Three urchins are present in Lough Hyne: Echinus esculentus, Paracentrotus lividus, and Psammichinus miliaris. All three urchins are formed from globular, calcerous tests, which are covered with moveable spines. The body has five double-rows of tube feet that, paired with these spines, allow it to move slowly. All have mouths on the undersurface of the test, and are equipped with a complex eating mechanism called an “Aristotle’s lantern” which includes a set of teeth that can move multi-directionally to help the urchin diversify its omnivorous diet.
The first, Echinus esculentus, is usually found to be the size of an adult hand, but at Lough Hyne, they can get a bit bigger. It is a fairly widely-distributed species, and found mostly while snorkeling in the lower shore of the Lough. Being equipped with the Aristotle’s lantern, this urchin eats seaweed and encrusting invertebrates by scraping rocks clear as they move across their habitat. Echinus reproduces via free-spawning in the spring, with large females producing as much as 20 million eggs. The egg will develop into echinopluteus for 8 weeks then will metamorphose into a 1mm (in diameter) urchin. This urchin, depending on conditions, can grow up to 40mm in the first year, and live for 12 years.
Paracentrotus lividus is about half the size of Echinus, and is found in the lower shore on rocky substrates. It is known to use its Aristotle’s Lantern and spines to bore into rocks to protect against wave action, desiccation and predation. Here at the lough, they are often found on the undersides and crevices of rocks. Paracentrotus scrapes at algal sporlings, seaweed, and detritus, acting as a control for rapidly growing species. For this reason, Paracentrotus is a key species in the lough, and its decline may potentially be related to the invasion and expansion of many seaweeds within the lough’s shores. Reproduction occurs similarly to Echinus, with juveniles that can grow to 35-50mm in about four years, and it lives up to nine years. Breeding occurs from January to March, and then again in August to September.
Psammechinus miliaris habitat overlaps with that of Paracentrotus. Psammechinus lives amongst the seaweeds, which are used as camouflage. Psammechinus eats a great variety of prey, mostly organisms that attach to rocks, such as ascidians, barnacles, and bivalves. Reproduction occurs similarly to the other two urchins, with reproduction occuring in the spring and summer. Plutei settle after four weeks, when they are at most 1mm in diameter. They grow up to 10mm in diameter in two years, living up to ten years.
Source: Fish, J.D., and S. Fish. A Student’s Guide to the Seashore. London: Unwin Hyman Ltd, 1989. Print.