Elasmopus vachoni Mateus and Mateus 1966
Creators: name: Gouillieux, Benoit
name: Guerra-García, Jose Manuel
name: Sorbe, Jean Claude
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Melitidae
Elasmopus
Elasmopus vachoni

description: Elasmopus vachoni Mateus and Mateus, 1966
Figs 1–6
Elasmopus vachoni Mateus and Mateus 1966: 181 (original description), fig. 7.— Afonso, 1976: 14, fig. 1.— Mateus and Mateus 1985: 66, fig. 24.— Menioui and Ruffo 1988: 165, figs 2–5.— Bellan-Santini et al. 1998: 839, fig. 566.— Vader and Krapp-Schickel 2012: 1201 (in key).— Gouillieux and Sorbe 2015: 116 (in key).
Elasmopus antennatus.— Ledoyer 1967: 419 –422.— Cejas et al. 1983: 321, fig. 3.
Material examined. Male, 6.34 mm (BL), (MNHN-IU-2014-17481), Tarifa Island, station ' Punta Marroqui’, Spain (36°00’00.70”N, 5°36’37.50”W); male, 6.11 mm (BL), (MNHN-IU-2014-17482), dissected specimen (19 slides); male, 4.21 mm (BL), (MNHN-IU-2014-17483), dissected specimen (21 slides); Male, 5.21 mm (BL), (MNHN-IU-2014-17484), rocky intertidal, on Gelidium corneum (Hudson) J.V. Lamouroux. 9 September 2006, collector J.M. Guerra-García.
Description. Head. Eyes subovoid; lateral cephalic lobe broad, truncated; anteroventral corner subquadrate, notched. Antenna 1 longer than antenna 2; peduncular article 1 shorter than article 2, without posterodistal robust seta; article 3 shorter than article 2; accessory flagellum short, 3-articulate, distal article tiny; flagellum with 12 articles. Antenna 2 peduncular article 2 cone gland reaching distal end of article 3, article 4 shorter than article 5; flagellum with 6 articles. Upper lip distally rounded, with many setules on distal margin. Mandible incisors asymmetrical, with smooth cutting edge and 2 apicomedial cusps; setal row with 4 serrulate setae (one of them hidden in Fig. 3 C); molar well developed, triturative; palp well developed, 3-articulate; article 1 longer than broad, shorter than article 2; article 2 slightly shorter than article 3, submarginal long and short setae on distal half; article 3 falcate, twice long as broad, distal two-thirds with comb-like row of setae, increasing in length distally, with 3 distal long simple setae. Lower lip with many small setae on apical and inner margins of inner and outer plates; one tiny duct on distomesial margin of outer plates; mandibular lobes elongated and pointed. Maxilla 1 inner plate elongate and narrow, slightly tapering distally, with 2 apical setae (a long plumose one and a short simple one) and many lateral simple setae on mesial margin; outer plate with few subapical simple setae on mesial margin, 7 distal stout setae (difficult to observe), innermost one simple with about 10 setules, other ones multicuspidate; palp 2- articulate, article 2 longer than article 1, with long simple and plumose setae on distal part. Maxilla 2 with outer plate slightly broader and longer than inner plate; inner plate with short simple setae on proximal part, 1 subapical long plumose setae, long serrate and many shorter setae in facial and marginal apical rows; outer plate with long serrate setae in facial and marginal apical rows. Maxilliped palp article 3 with small distal protuberance apically covered with many setules.
Pereon. Gnathopod 1 subchelate; coxa anteroventral corner slightly produced, rounded, anterior margin slightly concave; basis with long setae on posterior margin and a subdistal tuft of serrate setae on posterodistal corner, inner face with 2 clusters of 2 strong robust setae; ischium with subdistal tuft of setae on posterodistal corner; merus with subdistal long and short setae; carpus about 1.4 x as long as broad, slightly shorter than propodus, with many clusters of simple and serrate setae on posterior margin, inner face with long plumose setae (not drawn); propodus palm slightly convex, edge laminar and transversally striated, limited posteriorly by 2 robust sensory setae (1 on each face), outer face with submarginal row of short setae ending in one robust sensory seta, inner face slightly more setose; dactylus with a simple and a pappose setae on proximal anterior margin. Gnathopod 2 subchelate; coxa regularly convex distally, posterior margin slightly concave; basis posterior margin with 2 short and 2 long simple setae and a subdistal cluster of serrate setae, anterior margin with few short and long setae; ischium with two setae on posterodistal corner; merus posterodistal corner slightly pointed, posterior margin sparsely setose, inner face with a subdistal long median setae (not drawn); carpus compressed, lobate, broader than long, with many clusters of simple and serrate setae on posterior projection and 1 robust setae on anterodistal corner; propodus expanded, densely setose along almost entire length (long setae with one row of hook-like setules), inner face densely setose with many subdistal clusters of simple setae arranged in anterior and posterior rows, palm concave, with weak excavation in which distal part of dactylus rests, delimited by few setae and 2 sensitive robust setae, subquadrate distomedial shelf with some simple setae and 2 rows of 3 sensitive robust setae (one row on each side); dactylus apically blunt. Pereopods 3–4 similar, except coxae; coxa 3 regularly convex distally, posterior margin slightly concave; coxa 4 posterodistal lobe slightly developed and rounded; posterior margin of basis with long and short setae; dactylus with 1 pappose seta on proximal anterior margin and 2 simple setae on posterior margin, near junction with nail. Pereopods 5–7 broadly expanded; coxae 5 and 6 with 2 or 3 robust and few small setae on posterior lobe; basis posterior margin straight (coxae 5–6) or convex (coxa 7), serrate with short setae, posterodistal corner rounded; carpus and propodus with clusters of sensitive robust setae on anterior margin; propodus not expanded posterodistally; dactylus with 1 pappose seta on proximal anterior margin and 2 simple setae on posterior margin, near junction with nail.
