Elasmopus marcelae, García-Madrigal, María Del Socorro, 2010

García-Madrigal, María Del Socorro, 2010, Littoral Maeridae and Melitidae (Amphipoda: Gammaridea) from the Gulf of Tehuantepec, Mexico, Zootaxa 2623, pp. 1-51 : 26-27

Elasmopus marcelae n. sp.

( Figs 13 , 14 )

Type material: 21 specimens: UMAR-PERA-274, holotype male (5.5 mm), paratype female (5.7 mm), specimens mounted; paratypes 19 females (La Entrega Bay, July 4, 2007, intertidal algae, coll. B. Martínez et al.).

Description: based on holotype male, 5.5 mm, UMAR-PERA-274.

Head: elongate, the same size as combined length of first two pereon segments; anterior head lobe broadly rounded, and located below the inferior antennal sinus a projecting rounded lobe. Eyes: subtriangular, pigment light brown; width represents approximately 1/5 length of head. Antenna 1 is 1/2 the length of the body, first article of peduncle is approximately 1/6 longer than the second article and slightly thicker, second article twice the length of third article of peduncle. Accessory flagellum with two articles, second article is 1/ 5 longer than first article. Antenna 2 setose, less than 1/2 the length of antenna 1; the articles 4–5 are the same length; first article of flagellum is 1/3 the length of the fourth article of peduncle.

Pereon: medium body, length less than twice the length of antenna 1; dorsally smooth; color off-white in alcohol. Coxa 1 with anterior margin oblique and straight; coxae 2, 3 lateral margins oblique and straight; coxa 4 widest and slightly emarginated posteriorly; coxae 1, 3 are same length, ventral margin of the coxae 1– 4 with sparse long plumose setae, formula for coxae 1–4: 5–1–4–1; coxae 5, 6 with short robust setae, formula for coxae 5, 6: 2–2; coxa 7 trapezoidal shape, with long and short simple setae. Gnathopod 1: subquadrangular propodus; palm margin with numerous short robust and simple setae, and inferior lateral two short robust setae; two short robust setae at inner angle of the palm: one small spine and the other longer. Propodus of gnathopod 2 is 1/4 longer than dactyl; oblique palm margin, slightly concave to nearly straight, with scarce medium-sized plumose setae; palm margin with a small subrounded hump near dactylar hinge; palm defined by a small conical tooth to receive dactyl; along the inner face near the palm margin with various bundles of plumose setae in paralleling rows. Basis of pereopods 1–2 with long plumose setae; basis of the pereopods 3– 5 nearly semicircular, gradually widening, normally serrated with short simple setae. Dactyl of each pereopod with plumose setae near propodus hinge.

Pleon: epimera continuous with respect to general line of the body; ventral margin bearing only some short robust setae, formula for epimera 1–3 is 1:2, 2:3–1, 3:1–1–2–2–1–1. Posterior edge of epimeron 3 lightly convex and bearing weak acclivities, each one with short simple seta, posteroventral corner emarginated bearing a weak denticle. Uropod 3: long, inner and outer rami are the same size, outer margin of the outer ramous with three clusters of medial robust setae, inner margin of inner ramous with four short robust setae. Telson deeply cleft, lobes excavated, apices armed with three robust setae, decreasing in length in the inner setae, lateral seta longest, medial seta shorter than the submarginal seta.

Female: based on paratype female, 5.7 mm, UMAR-PERA-274. Length of propodus of gnathopod 2 is 1/ 2 longer than dactyl; oblique palm margin, slightly convex to nearly straight, slightly setose, with mediumsized simple setae; two robust setae at inner angle of the palm, one small seta and the other longer; along inner face of palm with various bundles of simple plumose setae in parallel rows. Formula for epimera 1–3 is 1:2, 2:2–1, 3:1–2–2–2–1; Uropod 3 with inner ramous approximately 1/8 less than the outer ramous, inner margin of inner ramous with two clusters robust setae; telson similar to male, but with one plumose seta on distal corner of each lobe and one on each lateral margin.

Etymology: I dedicate this species to my youngest daughther, Marcela Bastida because of her help in finding references on the web and sorting amphipod specimens.

Taxonomic comments: Elasmopus marcelae n. sp. resembles E. gracilis Schellenberg, 1938 ; however, it differs in some characters: Elasmopus marcelae n. sp. has a gnathopod with a small rounded hump on palm margin near dactylar hinge and palm defined by small conical tooth, while E. gracilis has two short robust setae on palm margin near dactylar hinge. Inner ramous of uropod 3 of E. gracilis is 1/4 shorter than the outer ramous, while E. marcelae n. sp. the inner and outer rami are the same size. Elasmopus gracilis has two medial robust setae on inner margin of the inner ramous of uropod 3, while E. marcelae n. sp. has four medial robust setae. Elasmopus gracilis has the outer margin of the outer ramous of uropod 3 with two clusters of medial robust setae, while Elasmopus marcelae n. sp. has three clusters of medial robust setae. Telson of E.

gracilis with two robust setae, one long and one short, the length of medial seta is approximately 1/2 shorter than lateral seta, while E. marcelae n. sp. has three robust setae, medial seta is approximately 4/5 shorter than lateral seta.

Figures

FIGURE 13. Elasmopus marcelae n. sp., paratype, female, 5.7 mm, UMAR-PERA- 274, from La Entrega, Oaxaca: A) habitus. Holotype, male, 5.5 mm, UMAR-PERA- 274, La Entrega, Oaxaca: B) coxa 1; C) coxa 2; D) coxa 3; E) coxa 4; F) coxa 5; G) coxa 6; H) coxa 7; I) accessory flagellum; J) antenna 1; K) antenna 2; L) gnathopod 2, internal side; M) gnathopod 1, external side; N) gnathopod 1, internal side; O) gnathopod 2, external side with details of palm margin without setae; P) epimera; Q) upper lip; R) lower lip; S) right mandible; T) maxilliped.

FIGURE 14. Elasmopus marcelae n. sp., holotype, male, 5.5 mm, UMAR-PERA- 274, La Entrega, Oaxaca: A) maxilla 1; B) maxilla 2; C) pereopod 1; D) pereopod 2; E) left pereopod 3; F) left pereopod 4; G) pereopod 5; H) uropod 1; I) uropod 2; J) telson; K) uropod 3. Paratype, female, 5.7 mm, UMAR-PERA- 274, La Entrega, Oaxaca: L) uropod 3; M) telson; N) gnathopod 1, external side; O) gnathopod 1, internal side; P) gnathopod 2, external side; Q) gnathopod 1, internal side.