Sea Potato, Echinocardium cordatum

The Sea Potato (Echinocardium cordatum) is a sea urchin belonging to the family Loveniidae. It’s located in sub-tidal regions in temperate seas around the globe and resides buried in the sandy sea floor.

The sea potato is a heart-shaped urchin clothed in a dense mat of furrowed yellowish colored spines which grow from tubercles and mainly point backwards. The upper surface is flattened and there’s an indentation close to the front. It’s a beige color but the tests that are found on the strandline have frequently lost their spines and are colored white. The spines ensnare the air which helps prevent asphyxiation for the buried urchin. The ambulacrum creates a broad furrow in a star-shape extending down the sides of test. There’s two series each of two rows of tube feet. The test reaches from 6 to 9 centimeters long.

This sea potato has a discontinuous cosmopolitan distribution. It’s found in temperate seas in the North Atlantic Ocean, the west Pacific Ocean, around Australia, New Zealand, South Africa and the Gulf of California at depths of down to 230 meters. It’s very common around the coasts of the British Isles within the neritic zone.

This species buries itself in sand to a depth of 10 to 15 centimeters. It occurs in sediments with a wide variety of grain sizes. It creates a respiratory channel leading to the surface and two sanitary channels behind itself, all line by a mucus secretion. The location of burrows can be recognized by a conical depression on the surface in which detritus collects. This organic debris is utilized by the buried animal as food and is passed down via a long tube feet found in the front of the ambulacrum.

The sexes are separate in the sea potato and the females and males both liberate gametes into the water table during the spring. The echinoplutei larvae that develop after the fertilization process have four pairs of arms and are flattened laterally. In late stage larvae, tube feet might be seen developing around the skeleton. The larvae are pelagic and create a portion of the zooplankton. Metamorphosis takes place about 39 days after the fertilization process with the larvae settling out and burrowing into the substrate. The lifespan of the sea potato is though to be at least 10 years.

In the sandy sea bed that it favors, the sea potato is frequently found in association with the bivalve mollusks Tellina fabula, Ensis ensis and Venus stritula.

The bivalve Tellimya ferruginosa is frequently found living inside the sea potato’s burrow as a commensal. Up to 14 have been found in one burrow with the young being attached to the spines of the urchin via byssus threads. Another species that utilizes the burrow is the amphipod crustacean, Urothoe marina.

Image Caption: This common heart urchin was sampled on the Belgian Continental Shelf in 2000. Credit: Hans Hillewaert/Wikipedia (CC BY-SA 3.0)