Often called Button polyps, zoanthids are very common inhabitants of reef aquaria. Zoanthids are found throughout the world s oceans but are most widely represented in warm waters; some 300 species have been described so far (Wilkens, 1990). They can occur as single polyps or as colonies, either connected by a comon tissue or unconnected. Some genera are found in wave-swept reefs or calm shallows (e.g. Isaurus, Palythoa spp., Protop-alythoa spp. and Zoanthus spp.) while others are found only in association with sponges, hydroids, worm tubes or gorgonians (e.g., Acrozoanthus, Parazoanthus and Epizoanthus spp.). Although zoanthids are related to stony corals, they do not produce a skeleton (except the poorly known genus Gerardid) but some genera do incorporate sediments into their body wall (mesoglea) giving them a rough texture, e.g. Palythoa spp. and Protopalythoa spp. (Mather and Bennett, 1993).
Despite their widespread availability and popularity with aquar-ists, the Zoanthidea are a relatively poorly understood, little studied order and their identification to species, and even genera can be challenging. This might seem surprising given how common they are in home aquaria and in nature, but there are many factors that come into play which affect the ease of identification. For instance, they exhibit a variety of colony and polyp morphology; they lack taxonomically significant skeletal structures like those found in stony and soft corals; and the reliance on old preserved specimens for taxonomic work makes comparisons to new samples very difficult. Furthermore the low number of studies on this group has contributed little information about this order (Muirhead and Ryland 1985; Mather and Bennett 1993). Finally, microscopic examination of internal features is often
The characteristic contrasting oral necessary to determine taxonomically important characteristics;
disc colours oi Zosnthussw- are something better left to the specialist (Mather and Bennett, 1993).
J c Deibeek However, we have included this information in the genera descriptions in chapter eight for those of you so equipped.
rallia), As a result, they share many anatomical features, but have
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