Curling arms of a crinoid (Petasometra clarae).
Nikonos RS SLR camera; Nikonos 50mm objective and Rene Aumann UW Services X2 teleconverter; two Nikonos S-105 strobes; Ektachrome VS 100 film; F4; 1/125s; TTL. Taken at: 6m depth; diving from MS. FeBrina. Trip organised by Chris Newbert of RS Tours. Shot on: 16:09 9th March 2005; sunny, no current. Crinoids may look like plants, but they area animals, related to star fish, sea urchins, sea cucumbers and brittle-stars. They feed by filtering plankton with their comb-like legs and curling these down to the central mouth. So they choose a point on the reef with strong current bringing nutrient-rich water streaming past, and hang on with claw-like legs, spreading their feathery arms up like a disk into the current. They can both walk with these claw-like legs and their feathery arms in a mix between a wave and a spider’s crawl, or they can swim using all arms simultaneously. The feathery arms have hooks that cling to anything that touches them, which makes them un-appetising to predators. As such the crinoid is also a good host for other animals seeking protection. Often a male and female pair of squat-lobsters grasp the legs or undersides of the arms, usually with a colour pattern similar to the host, so almost invisible. Several types of shrimp also find home in the arms – some perfectly camouflaged in the colour of the host, and others bizarrely black and white checker pattern making them very visible. Around the central mouth can often be found cling fish with the same colour and markings as the host crinoid. They form a sucker-cup with their petrel fins to hold on tight.
Size: 8273px × 5315px
Location: Deka Deka, Milne Bay, Papua New Guinea.
Photo credit: © Malcolm Ross / Alamy / Afripics
License: Licensed
Model Released: No
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