Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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218 Distribution Indonesia, Philippines, Japan. Type locality: Indonesia, 1°42.5’S, 130°47.5’E, 32 m. Family Aglaopheniidae Gymnangium longicorne (Busk, 1852) Fig. 65. Plumularia longicornis Busk, 1852: 399. Aglaophenia longicornis. – Bale 1884: 157, pl. 14: figs 7–8, pl. 17: fig. 5. Lytocarpus longicornis. – Allman 1883: 45, pl. 19: figs 4–6. Macrorhynchia (?) longicornis. – Stechow & Müller 1923: 474. Halicornaria longicornis var. sibogae Billard, 1913: 67, fig. 54, pl. 4: fig. 38. Halicornaria intermedia Billard, 1913: 65, fig. 53, pl. 4: fig. 37. Gymnangium longicorne. – Watson 2000: 60, fig. 48A–F. Material examined: Kei Islands Expedition stations: 67. – 68, 30 m and 50 m depth. – 71. – 73, with gonothecae. – 104. Description Colonies up to 20 cm high, multi-pinnate, branching in one plane; composed of a polysiphonic main trunk and pinnately arranged sidebranches bearing themselves pinnately arranged hydrocladia. Main trunk either unbranched or forked, strongly polysiphonic up to distal end, composed of a superficial primary tube and numerous auxiliary tubes. Primary tube with alternate hydrocladia, these short (2–3 hydrothecae) and often lost. No nematothecae on auxiliary tubes. From auxiliary tubes of main trunk issue pinnately arranged side-branches, these always monosiphonic, 1.5–2 cm long, at base a deeply cut, oblique hinge-joint rendering branch easily movable, other nodes only visible in more distal parts, each internode with an apophysis bearing a hydrocladium. Below hinge-joint no hydrocladia, only median nematothecae. Apophysis of hydrocladia associated with two nematothecae, one on abcauline end and one in upper axil, both nematothecae with two apertures, one aperture much larger than the other. Hydrocladia thin and dense, curved, not in one plane, planes forming an angle < 90°, hydrothecae facing towards above, hydrocladia relatively short, with up to 7 hydrothecae, with dis- P. SCHUCHERT tinct oblique nodes, internode length about 0.2 mm. Each segment with two well developed internal ribs. First or second hydrocladium of side-branch often modified into long, very flexible pseudophylactocarp; proximal 2–5 segments like in normal hydrocladia, then up to 12 modified segments with without hydrotheca but with three long nematothecae. Hydrotheca about 0.22 mm in total length, 1/5 of its upper end curved for nearly 90°, lower part straight or slightly curved, slightly inclined towards above, adcauline side adnate for ¾ of its length, opening-plane tilted towards above or parallel to internode axis, margin with two broad, rounded cusps, one on each lateral side and one frontal, the latter cusp shallow and appearing as frontal tooth in side view. Distal part of abcauline hydrothecal wall sharply bent, at site of bend an abcauline perisarc thickening projecting into hydrotheca, on adcauline side near base of hydrothecae a second, horizontal intrathecal ridge, length and thickness very variable, opening for hydranth below this ridge, axis of extended hydranth thus S-shaped within hydrotheca. Hydranth with about 10 tentacles. Median inferior nematotheca tubular, distal end sometimes slightly swollen, mostly very long, as long or longer as height of hydrotheca, the first hydrothecae of a hydrocladium may have much shorter median nematothecae. Median nematotheca adnate up to the middle of the hydrotheca, with three openings: one at distal end, one on upper side where becoming free from hydrotheca, and one leading into the lumen of the hydrotheca. Lateral nematothecae thin and tubular, straight, following free upper wall of hydrotheca, reaching beyond margin of hydrotheca. Gonothecae on upper axil of apophyses for hydrocladia, 0.4 mm long, leaf-shaped, flattened, rounded distal end without opening, aperture on side, slit-like, short pedicel near base. Remarks With its feather-like side-branches, pivoting at the slightest movement, the long nematothecae, and the lash-like modified hydrocladia, Gymnangium longicorne (Busk, 1852) is a very characteristic species. The very flexible hinge joint
HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS Fig. 65. Gymnangium longicorne (Busk, 1852); A, station 71; B–E, station 68; F, station 73. A. Colony silhouette. B. Part of sidebranch with apophysis (pointing towards right) and two nematothecae. C. Hydrocladial segment with common form of long median nematotheca. D. Segment of proximal region of hydrocladium with less common, short median nematotheca, same scale as C. E. Modified hydrocladium (pseudophylactocarp). F. Gonotheca, same scale as B. – Scales: A = 1 cm; B, F = 0.1 mm; C–D = 50 µm; E = 0.2 mm. of the side-branches, well described by Allman (1883), renders the side-branches very movable. The modified hydrocladia, named pseudophy- 219 lactocarps by Watson (2000), are normally regularly present, but some colonies have only few of them. Watson (2000) argued that these structures
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Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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