BIOLOGY

Biology

Biology

Article Suumary:"Patterns of stimulated bathochordaeus charon (Tunicata: Pyrosomatidae)"

The article states that the class Appendicularia is made up of one order, three families, and 64 species. Appendicularians are related to benthic tunicates and are commonly called larvaceans because they retain the larval tadpole stage as sexually mature adults. These animals are transparent and lack the outside covering, or tunic, of their benthic relatives. The body is composed of a trunk containing most of the internal organs and of a tail with a notochord running down the middle. The trunk secretes a mucous house, which may enclose the animal, as in Oikopleura and Bathochordaeus species, or enclose only the tail, as in Fritillaria species. The body and house appear jelly-like and are therefore grouped as gelatinous zooplankton. Larvaceans are small, ranging from a 0.04 in (1-mm) body length with a 0.2 in (4 mm) house to Oikopleura to 1 in (25 mm) body length with a house more than 6.6 ft (2 m) in diameter for the giant larvacean Bathochordaeus.

The article states that appendicularians move their tails rhythmically inside the house to produce a current that filters tiny food particles and to move the house through the water. If the filters become clogged or something bumps the house, the appendicularian abandons the house through a mucous trap door in the posterior of the house. The beginnings of a new house lie on the trunk of the body, and the animal inflates the new house and flips inside. Some appendicularians have bioluminescent granules embedded in the house wall. It is thought that predators of the animal may eat an empty house that is flashing light while the original house builder swims away to make another house. Surface waters of some coastal bays and harbors can look brilliantly bioluminescent from large aggregations of appendicularians.

All appendicularians are filter feeders with an amazing filtration apparatus. The mucous house has two prefilters embedded in the wall and an inner filter connected to the animal's mouth. The filters are made of strands of mucus that allow only the smallest food particles <0.0004 in (<1 µm) into the tube leading to the mouth. Appendicularians can be important prey for many animals, including larval and adult fish. At least one fish important to humans, the anchovy, relies heavily on appendicularians for food.

The article states that only sexual reproduction occurs in appendicularians. All except Oikopleura dioica are hermaphrodites. Gametes are shed directly into the surrounding water. Hermaphrodites release sperm, and the eggs burst out of the body wall, a process that results in the death of the animal. If phytoplankton numbers are high, production of a large number of eggs and a fast generation time result in rapid development of blooms of appendicularians, sometimes in a matter of a few days. Although there is much to be learned about the ecology of appendicularians, none of these species is known to be in danger of extinction. No species is listed by the IUCN. Because of potentially high population numbers, fast generation times, and ...