Sertularella paucicostata Vervoort 1993

Sertularella paucicostata Vervoort, 1993

Fig. 8I

Sertularella paucicostata Vervoort, 1993: 227, figs 51b–f, j.

Material examined

MUSORSTOM 3: Stn. DW809, several infertile stems, some branched, up to 1.3 cm high, epizoic on Sertularella folliformis sp. nov. (MNHN-IK-2012-16575).

Remarks

Surprisingly, Vervoort (1993) compared his new species with Sertularella costata Leloup, 1940, which is a much smaller and delicate hydroid (compare Fig. 8I and 8J), as illustrated by specimens of this species from the Andaman Sea, Thailand belonging to my private collection.

Sertularella costata is a rather poorly known species, with a few records around the world. Hirohito (1995) provided succinct measurements of the hydrothecae, while Calder et al. (2003) gave the first description and measurements of the gonotheca. The dimensions of the hydrothecae in the Thailand material are as follows: abcauline side 315–360 µm, free adcauline side 265–280 µm, adnate adcauline side 100–110 µm, maximum width 155–170 µm, diameter at aperture 130–140 µm. The external wall is provided with 10–13 transverse ridges, and three internal, submarginal cusps are present within the hydrothecae (Fig. 8K). Through the size of its hydrothecae, the material from Thailand comes close to the Japanese specimens examined by Hirohito and, through the number of external ridges, it approaches that of the Galapagos specimens, which is apparently 10–11 (Calder et al. 2003: fig. 14). In contrast, about 20 ridges ornament the hydrothecal walls in material from Japan (Leloup 1940; Hirohito 1995).

In my opinion, S. paucicostata most closely resembles both S. helenae and S. pseudocostata Vervoort, 1993. However, unlike S. paucicostata, S. helenae forms fascicled colonies with shorter internodes, and its hydrothecae are smaller (compare Fig. 8I and 8H) and provided with numerous perpendicular creases between the transverse ridges. According to Vervoort (1993), the hydrothecae of S. pseudocostata are comparatively larger and their outer wall has frilled ribs.

Geographical distribution

New Caledonia, Norfolk Ridge (Vervoort 1993), and the Philippines (present study).