Pleon. Pleonites 1–3 dorsally smooth. Epimera 1–3 with short robust setae along distal margin, some arranged in clusters. Epimera 1–2 posterodistal corner with small tooth. Epimeron 3 distal margin convex, posterodistal corner with small tooth, posterior margin straight and smooth. Urosomites 1–3 dorsally smooth. Uropod 1 peduncle longer than rami, with robust basofacial seta; rami subequal. Uropod 2 peduncle subequal in length to outer ramus; outer ramus shorter than inner ramus. Uropod 3 peduncle as long as outer ramus, as long as broad; rami short (length 1.5–1.8 x breadth), 1-articulate, distally truncated, with long and short apical robust setae; inner ramus shorter than outer ramus. Telson two-thirds cleft, broader than long, outer margin with two short submarginal pappose setae; each lobe with inner and outer subequal apical cusps, both apically acute; distal indentation with 1 small pappose setae and 3 apical robust setae, shortening from outer to inner (the outer one subequal to telson length).
Morphological variations. The material herein examined contained only 4 males (BL between 4.21 and 6.34 mm). In these specimens, some morphological variations were observed on the number of articles on antenna 1 main flagellum (12–15 articles), on antenna 2 flagellum (6–7 articles), on gnathopod 2 shelf (3–4 sensory robust setae) and on the ornamentation of antenna 1 peduncle article 1, with (MNHN-IU-2014-17482 and MNHN-IU- 2014-17484 specimens) or without (MNHN-IU-2014-17481 specimen) one posterodistal robust seta (antennae 1 lost in the fourth specimen).
Remarks. Vader and Krapp-Schickel (2012) published a world key to Elasmopus species, based on adult males. In this key, some updating is required on the shape of epimeron 3 posterodistal corner of E. vachoni. Epimeron 3 was neither described nor drawn in the first descriptions of the species (Mateus and Mateus 1966; Afonso 1976; Mateus and Mateus 1985). Subsequently, Menioui and Ruffo (1988) gave the only available drawing of this epimeral plate, showing a slightly pointed posterodistal corner as also observed in the present work. However, in couplet 51 of Vader and Krapp-Schickel’s key, E. vachoni is classified in the species group characterized by “Ep3 posterodistal corner with strong tooth or clearly acute”. According to the previous description by Menioui and Ruffo (1988) and to our own observations, we propose to place E. vachoni in the other species group of couplet 51 (“Ep3 posterodistal corner with small tooth, etc …”) and modify their key as follows:
79. Gnathopod 2 merus acutely produced, propodus shelf slightly developed, without stout setae; telson lobes with more than 3
stout setae..................................................................... E. antennatus (Stout, 1913) * - Gnathopod 2 merus slightly produced, propodus shelf well developed with 3 or 4 stout setae; telson lobes with 3 stout setae..
...................................................................... E. vachoni Mateus & Mateus, 1966 ** * according to Barnard description, 1962
** according to the present description
Moreover, E. gracilis Schellenberg, 1938 can no longer be maintained in couplet 79 as originally proposed by Vader and Krapp-Schickel (2012) because its gnathopod 2 dactylus is clearly longer than half propodus (see descriptions of Schellenberg 1938 and Myers 1986).
According to Mateus and Mateus’s original description (1986) as well as in the subsequent one by Menioui and Ruffo (1988), the antenna 1 of E. vachoni has a bi-articulate accessory flagellum whereas a third tiny article has been detected on this flagellum in the case of three specimens of our collection (antennae 1 lost in the fourth specimen). Such a morphological difference between males from distinct geographical areas is certainly related to their growth stage (4 mm specimen in Mateus and Mateus 1966; 5.5 mm specimen in Menioui and Ruffo 1988; 5.21 to 6.11 mm BL in the present work).
As in the original description, the male specimen (MNHN-IU-2014-17482) herein examined showed many long pectinate setae all along the posterior margin of gnathopod 2 propodus (hook-like short setules regularly arranged on the half distal part of these setae). However, these hooked setules were only observed upon one side of each seta, on the contrary to the first descriptions (Mateus and Mateus 1966; Afonso 1976) showing both one-sided and two-sided pectinate setae. Curiously, such pectinate setae were not mentioned in subsequent descriptions (Menioui and Ruffo 1988; Bellan-Santini et al. 1998).
Despite some morphological variations with the previous descriptions, we conclude that the Tarifa specimens herein examined actually belong to E. vachoni Mateus and Mateus, 1966. Furthermore, according to available descriptions, we think that all the E. antennatus specimens mentioned from European waters (Madeira Island: Ledoyer, 1967; Canary Island: Cejas et al. 1983) must be attributed to E. vachoni.
description: Published as part of Gouillieux, Benoit, Guerra-García, Jose Manuel & Sorbe, Jean Claude, 2017, Additional records of Elasmopus vachoni Mateus & Mateus, 1966 (Crustacea: Amphipoda: Maeridae) from European waters (Tarifa, southern Spain), pp. 561-571 in Zootaxa 4299 (4) on pages 562-569, DOI: 10.11646/zootaxa.4299.4.6, http://zenodo.org/record/837087