Class Branchiopoda (Branchiopods)
Major Atributes:
- Small, mostly freshwater crustaceans; usually live in absence of fish.
- Use leaf-like trunk appendages for swimming and filter-feeding.
- Flattened leg-like structures extend from first segment and act as gills ("Gill legs"--branchio-poda).
- Carapace present in all groups but one.
- Reproduce both sexually and asexually; keep eggs in brood chamber.
- Ability to resist dessication in eggs.
- Egg-laying is closely related to moulting.
Description:
The branchiopods
consist of two major groups, the
Anostracans and Cladocerans which are called fairy shrimp and water fleas respectively. Fairy shrimp live in freshwater pools and
springs, and unlike other branchiopods, they lack a carapace and have
stalked eyes. Their bodies are elongated, often with more than 20
trunk segments. Most are about 1cm in legth, however some giants have
been known to reach 10cm. Fairy shrimp swim upside down, beating
their trunk appendages in rhythm. Setea located on their legs capture
food particles throughout the beating movement and the particles are
then passed along a groove on the ventral side to the mouth. Mating
occurs by the male fairy shrimp clasping the female with its second
antennae. The female lays and stores its eggs in a brood sac before
releasing them. Fairy shrimp hatch as nauplii and are usually
mature adults in one week.
Water fleas are laterally flattened with a carapace which
covers the body trunk but not the head. Most of these branchiopods
are between 1-5mm in length. A powerful set of second antennae serve
in swimming and usually two of the five segments of the trunk serve as
filtering appendages. Most water fleas live in freshwater
environments, filtering small particles, however a few are marine
carnivores. These organisms reproduce mostly by parthenogenesis and
brood their eggs in a dorsal chamber.
Some Interesting Facts:
- The blood of the water fleas is remarkably like that in humans because it contains the red respiratory pigment, haemoglobin.
- The eggs which are released are extremely resistant to dessication. Some eggs hatch immediately when wetted, however some take more than one inundation because the environmental conditions are not appropriate for hatching. Thissort of diapause met
hod ensures that an entire population is not lost under poor conditions.
- A small group, called brine shrimps are found in brackish environments and have an incredible resistance to salt. Their ability to live in this particular environment eliminates most predators. Brine shrimp have been dried and subjected to high vac
uum, heated to 103 degrees Celsius for over and hour, and cooled to a temperature of liquid for hours and the eggs still hatched regardless of this harsh treatment.
- Populations may include only females which reproduce parthenogenically over several generations until a change in temperature or a shortened food supply causes a production of males.
- After being cast off, the brood chamber with eggs can withstand drying, freezing and even passage through the guts of vertebrates.
- Some water fleas exhibit a cycle of morphological changes (usually in head shape,) with the seasons, called cyclomorphosis.
Some Pertinent Books Found in Lamson Library:
- Banister, Dr. Keith and Dr. Andrew Campbell. 1985. The
Encyclopedia of Aquatic Life. New York: Facts on File.
- Bertin, Leon. 1976. Larousse Encyclopedia of Animal Life. New
York: The Hamlyn Publishing Group Limited.
(Danielle M. Mayhew, Fall 1994; edited by T. Shultz, Spring 1995)