Tubularia sp.

Peña Cantero, Álvaro L., 2022, On a few benthic hydroids (Cnidaria, Hydrozoa) from the Kerguelen Islands (southern Indian Ocean), including the description of a new species, Zootaxa 5165 (2), pp. 274-286 : 280-281

Tubularia sp.

( Fig. 3F )

? Tubularia indivisa .— Vanhöffen, 1910: 278–279, fig. 3.

Material examined. PROTEKER 2: Ile Suhm, several stems up to 50 mm high, with gonophores ( MNHN IK – 2012–10432). PROTEKER 3: Ile Shum, several stems up to 45 mm high, with immature gonophores ( MNHN IK –2012–10427).

Description. Stems up to 50 mm high, whitish (yellowish at the most basal part), thin, diameter only slightly increasing distally. Perisarc smooth, soft; softer and corrugated in the 3-mm-long neck region. Transparent perisarc film starting just below the polyp. Distinct constriction between polyp and neck region. Hydrocaulus with one larger and nine smaller peripheral longitudinal canals.

Polyp white ( Fig. 3F ), small, about 4 mm high and 3 mm wide. Polyp’s column relatively long. Hydranth with a whorl of about 20 aboral filiform tentacles (three or four originating from an inner position) and around 30 tentacles on hypostome column: ten or so oral tentacles, roughly in a circle; the remaining below, apparently in one level and partially fused to the polyp column for a significant proportion.

Some polyps with about eight unbranched blastostyles in a whorl just above the aboral tentacles. Blastostyles of different length, the longest with up to ten gonophores ( Fig. 3F ): the two or three most basal ones incipient, the others much more developed. Gonophores up to 500 µm high and 450 µm in diameter, pedicel about 200 µm long.

Cnidome (from MNHN IK–2012–10432) consisting of larger stenoteles [12.7±0.5 x 12.6±0.8 µm (n= 10), range 12–13.5 x 11–13.5 µm], smaller stenoteles [8.2±0.6 x 6.7±0.8 µm (n= 10), range 7.5–9.0 x 6.0–7.0 µm], haplonemes [12.8±0.9 x 4.6±0.6 µm (n= 10), range 12–14.5 x 4.0–5.5 µm], and desmonemes 6 x 5 µm.

Remarks. The material from MNHN IK–2012–10432 is in poor condition and it is not possible to count accurately the number of tentacles, let alone the oral ones, but there seems to be also 20 aboral tentacles. The polyps from MNHN ID–2012–10427 are in much better condition, yet the gonophores are barely developed.

The present material cannot be fully characterised due to the incomplete development of the gonophores.

Studer (1879) described as Tubularia ? kerguelensis a tubulariid from Kerguelen with smooth stems up to 3 cm. The present material is clearly distinguishable from it because Studer’s species had fewer oral tentacles (eight) than aboral ones (16). His material also lacked gonophores.

Vanhöffen (1910) reported Tubularia indivisa Linnaeus, 1758 from Kerguelen. The present material is morphologically close to Vanhöffen’s and could certainly be conspecific. According to him, the stems, 30–40 mm high, are smooth, without any annulation, and have clear longitudinal streaks. The polyp has 30–40 oral tentacles, arranged in several rows, and about 20 aboral ones.

Even if the present material was conspecific with the material assigned to T. indivisa by Vanhöffen (1910), it is not clear whether it actually belongs to this species. According to Petersen (1990), T. indivisa has stems up to 200 mm long, with firm perisarc, and the polyps have 40–60 oral tentacles. As indicated above, the present material has much shorter stems with soft perisarc and the number of oral tentacles is distinctly smaller. Vanhöffen’s material lacked gonophores and the gonophores in the present material are not completely developed. Therefore, it would be necessary to study well-preserved, mature material from the area to confirm the identification.

Ecology and distribution. Tubularia sp. was collected at depths from 14 to 43 m off Suhm Island.

Figures

FIGURE 3. Coryne pusilla Gaertner, 1774: A, distal part of polyp; B, larger and smaller stenoteles. Eudendrium tottoni Stechow, 1932: C, polyp; D, hydranth’s basal annular swelling; E, male gonophore. Tubularia sp.: F, hydranth and gonophores. Scale bar: 900 µm (F), 600 µm (F close-up), 200 µm (A), 100 µm (C, E), 50 µm (D), 10 µm (B).