Elasmopus oaxaquensis García-Madrigal, 2010, n. sp.
Creators: name: García-Madrigal, María Del Socorro
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Melitidae
Elasmopus
Elasmopus oaxaquensis

description: Elasmopus oaxaquensis n. sp.
(Figs 15, 16)
Type material: 751 specimens: UMAR-PERA-278, holotype male (8.5 mm), paratype female (8 mm), paratypes: 12 males (three specimens mounted), 229 females (two specimens mounted), 194 juv (Playa del Amor, Zipolite, July 3, 2007, algae from tide pool, coll. J. Jarquín et al.); UMAR-PERA-280, 64 males (two specimens mounted), 99 females (one specimen mounted), 151 juv (Aguete beach, August 25, 2006, intertidal algae, coll. R. Bastida et al.).
Additional material: 339 specimens: UMAR-PERA-275, 1 male (entrance of Chacahua Lagoon, April 13, 2007, algae with barnacles, coll. S. García et al.); UMAR-PERA276, 4 females, 1 juv (Santa Elena, March 11, 2004, intertidal algae, coll. R. Bastida); UMAR-PERA-277, 41 males, 106 females, 102 juv (San Agustinillo beach, July 3, 2007, intertidal algae, coll. J. Jarquín et al.); UMAR-PERA-279, 1 male, 1 female (Panteon beach, March 23, 2007, coral rock 3 m, coll. V. Mata); UMAR-PERA-281, 1 male (Estacahuite beach, April 18, 2005, sediments of coral rock 1–1.5 m, coll. S. García et al.); UMAR-PERA-282, 8 males, 7 females, 2 juv (Estacahuite beach, September 10, 2005, coral rock 2–4 m, coll. R. Bastida et al.); UMAR- PERA-283, 5 females, 4 juv (Estacahuite beach, August 25, 2006, coral rock 4 m, coll. R. Bastida et al.); UMAR-PERA-284, 2 males, 1 juv (Estacahuite beach, December 1, 2006, sediments of coral rock 4 m, coll. R. Bastida et al.); UMAR-PERA-285, 2 males, 1 juv (La Tijera beach, April 30, 2005, sediments from coral rock 4 m, coll. R. Bastida et al.); UMAR-PERA-286, 1 male, 1 female, 1 juv (Maguey Bay, July 4, 2007, intertidal algae, coll. B. Martínez et al.); UMAR-PERA-287, 4 males, 13 females (La Entrega Bay, July 4, 2007, intertidal algae, coll. B. Martínez et al.); UMAR-PERA-288, 2 males, 8 females, 19 juv (El Arrocito beach, July 4, 2007, intertidal algae, coll. B. Martínez et al.).
Description: based on paratype male, 7.6 mm, UMAR-PERA-280; paratype males, 6.6 mm, 9.4 mm, and holotype male, 8.5 mm, UMAR-PERA-278.
Head: elongated, but shorter than combined length of first two pereon segments; anterior head lobe grossly rounded, and inferior antennal sinus is projects obtuse lobe. Eyes: grape shape, very dark pigment; width represents approximately 1/3 length of head. Antenna 1 is 1/2 length of the body, first article of peduncle is approximately 1/4 longer than the second article and considerably thicker, and twice the length of third article of peduncle. Accessory flagellum with 2–3 articles, third article very small; total length about 1/4 longer than the length of first article of flagellum. Antenna 2: setose, approximately 1/2 shorter than the antenna 1; articles 4–5 are the same length; first article of flagellum is 1/4 the length of the fourth article of peduncle.
