Hydrodendrium gorgonoides Nutting, 1905

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 32-34

Hydrodendrium gorgonoides Nutting, 1905

Figs. 18–20

Hydrodendrium gorgonoides Nutting, 1905: 936 , pl. 1, figs. 1–6, pl. 7, figs. 1, 2. Type locality. USA: Hawaii, between Honolulu and Kauai, 541 m ( Nutting 1905).

Material examined. Kauai : Albatross Stn. 3991, off Molokea Point, 22º25.6944’ N, 159º 38.7500’ W, 497–541 m, 12.vi.1902, one fragmentary colony, with fragments to 15 cm high, with gonophores, USNM 22167 [HOLOTYPE].– Oahu: off Kaena Point, 21º37.4’N, 158º 22.3’W, 337–403 m, SANGO III, haul #2, tangle nets, 30.ix.1970, one fragmentary branched colony, 7.9 cm high, with hydranths, without gonophores, coll. R. Grigg, BPBM D520 .– Oahu : off Kaena Point, 21º35.9’N, 158º 23.5’W, 380–415 m, SANGO III, haul #2, tangle nets, 9.viii.1970, one fragmentary branched colony, 11.3 cm high, with hydranths and gonophores, coll. R. Grigg, BPBM D521 .– No collection data, one dried colony, 21 cm high, coll. R. Grigg, BPBM D522 .

Other type material. Kauai : Mokolea Point, 22.256944’ N, 159.387500’ W, 497–541 m, 12.vi.1902, one branch, Albatross Stn. 3991, CAS IZ163 (syntype) [PARALECTOTYPE; Fautin & Weitbrecht 1985] .

Description. Hydroid colonies fragmentary, robust, erect, dendritic, irregularly branched in one plane, reaching to 21 cm high, 1.9 cm wide. Hydrocaulus and branches forming a thick, woody, spongy, chitinous axis penetrated and overlaid by naked coenosarc; chitinous fibers of axis somewhat twisted, branched, running parallel or nearly so to axis of hydrocaulus and branches, appearing twisted. Hydranths in preserved material columnar, stout throughout, fairly short, to about 0.7 mm high, lacking perisarc, arising from coenosarcal strands overlying grooves in chitinous matrix, scattered irregularly over hydrocaulus and branches but most numerous in axils of branches; tentacles filiform, solid, about 10–13 in number, arranged in one whorl around hypostome, bearing warts and incomplete rings formed by batteries of nematocysts, hypostome dome-shaped to almost flattened, with central round mouth. Colour of preserved colony tan, hydranths and gonophores cream.

Gonophores styloid sporosacs, arising from essentially normal to slightly shrunken hydranths as sacshaped outgrowths of hydranth wall, with one per hydranth, becoming very large, laterally flattened, spadeshaped, with wide base connected to hydranth by a thick pedicel, round-pointed apex pointing away from hydranth, lacking spadix, radial canals, tentacle bulbs, and tentacles.

Nematocysts. desmonemes (5.6–6.1 µm long × 3.9–4.1 µm wide)

Heterotrichous microbasic euryteles (8.5–9.2 µm long × 3.8–4.0 µm wide)

Remarks. Hydrodendrium gorgonoides Nutting, 1905 was described from Hawaii on the basis of what appear to be fragments of a single colony. While the tallest intact specimen observed here (BPBM D522) was 21 cm high, Nutting believed that the hydroid may reach as much as a foot (30 cm) or more in height, based on fragments in his sample. Colonies are octocoral-like in colony form, as its specific name suggests.

In an earlier work ( Calder 2004: 20), this species was listed under the binomen Hydractinia gorgonoides . For reasons given immediately above, it is removed from Hydractinia Van Beneden, 1844a here and returned to Hydrodendrium Nutting, 1905 . Stechow (1923b: 71) had included it as Nuttingia gorgonoides .

Hydrodendrium gorgonoides , currently known only from Hawaii, is a poorly known species. Material examined here represents only the second published record of the species. The scarcity of records may be due in part to difficulties of sampling its rocky, rugged, deep-water habitat.

Although not unique among hydractiniids, it is unusual in being monomorphic and in having a massive, erect, porous skeletal axis formed of chitin and covered with naked coenosarc. A detailed account of the structure of its hydrocaulus was given by Nutting (1905). Gonophores of the species differ from other hydractiniids in being hernia-like sporosacs arising from the walls of normal hydranths. Colonies are said to be monoecious ( Nutting 1905).

Several other species of hydractiniids are known to have an erect and chitinous skeleton invested with coenosarc, including Hydractinia angusta Hartlaub, 1904 , H. dendritica Hickson & Gravely, 1907 , H. sodalis Stimpson, 1858 , H. rugosa Fraser, 1938b and its likely synonym, H. prolifica Fraser, 1948 (Calder et al. 2009), H. bayeri Hirohito, 1984 , H. cryptogonia Hirohito, 1988 , and H. antonii Miglietta, 2006 . All of these but H. cryptogonia differ from Hydrodendrium gorgonoides in having polymorphic rather than monomorphic colonies. Moreover, the chitinous skeletons of all but H. dendritica and H. cryptogonia bear large, jagged spines instead of being smooth. Hydractinia arborescens Carter, 1878 has a similar colony form, but that species was described from poor material and is known only from its skeleton. Based on current knowledge, it is considered a nomen dubium. The provenance of its type material was uncertain, possibly somewhere in Polynesia ( Carter 1878).

As for H. sodalis, Stimpson (1858) has consistently been cited as author of the name. It might be debated whether that author’s brief mention of it meets criteria of availability under Art. 12 of the ICZN. In describing a new pagurid crab ( Eupagurus constans ) from “Hakodadi” (Hakodate, Hokkaido, Japan), he wrote: “Carcinoecium corneum spirale, base convolutum, muricatum, a polypo hydroideo ( Hydractinia sodalis , nob.) constructum…” ( Stimpson 1858: 249). That perfunctory account has nevertheless been sufficient for the species to be recognizable, so prevailing authorship and date of the name have been retained here. A few more details of the hydroid, including an illustration, were provided by Stimpson (1907: 219, pl. 24, fig. 3) in a posthumous publication. Stechow (1907) provided the first detailed description of H. sodalis , now quite familiar in waters of Japan ( Hirohito 1988).

All eight gonophores examined microscopically by me from a single colony (BPBM D521) were male, but both male and female gonophores were reported on the same colony by Nutting (1905).

This hydroid has sometimes been overlooked in species lists and other accounts of Hydractiniidae L. Agassiz, 1862 . One of the colonies studied here (BPBM D521) had been examined and identified earlier as this species by both W.J. Cooke and W. Vervoort (from information on labels contained in the bottle). A dried colony also exists at the Bishop Museum (BPBM D522). Although likely from the Hawaiian islands, its provenance is not known. Collection data record the collector as R. Grigg of Hawaii, and the identifier as W. Vervoort. It is much branched and root-like in shape, measuring 21 cm high and 1 cm in diameter at the base (Fig. 18).

Reported distribution. Hawaii. Albatross Stn. 3991, “between Honolulu and Kauai…, 296 fathoms” (541 m) ( Nutting 1905) .

Worldwide. Known only from Hawaii.