INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 2 - G.I. Shcherbak - 1996

PHYLUM ARTHROPODA

SUBPHYLUM BRANCHIATA, OR CRUSTACEA

CLASS CEPHALOCARIDA

Representatives of the Class Cephalocarida were first described only in the mid-1950s. Currently, only 9 species are known. They are small in size, ranging from 2 to 4 mm. They inhabit the marine bottom among sediment particles at various depths.

The body consists of a horseshoe-shaped HEAD, a Thorax (8 segments), an abdomen (11 segments), and a telson with a furca bearing extremely long setae. The antennules are uniramous and well-developed, and the antennae are biramous (Fig. 68); eyes are absent; both pairs of antennae are located posterior to the Mouth, which is covered by a posteriorly directed labrum. The mandibles are very small. Both pairs of maxillae share the same Structure as the thoracic limbs: a leafless, unsegmented protopodite attached to unsegmented lamellar exopodites and epipodites, as well as a segmented swimming endopodite. The limbs perform locomotory and respiratory Functions, and also direct food particles toward the mouth opening. The abdomen lacks appendages.

The digestive gland is located in the head region; the excretory Organs in adults are the maxillary glands, while in larvae, the antennal glands also function; The Heart is multi-chambered, tubular, located in the thorax, and possesses a pair of ostia in each segment. The ventral nerve cord has a ladder-like structure.

Fig. 68. Cephalocarids - Hutchinsoniella in ventral view:

1 - antennule; 2 - antenna; 3 - limb

Cephalocarids are hermaphrodites; the Gonads are unpaired. The egg sacs are situated on a special appendage of the 1st abdominal segment; only a single pair of eggs is carried at a time. The eggs hatch into metanauplii that lead a benthic lifestyle; development involves 13 to 18 molts, with the number of segments increasing after each molt (anamorphosis).