Arbacia lixula

Key facts and history

The species was first described by Carl von Linné in 1758 under the name Echinus lixula.^[1] The genus name Arbacia was introduced by John Edward Gray in 1835, though its origin remains unclear.^[1] The species name lixula may come from the Latin word for a small cake or food preparation made from flour, water, and cheese.^[1] The test is flattened and almost always pink with ten red or brown bands that encircle the ambulacral zones in pairs.^[1]

In water, the spines are all of similar length and stay upright, never appearing messy.^[2] Four plates encircle the top anus, creating an anal valve.^[2] Crustose red algae and small filamentous algae make up the majority of this species' diet.^[3] Between 1983 and 1992, within a Mediterranean marine reserve, the density of this species rose from 8 to 100 individuals per square meter, a more than tenfold increase.^[3]

What the cited sources add

The DORIS account notes that Arbacia lixula is a small regular urchin with spines not exceeding three centimeters.^[1] The account also explains that A. lixula has a flattened test that is almost always pink with ten red or brown bands.^[1] It reports an individual with only three flaps in its anal valve, a symmetry considered non-existent in the animal kingdom except for a handful of archaic fossils.^[1]