Pereon: body length twice the length of antenna 1; dorsally smooth; color off-white in alcohol, sometimes retains purple and pink regions. Coxae 1–4 of subequal length; ventral margin of the coxae 1–4 with sparse long serrate setae, formula for coxae 1–4: 7–5–4–1; coxa 1 with rounded anteroventral corner and slightly produced; coxa 2 with rounded ventral margin; coxa 3 with anterior margin slightly concave; coxa 4 widest and slightly emarginated posteriorly; coxae 5, 6 with two short robust setae each; coxa 7 ovoid shape, with numerous short simple setae. Gnathopod 1 with propodus suboval; palm margin with numerous short robust setae on inner and outer margins, one robust seta at angle of the palm stronger and longer than those from palm margin; outer angle of carpus with longest robust setae. Propodus of gnathopod 2 approximately 1/4 longer than dactyl; palm slightly oblique and evenly convex, with long and dense plumose setae; palm margin with rounded setose hump near dactylar hinge, then middle blunt tooth, palm defined by a short mediofacial ridge, this ridge ends with a hood to receive dactyl, then a third small medial tooth seta, far from point of dactyl and often transparent and difficult to see among dense long plumose setae. Pereopods with merus anterodistally lobed; pereopods 3–5 with basis widening, nearly semicircular and increases gradually on posterior margin from minutely serrated (pereopod 3) to deeply serrated (pereopod 5); posterior margin of basis of pereopod 5 approximately 2/3 of its length deeply serrated.
Pleon: epimera narrow with respect to general line of the body; ventral margin bearing only some short spines, the formula for epimera 1–3 is 1:1, 2:2, 3:2–2–2–2; epimeron 3 convex on posterior edge and evenly and sparsely notched with four short simple setae, posteroventral corner emarginated bearing a weak tooth.
Uropod 3: peduncle is the same length as the outer ramous, with shortened inner ramous approximately 1/ 3 in respect to outer ramous; inner margin of the inner ramous bears one medial robust seta; outer margin of the outer ramous with three clusters of medial robust setae. Telson deeply cleft, lobes with weakly excavated apices, armed with 3–4 robust setae, three of them long (the length of the setae gradually decreasing towards the medial spines), and fourth, if present, very short; longest setae is subequal or shorter than the lobes of telson; outer angle of each lobe with a plumose seta, and outer margin of each lobe with two simple setae.
Female: based on paratype females, 7 mm, 8 mm, UMAR-PERA-278.
Inner margin of gnathopod 2 with robust setae, length of dactyl is 1/2 the length of propodus; two robust setae on each side of angle of palm of gnathopod 2, one robust seta on each side longer than those of palm margin. Formula for coxae 1–4: 4–3–3–3. Posterior margin of the basis of pereopods 3–4 crenulated with short simple setae and not as deeply serrate as male; pereopod 5 is serrated but not as deep as male; posterior margin of basis of pereopod 5 approximately 1/3 of its length deeply serrated. Formula for epimera is 1: 1, 2: 0, 3:1–1; epimeron 3 is lightly convex on posterior margin, evenly and sparsely notched with a short simple seta on each one, posteroventral corner emarginated bearing a weak tooth. Uropod 3 has outer margin of the outer ramous with two clusters of medial robust setae. Telson with four robust setae: two long, one medium, and the shortest seta submarginal.
Etymology: this species is dedicated to the Mexican State of Oaxaca, because it was one of the most abundant in the majority of localities.
Variations: the identification of juvenile females is complicated, as well as juveniles of indeterminate sex. In the case of juvenile males of Elasmopus oaxaquensis n. sp. the palms of gnathopod 2 have a slight mediofacial ridge and hood to receive dactyl but the third small blunt tooth is obsolete.
