Here are some pictures and some info. Invasive might be too strong of a word for these. It seems they have been around the Atlantic north of Cape Cod for a long time. They live in the sand and are related sea urchins with a very similar type shell.
This sea potato (Echinocardium cordatum) looks similar to its root vegetable namesake, but it's a sea urchin! The spines on this urchin are more hair-like than the spikes seen on some more commonly known urchins, and they lay flat across the urchin's body. They can be found buried in the sediments of the sea floor. In their burrow they separate themselves from the sand and mud with a layer of mucus, and they keep several holes in the sediment around them to breathe, eat and remove waste.
The sea potato is a heart-shaped urchin clothed in a dense mat of furrowed yellowish spines which grow from tubercles and mostly point backwards. The upper surface is flattened and there is an indentation near the front. This urchin is a fawn colour but the tests that are found on the strandline have often lost their spines and are white. During life, the spines trap air which helps prevent asphyxiation for the buried urchin.[3] The ambulacrum forms a broad furrow in a star shape extending down the sides of the test. There are two series each of two rows of tube feet. The test reaches from six to nine centimetres in length.[2]
The sea potato has a discontinuous cosmopolitan distribution. It is found in temperate seas in the Adriatic Sea,[4] 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 metres.[1] It is very common round the coasts of the British Isles in the neritic zone.
The sea potato buries itself in sand to a depth of ten to fifteen centimetres. It occurs in sediments with a wide range of grain sizes but prefers sediments with a size of 200 to 300 µm and a low mud content.[6] It makes a respiratory channel leading to the surface and two sanitary channels behind itself, all lined by a mucus secretion.[1] The location of burrows can be recognised by a conical depression on the surface in which detritus collects. This organic debris is used by the buried animal as food and is passed down by means of the long tube feet found in the front of the ambulacrum.[5]
The sexes are separate in the sea potato and the males and females both liberate gametes into the water table in the spring. The echinoplutei larvae that develop after fertilisation have four pairs of arms and are laterally flattened. In late stage larvae, tube feet may be seen developing round the skeleton.[7] The larvae are pelagic and form part of the zooplankton. Metamorphosis takes place about 39 days after fertilisation with the larvae settling out and burrowing into the substrate.[8] The lifespan of the sea potato is thought to be ten or more years.[9]
Ecology[edit]
In the sandy sea bed that it favours, the sea potato is often found in association with the bivalve molluscs Tellina fabula, Ensis ensis and Venus striatula.[10]
The bivalve Tellimya ferruginosa is often found living inside the sea potato's burrow as a commensal. Up to fourteen have been found in one burrow with the young being attached to the spines of the urchin by byssus threads.[11] Another species that makes use of the burrow is the amphipod crustacean, Urothoe marina.[12]
References[edit]
The dried shell (also known as the test) of this urchin resembles a potato, hence the common name – sea potato.
The sea potato, Echinocardium cordatum, is a common echinoderm found along beaches on all coasts of Britain and Ireland.
The sea potato is related to sea urchins, heart urchins, and sand dollars.
Most sea urchins live in rocky areas, but the sea potato prefers sand, particularly muddy sand.
The spines of this echinoderm are thin and flattened.
On the underside of the urchin are special spoon-shaped spines that help it to dig.
There are longer spines of the back of the sea potato which aid in helping to breathe while it is burrowing.
The sea potato can survive to depths of 650 feet.
Unlike regular urchins, the sea potato has a distinct front end (i.e., not circular).
The sea potato can grow up to 3 inches.
The sea potato is very fragile and rarely survives collection.
While alive the sea potato is deep yellow in color and covered in fine spines.
The sea potato prefers sub-tidal regions in temperate seas.
The sea potato are a type of heart-shaped urchin.
Sea potato are deposit feeders and tube feet on its underside the sea urchin pick up sediment from the front of its mouth.
The sea potato has no conservation concerns.
The sea potato often has a commensal symbiotic relationship with the bivalve Tellimya feringuosa attached to its anal spines.
