Family ALCYONIDIIDAE Johnston, 1838

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Family ALCYONIDIIDAE Johnston, 1838

Compiler and date details

July 2001 - Dr Philip Bock

Alcyonidulae Johnston, G. 1838. A History of British Zoophytes. Edinburgh, London & Dublin : W.H. Lizars 341 pp.
Alcyonidiidae Hincks, 1880.

Introduction

The Alcyonidiidae was introduced by Johnston (1838), and described in detail by Prenant & Bobin (1956) and by Hayward (1985). Colonies have autozooids which are generally contiguous without intervening kenozooids, although patterned groups of kenozooids and brooding zooids may occur in a few species (Cook 1979). Autozooids are often large, and box-like, with a distinct frontal wall including the orifice, which is often raised on a papilla. A range of larval types is known, even within some genera, and both planktotrophic and brooded lecithotrophic kinds have been described.

The family includes a very large number of nominal species assigned to the genus Alcyonidium Lamouroux (1813). They are usually found in shallow water, encrusting rocks, shells and algae, all over the world. Species apparently differ only in size and shape of autozooids, occurrence of oral papillae, and in a few cases, in budding pattern (Prenant & Bobin 1956). They have few features of superficial taxonomic use, and as a result, are often extremely difficult to identify with previous records. In addition, recent studies on population genetics, although they have confirmed some traditional morphologic features used to differentiate species, have also revealed a high degree of cryptic speciation. Many apparently homogeneous populations include more than one taxon (Hayward 1985). Alcyonidium has been the subject of a large number of genetic and experimental studies, reviewed by d'Hondt & Goyffon (1996).

Alcyonidium has rarely been reported from Australia, but, as noted by Bock (1982), it is probably widely distributed but unrecognised. Generally, colonies are encrusting, or rise in fleshy lobes. Zooids may be semi-transparent, or have fairly thick brownish, opaque cuticle. The tentacle number among species ranges from 15 to 25 (Soule in Osburn 1953). Some species develop an intertentacular organ between the distal pair of tentacles, and have a planktotrophic larva. In others, lecithotrophic larvae are brooded within the tentacle sheath. In at least one species, several larvae are brooded within the walls of a zooid in which the tentacles and viscera have degenerated. When mature, the larvae swim out of the zooid orifice (Hayward, 1985, Ström 1977).

Kirkpatrick (1888) described a species encrusting Amathia from Port Phillip, under the name of a European species, Alcyonidium mytili. Harmer (1915) doubted this identification, but himself figured a transparent species encrusting Euthyrisella obtecta from Torres Strait, calling it after another European form, A. polyoum. An unnamed colony from Bass Strait, encrusting shell, in the MOV collections, has transparent zooids and prominent white tentacles.

Other samples containing specimens of Alcyonidium species are in the collections of the Museum of Victoria, from Port Phillip, Westernport, Bass Strait, and off Tasmania, from depths of about 10 m down to 400 m. All are of encrusting forms. Most are inconspicuous, and appear under low power microscopy as a 'slimy' surface layer on shells, in which the organisation into zooids is not easily detectable.

Waters (1904) described A. antarcticum from deep water (459 m) from the Bellingshausen Sea (70°20'S, 83°23'W). Colonies were erect, rising from a kenozooidal encrusting base, with 3-5 zooids in alternating whorls, surrounding a hollow centre. Zooids were 0.50-0.70 mm long with a raised, papillate orifice and 25-26 tentacles, with an intertentacular organ. A. antarcticum was also recorded from Kerguelen Island by d'Hondt & Redier (1977), but these colonies were encrusting and seem to have been of another, unnamed species. D'Hondt (1984) listed, as A. mamillatum, a species from Kerguelen growing on a crustacean antenna from a depth of 937 m. Kirkpatrick (1902) recorded another Antarctic species, A. flabelliforme. Recently, another encrusting species, A. eightsi Winston & Hayward (1994) has been described growing on an erect bryozoan from the South Shetland Islands. It is possible that a small cyphonautes larva described from the Bellingshausen Sea by Shreeve & Hayward (1995) may belong to a species of Alcyonidium. In addition, pelagic colonies of Alcyonidium have been found in the southeastern Weddell Sea (Peck et al., 1995).

Diagnosis

Colony encrusting or erect, thin or fleshy. Autozooids often with a short peristome and puckered circular orificial region, mostly contiguous, not generally with kenozooids between them. Kenozooids, where present, non-spinose. Intertentacular organ present or absent.