Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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196 Hydrocladia alternate, in one plane, long and quite straight, usually unbranched, only rarely branched, nodes indistinct or absent, hydrothecae on a broad and short apophysis. Hydrotheca with short pedicel, without distinct node demarcating it from apophysis. Hydrotheca campanulate, 1–1.2 mm deep, diameter at opening 0.5–0.6 mm, slightly bilateral symmetric through bulging upper side and almost straight underside, at base a distinct diaphragm, margin either smooth or with four indistinct, broad cusps; below rim an internal annular ridge, operculum pyramidal and composed of four flaps, operculum frequently lost. Inside of hydrotheca covered by thin tissue layer with few large nematocysts. Hydranth with about 30 tentacles. Gonothecae on stem and hydrocladia, developing below hydrothecae on their apophyses, 1.8–2.4 mm, oblong oval, basal part tapering, end truncated, wall smooth. Male more slender, female thicker and end wider. Remarks See comments under T. torresii. The hydrothecae in living colonies have a characteristic rosepink colour, which is lost in preserved material (Millard 1975, Watson 2000). Distribution Tropical Indo-West Pacific, New Zealand, southern Africa, western Africa, Mediterranean. Type locality: Unknown. Thyroscyphus torresii (Busk, 1852) Fig. 50. Laomedea torresii Busk, 1852: 402. Campanularia Torresii. – Bale 1884: 52, pl. 11: fig. 3. Tyroscyphus simplex Allman, 1888: 25, pl. 13: figs 1–2. Tyroscyphus regularis Jäderholm, 1896: 9, pl. 1: fig. 8. Cnidoscyphus torresii. – Splettstösser 1929: 70, figs 68–77, map 2. – Vervoort 1941: 204, fig. 1. – Vervoort 1993: 104. Thyroscyphus torresi. – Jäderholm 1903: 273, pl. 12: fig. 6. – Stechow & Müller 1923: 466. – Watson 2000: 37, fig. 29B–C. Thyroscyphus fruticosus. – Mammen 1965: 31, fig. 64. [Not T. fruticosus (Esper, 1793)] Material examined: Kei Islands Expedition stations: 15. – 18. – 20. – 40. – 64. – P. SCHUCHERT Fig. 50. Thyroscyphus torresii (Busk, 1852); station 65. A. Two internodes with hydrothecae. B. Hydrotheca and gonotheca, same scale as A. – Scale: A–B = 0.5 mm. 65, with gonothecae. – 68. – 71. – 74. – 90. – 102. – 103. – 104. – 106. Differential diagnosis Similar to Thyroscyphus fruticosus, but epidermal lining of hydrotheca with a pad containing a dense cluster of large nematocysts; stems shorter (up to 10 cm); hydrocladia with distinct nodes, nodes alternately inclined left and right; hydrotheca demarcated by distinct node from apophysis, rim of hydrotheca with four distinct cusps, operculum regularly present. Diaphragm of hydrotheca more unequally developed. Gonotheca more barrel-shaped, 1.1 mm, lateral wall undulated in distal half.
HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS Remarks Thyroscyphus fruticosus and T. torresii share many characters, particularly in size of colony, habit and choice of habitat (Watson 2000). Their morphological similarity has probably led to some past confusion of the species. In the present Indonesian material, just as in the Australian one described by Watson (2000), T. torresii is relatively easy to distinguish from T. fruticosus through the distinct nodes of the hydrocladia and the distinct marginal cusps of the hydrotheca. Other populations may show intermediate characters. The figure of T. fruticosus in Millard (1975, fig. 104) resembles more T. torresii. The colour of the African material, however, matches T. fruticosus. Living colonies of T. fruticosus are rose-pink, while T. torresii are golden-yellow to golden-brown (Watson 2000). Using this colour information and his figures, it is evident that Mammen (1965) confounded the two species. His material identified as T. ramosus is actually T. fruticosus, while his T. fruticosus material belongs to T. torresii. A good character to distinguish both species are the large nematocyst batteries in the interior lining of the hydrothecae of T. torresii (Splettstösser 1929). However, these nematocyst clusters are often lost in dredged material. Splettstösser (1929) used this character to establish the new genus Cnidoscyphus. The validity of this genus was emphasized by Vervoort (1993), but other recent authors, e.g., Bouillon (1985a), Calder (1983), and Watson (2000), did not use it. Such thick nematocyst pads are also found in many species of the Sertulariidae, the closest relatives of the Thyroscyphidae, and thus likely represent a plesiomorphy. Because plesiomorphic traits are not suitable for detecting monophyletic groups, the genus Cnidoscyphus is not used here either. Mature gonothecae of this species have been described by Jäderholm (1903) and Splettstösser (1929). The gonothecae observed in the present material confirmed Jäderholm’s findings in that their distal half has an undulated wall. The male gonothecae may be more slender and smooth as Splettstösser’s (1929) figures suggest. Distribution Indonesia, northern and western Australia, 197 Queensland, China Sea, Mergui Archipelago. Type locality: Prince of Wales Channel, Torres Strait, Australia. Thyroscyphus sibogae Billard, 1930 Fig. 51. Thyroscyphus sibogae Billard, 1930: 230, fig. 1. – Pennycuik 1959: 198. – Gibbons & Ryland 1989: 427, fig. 41. Material examined: Kei Islands Expedition station 60, without gonothecae, few shoots on a synascidian. Description Colony forming erect shoots, up to 1 cm high, unbranched, without hydrocladia, with indistinct alternately oblique nodes, internodes smooth or slightly undulated, with subterminal apophysis for hydrothecae, apophysis demarcated from hydrotheca by node. Hydrothecae alternating, in one plane. Fig. 51. Thyroscyphus sibogae Billard, 1930. Hydrotheca. – Scale: 0.2 mm
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