Goodbody

Sea Squirts, otherwise known as Ascidians, are sessile marine animals living attached to hard substrates such as pier pilings, boat hulls, rocks or mangrove roots The body takes the form of a slightly flattened cylinder with two large tubular openings (siphons) at one end. They obtain their energy by sucking in and filtering large volumes of seawater.

Water enters the animal through one of the two siphons and small particles of organic material, bacteria and minute plants (phytoplankton) are trapped on a mucus sheet in a porous chamber or pharynx. Water is driven through the animal by small hair-like cilia on the inside wall of the pharyngeal chamber. The filtered water passes into a second (atrial) chamber surrounding the pharynx from which it is ejected from the animal through the second of the two siphons. The entire body of the animal is enclosed by a soft protective covering, the test or tunic.

In development the fertilised egg develops into a small (one milli-metre) larva consisting of a bulbous trunk propelled by a muscular tail. The trunk contains sensory structures responsive to illumination and gravity. The tail is of special interest as it contains a series of vacuolated cells providing a compression member foreshadowing the notochord of higher animals such as fish, reptiles and mammals. It is the notochord which gives rise to the vertebral column during the development of these vertebrate animals.

Like higher chordates the ascidian larval tail also contains a hollow dorsal nerve cord. Thus, the ascidian larva contains in its tail, structures which are peculiar to the chordate line of evolution leading to mammals and Man. This combination of characters leads us to postulate that in the course of evolution our chordate ancestry may have been derived from an ascidian larval type of organism.

Many ascidians are solitary animals (3-8cm in length) lacking close association with others of their species. Others are able to replicate to form a set of clones (zooids) gathered together to form a colony of small (1-5mm) zooids. Colonies may exist as clusters of zooids or as cushions in which many zooids are embedded in a common test material. Others form encrusting sheets or grow like small vines in which individual zooids are connected by common vascular strands. Ascidians live in all oceans of the world and have been found at all depths from shallow coastal environments down to several thousand metres in depth.

Some Interesting facts about Ascidians

Clavelina Puertosecensis

The heart is tubular and can alternately pump blood in both directions.

Some blood cells contain metallic compounds of vanadium, iron, tantalum, and related metals. These blood cells contain strong sulphuric acid.

Compounds of pharmaceutical interest have been extracted from a few species.