Antennella incerta, 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 : 25-26

Antennella incerta sp. nov.

(fig. 6H1, J, K)

Type material. Stn.12: 30.11.2009, 12–15 m—numerous sterile stems to 5 mm high, on algae (MHNG- INVE-68729).

Additional material examined. Stn.9: 21.11.2009, 21 m—two sterile colonies with numerous stems to 4 mm high, both on worm tubes. Stn.10: 0 2.12.2009, 15–20 m—sterile stems to 4 mm high, on stems of unidentified hydroid.

Description. Colonies comprising upright shoots arising from ramified, tubular hydrorhiza; no stolonal nematothecae. Stems composed of a short proximal part devoid of hydrothecae, but bearing 2–3 nematothecae in a single, longitudinal, centrally-placed row; divided into a few segments of varied length by means of transverse nodes, distalmost node oblique; occasionally, marks of breakage and subsequent regeneration present. Remainder of stem heteromerously segmented by alternating oblique and transverse nodes, the latter slightly marked. Ahydrothecate internodes short (130–265 µm), with proximal end transverse (nodes 30–40 µm wide) and distal end oblique; bearing one nematotheca (exceptionally two, exclusively found on proximal-most internode) on frontal side. Hydrothecate internodes, up to ten per erect shoot, 245–275 µm long, with proximal oblique node and distal transverse node; bearing one hydrotheca and four nematothecae: one mesial, a pair of laterals, and one axillar. Hydrotheca cup-shaped, axis oblique to that of internode; abcauline wall 135–150 µm long, straight to slightly concave, perisarc thick, with a more or less prominent internal projection above hydrothecal base (fig. 6J, arrowhead); adcauline wall adnate for two-thirds, free part 70–80 µm long, straight, perisarc thinner than on abcauline side; rim even, not everted, diameter at aperture 155–170 µm. All nematothecae bithalamic. Cauline and mesial nematothecae with lowered adcauline wall; mesial nematotheca not reaching hydrothecal base. Lateral nematothecae, 50–60 µm long, borne on quite long (70–80 µm) apophyses; apophyses alone almost reaching hydrothecal rim; distal end of nematothecae surpassing hydrothecal rim; basal chamber deeper than upper chamber, the latter barrel-shaped, ca. 30 µm wide, adaxial side with conspicuous emargination. Axillar nematotheca randomly displaced left or right; borne on adaxial side of apophyses supporting the lateral nematothecae; bithalamic, with adcauline wall of upper chamber lowered. Hydranths with ca. 14 filiform tentacles. Nematocysts (undischarged) of three types: small, egg-shaped capsules (3.7–4.7) × (2.4–2.8) µm; microbasic mastigophores (5.7–6.0) × (1.7–1.8) µm; large capsules of unidentified type (16.1–18.0) × (5.6–6.3) µm. Gonothecae absent.

Remarks. Upon examination of numerous (ca. 20) stems with perfectly cleared hydrothecae, it appears that only one axillar nematotheca is randomly present on either side behind the hydrothecal wall. No apparent signs of possible breakage of a putative paired nematotheca were detected.

Antennella species with laterally-displaced axillar nematotheca have been rarely recorded, as for instance the material assigned to Antennella sp. by Hirohito (1974). However, the Japanese species has lateral nematothecae with the rim of upper chamber entire, not deeply emarginated as in A. incerta .

The nematocyst complement of the new species was compared to that of A. armata sp. nov. and A. secundaria ( Gmelin, 1791) , and it appears to comprise comparatively larger capsules (fig. 6H1). Additionally, the stems of the new species are shorter and much more slender, and the hydrothecae smaller than those of A. secundaria belonging to the present collection. In A. incerta , the distal end of the hydrothecate stem internodes end just above the axil of hydrotheca, never coming close to its rim, while in A. secundaria it easily reaches, or slightly surpasses the rim. The upper chamber of lateral nematothecae was not emarginated in any of the specimens of A. secundaria examined, and the axillar nematotheca was always placed centrally behind the hydrotheca. Moreover, the abcauline wall of the hydrotheca of A. incerta is conspicuously thickened and exhibits an internal tooth above the diaphragm, similar to A. curvitheca Fraser, 1937 .

Etymology. The specific name is the Latin adjective incertus/ incerta /incertum, meaning indecisive, illustrating the random position of the axillar nematotheca.

Caribbean records. Known only from the type locality.