Echinoidea

The Echinoidea includes the familiar sea urchins and irregular urchins (sand dollars and spatangoids). On the GBR most sea urchins are cryptic during the day, with species such as Diadema savignyi (Fig. 26.8A) and Echinometra mathei (Fig. 26.8C) emerging at night. Echi-nostrephus species excavate holes in coral to form a permanent residence from which its spines emerge. The

Figure 26.6 Ophiuroidea. A, Ophiocoma dentata (x 0.50); B, Ophiocoma scolopendrina (x 0.50); C, Ophiocoma erinaceus (x 0.33); D, Ophiarthrum pictum (x 0.38); E, Ophiarthrum elegans (x 0.50); F, Ophiomastix janualis (x 0.38); C, Ophiomastix mixta (x 0.50); H, Ophiomastix caryophyllata (x 0.50); /, Ophiomastix annulosa (x 1.00) (photo: S. Uthicke). (Photos: M. Byrne, unless noted.)

Figure 26.6 Ophiuroidea. A, Ophiocoma dentata (x 0.50); B, Ophiocoma scolopendrina (x 0.50); C, Ophiocoma erinaceus (x 0.33); D, Ophiarthrum pictum (x 0.38); E, Ophiarthrum elegans (x 0.50); F, Ophiomastix janualis (x 0.38); C, Ophiomastix mixta (x 0.50); H, Ophiomastix caryophyllata (x 0.50); /, Ophiomastix annulosa (x 1.00) (photo: S. Uthicke). (Photos: M. Byrne, unless noted.)

commercial urchin Tripneustes gratilla (Fig. 26.8D) is common in sea grass areas. Common irregular echi-noids include the sand dollar Peronella lesueuri that occur in abundance along the Queensland coast and the spatangoid urchin Breynia australasiae that burrows in sandy inter-reefal areas and can be locally abundant. The burrowing activity of echinoids, particularly by Echinometra species, is important in bioerosion of coral reef and intertidal habitats (see Chapter 8).

Most sea urchins are grazers, using their hard calcareous teeth to remove algae and encrusting organisms from the surface. As a member of the grazing guild on coral reefs, sea urchins contribute to keeping the biomass of algae low, thereby preventing overgrowth of algae over coral substrate. Sand dollars are suspension feeders, collecting particles from flow and transferring these by specialised tube feet down the food groves on the surface of the test to the mouth. Spa-tangoids have a secondary bilateral profile associated with their burrowing life style. They are deposit feeders removing organic matter from ingested sand as they propel themselves through sediments using their specialised 'rowing' spines.

Figure 26.7 Ophiuroidea. A, Ophiarachna incrassata (x 0.71); B, Ophiarachnella gorgonia (x 0.50) (photo: J. Keesing); C, Ophiopeza spinosa (x 2.50); D, Ophiolepis elegans (x 0.63); E, Ophiomyxa australis (x 0.25); F, Ophionereis porrecta (x 0.50); G, Macrophiothrix lorioli (x 0.33) (photo: J. Keesing); H, Macrophiothrix nereidina (x 0.33) (photo: J. Keesing); I, Amphipholis squamata (x 8.33). (Photos: M. Byrne, unless noted.)

Figure 26.7 Ophiuroidea. A, Ophiarachna incrassata (x 0.71); B, Ophiarachnella gorgonia (x 0.50) (photo: J. Keesing); C, Ophiopeza spinosa (x 2.50); D, Ophiolepis elegans (x 0.63); E, Ophiomyxa australis (x 0.25); F, Ophionereis porrecta (x 0.50); G, Macrophiothrix lorioli (x 0.33) (photo: J. Keesing); H, Macrophiothrix nereidina (x 0.33) (photo: J. Keesing); I, Amphipholis squamata (x 8.33). (Photos: M. Byrne, unless noted.)

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