Pectis Haeckel 1879

Genus Pectis Haeckel, 1879

Pectis Haeckel, 1879: 266; 1881a: 12; 1881b: 14.

Voragonema Naumov, 1971: 13 (syn. nov.).

Voragonema – Bouillon & Boero 2000: 69, 73. — Bouillon et al. 2006: 113, 121. — Antsulevich 2015: 717–718, 727, 773.

Rhopalonematid medusae with dome-shaped umbrella; exumbrella with numerous, Fne, meridional ridges; subumbrella pigmented; with gastric peduncle; manubrium with or without outer gastric pouches; mouth with 4 simple lips; 8 radial canals connect to the ring canal, the latter giving rise to a varied number of regularly- or irregularly-shaped centripetal canals; 8 narrow, elongated gonads, distally pendant, on the radial canals; tentacles very numerous, in superimposed rows, of two types: outermost large and solid, and innermost thinner, shorter and hollow; statocysts numerous and free.

When Haeckel (1879) described the genus Pectis, he notably emphasized the “eight genitalia in the course of the eight radial canals, between which blind centripetal canals run from the annular canal”. It will be shown in the next section that its type species, P. antarctica Haeckel, 1879, shows all the distinctive characters of the genus Voragonema Naumov, 1971, and in particular of V. laciniata Bouillon et al., 2001.

Reversal of precedence (ICZN Art. 23.9) for the generic name cannot be applied for the following reasons: the senior synonym, Pectis, has been used as a valid name after 1899 (e.g., Browne 1903: 29), so Art. 23.9.1.1. is not fulFlled; the junior synonym, Voragonema, has been used, to our knowledge, in only 22 out of the 25 published works etc., required to meet the conditions of Art. 23.9.1.2. The presumed valid name appears in: Naumov (1971), Bouillon (1985), Beliaev (1989), Larson & Harbison (1990), Larson et al. (1991), Bouillon (1993), Gili et al. (1998), Bouillon & Boero (2000), Bouillon et al. (2001), Thuesen (2003), Bouillon et al. (2006), Stepanjants et al. (2006), Stepanjants (2007), Pagès et al. (2007), Hosia et al. (2008), Lindsay & Miyake (2009), Lindsay & Pagès (2010), Zeidler (2012), Antsulevich (2015), Chen et al. (2015), Jamieson (2015), and Minemizu et al. (2015).

Consequently, the genus Pectis is taken as valid, and Voragonema is included in its synonymy. Presently, the genus contains four species, namely: P. antarctica, P. pedunculata (Bigelow, 1913), P. profundicola (Naumov, 1971), and P. tatsunoko (Lindsay & Pagès, 2010).

The diagnosis given above is based on that provided by Bouillon et al. (2006) for the genus Voragonema Naumov, 1971, and it is broadened so as to include the bell shape, the presence of meridional ridges on the exumbrella, the colored subumbrella, the shape of the gonads, and the types of marginal tentacles.

The gastric pouches are recognized as speciFc rather than generic features. Indeed, they are present in P. antarctica, but are lacking in both P. pedunculata and P. tatsunoko. It is unclear whether the eight wavy manubrial ridges reported by Naumov (1971) in P. profundicola represent the same anatomical structures.

Several authors (Bouillon et al. 2001; Lindsay & Pagès 2010) drew attention to several supposed “peculiarities” exhibited by the type species of the genus Voragonema, V. profundicola, notably:

1) the apparent lack of pigmentation of its subumbrella. Indeed, besides the transparent umbrella, the brown manubrium, and the colorless radial canals and tentacles, Naumov (1971) did not make any speciFc reference to the pigmentation of the subumbrella, though he stated that the colors exhibited by his species were typical of deep-water medusae. It is likely, however, that the color of the subumbrella in these species fades over time, as remarked on by Bigelow (1913) in P. pedunculata: “the pigmentation covered the entire subumbrella, though now it is intact over occasional patches only”. On the other hand, some species, such as P. tatsunoko, may be only lightly pigmented in life (“subumbrella pale roseorange”, Lindsay & Pagès 2010), and the color of Fxed specimens changes to nearly white-opaque (see Fig. 2 A in their paper).

2) the lesser number of marginal tentacles (ca 500, Naumov 1971), compared to that of P. antarctica (1000–1200), P. pedunculata (1000–2000), and P. tatsunoko (ca 1050) (Lindsay & Pagès 2010). However, it should be noted that the type of P. profundicola was a young, immature specimen, measuring only 1 cm high and 1.5 cm wide (Naumov 1971), while much larger individuals were obtained for P. antarctica (30 mm high and 35 mm wide), P. pedunculata (up to 31 mm high and 41 mm wide), and P. tatsunoko (14 mm high and 19 mm wide) (Lindsay & Pagès 2010). Since it is acknowledged that tentacles are added continually to the bell margin during the growth of the medusa, it is not surprising for there to be a lesser number in younger individuals compared to more aged ones.

3) the lack of gonads in the type. It is highly improbable that the gonads of this rhopalonematid medusa are formed elsewhere than along the radial canals.

The genus Pectis is immediately distinguished from its allies Benthocodon Larson & Harbison, 1990, Crossota Vanhöffen, 1902, and Vampyrocrossota Thuesen, 1993 through the presence of centripetal canals arising from the ring canal. It shares the presence of exumbrellar furrows with both Crossota and Vampyrocrossota, the occurrence of a gastric peduncle with Benthocodon, and the presence of statocysts, again, with Crossota.