Crinoidea

Most crinoids on the GBR are subtidal and a few are abundant in lower intertidal areas. Reefs along the GBR have a diverse assemblage of crinoid species. Some species occupy the surface of soft sediments. There are several taxonomic reviews and surveys of the crinoid fauna of the GBR (see Additional reading). The Comas-teridae is a major family of tropical crinoids including Comanthus (Fig. 26.8G), Comaster (Fig. 26.8H), Comatella, Comatula, Oxycomanthus and Phanogenia species. The Mariametridae also has a number of genera on the GBR including Dichrometra, Lamprometra, Mariametra, Himermetra (Fig. 26.8I), and Stephanometra.

Crinoids are locally abundant on the GBR, as shown in a number of investigations of their population ecology. They extend their feather-like arms into the water column and may or may not have cirri, basal claw-like appendages, to cling to the substrate. Those that lack cirri use their arms for attachment. Many crinoids are fully or partially concealed within the reef infrastructure during the day and emerge at night to feed. Other crinoids are fully exposed at all times. The cryptic behaviour of crinoids may be to avoid predation by fishes, and several species have defensive chemicals that may deter predators. When disturbed from their perch, crinoids exhibit a striking

Figure 26.8 Echinoidea. A, Diadema savignyi (x 0.14) (photo: A. Hoggett); B, Echinothrix diadema (x 0.23); C, Echinometra mathaei (x 0.54); D, Tripneustes gratilla (x 0.50) (photo: U. Bové); E, Mespilia gobulus (x 1.00); F, Eucidaris metularia (x 1.00) (photo: A. Hoggett). Crinoidea. G, Comanthus alternans (x 0.16) (photo: A. Hoggett); H, Comaster schlegelii (x 0.20) (photo: A. Hoggett); /, Himerometra robustipinna (x 0.10) (photo: A. Hoggett). (Photos: M. Byrne, unless noted.)

Figure 26.8 Echinoidea. A, Diadema savignyi (x 0.14) (photo: A. Hoggett); B, Echinothrix diadema (x 0.23); C, Echinometra mathaei (x 0.54); D, Tripneustes gratilla (x 0.50) (photo: U. Bové); E, Mespilia gobulus (x 1.00); F, Eucidaris metularia (x 1.00) (photo: A. Hoggett). Crinoidea. G, Comanthus alternans (x 0.16) (photo: A. Hoggett); H, Comaster schlegelii (x 0.20) (photo: A. Hoggett); /, Himerometra robustipinna (x 0.10) (photo: A. Hoggett). (Photos: M. Byrne, unless noted.)

swimming behaviour with co-ordinated movement of the arms.

Crinoids are filter feeders, extending their featherlike arms above the substrate to capture food particles on their small tube feet that line the arms. The food is captured from flow and so crinoids take up positions on the reef and adjust the arrangement of the arms to take advantage of the ambient water movement. Food particles are conveyed to the mouth in the centre of the disc on food tracts.

Any collecting of echinoderms requires a permit (see Chapter 12).

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