Reproduction and Development
Sea urchins are dioecious, meaning they either contain male or female reproductive organs. They contain five gonads tucked under the test. These are located close to the anus and are protected by genital plates. One of these plates is perforated, and also acts as the madreporite. Sea urchins all release their eggs or sperm directly into the water column at the same time to ensure fertilization. It is not understood what causes S. droebachiensis to release their sperm or eggs, but it may have to do with temperature, because they usually reproduce in early spring.
Once fertilized, the gamete grows via mitosis and eventually becomes a larva capable of simple swimming called an echinoplutes. The metamorphosis from larva to a radially symmetrical adult is hugely complex, and only some of the more basic details are included here. The larva swims to the appropriate substratum where it attaches, usually with the “left and right” sides of the larva, becoming the “mouth and anus” sides. The embryonic openings for the mouth and the anus disappear completely, and new openings are created in the proper position. The ring canal grows radial extensions becoming the lateral canals. At this point in development, the sea urchin settles down to a benthic life.
Read more about this topic: Strongylocentrotus Droebachiensis
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