We had a wonderful time on Tuesday morning collecting plankton with colleagues from University College Cork. We learned about methods of plankton collection and how to do comparative plankton sampling.
In the plankton, we were excited to find a diversity of invertebrate larvae. Brittle star larvae (ophiurid plutei) were particularly common in our samples. These larvae have long arms supported by skeletal rods. The arms are ciliated to aid in swimming and capturing food. They spend weeks developing in the water, growing more arms, then growing juvenile rudiments inside of the larva. We found larvae in a range of developmental stages, from early pluteus with just four arms, to advanced larvae with complete juvenile rudiments in the process of metamorphoisis.
We also found an actinotroch - a larva of a phoronid worm (or horseshoe worm). This larva has a hood at the front end, a set of tentacles around the mouth, and a ring of cilia at the back end.
The last sample we examined had an giant advanced stage larva of a sea star. The elongated pre-oral lobe is a characteristic of the genus Luidia. We have only seen one adult Luidia in the lough - they are unique in having no suction cups on their tube feet.
A few days later, while snorkeling, we saw more of these giant larvae in the water. It was amazing to swim amongst the larvae and watch them move - they constantly sway back and forth by bending their pre-oral lobe, which appears to be a modified swimming structure.