Eusymmerus antennatus Richardson 1899
Creators: name: Hendrickx, Michel E.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Idoteidae
Eusymmerus
Eusymmerus antennatus

description: Eusymmerus antennatus Richardson, 1899
(Figs. 2, 3)
Eusymmerus antennatus Richardson, 1899a: 852–853, figs.26–27. — Richardson,1989b:273; Richardson, 1905: 399–400, figs.445–446. — Schultz, 1969: 83, fig. 108. — Brusca and Wallerstein, 1977: 7, figs. 4, 5; — Brusca and Wallerstein, 1979: 269 (key). — Brusca, 1980: 237, fig. 12.27. — Vargas et al., 1985: 338. — Calderon-Aguilera and Campoy-Favela, 1993: 418. — Espinosa-Pérez and Hendrickx, 2001: 50 (list). — Espinosa-Pérez and Hendrickx, 2006: 241. — Brusca et al., 2005: 136.
Material examined. Alcatraz Island, Kino Bay (28°48’56”N 111°57’51”W), Sonora, Mexico, Sonora, Mexico, 5 males (TL 7.8–13.8 mm) and 3 ovigerous females (TL 8.6–9.3 mm), 8 March 2007, 0.5–1.2 m depth, among sea grasses (ICML-EMU-12092).
Distribution. Abreojos Point (type locality) and Eugenio Point, west coast of Baja California Sur; Puerto Peñasco, Algodones Bay and San Francisco Bay, Sonora; Mazatlán, Sinaloa; Sayulita and Raza Point, Nayarit; Chamela Bay, Jalisco; Santa Lucia Bay, Acapulco, Guerrero; and Salina Cruz, Oaxaca, Mexico. Gulf of Nicoya, Costa Rica (Richardson, 1905; Brusca and Wallerstein, 1977; Espinosa-Pérez, 1999; Brusca et al., 2005).
Remarks. The original description by Richardson (1899a) includes a dorsal view of a specimen and a figure of the maxilliped (republished, Richardson, 1899b). The same dorsal figure and a more detailed maxilliped illustration were used by Richardson (1905). In both cases, she did not mention the sex of the single specimen available. Brusca and Walerstein (1977) redescribed E. antennatus in details (female: dorsal view; antenna and antennula; pereiopods 1 and 5; maxilliped, maxilla 1 and 2, mandible; pleopods 1–5; uropods) since Richardson (1899a, 1899b, 1905) had not illustrated properly the appendages of this species. The dorsal figure of the female specimen in Brusca and Wallerstein (1977), later reproduced by Brusca (1980), is quite different from the illustration of Richardson (1899a, 1905) in that it is narrower, eyes are located dorso-laterally (instead of dorsally), it features a medial dorsal tubercle (not illustrated or reported in the original description), and the antero-lateral margin of pereonite1 extends anteriorly to the eye level (not overreaching the cephalon level in the original description). All illustrations of a female in dorsal view available to date clearly show antero-laterally rounded pereonite 1 and smoothly rounded lateral margin of all other pereonites, and a triangle-shape pleotelson with lateral margins regularly convex. The material from Kino Bay included both males and females. In both sexes the antero-lateral margin of pereonites 1–3 is clearly angular and the margin straight (Fig. 2A, F). In males, the pleotelson lateral margin has a sharp angle at about 2/3 of its length (Fig.2A), which is different from what is observed in females: lateral margins “tapering posteriorly to a rounded apex” (Brusca and Wallerstein, 1977). Females collected in Kino Bay (Fig. 2F) are also much narrower than previously illustrated.Pereiopods 1 and 3 of the Kino Bay specimens are similar (Fig. 3A, B) to those illustrated by Brusca and Wallerstein (1977), with bifid dactyls and with robust and weaker spines on the inner margin of the carpus of pereiopod 1. Distal article of antenna 1 (Fig. 2D) bears short, isolated setae and a tuft of terminal setae, as illustrated by Brusca & Wallerstein (1977). Tergites of pereonites are covered with minute scales (Fig. 2E), not reported previously for this species.
The buccal appendages (Fig. 3) fit well the redescription of E.antennatus by Brusca and Wallerstein (1977),although some small differences were observed. Maxilliped (Fig. 3 C) features a 4-segment setose palp and the endite is similar to that described by Brusca and Wallerstein (1977), with one short coupling hook, but terminal setae have pseudo-articulations. Maxilla 1 exopod has a similar number of large apical spines but these appear proportionally longer in the Kino material (Fig. 3D), and the endopod ends in 3 (instead of 2) “setose spines” which are actually plumose setae with pseudo-articulations (Fig. 3D). The left mandible is similar to the description provided by Brusca and Wallerstein (1977), including the additional 3-pointed “setose spine” between the incisor and the lacina mobilis (Fig. 3E).
The discovery of sympatric,reproducing populations of S. harfordi and E. antennatus in a coastal ecosystem in the northern Gulf of California brings additional information on the general distribution and abundance of these two species in the eastern Pacific.
description: Published as part of Hendrickx, Michel E., 2018, Notes on two shallow water isopods (Crustacea: Peracarida: Isopoda: Idoteidae) from Kino Bay, Gulf of California, Mexico, pp. 1-7 in Nauplius (e 2018027) (e 2018027) 26 on pages 3-6, DOI: 10.1590/2358-2936e201802710.1590, http://zenodo.org/record/14721064