Cladocera
Latreille 1829
Taxonomy
| Phylum | Arthropoda |
| Subphylum | Crustacea |
| Class | Branchiopoda |
| Order | Cladocera |
Size
- Approximately 1 mm long.
Description
- Commonly called water fleas.
Distinguishing characteristics
- The thoracic appendages (pereiopods) are typically leaf-like, lobed and densely setose.
- These appendages also bear gills and explain the derivation of the name Branchiopoda (gill-feet).
- The carapace of cladocerans is folded along the back, giving a bivalve appearance, but there is neither a dorsal hinge nor an adductor as seen in scallops, mussels and ostracods.
- The carapace terminates posteriorly with an apical spine.
- The first antenna is uniramous and short.
- The second antenna is biramous and used for swimming.
- Cladocerans are generally transparent with little pigmentation except for the single black compound eye.
Distribution
- Widely distributed throughout the world.
- Common in coastal waters and can also be found in open ocean systems.
Ecology
- Marine cladocerans are usually herbivorous filter feeders that sieve phytoplankton from the water using setae on the pereiopods. However, they also graze on bacteria and microzooplankton including protozoans.
- Quite selective in their feeding, preferring certain species of phytoplankton to others.
- Asexual reproductive strategies allow cladocerans to exploit favourable food conditions.
- Environmental stress may induce females to produce male offspring, thus leading to bisexual reproduction.
- After copulation and internal fertilization, the eggs are brooded in a pouch within the carapace of the female until they are ready to hatch as miniature adults.
- Cladocerans can also reproduce asexually through a process called parthenogenesis, which results in females dominating the population before reverting to sexual reproduction.
- In some cases, paedomorphosis has been observed where developing embryos in the mother's brood pouch become sexually mature and can themselves carry eggs.