Hebella venusta Allman 1877

Hebella venusta (Allman, 1877)

(fig. 4E–G, table 1)

Lafoea venusta Allman, 1877: 11, pl. 6 figs 2, 3. Hebella venusta ― Calder, 1991: 41, fig. 25.

Material examined. Stn.9: 21.11.2009, 21 m—a rich, sterile colony on stems of Thyroscyphus marginatus (Allman, 1877). Stn.10: 0 2.12.2009, 18 m—a few hydrothecae, but no gonothecae, on stems of Eudendrium sp. Stn.11: 30.11.2009, 15–18 m—several sterile colonies on stems of T. marginatus. Stn.12: 30.11.2009, 12– 15 m—several sterile colonies on stems of T. ramosus Allman, 1877. Stn.13: 19.11.2009, 13 m—small, isolated, sterile colonies on T. marginatus; 0 3.12.2009, 10–15 m—several colonies creeping on T. marginatus, two gonothecae found (MHNG-INVE-68720).

Description. For synonymy and a description of the trophosome, see Calder (1991). Nematocysts: microbasic mastigophores (6.3–6.4) × (1.8–2.0) µm (undischarged capsules). Two empty gonothecae present. Gonothecae arise directly from hydrorhiza, cornucopia-shaped, with irregularly undulated walls, tapering imperceptibly into short, indistinct pedicel (dimension in table 1). Aperture truncated, roughly rounded, widely opened; rim of one gonotheca (fig. 4F, left) with apparently at least 3 triangular cusps separated by large, shallow embayments, possibly corresponding to insertion of putative opercular flaps.

Remarks. The gonothecae of this species are described herein for the first time. Since only a couple of gonothecae3 were found in the present material, and they are mostly covered by silt particles and devoid of gonophores, additional specimens are required to gain more knowledge of the reproduction of this species. It is here kept in the genus Hebella Allman, 1888, pending the discovery of its gonophores.

3. The gonothecae are expected to occur more frequently than thought among the colonies because they can be easily overlooked during routine examination of samples.

TABLE 1. Comparative measurements of Hebella venusta (Allman, 1877) and related species, in µm. 1Approximate

dimensions calculated from fig. 7 in Boero et al. (1997).

Boero et al. (1997) considered H. venusta as doubtful, arguing that its available descriptions could apply to either Anthohebella tubitheca (Millard & Bouillon, 1975) or Hebella muscensis Millard & Bouillon, 1975, an opinion not shared here. Based on the available measurements, it is possible to demonstrate that H. venusta is morphometrically different from its relatives: its hydrothecae are comparatively smaller and the pedicels much longer (see table 1), and the ratio length/width of hydrotheca is always less. Additionally, the remoteness of geographical locations of both A. tubitheca and H. muscensis points towards separate species.

Additional hydroids with transversely annulated hydrothecae resembling those of H. venusta are: H. brochii (Hadži, 1913), H. corrugata (Thornely, 1904), H. costata (Bale, 1884), Scandia corrugata Fraser, 1938a, and S. expansa Fraser, 1938b.

The gonosomes of both H. corrugata and H. costata are unknown and they could not be confidently separated morphologically based on sterile specimens. The decision made by Millard & Bouillon (1975) to consider them as nomina oblita is unfortunately untenable, according to the reasons evoked by Calder (1991). Bale’s (1884) species was recently redescribed by Watson (2000), yet based on sterile material.

Hebella brochii, reportedly endemic to the Mediterranean, grows specifically as an obligate epibiont of Synthecium evansi (Ellis & Solander, 1786), and its hydrothecae are provided basally with a perisarc diaphragm (Boero et al. 1997).

The eastern Pacific species S. corrugata and S. expansa, though briefly described by Fraser (1938a, b, respectively), could be distinguished from H. venusta, as follows: the former has very short hydrothecal pedicels and its barrel-shaped gonothecae are smaller than the hydrothecae; the latter species has hydrothecal pedicels as long as the hydrothecal depth, while in H. venusta the hydrothecae are always longer than their respective pedicels.

Caribbean records. Anguilla (Jäderholm 1903), Trinidad (Fraser 1943), St. Thomas (Vervoort 1968), Belize (Spracklin 1982).

World distribution. Dry Tortugas (Allman 1877, Leloup 1935), off Zoblos Island (Clarke 1879), Bahamas (Nutting 1895, Fraser 1943), Bermuda (Ritchie 1909, Bennitt 1922, Calder 1991), off W Florida (Ritchie 1909, Fraser 1943), Venezuela (Leloup 1937), Belize (Spracklin 1982), Colombia (Flórez González 1983).