Pectis antarctica Haeckel 1879

Pectis antarctica Haeckel, 1879

Fig. 5, Table 2

Pectis antarctica Haeckel, 1879: 266.

Voragonema laciniata Bouillon et al., 2001: 841, Fgs 4–5 (syn. nov.).

Pectis antarctica – Haeckel 1881a: 13, pls 5–6; 1881b: 15, pls 5–6. — Browne 1903: 29. — Maas 1906a: 484. — Kramp 1957: 46. — Beyer 1959: 128.

Ptychogastria antarctica – Maas 1906a: 493; 1906b: 19. — Mayer 1910: 375. — Vanhöffen 1912: 386. — Thiel 1932b: 478. — Kramp 1947: 5; 1957: 46; 1961: 241; 1968: 111, 174. — Bouillon & Boero 2000: 68. — Bouillon et al. 2006: 112.

Voragonema laciniata – Lindsay & Pagès 2010: 36–37.

According to Haeckel (1879, 1881a, 1881b), Pectis antarctica is a hydromedusa exhibiting the following characters: 1) bell nearly hemispherical; 2) exumbrella Fnely ribbed radially; 3) mesoglea moderately thick in the upper half, and comparatively thinner in the lower half; 4) eight radial canals connecting with the ring canal, the latter giving rise to 11–13 centripetal canals in each octant; 5) eight ovoid, convoluted gonads, extending along the proximal half of the radial canals; 6) a quadrangular manubrium provided with 8 pairs of outer, hollow, hemispherical pouches; 7) a strong, muscular velum; 8) a great number of solid marginal tentacles not arising in distinct clusters, but showing a certain regularity in their arrangement around the bell margin; 9) a continuous ring of nematocysts between the velum and the lowest row of tentacles; 10) the occurrence of a number of free, small, club-shaped statocysts with single, spherical statoliths.

In light of these characters, especially the presence of centripetal canals, also found in Ptychogastria polaris Allman, 1878, Maas (1906a) transferred Haeckel’s species to the genus Ptychogastria Allman, 1878. He acknowledged only “relative” differences in the arrangement of the marginal tentacles, and noted a remarkable reduction of the “mesenteries” (sic!) compared to both Pt. polaris and Pt. asteroides (Haeckel, 1879).

According to Browne (1903), the type specimen of Pe. antarctica “had been thoroughly dissected by Haeckel and just a few pieces placed back into a bottle”, an observation later conFrmed by Kramp (1957), who added that the “tiny fragments […] give no idea of the original appearance of the medusa”.

Earlier, Kramp (1947) acknowledged that “ Ptychogastria antarctica (Haeckel) differs too much from P. polaris to be placed in the same genus, or even in the same family”. Later, he added: “if Haeckel’s account […] is correct, this species is entirely different from P. polaris (including opposita)” (Kramp 1957). He noted that “the numerous and closely packed tentacles were not arranged in groups as in P. polaris. The ring of tentacles seems to be homogenous, equally thick and dense”.

Although his remark is entirely justiFed, a couple of morphological features resulting from Haeckel’s (1881b) account are noteworthy:

1) unlike Ptychogastria, the gonads of which occur in pairs on either side of the manubrial lobes, those of Pe. antarctica are not only conFned to the radial canals, but they also exhibit a radically different shape, being “wide, folded, thick-walled” and slightly pendant distally (Haeckel 1881b: pl. 5 Fg. 2);

2) the mesoglea of Pe. antarctica is “very much thickened in the centre of the apex, and projects into the fundus of the gastral cavity in the form of a short, conical, gelatinous appendage”, leaving no doubts that this corresponds in fact to a gastric peduncle, even though the illustrations given by Haeckel (1881b: pl. 5 Fgs 2, 4) are misleading.

It is realized that, taken together, the morphological characters displayed by Pe. antarctica are distinctive features of the genus Voragonema Naumov, 1971. Among the four species assigned to it (see Lindsay & Pagès 2010), V. laciniata Bouillon et al., 2001, originating from the Weddell Sea, shows striking resemblances with the present species, and both are thought to be coterminous.

