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

General introduction
lividus reaches a maximal test diameter of 65 to 70 mm (Grosjean, pers.
obs.).
Figure 4. Internal anatomy of a regular sea urchin, side view. (modified after Reid, W.M., In:
Ruppert & Barnes, 1994).
The regular sea urchin body can be divided in two hemispheres: an oral
pole where the mouth opens, directed towards the substratum, and an
opposed aboral pole bearing the anus. The mouth opens in a short pharynx
surrounded by a complex scraping apparatus –recall that P. lividus is a
grazer– called Aristotle's lantern (Fig. 4). It is composed of 5 pyramids
radially arranged around the mouth and each holds one tooth (Fig. 3A).
The digestive tract forms two complete turns around the inner side of the
test wall, one in one way and the other one in the opposite direction,
leaving much space in the internal cavity for gonads (Fig. 4).
The anatomy of the reproductive organs reflects the radial symmetry of
the animal (Fig. 5). Five gonads open in genital pores close to the anus and
are disposed radially in the coelomic cavity along the ambulacral zones.
They start developing when the echinoid is still very small, around 4 to 6
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