Cnidostoma fallax Vanhöffen, 1911

Júnior, Miodeli Nogueira, 2012, Gelatinous zooplankton fauna (Cnidaria, Ctenophora and Thaliacea) from Baía da Babitonga (southern Brazil), Zootaxa 3398, pp. 1-21 : 8-10

Cnidostoma fallax Vanhöffen, 1911

(Figs. 21–24)

Material examined: 01/24/2008 —two medusae ( MZUSP 1628); 04/25/2008 —one medusa; 05/26/2008 —one medusa ( MZUSP 1627).

Description. Umbrella transparent, conical, measuring 0.6–0.8 mm high and 0.5–0.8 mm wide; mesoglea thick in the apex, representing up to ~35% of bell height, and thinner laterally. Four well-developed bulbs, each with an adaxial ocellus (missing in some bulbs). Each bulb with a single tentacle. Manubrium tubular, of variable extension, up to ½ of sub-umbrelar cavity. Medusoid buds on different developmental stages on manubrium walls without well-defined position. Mouth rim with four evident clusters of stalked cnidophores in perradial position.

Remarks. The four sampled medusae assigned to this species completely match the descriptions of C. fallax ( Vanhöffen 1911; Picard & Rahm 1954 as Archeoceania tournieri ; Kramp 1959a, b; Bouillon 1999 as Hydractinia tournieri ). The main characters of this species are the mouth with perradial clusters of stalked cnidophores, stomach with medusa buds, four large tentacle bulbs each with one tentacle and an adaxial ocellus. The gonads of this species were undescribed to date and were also absent in the studied medusae.

The systematic position of this quite unique medusa is controversial being already placed in Oceaniidae ( Picard & Rahm 1954) , Cytaeididae ( Kramp 1961) , Clavidae ( Bouillon 1985) and Hydractiniidae ( Kramp 1961 and Bouillon 1999 as Hydractinia tournieri ; Schuchert 2004, 2009a).

Distribution. There are only three previous records of this species ( Vanhöffen 1911; Picard & Rahm 1954; Kramp 1959b), on the Mouth of River Congo and in Ebrié Lagoon, Ivory coast, all of them in brackish waters with salinities ranging from 10 to 30 ( Picard & Rahn 1954). The medusae sampled herein, in salinities between 23 and 27, corroborate its brackish water habitat and represent the first record of this species in the southwestern Atlantic.

FIGURES 3–20. Examples of gelatinous zooplankton from Baía da Babitonga, S Brazil. Hydractinia sp.2 (3); Turritopsis nutricola (4); Corymorpha forbesi (5); young Moerisia inkermanica (6); Ectopleura dumortieri (7); Cirrholovenia tetranema (8); Eucheilota duodecimalis , oral view (9); Abylopsis tetragona , eudoxid stage (10); Diphyes bojani , anterior nectophore (11); Muggiaea kochi , polygastric stage (12); Nanomia bijuga , colony with a single nectophore and the siphosome (13), detail of nectophore in upper (above) and lower (below) views (14); Cunina octonaria , oral view (15); Chrysaora lactea , ephyra (16); young Beroe ovata (17); Doliolum nationalis , lateral view of phorozooid (18), gonozooid (19) and old nurse (20).

FIGURES 21–24. Cnidostoma fallax Vanhöffen, 1911 . Lateral view of the medusa (21). Aboral view of manubrium with medusoid buds; notice buds in different developmental stages (22). Lateral view of manubrium showing buds and the cnidophores on mouth rim (23). Detail of the mouth rim with stalked cnidophores (24).