Antennella similis, Galea, Horia R., 2013

Galea, Horia R., 2013, New additions to the shallow-water hydroids (Cnidaria: Hydrozoa) of the French Lesser Antilles: Martinique, Zootaxa 3686 (1), pp. 1-50 : 30-31

Antennella similis sp. nov.

(Fig. 7 O –S; Table 4 )

Material examined. Stn. 1, 18.ii.2012, 10– 13 m, M212: numerous stems, mostly sterile, at least one bearing a male gonotheca, on algae and sponge (MHNG-INVE-82930); 26.ii.2012, 10– 15 m, M262: colony on sponge, with female gonothecae and stems up to 1.5 cm high (holotype: MHNG-INVE-82931). Stn. 7, 24.i.2012, 6– 8 m, M034: several stems, up to 1.1 cm high, on sponge, two of which bear gonothecae (one female, the other male) (MHNG- INVE-82929). Stn. 9, 16.ii.2012, 5– 15 m, M207: several stems, up to 1.5 cm high, on sponge, some bearing male gonothecae (MHNG-INVE-83051).

Description. Stems up to 15 mm high, arising from a creeping, branching hydrorhiza; basal part devoid of hydrothecae, but carrying a varied number of frontal nematothecae (up to 12); there is a basal constriction a short distance after the origin from stolon, as well as several additional, irregularly placed, transverse nodes; last node oblique, followed by the first hydrothecate segment. Stem above basal part heteromerously divided into hydrothecate and ahydrothecate internodes by means of alternating oblique and transverse nodes, all well marked. Ahydrothecate segments with a basal transverse node and a distal oblique node; there is characteristically a second transverse, though incomplete, node immediately above the proximal node, not reaching the rear side of the stem (Fig. 7 O); each internode provided with two nematothecae on frontal side; occassionally three of these may be present in basalmost parts of the stem. Hydrothecate internodes very short, just as long as to accommodate a hydrotheca and its associated nematothecae: a mesial inferior, not reaching the hydrothecal base, a pair of laterals shorter than the free adcauline wall of the hydrotheca, as well as an axillar nematotheca. Stem, mesial and axillar nematothecae with upper chamber lowered on adaxial side, while a central, rounded lobe is present on the side adnate to the hydrotheca in the lateral nematothecae. Hydrotheca half-length adnate, lower and upper walls slightly divergent; free adcauline side straight, abcauline wall equally straight for most of its length, except distally, where it is slightly flared; aperture circular. Gonothecae arising from stem just below the base of a hydrotheca through a two, short-segmented pedicel. Female gonotheca large, cornucopia-shaped, with two (sample M262), rarely three (sample M034) basal nematothecae; aperture distal, perisarc conspicuously thickened immediately below margin, operculum watch glass sheped. Male gonothecae ovoid, with no aperture, provided with a pair of basal nematothecae.

Remarks. One stem in sample M207 is likely aberrant and bears a short side branch distally. It is given off like a gonotheca, from below the base of a stem hydrotheca, through a two segmented pedicel; follows an ahydrothecate segment with a straight proximal node and an oblique node distally, next to which a hydrothecate segment occurs, in which the axillar nematotheca is missing (possibly lost ot not yet formed).

The present taxon belongs to a group of species morphologically similar to A. secundaria , with respect to the heteromerous segmentation of the stem, the presence of two nematothecae on the ahydrothecate segments, and the occurrence of an axillar nematotheca behind the hydrotheca. Comparison of the new species with the Mediterranean and Caribbean A. secundaria reveals some discrete, not insignificant differences, such as: 1) the exclusive occurrence of very short hydrothecate segments, ending immediately above the axillar nematotheca, a situation not met with in A. secundaria ; 2) the presence of an incomplete, basal, transverse node in the ahydrothecate segments, analogous to the small, rectangular, intermediate, ahydrothecate segment of A. peculiaris sp. nov., which is always missing in Gmelin's species; 3) the comparatively bigger female gonothecae (1.5–2 times bigger than those of A. secundaria ).

Etymology. From the Latin similis , meaning similar, on the account of its general resemblance to A. secundaria (Gmelin, 1791) .

Geographical distribution. Only known from Martinique.