Strongylocentrotus droebachiensis (northern sea urchin) (Seawall Beach, Mt. Desert Island, Maine, USA)

Description:

Description: English: Strongylocentrotus droebachiensis (Müller, 1776) - northern sea urchin test in Maine, USA. (Left: aboral side; right: oral side) 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" that is used to graze on algae and other biofilms on hard substrates. Classification: Animalia, Echinodermata, Echinoidea, Strongylocentrotidae Locality: Seawall Beach, Acadia National Park, Mt. Desert Island, Maine, USA See info. at: en.wikipedia.org/wiki/Strongylocentrotus_droebachiensis and en.wikipedia.org/wiki/Sea_urchin. Date: 6 July 2020. Source: https://www.flickr.com/photos/47445767@N05/50084301837/. Author: James St. John.