setae midway, and three subdistal robust setae in anterior margin; dactylus 0.7× as long as propodus.

Telson ( Figure 7 (b)), 1.5× longer than wide, bilobed, notch 0.6× length, each distal tip bifid, bearing one long robust and one short simple setae, one robust and another simple seta, midway in lateral margins.

Pleopod 1 ( Figure 7 (c)), coupling spines on peduncle dissimilar; distal ‘W’ shape (never mentioned before in the species of the genus or in any member of the family Eriopisidae ), the proximal simple, but blunt. Pleopod 2 ( Figure 7 (d)), coupling spines alike, with distal tiny teeth. Pleopod 3 ( Figure 7 (e)), coupling spines alike, but simple.

Epimeral plates ( Figure 8 (a)); epimeron 1 ventral margin straight, three short setae in anterior half, posteroventral corner acute; epimeron 2 ventral margin concave, six long setae midway in ventral margin, posterior margin with one simple seta, posteroventral corner very acute; epimeron 3 ventral margin slightly convex, four equidistant robust setae, posterior margin with one simple seta, posteroventral corner forming an acute angle.

Uropod 1 ( Figure 8 (b)), peduncle 1.4× as long as rami, one basal strong robust seta on outer margin, and a row of nine equidistant setae in inner margin, two interramal robust setae; outer ramus with two short robust setae in inner margin, and two long and two short distal robust setae; inner ramus with three robust setae midway in inner margin, and two long and two short robust setae. Uropod 2 ( Figure 8 (c)), peduncle 0.8× as long as outer ramus; inner margin with two robust setae, a tuft of four robust setae in outer distal corner and another in inner corner; outer ramus with five robust setae in outer margin and two in outer, four robust setae, distally; inner ramus 0.8× as long as outer, one seta in inner margin and two in outer margin, two long and three short setae, distally. Uropod 3 ( Figure 8 (d,e)), very long, articles somewhat flattened and bearing pairs of short setae, 0.4× as long as total length of body; peduncle 0.3× as long as basal article of exopod; distal article of exopod 0.7× as long as basal, a distal tuft of 10 setae, scale (inner ramus) as long as peduncle, two long robust and one simple setae.

Female unknown.

Type locality

Continental slope, Bay of Campeche, SW Gulf of Mexico .

Habitat

In soft bottom, interstitial, 1317 m; sediment with high proportion of silt, rich in organic carbon but well oxygenated and with moderate carbonate content.

Etymology

The new species is named to honour Professor Hector Barrera Escorcia (FES Iztacala, UNAM), for his valuable contribution to the study of cell biology in Mexico. It is derived from the noun ‘barrera’ in the genitive case.

Remarks

Males of Psammogammarus barrerai sp. nov. are morphologically most similar to males of P. stocki . These two species share the endopod of uropod 3 less than half the length of article 1 of exopod, and the gnathopod 2 palmar margin notched, bearing two strong short robust setae on the distal half of the posterior margin. Males of Psammogammarus barrerai sp. nov., however, can be easily distinguished by the following characters: (1) P. barrerai sp. nov. differs by having a more shallow notch in palmar margin of gnathopod 2 vs deeper in P. stocki ; (2) maxilliped articles 3–4 narrow in P. barrerai sp. nov., vs wide in P. stocki ; (3) the two big robust spines on the palmar angle of gnathopod 2 are separated in P. barrerai sp. nov., vs adjoining in P. stocki ; (4) a shorter and subtriangular head in P. barrerai sp. nov., vs longer and subquadrangular in P. stocki ; (5) a different type of retinacula on pleopod 1 (distal ‘W’ shape).

Only two Psammogammarus species have been collected from soft-bottom samples of the deep sea: P. barrerai sp. nov., and P. caecus . The former differs by article 1 of exopod of uropod 3 being longer than article 2, vs subequal in length in P. caecus ; basis of pereopod 7 with strong serrated posterior margin in P. barrerai sp. nov., vs slight serrated in P. caecus ; article 2 of accessory flagellum shorter than article 1 in P. barrerai sp. nov., vs as long as article 1 in P. caecus ; epimerum 3 with four strong robust setae on ventral margin in P. barrerai sp. nov., vs epimerum without long setae on ventral margin in P. caecus . The main morphological differences between Psammogammarus barrerai sp. nov. and other Psammogammarus species can be found by using the provided male and female keys.

Figures

Figure 2. Psammogammarus barrerai sp. nov. Lateral view of body, with magnification of accessory flagellum of antenna 1.

Figure 3. Psammogammarus barrerai sp. nov. (a) Lateral view of head; (b) lower lip; (c) maxilla 1; (d) maxilla 2.

Figure 4. Psammogammarus barrerai sp. nov. (a) Maxilliped; (b) upper lip; (c) left mandible; (d) right mandible; (e) mandible palp.

Figure 5. Psammogammarus barrerai sp. nov. (a) Gnathopod 1; (b) gnathopod 2.

Figure 6. Psammogammarus barrerai sp. nov. (a) Pereopod 3; (b) pereopod 4; (c) pereopod 5; (d) pereopod 6.

Figure 7. Psammogammarus barrerai sp. nov. (a) Pereopod 7; (b) telson; (c) pleopod 1; (d) pleopod 2; (e) pleopod 3.

Figure 8. Psammogammarus barrerai sp. nov. (a) Pereonites 1–3; (b) uropod 1; (c) uropod 2; (d) proximal part of article 1 of exopod and scale-like endopod of uropod 3; (e) article 2 of exopod of uropod 3.