Antennella armata, Galea, Horia R., 2010

Galea, Horia R., 2010, Additional shallow-water thecate hydroids (Cnidaria: Hydrozoa) from Guadeloupe and Les Saintes, French Lesser Antilles, Zootaxa 2570, pp. 1-40 : 24-25

Antennella armata sp. nov.

(fig. 6D–G, H2)

Type material. Stn.10: 0 2.12.2009, 15–20 m—a single colony with numerous stems to 7 mm high, two of which bear one gonotheca each, growing on dead gorgonian overgrown by algae and bivalve shells (MHNG- INVE-68728).

Additional material examined. Stn.10: 19.11.2009, 17 m—a few sterile stems to 4 mm high, on bivalve shell; 0 2.12.2009, 15–20 m—a colony composed of several stems to 5 mm high, some bearing gonothecae, epizoic on sponge.

Description. Stems to 7 mm high, arising from creeping, branched, anastomozing, hydrorhiza; no stolonal nematothecae. Basal part with one or more athecate internodes of varied length, sometimes with signs of breakage and subsequent regeneration; nodes transverse except distalmost, which is oblique; nematothecae, variable in number, in two frontal, parallel rows. Distal, much longer part of stems, composed of alternating hydrothecate and ahydrothecate segments; segmentation heteromerous. Hydrothecate segments, as much as twelve per erect shoot, with oblique nodes proximally and transverse nodes distally; 195–230 µm long; with one hydrotheca placed towards distal end and four nematothecae: one mesial, a pair of laterals, and one axilar. Hydrotheca cup-shaped, axis oblique to that of internode; adcauline wall straight and adnate for about twothirds of length, free part 60–65 µm long; abcauline wall 115–130 µm long, slightly sigmoid, concave basally and convex below rim. Margin entire, slightly flaring, perpendicular to long axis of hydrotheca, 140–155 µm wide. Ahydrothecate segments with transverse proximal node (40–45 µm wide) and oblique distal node; comparatively longer (230–620 µm) than hydrothecate segments; with 3–8 frontal, alternate nematothecae in two parallel rows. All nematothecae bithalamic, basal chamber deeper than upper chamber; all movable except mesial and possibly axillar ones; all with lowered rim on adaxial side of upper chamber. Axillar nematothecae placed centrally, just behind adcauline wall of corresponding hydrothecae. Gonothecae pearshaped, 335–350 µm long, ca. 205 µm wide, arising through a two-segmented pedicel (each 25–30 µm long) from below base of hydrotheca; basal part tapering abruptly, provided with two long (80–90 µm), bithalamic nematothecae; aperture of gonotheca 150–155 µm wide, closed by watch glass-shaped lid. Nematocyst (undischarged) of three types: egg-shaped capsules (3.7–4.1) × (2.3–2.4) µm; microbasic mastigophores (6.3– 6.6) × (1.8–2.0) µm; larger capsules of unidentified type (9.6–10.1) × (3.1–3.3) µm.

Remarks. The new species has a single axillar nematotheca, similar to A. secundaria ( Gmelin, 1791) . However, in the latter species, the ahydrothecate segments bear generally 2 (occasionally 1 to 3) nematothecae in a single, median row ( Schuchert 1997), thus differing from A. armata whose cauline nematothecae form two parallel rows. In this respect, the new species is close to A. varians ( Billard, 1911) and A. sibogae ( Billard, 1911) , but these are provided with two pairs of lateral nematothecae and the axillar one is missing ( Schuchert 1997).

Additionally, the cnidome of A. armata was compared to that of A. secundaria , a species abundantly occurring in the present collection. It appears that the larger capsules found in the new species (fig. 6H2) are of a different size and may belong to a different type of nematocyst than those found in the latter species (fig. 6H3).

Etymology. The specific name is derived from the Latin adjective armatus / armata /armatum, meaning armed, illustrating the presence of numerous stem nematothecae.

Caribbean records. Only known from type locality.