Slate pencil urchin

Distribution

The slate pencil urchin can be found on both sides of the Atlantic, and throughout the Caribbean. On the western side of the Atlantic, the slate pencil urchin has been found as far north as Cape Hatteras, North Carolina, and as far south as Rio de Janeiro. In the Gulf of Mexico, populations have been reported at Alacran Reef, Campeche Bank. On the eastern side of the Atlantic, a closely related sub-species, "Eucidaris tribuloides var. africana", has been reported at Cape Verde Islands, in the Gulf of Guinea, and at the Azores and Ascension Islands.

Behavior

When its development is contrasted to the cidaroid sister subclass Euechinoidea, "E. tribuloides" becomes a very interesting organism from the standpoint of developmental and evolutionary biology. In euechinoid embryonic development, e.g. in the purple sea urchin, the micromeres comprise a set of four small cells that reside at the base of the vegetal plate. They are a "precociously invaginating lineage", meaning that they move into the blastocoel just prior to gastrulation; these four cells then eventually give rise to the larval skeleton. Similarly, "E. tribuloides" also possesses a larval skeleton that arises from a special lineage of cells. In contrast, however, the number and size of its micromeres can vary, and they do not precociously invaginate; rather, they ingress during gastrulation and bud off from the tip of the growing archenteron. Although there are numerous molecular differences between the "spicule-forming cells" of "E. tribuloides" and the primary mesencyhme cells of euechinoids, these two cell lineages are thought to be homologous and have been contrasted in developmental evolution research.

Reproduction

Reproduction in "E. tribuloides" seems to be sensitive to seasonal cycles, solar cycles, and the lunar cycle. In the Florida Keys, "E. tribuloides" was found to obtain peak gravidity in the late summer and early fall. Populations in Panama, however, were found to be gravid in the spring, summer and fall, with peak gravidity occurring around the full moon.