Eirene

Júnior, Miodeli Nogueira, 2012, Gelatinous zooplankton fauna (Cnidaria, Ctenophora and Thaliacea) from Baía da Babitonga (southern Brazil), Zootaxa 3398, pp. 1-21 : 13

Eirene sp. (young E. viridula ?)

(Figs. 28–30)

Material examined. 01/24/2008: one medusa ( MZUSP 1617); 04/25/2008: one medusa ( MZUSP 1616).

Description. Umbrella transparent, flat (MZUSP 1616) or somewhat globular (MZUSP 1617), with very thick jelly especially at the apex. The gastric peduncle is very thick and short, with length of 0.8 mm in the medusa with 6 mm in bell diameter (MZUSP 1617) and 1.4 mm in the medusa with 6.5 mm (MZUSP 1616). The peduncle passes beyond the bell margin since the sub-umbrellar cavity is almost absent. Manubrium short (0.5 and 1 mm in length respectively), with four relatively short and pointed lips. Gonads small, elongated to slightly oval on the four radial canals near the margin, but not in contact with the ring canal; 23 or 28 tentacles with round or conical bulbs with different sizes. Almost one rudimentary bulb between every tentacle. All bulbs without lateral cirri and with an adaxial excretory pore. Nearly one very small statocyst between every bulb (rudimentary or not).

Remarks. The two medusae reported here clearly belong to the genus Eirene Eschscholtz due to the presence of a distinct gastric peduncle, tentacular bulbs with excretory pores, complete absence of cirri and the presence of several closed statocysts ( Russell 1953; Kramp 1961; Bouillon 1999; Bouillon et al. 2004, 2006). Within this genus 22 species are recognized ( Schuchert 2009a; Du et al. 2010; Huang et al. 2010) and the medusae studied here resemble that of E. viridula (Péron & Lesueur) (see Russell 1953; Bouillon 1999), the only species of the genus recorded at the Brazilian coast and in the South Atlantic as well ( Bouillon 1999; Migotto et al. 2002). However both individuals sampled are still young with small, developing gonads and differ from E. viridula in some characteristics: i) the peduncle is relatively shorter, being not larger than ¼ of bell diameter in the present material; ii) their gonads are short, elongated-to-oval-shaped placed on the distal fourth of radial canals, while those of E. viridula are linear across the whole radials canals; iii) all accounts of E. viridula mention evident adaxial excretory papillae on both tentacular and rudimentary bulbs, while the bulbs of the present material all have a distinct adaxial excretory pore but lack the papillae.

These differences may all be attributed to the early stage of development of the two medusae examined. A detailed comparison of the early stages of E. viridula from Russell (1953) shows several similarities with the present material, including the initial position of the gonads. However, Eirene medusae commonly undergo a considerable morphological change throughout development (e.g. Kubota & Horita 1992; Guo et al. 2008) and the only record of E. viridula from the Southwestern Atlantic is several thousand kilometers northwards (off Amazonas River; Alvariño 1968), therefore more material is needed to confirm the identification of this species.

Distribution. The genus Eirene is widespread worldwide (except Arctic and Antarctic regions), as also is E. viridula ( Bouillon 1999) . In Brazil there is a single record of E. viridula on its North Coast (~0° Lat; Alvariño 1968) and the present investigation is the first record of the genus Eirene on the south Brazilian coast.