a weird mollusc in Mylor Marina

In the series ‘pontooning‘, I returned to Mylor a week ago Friday to have a quick look around in the marina. The water was choppy, but visibility on the sheltered side of the pontoons was OK. I noticed a brown slug-like thing flapping about next to a boat. My first thought was a sea hare (I have seen plenty but have not yet seen them swimming). Upon closer inspection, I saw that it was something else, it had a shell like Haminoea or Akera, species I had never seen, especially not swimming. It turns out that it was Akera bullata, an Ophistobranch mollusc that is rarely seen in Cornwall and generally is observed crawling on the mud, not swimming. Why they swim is not well understood, but they usually swarm in numbers and so there must be some general response to the environment or mating behaviour going on. I saw four other individuals nearby so that fits. I made a couple of movies but as I could not look through the viewfinder the footage is not great (I went back Saturday and Sunday to try and find them back but was not able to). The shell can be clearly seen hanging down (Akera is related to the Sea hare but has retained its external shell). When lifted out of the water, the animal folds its mantle around its shell.

IMG_9973There were some other interesting things to see. The dominant organism on the pontoons is the tunicate Cione intestinalis (I see there are some other tunicate species hiding in these pictures; I will have to take a closer look next time). Amongst it grows the purple invasive Bryozoan Bugula neritina. Next, a colonial tunicate thta could be Botrylloides violaceus, Trididemnum cereum or Didemnun maculosum (or something else again). After that, the beautiful Lightbulb sea squirt Clavelina lepadiformis.IMG_1849IMG_1656IMG_1677IMG_1704Plumose anemones Metridium senile are always common here. I for the first time noticed another species Diadumene cincta, very pretty! IMG_1867IMG_1859 IMG_1754 IMG_1745

Botrylloides leachi

One of the most beautiful organisms growing on the rocky shore: the colonial ascidian Botrylloides leachi (it does not have a common name). This is a type of Tunicate. The colony is embedded in a gelatinous but hard test, which is unusual to the touch. The test contains strings of individual tunicates (zooids); you can see each has a siphon on the top, water enters here, and is filtered by a mucus-net that is eaten along with the filtered microbes. Filtered water exits from a shared siphon in the middle of the colony. I am not sure what the yellow ‘stiles’ are, but suspect that they are budding zoids. In the related species Botryllus schlosseri (I will post some pictures of this species in another post), a model system for research, each zoid is resorbed in the test and replaced by a newly bud zoid on a weekly basis.




P.S. In hindsight, this might be B. violaceus (see here)