The “eight narrow mesogonia” apparently occurring in Pe. antarctica represent, with little doubt, nothing more than the proximal parts of the gonads. The observation that the tentacles are “rather arranged in eight larger and thirty-two smaller groups” (Haeckel 1881b) around the umbrella margin, is possibly not totally unfounded. Indeed, Lindsay & Pagès (2010) noted a “regular pattern” in the arrangement of tentacles in P. tatsunoko, and it is quite possible that a similar situation may occur in Haeckel’ species as well.

Last but not least, Haeckel’s statement that “All the tentacles of this genus are solid; their endodermal axis consists of large, clear chordal cells which are sometimes placed in a discoid row one behind the other” is more problematic in its interpretation. Indeed, we cannot be sure whether or not Haeckel made sections through both the large, outermost and the shorter, innermost tentacles, given that only the latter are reportedly hollow in Pectis (Lindsay & Pagès 2010, as Voragonema). It has been proved, indeed, that Haeckel’s observations on the hollow nature of the tentacles of Pt. asteroides were totally unfounded (Picard 1955), even though he provided an illustration (Haeckel 1881b: pl. 7 Fg. 4), of apparently irrefutable evidence, to support his statement. It is also interesting to note that Bouillon et al. (2001) noted only hollow tentacles in P. laciniata, although it was shown that two types, solid and hollow, occur in this species (Lindsay & Pagès 2010).

Reversal of precedence for the speciFc name could not be applied for the following reasons: the senior synonym, antarctica, has been used several times as a valid name after 1899 (see synonymy), so the conditions relative to Art. 23.9.1.1. are not met; the junior synonym, laciniata, has been used only Fve times in the literature (Bouillon et al. 2001, 2006; Stepanjants et al. 2006; Lindsay & Pagès 2010; Mahuzier & Sylvestre 2016), instead of at least 25 times, and Art. 23.9.1.2. is not fulFlled.

Consequently, prevailing usage of laciniata could not be maintained, and this name should be assigned to synonymy with antarctica. For a modern description of this species, refer to Bouillon et al. (2001, as V. laciniata).

Almost nothing, except for the depth range of its habitat, is known about the ecology of this species. It was recorded from 1583 m (Bouillon et al. 2001) and ca 2300 m (Haeckel 1881b).

Recorded so far from two localities, one situated 500–600 km off eastern Antarctica (60°52’ S, 80°20’ E; Haeckel 1881b) and the other in the Weddell Sea (73°27.5’ S, 22°43.1’ W; Bouillon et al. 2001).

A new hydromedusa is described based on specimens from westernAntarctica. Some of its morphological features, viz. the number of radial canals, the number and arrangement of gonads, the lack of a gastric peduncle, the numerous tentacles occurring in superimposed rows, and the presence of free statocysts, place it within the family Ptychogastriidae Mayer, 1910. Unlike both Ptychogastria Allman, 1878 and Tesserogastria Beyer, 1959, this medusa has a Fattened, watch glass-shaped umbrella, and is devoid of a velum. These features justify the creation of a new, presently monotypic genus, Glaciambulata, to accommodate these new character combinations.

The revision of the genus Ptychogastria provided herein demonstrates that Pectis antarctica Haeckel, 1879, a species assigned to it by a number of authors, does not belong here. Indeed, its Fnely ribbed exumbrella, the pigmented subumbrella, the presence of a gastric peduncle and of centripetal canals, the number and arrangement of gonads, the types and arrangement of the marginal tentacles, and the occurrence of free statocysts, are characters of the contemporary rhopalonematid genus Voragonema Naumov, 1971. Moreover, it is demonstrated that V. laciniata Bouillon et al., 2001 is coterminous with P. antarctica, thus clarifying the morphology and the taxonomic status of this poorly-known species, 137 years after its discovery. The binomen Pectis antarctica is retained in light of the Principle of Priority of ICZN.