CLADOCERA

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CLADOCERA
About 450 species, 0.2 - 6 mm (Leptodora kindtii 18 mm).

The group of the Cladocera is a subdivision of the large aquatic arthropod class, the crustacea. Within these, the cladocera are subsumed in a group which is called Phyllopoda (gr.= leave-like feet). This is due to a phylogenetic reorganisation of the arthropod extremity which in the Cladocera no more shows the typical pattern of distinctive parts but resembles more a leave-like structure. Cladocera mainly inhabit fresh waters, only eight species are real marine animals. Their main feeding source is phytoplankton which they filter through the hole left by the carapax.

Body Plan
Cladocerans consist of a head, a thorax and an abdomen. The head is applied with a rostrum in whose vicinity usually the chemosensoric antennulae are located. Additionally, for male animals the antennulae serve to hold the female in position for copulation. From the thorax the 5 or 6 pairs of legs bud off. The abdomen shows in the embryonic stage and in adult Leptodora four segments. To it, a so called postabdomen is appended which ends in furca claws. These claws function as abreptor (cleaning the body cavity). Two rudder bristles are also appended to the abdomen.

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Side view of Daphnia.

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antenna
compound eye
enzyme gland
esophagus
heart
nauplius eye
antennula
phyllopods
ovar
furca claws
postabdomen
brood
carapax shell
rudder bristle
spina

The Carapax
The carapax, the characteristic stiff cuticule structure of the crustacea, is rigid in the cladoerans. It shelters only rump and legs, in the Haplopoda and Polyphemoidea it is reduced to a dorsal brooding bag. With the head cuticule, the carapax is only dorsally connected. Two thin sphincter muscles in vicinity to the first thorakopode can close the carapax shells. In some species (e.g. Daphnia), a dorsocaudal elongation, the spina, can be found. A ventral tip is found in Scapholeberis. It is named mucro. The ventral side of the carapax is often applied with pricks and bristles, which especially for the benthic species serve for locomotion.

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The Antennae
The antennae, are the main means of locomotion. They are comprised of two branches and very fine hair highly enlarge the antenna surface thereby making up a paddle. To raise of the power for locomotion strong muscles are there and the so called fornix, a chitinous cuticule structure, acts as a stiff joint, giving enough stability for the antenna.

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The Thorakopods
The thorakopods act mainly as filter legs. Only the haplopod and the polyphemoid cladocerans have 4 pairs of limb legs. The other species own 5 or 6 pairs of phyllopods. Phylogenetically primitive is maybe the 6 pair situation which is found in the Sididae. In male animals, the first and second pairs of legs show hook-like appendages which serve as a grip on the female in the copulation situation. Mostly, the different thorakopods exhibit a strong differentiation correlating to their individual functions. The last thorakopod, e.g. is thought to act as a shutter of the body cavity.

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The Cuticule
This very prominent structure of cladocerans is mostly transparent and usually exhibits nice and very regular pattern. The staining of the animals comes either from hemoglobin which is solved in the hemolymphe or it is due to the lipid body which contains carotinoids or stored stuff.

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Front view of Scapholeberis. Note mucro and spine on the head armour.

This page last updated Oct 7th, 2004.