Inspired by Quixote’s excellent post about ascidians–my firstest study organism EVAH–I’ve decided to delve into the archives and repost something of my own about ascidians.
I used to study botrylloid ascidians (Botrylloides diegensis to be exact). Ascidians are one of our closest invertebrate relatives. In their larval stage, they look like little tadpoles and even have a notochord (picture taken from here):
Within a few hours, the tadpole settles on a flat surface, and resorbs its tail, and essentially turns itself into a giant pair of vocal chords that are wrapped in mucus. The whole structure is covered with a tunic, that has an inflow tube and an outflow siphon. It then filters food out of the water (look at the top critter; it’s about 4mm in diameter; taken from here):
Those little orange bulbs around the edges of the colony are the ampullae, which are involved in circulation (they’re kind of like hearts). A complete aside: ascidians use vanadium in their blood pigment (vanadium is toxic to most organisms). Back to our original programming… If it’s a colonial ascidian (and botrylloids are colonial), it begins budding off more siphons (look at the bottom colony above). Eventually, it grow into a nice big colony that looks like this (taken from here):
On the East Coast, Botrylloides diegensis is an invasive marine species; I’ve personally seen habitats in Maine where they’ve been so successful that all the native filter feeding species have been driven into refuge habitats, such as the underside of kelp fronds. One of the cool things about botrylloid ascidians is that genetically distinct colonies can fuse… but I’ll talk about that next week (and hopefully, I’ll be able to dig up some old photos).
Here’s what a colorful relative (unknown species) looks like (taken from here):