Macrorhynchia phoenicea (Busk, 1852)

Macrorhynchia phoenicea (Busk, 1852) View in CoL

Figs 16 View Fig C–D, 18A

Macrorhynchia phoenicea View in CoL – Di Camillo et al. 2009: 218, figs 2h–i, 6, 9.

Material examined

PACIFIC OCEAN • 1 profuse colony on gorgonian, with stems up to 10 cm high, some bearing phylactocarps; off New Caledonia, stn DW4945; 25°22ʹ S, 159°43ʹ E; 130– 108 m; 4 Sep. 2017; KANADEEP leg.; MNHN-IK-2015-510 GoogleMaps • 1 colony, composed of a couple of stems, 2.5 and 4 cm high; off New Caledonia, stn DW4775; 23°03ʹ S, 168°17ʹ E; 140–277 m; 28 Aug. 2016; KANACONO leg.; MNHN-IK-2015-511 GoogleMaps • 5 colonies, 2.5–3.5 cm high, of which 4 bear incipient phylactocarps; off New Caledonia, stn DW4774; 23°01ʹ S, 168°19ʹ E; 100– 90 m; 28 Aug. 2016; KANACONO leg.; MNHN-IK-2015-512 GoogleMaps .

Comparative material

PACIFIC OCEAN • 1 complete colony, 6.5 cm high, as well as 3 fragments (1.5, 2.5 and 3.5 cm long) of Macrorhynchia disjuncta (Pictet, 1893) , all fertile; off Vanuatu, stn CP1104; 15°04ʹ S, 167°07ʹ E; 125–129 m; 7 Oct 1994; MUSORSTOM 8 leg.; MNHN-IK-2015-513.

Remarks

For a recent description of this well-known species, refer to Di Camillo et al. (2009), who also provide an extensive synonymy.

Schuchert (2003) noted striking resemblances between the hydrothecae of Aglaophenia disjuncta Pictet, 1893 , a hydroid with a so far unknown gonosome, and those of the present species, and questioned their possible conspecificity. A few well-preserved, fertile specimens, undoubtedly assignable to Pictet’s species, occur in material from off Vanuatu gathered during the MUSORSTOM 8 Expedition. Their appearance ( Fig. 16D View Fig ) immediately distinguishes them from typical colonies of M. phoenicea ( Fig. 16C View Fig ), in being more delicate, with a less rigid and straw-colored perisarc, with more distant and comparatively longer cladia, with longer cormidia and slightly larger hydrothecae.

Stems of the species described by Pictet (1893) are lightly fascicled and scarcely branched, as for instance with one branch occurring in the tallest (6.5 cm high) specimen available. The stem and side branches are transversely divided into moderately long internodes, each bearing a cladial apophysis and 3 nematothecae, two large and one reduced: one at the base of the apophysis, a second axillar, and a short, conical theca on a mamelon ( Fig. 18B View Fig ). The large nematothecae are half adnate to the internode and possess a small, rounded aperture projecting laterally, as well as a large, broadly ovoid aperture behind. The proximal parts of the stem and branches are devoid of cladia, bear a row of large nematothecae with a conical distal half and have one of their apertures pointing upwards, while the other is comparatively larger and situated behind. The characteristic shape of the hydrothecae is depicted in Fig. 18C View Fig . The gonosome is typical of Macrorhynchia , and replaces a normal cladium, not forming pseudo-corbulae, but isolated phylactocarps; the proximalmost internode is a normal cormidium, on the distal part of which is inserted a long appendage with pinnate appearance resuting from the presence of (often) opposite pairs of exceedingly long nematothecae with two apertures: one small, apical, the other ovoid, at the base of the nematotheca. Occasionally, a few additional nematothecae in a row are to be found on the outer side of the phylactocarp. The gonothecae are large and lenticular, with flimsy perisarc, and are borne near the base of the appendage, amongst the proximalmost nematothecae.

Distribution

Widespread in the tropical parts of the Indian and southern Pacific oceans ( Di Camillo et al. 2009).