Hebella sp.

Hebella sp.

( Fig. 4E–G View FIGURE 4 ; Table 2)

Material examined. BISSAU-0810, stn BS191, 10º18'25"– 10º19'20"N, 16º08'47"– 16º08'47"W, 24–25 m, 3-XI-2008: two colonies without gonothecae, growing on unidentified hydroids.

Description. Hydrorhiza tubular, from which arise scattered, slightly undulated, pedicels varied in length, each bearing atop a hydrotheca.

Hydrotheca longer than broad, cylindrical, with almost parallel walls narrowing basally. Hydrothecal walls with six well-developed transverse ridges. Aperture everted, circular, margin smooth. Polyps with 10–12 tentacles.

Gonothecae not observed.

Remarks. The morphology of this hydroid is similar to that of Hebella venusta ( Allman, 1877) and H. muscensis Millard & Bouillon, 1975 , especially with respect to the undulated condition of the hydrothecal walls; however, several features convinced us that this material represents a new species.

The cnidome of H. venusta was studied by Galea (2010), but Galea (2013) commonly found four types of nematocysts in hydroids of this genus; however, in our material only two different types occurred ( Fig. 4G View FIGURE 4 ), probably due to the poor condition of the colonies. Notwithstanding, their dimensions differ from those of the material described by Galea (see Table 2). We also compared our measurements with those given by Galea (2013) for his four unnamed species from Martinique; however, all his measurements exceed those obtained by us.

The hydrothecae of H. muscensis are curved to one side, with an obliquely-set aperture and an asymmetrical basal part ( Millard & Bouillon 1975); however, in our specimens, the hydrothecal walls are strictly parallel and have the same length on both sides, and the base is symmetrical ( Fig. 4E–F View FIGURE 4 ). Furthermore, H. muscensis is only known from the Seychelles and Papua New Guinea.

Hydroids belonging to the genus Hebella are hardly distinguishable from members of Anthohebella Boero, Bouillon & Kubota, 1997 and Staurodiscus Haeckel, 1879 ( Boero et al. 1997; Bouillon et al. 2006). However, Anthohebella is known as a genus whose hydrothecae are borne on short pedicels ( Boero et al. 1997: 23), while in Staurodiscus the hydrothecae are characterized by being “sharply or slightly oblique” ( Bouillon et al. 2006: 329). In none of the hydrothecae from our colonies these characters were met with. For these reasons, and also due to the great morphological similarity of our colonies with the fertile material described by Galea (2010), we believe that our material belongs undoubtedly to the genus Hebella .

Our finding represents the first record of this species for Guinea-Bissau.

Biology. Both colonies were found growing on unidentified hydroids.

Distribution. This species, only known from Guinea-Bissau, was collected at a single station at 24–25 m depth.