Dentitheca dendritica ( Nutting, 1900 )

Galea, Horia R., 2010, Additional shallow-water thecate hydroids (Cnidaria: Hydrozoa) from Guadeloupe and Les Saintes, French Lesser Antilles, Zootaxa 2570, pp. 1-40 : 28-29

Dentitheca dendritica ( Nutting, 1900)

(figs 1F, G; 7A–G)

Plumularia dendritica Nutting, 1900: 67 , pl. 8 figs 4–6.― Jäderholm, 1920: 8.― Fraser, 1944: 342, pl. 73, fig. 330. not Plumularia dendritica ― Nutting, 1927: 224 [= Dentitheca habereri ( Stechow, 1909) ]. Dentitheca dendritica ― Calder & Kirkendale, 2005: 482.

Sphaerocystis heteronema Fraser, 1943: 85 .― Fraser, 1944: 359, pl. 78 fig. 350. Plumularia habereri ― Van Gemerden-Hoogeveen, 1965: 60, figs 34–36 [not Plumularia (= Dentitheca ) habereri Stechow, 1909 ].

Material examined. Stn.8: 0 5.12.2009, 17 m—two sterile colonies 37 and 45 cm high, respectively, partly covered with zoanthids, growing upright through sand of sea bottom (MNHN-IK.2009-812). Stn.12: 30.11.2009, 12–17 m—a single, sterile, 16 cm high colony, from sediment bottom. Stn.14: 0 1.12.2009, 15–25 m—a 35 cm high colony and four fragments, 3.4–16.5 cm high, detached from sediment bottom, all sterile and partly covered with zoanthids (MHNG-INVE-68731). Stn.20: 26.11.2009, 20 m—four sterile fragments, 6.0– 13.5 cm high, from large colonies, partly invested by two zoanthids, from sediment bottom.

Description. Large, fan-shaped (to 45 cm high and 20 cm wide) colonies, arising from thick matted rootlike hydrorhizal fibers interwoven with sand. Perisarc brown. Stems woody, to 5 mm thick at base, comprising a thightly-packed mass of thin, parallel tubes; irregularly branched, mainly in one plane or nearly so. Main stem and first order branches bearing irregular to pinnately-arranged, less polysiphonic branchlets (1.5–9.0 cm long), all carrying regularly-spaced, monosiphonic, alternate hydrocladia. Auxilliary tubes in polysiphonic parts of colonies devoid of hydrothecae, but carrying bithalamic nematothecae, often broken off (fig. 7A). Main tube occasionally divided into internodes by weak transverse nodes, often indistinct (fig. 7B). Internodes bearing alternate apophyses supporting cladia, and a lateral nematotheca above each apophysis (fig. 7B). Apophyses prominent, ending in distal, oblique node; each carrying two axillar, bithalamic nematothecae (one anterior, the other posterior), and a mamelon ending in a cone-shaped nematotheca (fig. 7C). Hydrocladia homomerously segmented into hydrothecate internodes separated by oblique nodes. Each internode with a centrally-placed hydrotheca, and three nematothecae, one mesial and a pair of laterals. Hydrotheca tubular, entirely adnate, abcauline side straight to slightly convex, slightly everted at rim. Margin of hydrotheca flanked by two conspicuous lateral processes, triangular in shape, with rounded tips. Mesial and lateral nematothecae borne on conspicuous apophyses; all nematothecae bithalamic and movable; mesial one not reaching hydrothecal base and having the adaxial wall of the upper chamber lowered; laterals slightly surpassing the tips of lateral projection of the rim, with incised adaxial wall of both upper and lower chambers. There is an internal, rounded, plate-like perisarc cusp projecting into the hydrothecal cavity at level, and between the apophyses supporting the lateral nematothecae (fig. 7D, E). The internode has up to seven internal ridges of perisarc (fig. 7E): one above the proximal node, another above the process carrying the mesial nematotheca, one at the angle formed by the base and the adcauline wall of hydrotheca (may be absent), three on back side of the adcauline wall, and one just below the distal node. Gonothecae absent.

Remarks. Nutting (1900) mentioned large colonies (to ca. 45 cm), with very thick (ca. 1 cm), polysiphonic stems, and side branches of up to 6th order. One colony in the present material is comparable in size with Nutting’s material, but only second order branches were formed.

Based on the monograph by Fraser (1944), Sphaerocystis heteronema Fraser, 1943 appears as morphologically indistinguishable from D. dendritica . Although it is mostly unrecognizable from the description provided, it can be confidently assigned to the present species based on the accompanying figures.

The gonothecae have never been found in D. dendritica since its original description, but are known in D. alata ( Bale, 1888) (see Watson 1997), D. asymmetrica ( Bale, 1914) , D. bidentata ( Jäderholm, 1920) (see Migotto & Marques 1999), D. habereri ( Stechow, 1909) (see Di Camillo et al. 2010), and D. hertwigi ( Stechow, 1907) (see Hirohito 1995). The dispersive stage, a medusoid, is well documented solely in D. bidentata (see Migotto & Marques 1999).

Symbiotic association between zoanthids and species of Dentitheca were reported for D. asymmetrica (see Watson 2005), D. dendritica (see Swain 2009), and D. habereri (see Di Camillo et al. 2010).

Caribbean records. Anguilla ( Jäderholm 1920), Curaçao ( Van Gemerden-Hoogeveen 1965, as Plumularia habereri ), Colombia ( Flórez González 1983, Bandel & Wedler 1987, both as P. habereri ), Caribbean coast of Panama ( Calder & Kirkendale 2005).

World distribution. Bahamas ( Nutting 1900; Fraser 1943, 1944, as Sphaerocystis heteronema ).