Notes on two shallow water isopods (Crustacea: Peracarida: Isopoda: Idoteidae) from Kino Bay, Gulf of California, Mexico

Abstract

Two species of isopods of the family Idoteidae were collected in the same sample, among sea grasses, in the northern Gulf of California, Mexico. The first species, Synidotea harfordi Benedict, 1897, was more abundant (46 specimens) than the second species, Eusymmerus antennatus Richardson, 1899 (eight specimens). Synidotea harfordi has previously been considered uncommon in the Gulf of California, and more like a component of warm-temperate to colder-water fauna. The male of E. antennatus has not been illustrated but SEM photographs are provided and show angular margins of the first three pereonites and a sharply bent lateral margin of the telson. Females also have angular first pereonites. All previous illustrations show rounded pereonites margins. Buccal appendages of E. antennatus are illustrated and compared with previous descriptions.

Key Words
Isopoda; western Mexico; sea grasses

Isopods are common inhabitants of marine vegetation, including algae and sea grasses, which they use as shelter and food (Boström and Mattila, 1999; 2005). They play an important role in fragmentation of vegetation and its incorporation into the trophic webs (Robertson and Mann, 1980). Idoteidae are also important prey of larger predators such as fishes (Wallerstein and Brusca, 1982).

Idoteidae of the Gulf of California were reviewed by Brusca and Wallerstein (1977) who listed eight species in four genera. Two years later, the same authors reported a total of 11 species and proposed a key to the species known from the Gulf of California (Brusca and Wallerstein, 1979). Espinosa-Pérez and Hendrickx (2001) included 13 species of Idoteidae for the entire tropical eastern Pacific (western Mexico to northern Peru). Of these, all, except Edotia sublittoralis Menzies and Barnard, 1959, have been recorded in the Gulf of California at that time. More recently, Brusca et al. (2005) reported 13 species from the Gulf of California including a 13th species, Idotea metallica Bosc, 1802, which has not been reported in previous compilations.

During sampling in Kino Bay, in the northern Gulf of California, many crustaceans were collected among sea grasses. This material included two species of Idoteidae which are reported here.

Material and Methods

Specimens were collected with a dredge ca. 40 cm wide and 15 cm high, at depths of ~0.5−1.2 m, on the protected side of Alcatraz Island, Kino Bay. The dredge was fitted with a 0.5 cm mesh size net. The material was preserved in the field in a mild formaldehyde solution, later washed with sea water and conserved in 70% ethanol. In the laboratory, isopods were separated, identified, assigned a catalogue number, and kept in the holdings of the Regional Collection of Marine Invertebrates (ICML-EMU) in Mazatlán, Mexico. Measurements (total length) were obtained to the nearest 0.1 mm. Abbreviation: TL, total length.

Results and Discussion

Idoteidae Samouelle, 1819

Synidotea harfordi Benedict, 1897

Figure 1

Figure 1
Synidotea harfordiBenedict, 1897, male, TL 18.9 mm. A. Dorsal view. B. Detail of antenna 1, dorsal. C. Detail of cephalon, lateral.

Idotaea marmorataHarford, 1877: 117.

Synidotea harfordiBenedict, 1897: 402, fig. 13. -Richardson, 1899a: 849. -Richardson, 1899b: 269. -Richardson, 1905: 387-388, figs. 427-428. -Johnson and Snook, 1927: 290. - Schultz, 1969: 67. -Menzies and Miller, 1972: 16-18, fig. 6. -Brusca and Wallerstein, 1979: 260-261, fig. 3, 269 (key). -Austin, 1985: 581. -Espinosa-Pérez, 1999: 156. -Espinosa-Pérez and Hendrickx, 2001: 50 (list). -Espinosa-Pérez and Hendrickx, 2006: 242. -Brusca et al., 2001: 31 (list), fig. 91. -Brusca et al., 2005: 137 (list).

Synidotea hartfordi. -Wallerstein, 1980: 338. -Vargas et al., 1985: 234.

Material examined. Alcatraz Island, Kino Bay (28°48'56"N 111°57'51"W), Sonora, Mexico, 25 males (TL 7.8-20.6 mm) and 21 ovigerous females (TL 11.1-13.3 mm), 8 March 2007, 0.5-1.2 m depth, among sea grasses (ICML-EMU-12093).

Distribution. Magdalena Bay (type locality). Oregon and Morro Bay, California, USA. Cedros Island, Baja California, Mexico. Gulf of California, Mexico: Chivato Point, near Santa Rosalia, Baja California Sur; Estero del Soldado, Guaymas, and Bacochibampo, Sonora; Chamela, Jalisco; Acapulco, Guerrero. Gulf of Nicoya, Costa Rica (a single record). Introduced in Japan (Richardson, 1905; Menzies and Miller, 1972; Brusca and Walerstein, 1979; Vargas et al., 1985; Espinosa-Pérez, 1999; Brusca et al., 2001, 2005).

Remarks. The illustration by Richardson (1905; dorsal view and maxilliped) was of poor quality. Menzies and Miller (1972) provided a detailed series of illustrations of S. harfordi, including a dorsal view, and figures of pereopods 1 and 7, buccal appendages (mandible, maxilla 1 and 2, maxilliped), appendix masculina, and pleopods 1 and 2. Other illustrations were provided by Brusca and Wallerstein (1979, dorsal view and maxilla 2), and Brusca et al. (2001; dorsal view), but were not very detailed.

The material examined herein (Fig. 1) fits well the description of Menzies and Miller (1972). Pairs of setae illustrated on the last antenna 1 article (Fig. 1B) by these authors are aesthetascs. With a total of 46 specimens collected in a single seagrass sample during this study, S. harfordi does not appear to be as uncommon as previously reported for the Gulf of California (Brusca & Wallerstein, 1979), at least in its northern part. Males and females were found in roughly the same number, and all females were ovigerous. Menzies and Miller (1972) emphasize that the thermal distribution of S. harfordi ranges from warm-temperate to colder waters at 34°30'N. Therefore, the presence of this species in Kino Bay, where shallow-water summer temperatures can be in the range of 25−30°C, is noteworthy.

Eusymmerus antennatus Richardson, 1899

(Figures 2, 3)

Figure 2
Eusymmerus antennatusRichardson, 1899. A-C, male, TL 7.5 mm; D, female, TL 8.6 mm. A. Dorsal view. B. Same, dorsal view of cephalon and first pleonite. C. Same, cephalon, lateral view. D. Antenna 2 distal article. E. Detail of tergite of pereonite 3, showing minute scales. F. Dorsal view.

Figure 3
Eusymmerus antennatus Richardson, 1899, male TL 13.8 mm. A. Pereiopod 1. B. Pereiopod 5. C. Maxilliped and tip of endite with terminal setae omitted. D. Tip of maxilla 1 exopod and endopod. E. Left mandible.

Eusymmerus antennatusRichardson, 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 pereonite 1 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.

Acknowledgments

Thanks to Philippe Willenz for his invitation and to Julien Cillis, SEM service, Institut Royal des Sciences Naturelles de Belgique, for taking and processing the SEM photographs of figure 2. The author also thanks Mercedes Cordero Ruiz for editing figures 1-3.

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Publication Dates

• Publication in this collection
  03 Dec 2018
• Date of issue
  2018

History

• Received
  09 Mar 2018
• Accepted
  29 June 2018