Halecium calderi, 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 : 9-10

Halecium calderi sp. nov.

(fig. 3A–J)

Type material. Holotype: Stn.11: 30.11.2009, 15–18 m—a single, 5.0 cm high colony with numerous female gonothecae, on concretions (MHNG-INVE-68718). Paratype: Stn.8: 0 5.12.2009, 17 m—a single, 2.8 cm high colony with four immature (presumably female) gonothecae, from hard substrate (MHNG-INVE- 68719).

Additional material examined. Stn.10: 19.11.2009, 17 m—five sterile stems, 1.4–4.0 cm high, from hard substrate. Stn.12: 30.11.2009, 12–15 m—a single, 3.5 cm high colony, with one female gonotheca, from hard substrate. Stn.13: 0 3.12.2009, 10 m—a single stem, 2.8 cm high, with a few female gonothecae.

Description. Colonies erect, to 5 cm high, arising from root-like hydrorhiza attached to concretions; imperfectly pinnate, varied in appearance (fig. 3A). Main stems and branches polysiphonic proximally, thinning out to end monosiphonic distally; branching typically in one plane; with up to 3rd order branches. Internodes long (600–1020 µm), perisarc smooth, slightly zigzagging in opposite directions to nearly straight; delimited by oblique nodes (diameter 120–170 µm), more obvious towards distal parts. Each internode bearing distally a short hydrophore, barely surpassing the node. Hydrothecae sessile, moderately deep (40–55 µm), walls diverging from base (diameter 150–175 µm) towards aperture (220–250 µm wide); rim widelyflared, distal perisarc often collapsed outwards; renovations frequent, up to 5 per primary hydrotheca. An internal perisarc plug on adaxial side of hydrophore (fig. 3G); pseudodiaphragm absent. Hydranths large, typical of the genus, with 22–26 tentacles. Nematocysts (only undicharged capsules were measured): microbasic mastigophores [(6.5–6.6) × (1.8–2.0) µm], and two size classes of microbasic euryteles [slender capsules (6.2–6.9) × (2.1–2.5) µm; swollen capsules (6.3–7.2) × (3.3–3.5) µm]. Gonothecae arising from primary hydrophores by means of short (ca. 200 µm), smooth, slender (ca. 150 µm wide) pedicel; female, in all examined fertile specimens, broadly ovoid, with more truncated base, 1045–1445 µm long, 885–990 µm wide in middle; imperceptibly flattened laterally (715–740 µm wide). In frontal view, perimeter of gonotheca provided with spines: two very prominent flanking the aperture (the latter not well formed in specimens examined), and 4–6 shorter on each side. About 12 eggs per gonotheca encircling lower half of blastostyle, not occupying the whole lumen of gonotheca. Male gonothecae unknown.

Remarks. The main distinguishing feature of this species is found in its peculiar female gonotheca, provided with spines. In this respect, Halecium calderi is closest of all to the Arctic H. minutum Broch, 1903 . However, the gonothecae of H. minutum arise from the stolon, are comparatively larger [2–3 mm, according to Schuchert (2001)], and strongly flattened laterally. Additionally, the hydrothecae of H. minutum are very deep and provided with a pseudodiaphragm, and the species is monosiphonic in habit.

Female gonothecae provided with crests or spines are also found in H. birulai Spassky, 1929 , H. flabellatum Fraser, 1935 , and H. muricatum (Ellis & Solander, 1786) . The gonothecae of the northern H. birulai are lenticular in shape and harbor radial keels running from the base of spines along the flattened sides of the theca. Additionally, its hydrothecae are comparatively deeper and provided with a pseudodiaphragm (see Schuchert 2001). The gonothecae of the Japanese H. flabellatum superficially resemble those of H. calderi , but are slightly larger, more rounded in frontal view, and considerably flattened laterally, with the aperture situated in middle of an apical depression, and are borne on a short pedicel (see Hirohito 1995). The northern-temperate to Arctic H. muricatum has gonothecae provided with 10–16 longitudinal rows of spines recovering their whole surface (see Schuchert 2001), thus substantially differing from H. calderi .

Etymology. The species honors Dr. Dale R. Calder (Royal Ontario Museum, Canada) for his noteworthy contribution to hydrozoan taxonomy.

Caribbean records. Only known from Guadeloupe (present study).