Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

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152 Halecium halecinum var. minor Pictet, 1893 Halecium halecinum var. minor Pictet, 1893: 20, pl. 1: figs 14–15. Type material examined: MHNG INVE 31408, type colony of H. halecium var. minor, coll 10 Aug 1890 by M. Bedot and C. Pictet, Bay of Ambon, Indonesia. Description Colonies 2–4 cm high, branching irregularly, primarily in one plane; main stem and some side-branches polysiphonic from which arise monosiphonic branches. Monosiphonic parts with regular nodes, these transverse to slightly oblique. Hydrothecae on alternating sides of distal ends of internodes, sessile, adcauline wall adnate to internode, hydrothecal wall very short, straight, opening slightly tilted downwards. Gonothecae absent. Dimensions Length of internodes about 0.5 mm, diameter of hydrotheca 0.13 mm, depth of hydrotheca 20 µm. Remarks Pictet’s colonies lack the typical regular and parallel side-branches of H. halecinum (Cornelius 1995a, Schuchert 2001). Furthermore, H. halecinum is a species mostly known from temperate to cool waters. It is therefore improbable that the present material genetically belongs to H. halecinum. The material also conforms with H. sessile Norman, 1876, a species which is reportedly cosmopolitan (Millard 1975, Hirohito 1995) and which has been recorded in Indonesian waters by Vervoort (1941). Likewise, Pictet’s material could also be identified as H. beanii, a species closely resembling H. sessile. However, in the absence of information on the gonotheca, Pictet’s material cannot be identified with sufficient accuracy. Distribution Only known with certainty from type locality: Bay of Ambon, Indonesia. P. SCHUCHERT Fig. 12. Halecium humile Pictet, 1893; after type material. A. Single shoot. B. Hydrotheca and side-branch. – Scales: A = 0.5 mm; B = 0.1 mm. Halecium humile Pictet, 1893 Fig. 12. Halecium humile Pictet, 1893: 23, pl. 1: figs 16–17. Type material examined: MHNG INVE 25036, Port of Ambon, Moluccas, slide and alcohol material, 1 mm high shoots with 2–3 hydranths, 20– 22 tentacles, internode walls smooth. Remarks No new material of this species could be obtained. Its gonothecae are unknown, which makes identification difficult. The hydrothecae are very shallow and much everted (depth 50 µm, diameter at diaphragm 150 µm, at rim 220 µm) and might render the species recognizable. It closely resembles Halecium pygmeum Fraser, 1911 (see Fraser 1937, Hirohito 1995). Also Halecium sp. 1 depicted in Gibbons & Ryland (1989) might belong to it. A similar Indonesian species is Halecium scalariformis Billard, 1929c, which, however, has straight hydrothecal walls. New material from the type locality must be examined to complement the description of H. humile. Distribution Only known from type locality: Port of Ambon, Moluccas.
HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS Mitrocomium simplex (Pictet, 1893), n. comb. Halecium simplex Pictet, 1893: 22, pl. 1: figs 16–17. – Ritchie 1910b: 807, pl. 77: figs 10–11. Campalecium cirratum. – Millard & Bouillon 1975: 7, fig. 2C–E. Type material examined: MHNG INVE 25037, as Halecium simplex Pictet, 1893, Bay of Ambon. Remarks The taxonomic situation of the various species referable to Campalecium or Mitrocomium is complicated and unresolved (see Calder 1991). The following hydroids referable to the genus Campalecium have been described: C. simplex (Pictet, 1893); C. medusiferum Torrey, 1902; C. torreyi (Motz-Kossowska, 1911); C. microtheca Hadzi, 1914; and C. alcoicum Watson, 1993. Due to their similarity, several authors regarded most of them as conspecific or questionably conspecific (Calder 1991). Brinckmann (1959) – working with Mediterranean material – examined fertile polyps clearly referable to C. microtheca. She was able to rear the medusa until the onset of gonad development and she allocated her material to Mitrocomium cirrata Haeckel, 1879 (as Eucheilota cirrata), an uncommon medusa originally described from the Mediterranean. Brinckmann’s medusa agreed reasonably well with Haeckel’s medusa, especially in having several lateral cirri. The only serious difference was the tentacle number which was only four in the oldest obtained medusae, while Haeckel’s original medusae had 8 tentacles (for a more recent description and figure of M. cirratum see Pagès et al. 1992). This difference can, however, easily be attributed to the younger age of Brinckmann’s medusae. The medusae observed by Brinckmann were sufficiently old to be allocated to the Lovenellidae (sensu Russell 1953, not Bouillon 1984a). As other medusae of the Lovenellidae have either campanulid or lovenellid hydroid stages, it seems appropriate to keep the genus Mitrocomium with its Halecium-like hydrotheca until a comprehensive phylogenetic analysis enables recognition of monophyletic groups (see also discussion in Calder 1991). Because Brinckmann (1959) did not rear her medusae to full maturity, Bouillon (1985a: 149) doubted that C. microtheca is the hydroid of M. 153 cirratum, although earlier he embraced this view (Millard & Bouillon 1975: 8) and regarded all Campalecium-type hydroids known at that time as conspecific with M. cirratum. Boero (1981: 188) objected to this because he found a Mediterranean Campalecium-like hydroid which reportedly produced a medusa differing from the one described by Brinckmann (1959) and because he found that his polyps had nematocysts that differed from the ones described by Millard & Bouillon (1975). While the umbrellula of the polyps of Millard & Bouillon from the Indian Ocean had large microbasic mastigophores, Boero’s were initially identified as macrobasic mastigophores, later corrected to merotrichous isorhizas (Boero & Sarà 1987). Unfortunately, Brinckmann (1959) did not identify the large nematocysts of her polyp. However, I can find no significant difference in the figures of the newly released medusae depicted by Boero (1981: fig. 5, as Campalecium medusiferum?) and Brinckmann’s medusa (1959: fig. 2e) and I therefore suspect that Boero (1981) in fact had M. cirratum. But Boero is correct in that his material differs from Millard & Bouillon’s (1975) specimens from the Indian Ocean and that the latter material does not belong to M. cirratum because it has different nematocysts. It could belong to M. medusiferum or more probably M. simplex. Lifecycle studies on Indo-Pacific and Californian material are needed to resolve the problem. Pictet’s material of H. simplex was infertile and it was Ritchie (1910b) who described the gonothecae for the first time, this based on material from the Mergui Islands. The true nature of the gonotheca content of Ritchie’s material was later described by Millard & Bouillon (1975), who recognized that the gonothecae contained medusa buds. Unfortunately, no new material of M. simplex could be found, but the type material of Halecium simplex was re-examined and it proved to have many large microbasic mastigophores identical to the ones depicted in Millard & Bouillon (1975) for their material from the Seychelles. It thus appears very probable that Millard & Bouillon (1975) as well as Ritchie (1910b) had Mitrocomium simplex and not M. cirratum. Future studies on living material from the type locality of M. simplex must substantiate this, however.
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