Friday, September 14, 2012

Top five on Friday

On his website "Why Evolution is True", Jerry Coyne has posted pictures of a pretty spectacular looking snail, Blaesospira echinus. So, I thought that today I would post my top five favourite mollusks. There were two mollusks in last week's list of my top five favourite marine animals. To give the other amazing species in phylum Mollusca a chance, I'll leave them out.

It was hard to keep this one out of last week's list. Like Glaucus atlanticus (who was number 1 last week), it steals cells from the organisms it eats and uses them for its own ends. In Elysia's case, it steals chloroplasts from the seaweed Vaucheria litorea. It's able to keep these alive for up to 9 or 10 months, which indicates that it has acquired genes for this task, probably by horizontal gene transfer.

The beautiful and fascinating Elysia chlorotica (Photo Wikipedia)
2. Giant squid, Archieteuthis dux

It's the second biggest invertebrate, after the colossal squid. And like the colossal squid, it has the biggest eyes of any animal. Eight species of giant squid have been named, but it's almost certain that there are fewer species and there may be only one, A. dux

The first live giant squid ever to be photographed in its natural habitat, the deep sea (photo Kubodera and Mori)
3. Dorytethis opalescens (formerly Loligo opalescens)

Like most cephalopod mollusks, D. opalescens is an amazing colour changer. But, unlike many other cephalopods it uses two different cell types to change colour (see here for an amazing bit of science communication explaining it all). It lives close to the surface and one of the reasons for its colour changing skill is thought to be that it avoids predators by countershading the light-dark patterns of wave lensing.

Doryteuthis opalescens (photo Wikipedia)
Wave lensing pattern on a sandy seafloor (Photo National Geographic)
4. Giant clam, Tridacna gigas

It's big, it's beautiful. Like corals, all of its colouration comes from symbiotic algae living inside its body.
The giant clam, Tridacna gigas (photo Wikipedia)

A bubble rafting snail that lives in the open ocean. The bubble raft is likely to have evolved from an ancestral egg coat.

The bubble rafting snail Janthina janthina (photo Denis Riek)

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