Also known as Sea Squirts.

This is a very diverse group of invertebrates, whose life style is similar to sponges but their structure is more complex.

They all feed by sucking water in through one opening and blowing it out through another.  Many are individual animals, but perhaps living in a group, others form attached colonies.  These colonies may have special structures, like stems that support the whole colony. I don't understand how a co-operative structure like that develops - or evolved.  It does not seem to be a part of any individual member.
 Top Row.  
These are common types showing the two openings clearly.
is a translucent form, hard to see the openings but instead the internal organs show up looking like filaments of a light bulb.
Row above
This a common form growing to about 120cm across, not sure if this is a single individual or a colony.
These are the colonies that develop a stalk - I guess the stalk gets them into better water flow and so more food.
Feb 2nd 2001