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Echinoderms

Most echinoderms of the rocky and sandy seashore have a larval form living in the plankton. The proximity of the sandy beach at Dale means that the pluteus larva of the Sea Potato Echinocardium cordatum, common at low tide in the sand, is the most likely example to be found in the plankton samples during the summer (June -August). Photo right, is an early stage larva

Pluteus larva of Echinocardium, sea potato, early stage x200
Pluteus larva of Echinocardium sea urchin

Early pluteus of the Sea Potato, taken with phase contrast lighting

Ophiopluteus of brittlestar, calcite rods 400mn

Ophiopluteus of a brittlestar and taken with DIC lighting. This shows up the beautiful calcite rods that form a type of skeleton. 

Auricularia larva of Sea Cucumber (Holothuria)

The auricularia  larva of the sea cucumbers (holothurians) is large and complex. Nearly 1mm long it is difficult to see under the microscope as it is so transparent. All the edges shimmer as they are edged in cilia. The stomach is the large organ in the centre and near is a trapped Sabellaria larva. Bottom left are 2 ossicles (closeup photo below). This is the only specimen found over the last 3 years but this may be due to the short time they spend in the plankton and only a few species have planktonic larvae. Generally they are difficult to find.

This was photographed in 12 sections with DIC light, each a composite of about 20 images. Then the 12 composites were stitched to create one image. To increase contrast the photo was reversed to make a negative.

Auricularia larva Holothuria ossicles x400

Ossicles of the auricularia x400

Bipinnaria larva early stage of starfish
Bipinnaria larva early stage of starfish, labels

Bipinnaria larva in a starfish, probably the common starfish Asterias rubens.

Size is around 200 microns and typically found in spring although they are never common in the plankton.

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