Gossea brachymera Bigelow, 1909

Júnior, Miodeli Nogueira, 2012, Gelatinous zooplankton fauna (Cnidaria, Ctenophora and Thaliacea) from Baía da Babitonga (southern Brazil), Zootaxa 3398, pp. 1-21 : 14-15

Gossea brachymera Bigelow, 1909

(Figs. 36–39)

Gossea brachymera Bigelow 1909: 103 –105, pl. 30 figs 1–10, Acapulco ( Mexico).

Octobulbacea montehermosensis Zamponi 1983b: 176 –178, pl. 1 figs 2–3, Monte Hermoso ( Argentina). [syn. nov.]

Material examined. 10/18/2007 —one young medusa ( MZUSP 1614); 11/16/2007 —one young and four adult medusae; 05/26/2008 —one young medusa; 07/10/2008 —one young medusa; 08/08/2008 —three young medusae ( MZUSP 1615); 06/19/2009 —one young and one adult medusa.

Description. The two smaller medusae (0.6 and 1.2 mm wide) were dome-shaped (almost as high as wide) with relatively thin mesoglea (Fig. 36). Stomach short, without peduncle or evident lips or warts on the mouth. No signs of gonads could be observed. Four perradial and four interradial large swollen pads with two moniliform tentacles each (Fig. 36). Eight additional adradial smaller tentacles on bell margin.

Among the five medusae between 2 and 4 mm in bell diameter, only a single one was in a very good state (Fig. 37). Its mesoglea is considerably thicker, representing almost 30% of bell height. Tentacle arrangement and morphology fits the description above (Fig. 38), except that small pads could be noticed at the base of the adradial tentacles. The manubrium differed from the smaller medusae described above by being relatively longer (almost ½ of bell cavity) with four evident lips and numerous warts along its margin. Rudiment of gonads can be observed in the basal part of radial canals (Fig. 39 arrows). The other analyzed G. brachymera medusae within 2 and 4 mm (n = 4) had the bell damaged, not allowing comparison of general shape, mesoglea thickness or shape and size of the manubrium. Some characters, however, such as tentacle morphology and arrangement and gonads could be clearly distinguished, differing from the described above only by the gonads being slightly more developed in two of them.

A single individual 4.2 mm wide was very similar to these ones, but the beginning of a gastric peduncle already could be clearly seen and the gonads were more developed and already advancing on the proximal ¼ of the radial canals. Also, eight small tentacles interspersed among the other ones were present on the margin. The adults of G. brachymera were described in detail by Bigelow (1909) and Russell (1938).

Remarks. The observed specimens in different developmental stages show that G. b r a c h y m e r a passes through considerable morphological changes during its growth, mainly relating to the peduncle, absent in juveniles, the mouth and the general shape of umbrella and mesoglea thickness, beyond the number of tentacles and presence of gonads. Based on tentacle morphology, Genzano et al. (2008) suggested that Octobulbacea montehermosensis Zamponi, 1983 , considered endemic from the Argentinean coast, is in fact juvenile G. brachymera . The present observations on the young stages of G. brachymera strongly support this view. The animals described herein completely match Zamponi’s (1983b) description, except by the gonads which he states to be in the interradial base of the manubrium walls. However, this location is not evidenced by its drawing and perhaps the author has misinterpreted it. Although the types were lost ( Genzano et al. 2008), the very close resemblance strongly indicates that O. montehermosensis is not a valid species, and instead should be regarded as a junior synonym of G. b r a c h y m e r a. Since this is the only species of the genus Octobulbacea , this generic name must also be abandoned, regarded as synonym of Gossea .

Distribution. Gossea brachymera is mostly common in or near estuaries and/or rivers, occurring on both sides of the American coasts. This species was recorded on the Mexican Pacific coast, Gulf of Mexico, Strait of Magellan and Argentina ( Bigelow 1909; Russell 1938; Vannucci & Tundisi 1962; Segura Puertas et al. 2003). In Brazil, Navas-Pereira (1981) recorded a single individual on the Rio Grande do Sul Shelf, therefore the present record extends northwards its known distribution in Brazil.

FIGURES 37–40. Young stages of Gossea brachymera Bigelow, 1909 ; lateral view of young medusae (37); lateral view of a medusa with incipient gonads (38), detail of its margin and tentacles (39), and of its manubrium and rudiments of gonads (arrows) beginning to appear (40).