Ascidians are sessile (permanently attached) animals that are either solitary or colonial. Solitary ascidians are rather large, with a sack-like body attached to the substrate either by a flattened base, which may have a root-like hapteron, by a stalk, or by the ventral surface. The free end of the body is equipped with two siphons through which water enters and exits the body.
Ascidians can reproduce both sexually and asexually. Sexual reproduction results in the formation of a tadpole larva that is free-swimming for only minutes or hours before it settles on a hard substrate. The few predators that are known to take ascidians include some flatworms, gastropod mollusks, crabs, sea stars, and some fishes. Ascidians are suspension feeders, with prey including a variety of invertebrate larvae.
The Class Ascidiacea is further organized into finer groupings including:
- Order (5): Aplousobranchia · Enterogona · Phlebobranchia · Pyrosomida · Stolidobranchia
- Species: ZipcodeZoo has pages for 470 species and subspecies in the Class Ascidiacea.
Aplousobranchia is a suborder of sea squirts in the order Enterogona. They are colonial animals, and are distinguished from other sea squirts by the presence of relatively simple pharyngeal baskets. The posterior part of the abdomen contains the heart and gonads, and is typically larger than in other sea squirts. [more]
Enterogona is an order of tunicates in the class Ascidiacea. It describes a group of marine animals. [more]
Phlebobranchia is a suborder of sea squirts in the order Enterogona. The group includes both colonial and solitary animals. They are distinguished from other sea squirts by the presence of longitudinal vessels in the pharyngeal basket and by the gonads being surrounded by a loop of gut. The posterior part of the abdomen is absent, and many species also lack the epicardial cavity that surrounds the heart and other internal organs in many other sea squirts. [more]
Stolidobranchia is an order of tunicates in the class Ascidiacea. The group includes both colonial and solitary animals. They are distinguished from other tunicates by the presence of folded pharyngeal baskets and the complete absence of an abdomen. The abdominal organs of other tunicates are instead located to one side of the pharyngeal basket in this group. [more]
At least 628 species and subspecies belong to the Order Stolidobranchia.
More info about the Order Stolidobranchia may be found here.
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