INVERTEBRATE ZOOLOGY IN THREE VOLUMES - BOOK 2 - H.I. Shcherbak - 1996

PHYLUM ARTHROPODA

SUBPHYLUM CHELICERATA

CLASS MEROSTOMATA

SUBCLASS EURYPTERIDA

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This subclass comprises the largest Arthropods that ever existed on Earth. Although most known representatives were relatively small (10–20 cm), certain forms reached 100–180 cm in length.

The body of eurypterids is elongated, with a prosoma (cephalothorax) of various shapes (rounded, square, trapezoidal, semi-oval, etc.) covered by a single dorsal shield. Simple ocelli (often closely positioned) are located along the mid-dorsal line, while compound faceted eyes of various Sizes and Shapes are situated laterally.

The chelicerae are of varying sizes and chelate; the pedipalps and the posterior four pairs of limbs are adapted for locomotion and the trituration of food using gnathobases. Sometimes the pedipalps and the subsequent pair of limbs work together with the chelicerae to capture and hold prey, while the sixth pair is often modified into swimming legs.

The abdomen (opisthosoma) of eurypterids is divided into 12 movable segments, of which the first seven anterior segments form the mesosoma, and the five posterior segments form the metasoma. The body terminates in a telson bearing a spine, spike, or flattened expansion. The mesosoma bears lamellar appendages: one pair is modified into genital opercula, while the others function as branchial (gill) limbs. The metasoma lacks appendages (Fig. 184).

Fig. 184. Eurypterida: Mixopterus (dorsal (a) and ventral (b) views)

Eurypterids have been found in continental deposits, indicating that they inhabited fresh and brackish waters and were predominantly benthic dwellers, although forms possessing swimming legs were capable of active swimming.