Growth model of the reared sea urchin Paracentrotus ... - SciViews

General introduction
substrate to settle and metamorphose. An adequate chemical stimulus is
required (Gosselin & Jangoux, 1996). Metamorphosis lasts less than one
hour: the echinoid rudiment is evaginated and most larval tissues are
resorbed. The postlarva resembles a miniaturized adult (Fig. 2B) but has
no mouth and no anus, and is thus endotrophic (Gosselin & Jangoux,
1998). After a week the postlava has undergone some major changes and
becomes an exotrophic juvenile with a fully developed and functional
digestive tract. It then begins foraging.
Figure 3. External anatomy of a regular sea urchin. A. Oral view. B. Aboral view. (after
Reid, W.M,. In: Ruppert & Barnes, 1994).
From an anatomical point of view, the body of the postmetamorphic
echinoid has a quasi-spherical shape (for regular sea urchins such as P.
lividus) with a pentaradial symmetry (Fig. 3). Its shape is constrained by
an endoskeleton, located just under the epidermis, composed of calcareous
ossicles sutured together in a solid test. This test supports movable spines
that cover the body of the animal and are the origin of the name
Echinoidea, "like a hedgehog (porcupine)" (Ruppert & Barnes, 1994). P.
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