Eudendrium tottoni Stechow, 1932

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 : 279-280

Eudendrium tottoni Stechow, 1932

( Fig. 3C–E )

Eudendrium insigne .— Hickson & Gravely, 1907: 7–8, pl. 1 fig. 4.

Eudendrium antarcticum Totton, 1930: 140–141 .

Eudendrium tottoni Stechow, 1932: 84 .— Millard, 1977: 4.

Material examined. PROTEKER 3: Ile Suhm, a few stems up to 23 mm high, with male gonophores, on alga and tubulariid ( MNHN IK –2012–10426).

Description. Monosiphonic stems up to 23 mm high, irregularly, and sparsely branched; usually with only a few primary branches, but occasionally with second-order branches. Stolon with smooth perisarc. Stems densely ringed basally over a long extension, but smooth distally; some small stems almost completely annulated.

Hydranth 500–600 µm high and 270–350 µm in maximum diameter, with a distal crown of around 20 tentacles ( Fig. 3C ) and a basal annular swelling related with perisarc formation ( Fig. 3D ).

Male gonophores one-chambered, on completely reduced polyps; over 20 gonophores per polyp ( Fig. 3E ).

Cnidome consisting of microbasic euryteles of two size classes: 7–8 x 3.5–4 µm and 17±0.8 x 7.5±0.6 µm (n= 10), range 15.5–18.5 x 7.0–8.5 µm, the latter concentrated on hypostome.

Remarks. Stem annulation is quite variable. As noted above, some small stems are almost completely ringed, but larger stems have the annulations restricted to some parts. As a general rule, the basal part is usually ringed. As an example, in a 15-mm-high stem, the most basal 2 mm are densely and completely annulated with more than 45 rings, but this annulation progressively vanishes after the first branch, even though it continues for four millimetres more. The first branch is also densely ringed until it passes a gonophore-bearing pedicel, which, in turn, is completely annulated. The rest of the stem and branches are smooth in general, although sometimes there are a few rings at the origin of branches.

Millard (1977) reported two species of Eudendrium from Kerguelen, Eudendrium rameum ( Pallas, 1766) and Eudendrium tottoni Stechow, 1932 . Our material is morphologically close to the latter, which had delicate colonies up to 16 mm high, but unfortunately her material was too poorly preserved to provide information on the cnidome. Millard’s material had both male and female gonophores, the former being one- to two-chambered, which would agree with our material. However, she indicated that the tentacles of the fertile polyps appear to be persistent, whereas in the present material male gonophores are on completely reduced polyps. In addition, in Millard’s material, groups of annulations are present at branch origins and rarely at other points.

According to Hickson & Gravely (1907:7), in their material of E. insigne , which was selected as the holotype of E. antarcticum by Totton (1930), “At the base of the hydranth there is a circular groove bounded proximally by a collar of very conspicuous deeply-staining cells. Occasionally both collar and groove are apparently absent”. Subsequently, they added that “the lower margin of the groove was sometimes slightly swollen out to form a collar”, which was also depicted by them in Figure 4 of Plate I. As noted above, in the present material there is usually a basal annular swelling.

Stechow (1932) gave the name Eudendrium tottoni to Totton’s E. antarcticum because this was a pre-occupied name.

According to Marques et al. (2000), Eudendrium tottoni , a species restricted to the Antarctic and sub-Antarctic regions, was dubious as it was poorly defined and its cnidome was unknown.

I have assigned the present material to Eudendrium tottoni because of its similarities with earlier records, particularly those by Hickson & Gravely (1907) and Millard (1977), even though the absence of information on the cnidome in previous records makes it uncertain. If confirmed, this record would improve the knowledge of this species by providing information on its cnidome.

Ecology and distribution. Eudendrium tottoni was collected at a depth of 14 m off Suhm Island; gonophores in December. Millard (1977) found it at depths between 620 and 650 m, east off Kerguelen; gonophores in April.

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).

FIGURE 4. Campanularia sp.: A–B, hydrothecae; C, hydrothecal distal part showing cusps; D, distal part of pedicel, basal spherule and hydrothecal basal part. Sertularella contorta Kirchenpauer, 1884: E–F, hydrothecae; G, hydrotheca and basal part of branch; H, hydrotheca showing polyp and location of basal ‘tentacles’ (close-up showing tentacles). Scale bar: 200 µm (A, B, E–H), 100 µm (C, D).