Caprella equilibra Say 1818

Caprella equilibra Say, 1818

(Figure 2)

Caprella equilibra Say, 1818; Steinberg and Dougherty, 1957: 273–274, figs 1, 2. McCain, 1968: 25–30, figs 12, 13. McCain and Steinberg, 1970; Cavedini, 1982; Lazo-Wasem and Gable, 1987: 335–336, fig. 10. Krapp-Schickel, 1993: 782–783, fig. 533. Serejo, 1998; Ortiz et al., 2002, fig. 21. Foster, Thomas, et al., 2004: 162, 167–168, fig. 7. Diaz et al., 2005: 3–4, fig. 4. Winfield, Escobar-Briones, et al., 2007: 44, fig. 14. Guerra-García and Ros, 2012: 76–78, fig. 2.

Caprella aequilibra Mayer, 1882: 45, pl. 1, fig. 7, pl. 2, figs 1–11, pl. 4, figs 20–25, pl. 5, figs 16–18. Chevreux and Fage, 1925: 455, fig. 433.

Caprella bermudia Kunkel, 1910: 108–110, fig. 42. Lazo-Wasem and Gable, 1987: 335–336, fig. 10.

Station 33, two males, six females, two juveniles (one male and one female from this station used for figures), BRTC 2–9489.

Charleston, South Carolina.

Cosmopolitan (McCain 1968; Krapp-Schickel 1993).

MEX: Tamaulipas and Veracruz continental shelf (Escobar-Briones and Winfield 2003); Mexican ridges and Sigsbee abyssal plain at southwest (Winfield et al. 2006). USA: Port Aransas (Steinberg and Dougherty 1957); Port Isabel; Galveston; Grand Isle; Panama City (McCain 1968); Louisiana Offshore (Lewbel et al. 1987); Coast of Mississippi; St Andrew Bay (Foster, Thomas, et al. 2004); Port Aransas Offshore (present study).

Caprella equilibra has been found on seagrasses, green and red algae, sponges, hydroids, alcyonarians, bryozoans, gorgonians, and ascidians (McCain 1968; Gable and Lazo-Wasem 1987; Alarcón-Ortega et al. 2012). It has also been found in plankton samples, artificial substrata (Lewbel et al. 1987; Takeuchi and Sawamoto 1998; present study) and on the carapace of the loggerhead sea turtle Caretta caretta (Caine 1986). The depth range reported is shallow water extending to 3700 m (Winfield et al. 2006; Winfield and Escobar-Briones 2008; LeCroy et al. 2009).

In the Gulf of Mexico, C. equilibra is similar to C. danilevskii because both lack a cephalic spine. However, these species can be easily separated because C. equilibra has a ventral spine between the bases of the second gnathopod, whereas C. danilevskii does not.

A recent morphological study of C. equilibra in southern Spain has revealed intraspecific variation in the female abdomen, even within the same population (Guerra-García and Ros 2012). According to the diagnosis of the genus Caprella by McCain (1968), the abdomen of males is provided with a pair of uni- or bi-articulate appendages and a pair of lobes; females only have the pair of lobes and lack appendages. However, a few females of C. equilibra found in southern Spain were provided with abdominal appendages. The study provided evidence supporting the idea that the abdominal appendage is a polymorphic and symplesiomorphic character in Caprella and Metacaprella Mayer, 1903 (another genus with the same morphological variation), and that Metacaprella is not a valid genus (Guerra-García and Ros 2012).