Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Metazoa
Arthropods
Subphylum Branchiopoda - Class Crustacea - Order Anostraca

Branchiopod crustaceans are characterized by a well-developed carapace and the presence of leaf-like thoracic appendages. The carapace resembles a pitched roof or a bivalve shell, and it almost entirely covers the crustacean's body. These leaf-like appendages play a key role in locomotion, directing food toward the Mouth, and Respiration.

Among branchiopods, the most well-known representatives are from the suborder Cladocera—daphnians, or Water fleas (Fig. 50). These are small planktonic crustaceans, about 2–3 mm in length. Except for the HEAD, their body is enclosed in a developed thin-walled carapace. Both compound and simple eyes are located on the head. The antennules are short, while the antennae are strongly developed, branched, and setose. Serving as swimming Organs, they are powered by strong Muscles. With each stroke of the antennae, the crustacean leaps upward and forward. The antennae are then brought back for the next stroke while the crustacean sinks slightly. Because of this distinctive swimming pattern, daphnians are commonly called "water fleas." They possess 5–6 pairs of thoracic limbs. These limbs are short, densely covered with setae, and bear branchial plates. The beating of the limbs draws water into the shell to bathe the gills, while suspended microscopic organisms and other particles are filtered out and directed toward the mouth. Daphnians inhabit our ponds and lakes, often appearing there in massive numbers. Their dense aggregations can be seen from the shore as a swirling reddish cloud in the water. Daphnians constitute a major food source for freshwater fish, especially fry. Consequently, fish farmers are keen on boosting the populations of these crustaceans in water bodies.

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Fig. 50 Internal Structure of a daphnian:

1 — antennules; 2 — branched antennae; 3 — simple eye; 4 — compound eye; 5 — excretory gland; 6 — Heart; 7 — thoracic limbs; 8 — abdomen; 9 — brood pouch.

In this regard, various Methods for the artificial breeding of daphnians and the enrichment of ponds with them have been developed and applied in practice.