Sea urchins are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the Echinoids dates from the Ordovician period, some 450 million years ago.

Illustration of the typical life cycle of a sea urchin (not to scale). While the sea urchin we're most familiar with is hard, spikey, and lives along the seafloor, a sea urchin's life actually starts in a completely different form, floating through the water as plankton.

Jan 11, 2025 · Sea urchins, or simply urchins, are globular echinoderms of the phylum Echinodermata (consisting of starfish, sea cucumbers, sand dollars, brittle stars, and crinoids), forming the class Echinoidea. These animals begin their life as bilaterally symmetrical larvae but develop into adults with pentamerous or five-fold symmetry.

Jan 9, 2025 · Sea urchin, any of about 950 living species of spiny marine invertebrate animals (class Echinoidea, phylum Echinodermata) with a globular body and a radial arrangement of organs, shown by five bands of pores running from mouth to anus over the test (internal skeleton).

The sea urchin embryo initially undergoes ten cycles of cell division forming a single epithelial layer enveloping a blastocoel, followed by gastrulation producing the three germ layers.

Oct 19, 2017 · Sea urchins gather in large groups that contain both males and females. The females expel hundreds of millions of orange eggs, which prompts the males to release their clouds of white sperm. Urchin eggs float in the warm sea water for up to eight weeks.

Sea urchins which must pass through a feeding larval stage in their life cycle are termed planktotrophs. The opposite condition, where the larva develops directly into the adult form without needing to feed is called lecithotrophy. A schematic life cycle is shown below.

Jan 31, 2023 · Thanks to a tool called Virtual Urchin, students can explore and conduct detailed urchin experiments as well as learn how our changing ocean may impact these organisms without ever setting foot in a laboratory. This diagram shows the stages of the sea urchin life cycle. Students learn about each stage on the Virtual Urchin tool website.

It includes the follow- ing: a description of the reproductive cycle of sea urchins; the factors that cause variations in the size and quality of the gonad; methods for sampling sea urchin gonads; and a guide to reading the histology slides of sea urchin gonads in order to be able to classify them into the dif- ferent stages of the reproductive ...