Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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244 mary tube and a bundle of auxiliary tubes. Primary tube of side-branches originate from primary tube of stem, branching points of primary tubes often overgrown by few auxiliary tube. Primary tubes segmented in terminal parts, each segment with an apophysis for hydrocladium and two nematothecae at side of apophysis. Primary tubes usually with hydrocladia, but these may be broken off in proximal part of stem. Stolons tangled, creeping, anchoring colony on solid substrata. Inside of periderm of whole colony densely covered by a lining of spherical zooxanthellae, size 7–9 µm. Hydrocladia alternate, thick and bristly, making colony resemble a fir twig, hydrocladia 3–5 mm, 6–11 hydrothecae, length within one colony similar, flattened laterally, rear side keeled, regularly segmented by transverse nodes, each segment with one hydrotheca, with two strong internal ribs (ridges, thickenings) at the level of the hydrotheca, these ribs irregularly curved, fused to a longitudinal ridge running along rear side, rear wall otherwise remarkably thin. Hydrotheca relatively narrow, depth 0.25– 0.28 mm, diameter 0.13–0.15 mm, campanulate, not curved, adcauline side completely adnate, opening slightly inclined towards below (approx. 30°), lateral margin slightly undulated or with a distinct antero-lateral cusp, hydropore at base of rear wall, above hydropore a very short adcauline shelf which is continued as a transverse internal ridge, presence variable. Median inferior nematotheca very stout, breadth in lateral view 2/3 or more of hydrothecal diameter, completely adnate, reaching to the level of hydrotheca, margin with two broad lateral cusps (or free end gutter-shaped), on inside near upper third an oblique septum with a pore on adcauline side; no foramen into hydrotheca. Lateral nematotheca overtop hydrotheca, ovoid to cup shaped, about half as high as hydrotheca, opening directed towards above or inclined towards rear. Gonothecae in closed corbula which replaces a hydrocladium. Corbula 1.7–2.5 mm long, tubular, first segment like in ordinary hydrocladia, then with leaf-like costae, 5–8 per side, fused to form a cylinder but with slit-like lateral openings, costae with one row of nematothecae, basal 2–3 may be on a raised lobe. P. SCHUCHERT Remarks The samples from 1 m and 10 m water depth showed very obvious differences that are very likely attributable to their different environment (cf. Fig. 81A–C and 81D–F). The colonies from 10 m depth were dark brown, while those from 1 m were bright amber coloured. Furthermore, the colonies from 10 m were more branched, more flexible, less bristly, had longer and thinner hydrocladia. There was also a difference in the corbulae. This difference, however, could be either due to depth or sexual dimorphism. The limited number of independent colonies did not make it possible to draw a reliable conclusion. The difference was mainly confined to the presence or absence of a raised lobe near the base of each costa. This lobe had 2–3 nematothecae. The opening behind this lobe was also larger than the usual slits. In the examined material this type of corbula contained gonothecae with eggs, while the other type of corbula was quite certainly male. Both type of corbulae have been described by other authors. Billard (1913) depicts the form without lobe, while Millard & Bouillon (1974) depict a corbula with a basal lobe. Bale (1915) also described such a lobe and he also thought of a possible sexual dimorphism. Aglaophenia cupressina is a very characteristic species and especially the microscopic structure make its identification easy (see Fig. 81B and 81E). The colonies often occur in very shallow waters and are thus easily encountered. They are very notorious for their painful stings. Naumov (1969, as Corbulifera macgillivrayi) reported this otherwise tropical shallow water species from the arctic sea of Okhotsk and from deep waters near the Kuriles. His material was sterile. For biogeographic reasons I doubt somewhat that Naumov’s specimen belonged to A. cupressina, although his figures look identical to the present material. Although A. cupressina is widespread in the tropical Indo-Pacific, interestingly, it is not known to occur on smaller islands of the tropical Pacific (Polynesia). Distribution From Zanzibar and Mozambique to Great Barrier Reef, Indonesia, New Guinea, Philippines, Japan. ?Sea of Okhotsk. Occurs even in very shal-
HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS low water (1 m), but Billard (1913) found it down to 564 m. Type locality: East Indies (Lamouroux, 1816). Aglaophenia sibogae Billard, 1913, n. status Fig. 82. Aglaophenia pluma var. sibogae Billard, 1913: 101, figs 90– 91. Material examined: Kei Islands Expedition station 65, one plume, with corbulae. Description Colony pinnate, 3 cm high; stolons creeping; stem with prosegment, monosiphonic, with oblique hinge-joint, with regular nodes, segments with hydrocladial apophysis bearing a mamelon and three nematothecae: two on each side of the apophysis and one below. Hydrocladia alternate, thin and flexible, up to 4 mm, regularly segmented by slightly oblique nodes, segments without internal ribs. Hydrothecal walls U-shaped in side view, depth 0.30–0.35 mm, adcauline wall not entirely adnate, free for about 1/7 of total abcauline length, hydropore close to base, diameter of opening 0.15–0.17 mm, opening slightly inclined towards below, margin with 9–10 sinusoid cusps: one median abcauline (largest), four laterals, and sometimes a shallow and broad adcauline one (the latter can be absent). Median inferior nematotheca nearly completely adnate, tip reaching to base of abcauline cusp, free part about 1/7 of length, gutter-shaped, with foramen leading into hydrotheca, perisarc of outer wall thickened where nematotheca joins internode. Lateral nematothecae ovoid to cupshaped, reaching just below tips of marginal cusps, height relatively small (60 µm high), inner wall reduced. Gonothecae protected in corbulae. Corbula open, replacing a hydrocladium, shorter than hydrocladium, first segment identical to the ones of normal hydrocladia, followed by rachis bearing two rows of alternate costae, about 8 per side; costae rod-shaped, free, with two rows of lateral nematothecae and an additional one in axil to rachis. Gonothecae oblong, about 0.6 mm. 245 Fig. 82. Aglaophenia sibogae Billard, 1913. A. Colony silhouette. B. Stem segment. C. Two hydrocladial segments. D. Hydrotheca seen from abcauline side, same scale as B. E. Corbula in side view, only one row of costae shown. – Scales: A = 1 cm; B, C = 0.1 mm; E = 0.4 mm .
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Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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