Arbacia punctulata (purple sea urchin) (Sanibel Island, Florida, USA) 2

Description:

Description: English: Arbacia punctulata (Lamarck, 1816) - purple sea urchin (oral side) in Florida, USA (December 2013). The echinoids are a group of echinoderms - they are starfish relatives. On modern Earth and in the fossil record, echinoids are exclusively marine. Two broad groups exist - the regular echinoids (sea urchins) and the irregular echinoids (heart urchins and sea biscuits and sand dollars). Sea urchins have subglobular to slightly flattened, radially symmetrical skeletons (tests) composed of calcite (CaCO3 - calcium carbonate). The sea urchin test is covered with spines - these readily detach after death. Sea urchins have a mouth with a pentaradial structure called an "Aristotle's lantern" (see the center of the urchin in the above photo) that is used to graze on algae and other biofilms on hard substrates. The dead sea urchin shown above is Arbacia punctulata, the purple sea urchin. The specimen sits on a marine beach dominated by siliciclastic sand. Classification: Animalia, Echinodermata, Echinoidea, Arbacioida, Arbaciidae Locality: Algiers Beach, southern shore of Sanibel Island, Gulf of Mexico coast of southwestern Florida, USA (vicinity of 26° 25' 27.64" North latitude, 82° 03' 56.17" West longitude) More info. at: en.wikipedia.org/wiki/Arbacia_punctulata. Date: 16 December 2013, 17:24:06. Source: https://www.flickr.com/photos/47445767@N05/25087883352/. Author: James St. John.