Taxonomic comments: Elasmopus oaxaquensis n. sp. resembles E. serricatus (Barnard, 1969b); however, it differs in several major characters (see Table 4) such as: the palm of gnathopod 2 of male of E. serricatus has a middle tooth proximal to hinge hump, palm defined by a ridge bearing one robust setae, palm and posterior margin of hand are setose throughout all, while Elasmopus oaxaquensis n. sp. has a middle tooth far from hinge hump, the palm has a mediofacial ridge, this ridge ends with hood to receive dactyl (but never with a robust setae), then occasionally (in terminal male) a third small tooth, palm and margin of hand setose throughout before ending in third tooth. Uropod 3 of E. serricatus has inner ramous with of two medial robust setae, while Elasmopus oaxaquensis n. sp. has inner ramous bearing one medial robust seta. Telson of E. serricatus armed with 4–5 robust setae: two long and two short in male, and 2–3 long and two short setae in female, while the male of Elasmopus oaxaquensis n. sp. has 3–4 robust setae, three of them long (decreasing in length of the inner spines) and the fourth, if present is shortest; the females have four robust setae, three long (decreasing of length in the inner spines), but one shortest submarginal spine. Telson of one male (6.6 mm) from the Playa del Amor, Zipolite has the morphology of telson shared by Barnard (1979) de Puerto Peñasco, where the submarginal spine is shorter then the medial spine; this is noticed in the female of Elasmopus oaxaquensis n. sp. The male from the Playa del Amor has a slight mark of the mediofacial ridge and a third tooth on palm of gnathopod 2 like male adults of Elasmopus oaxaquensis n. sp. A terminal male (6.6 mm) present both lobes of the telson are fused completely, according to Barnard (1979) this is a major characteristic of E. rapax group and it is not common to find aberrations. This could be a mark of speciation inside of the group.
Remarks: Barnard (1969b) described E. rapax serricatus as a subspecies. Later, Barnard (1979) rectified and elevated it to full specific status. According to Barnard (1969b), the telson of male has 5–8 robust setae (four in juveniles); however, in 1979 he rectified the number of robust setae to 4–5 robust setae. Also, in the variation section, Barnard (1979) considered the following “ Panama material middle tooth on palm of male of gnathopod 2 becoming obsolete in adults, and in juveniles specimens more proximally located (away from hinge tooth) than in the Californian specimens. Galapagos material: medial face of hand of male gnathopod 2 either bearing or lacking the small ridge, when present ridge armed only with a seta”. The palm of Elasmopus oaxaquensis n. sp. has a short mediofacial ridge without seta, but ended with hood to receive dactyl, then it has a third small blunt tooth on palm but only in some terminal males. Possibly, Barnard (1979) confused the material from Panama (it probably is Elasmopus oaxaquensis n. sp.) and Gulf of California with E. serricatus from California. The other possible case is, E. ecuadorensis Schellenberg, 1938 is also present in the coast of South Pacific Mexico (records not yet published) and this species has an obsolete mediofacial ridge and middle tooth on palm of gnathopod 2 male adults. Gulf of Tehuantepec is a locality with heterogeneous habitats, useful in sheltering many similar intertidal forms; this group of similar forms increases the difficulty of identifying the species, principally females and juveniles, specifically of genus Elasmopus. An example of this: the male of Elasmopus oaxaquensis n. sp. shares some characters (e.g. telson, uropod 3) with the female E. ecuadorensis Schellenberg, figured from the Galapagos Islands. Also, the female of Elasmopus oaxaquensis n. sp. shares some characters (e.g. telson, uropod 3) similar to male of Elasmopus serricatus illustrated from the Gulf of California. This could confirm the hypotheses of Barnard (1979) that “on the Pacific are (sic) a mark of speciation” According to Barnard (1979), these characters that have highest taxonomic value are the gnathopod 2 and telson. However, these characters in Elasmopus oaxaquensis n. sp. and E. serricatus are observed as highly variable in varying degrees between the samples from California, Gulf of California and the Gulf of Tehuantepec; probably it is a complex of species. Thus, a regional revision is necessary to know the limits of the range of variation between these species.
oaxaquensis n. sp.
Character/ species E. serricatus E. serricatus Elasmopus oaxaquensis n. sp.
Barnard, 1969a Barnard, 1979
Locality La Jolla, California Puerto Peñasco, Gulf of Playa del Amor and Aguete,
California Oaxaca
Body length 8.0 mm 7.91 mm 7.6 mm
description: Published as part of García-Madrigal, María Del Socorro, 2010, Littoral Maeridae and Melitidae (Amphipoda: Gammaridea) from the Gulf of Tehuantepec, Mexico, pp. 1-51 in Zootaxa 2623 on pages 29-31, DOI: 10.5281/zenodo.198142