NAME: ASCIDIANS, OR SEA SQUIRTS
SCIENTIFIC NAME: PHYLUM: CHORDATA; SUBPHYLUM: UROCHORDATA;
CLASS: ASCIDIACEA
LOCATION:  ALL OCEANS AND SEAS, FROM TIDAL POOLS TO DEEP ABYSSES
RECOGNITION FEATURES: TYPICALLY SAC-LIKE CREATURES OF VARYING COLORS (YELLOW, RED, BROWN, AND RARELY BLUE) WITH TWO HOLES (SIPHONS) THAT INJECT AND EJECT WATER FOR FEEDING, CAN LIVE ALONE, OR IN COLONIES UP TO MANY FEET IN SIZE

DETAILS:  Ascidians, or sea squirts, as they are more commonly known, are stationary creatures for most of their lives, affixing themselves to the ocean floor, coral, larger shells, algae, or underwater rocks at a young age and remaining there for their entire lives.  Other species  have adapted to living on sandy or muddy bottoms, and are not securely attached, but have small hairlike growths that help them stay fairly well-anchored to the surface.  Their bodies are fairly simple structures, consisting of an siphon which takes water in, another which ejects it, a heart, stomach, gonads, anus, and intestines.  Ascidians are filter feeders, dieting on plankton and other small particles by inhaling water which passes over a mucous layer, filtering the particles and passing them to the stomach, before the water is ejected.  This process of ejecting water is also a defense mechanism which the ascidian can use to frighten predators away.

 
Ascidians have an interesting blood circulation system, in which the heart beats roughly 100 times and pumps the creature’s clear blood in one direction.  Then the beating stops for a few moments, before restarting with the blood flowing in the opposite direction. 

 
Since there are well over 2000 species of ascidians in the world, the shapes, colors, and characteristics can vary quite a bit.  Some are large, smooth, and cylindrical, while others are spiny, thin, and resemble rocks.

 
Ascidians can either be solitary creatures, or can live in colonies with others, that can measure up to 23 feet wide.  Solitary ascidians can measure anywhere from .04 inches to 19.7 inches.  Most species, though, are typically less than one inch in height.  Colors vary throughout the species as well, and can be found in red, brown, yellow, and occasionally blue.  Other species are transparent, with small colored lines, or spots.  Ascidian colonies can be very beautiful, with different colored species making up varieties of colored patterns and textures.

Ascidians populate all the seas and oceans of the world, from the shallowest tidal pools, to the deepest depths of the oceans.  Some species have been found living in depths up to 5000 meters.  There have been cases discovered of ascidians living in brackish and even freshwater.