Animal Diversity Web

Approximately 800 species of branchiopods are found worldwide in freshwater ponds, lakes, and inland saline waters such as the Great Salt Lake in Utah. Their fossil record includes the extinct order Lipostraca and dates back to the Devonian period (approximately 400 - 360 million years ago). Some references recognize four extant orders: Anostraca (fairy shrimps), Notostraca (tadpole shrimps), Cladocera (water fleas), and Conchostraca (clam shrimps). Members of these orders are commonly used for aquarium fish food, scientific research, and once were marketed as pets called sea monkeys. These small crustaceans are a very important source of food for fish and birds in nature.

Distinguishing features of a branchiopod include a small body (0.25 mm - 10 cm long), paired compound eyes, single simple eye, simple mouth parts, leaflike or phyllopodous appendages, and minimal body tagmosis. The nervous system and sensory system are simple, although some species vibrate their compound eyes to gather more visual information. Branchiopods use their leaf-like appendages for feeding, locomotion, and respiration. Gathered food particles are pushed into a ventral food groove that leads to the mandibles , then the mouth and, in turn, a complete gut . Undigested particles exit through the anus and nitrogenous wastes are eliminated through maxillary glands. These glands, located near the maxillae , also function in osmoregulation. Locomotion is generally achieved by metachronal beating of the appendages. The leaflike portions of the appendages have a large surface area that functions in gas exchange. Since most branchiopods are small with a thin cuticle, gas exchange can occur across the body wall as well. The circulatory system includes a heart that pumps blood into an open body cavity or hemocoel. The pigment in the blood of some species is hemoglobin.

Brine shrimp, of the order Anostraca, are most noted for their desiccation-resistant eggs that will hatch in salt water. Most species of branchiopods are gonochoric and some are parthenogenetic. Those species that have indirect development produce nauplius larvae.

References:

Brusca, R.C. and G.J. Brusca. 1990. Chapter 18: Phylum Arthropoda: The Crustaceans. Invertebrates. Sinauer Associates, Inc. Sunderland, Massachusetts.

Kozloff, E.N. 1990. Chapter 17: Subphylum Crustacea. Invertebrates. Saunders College Publishing. Philadelphia and other cities.

Encyclopedia Britannica, 2003. Branchiopod. Encyclopedia Britannica Online http://search.eb.com/eb/article?eu=118970