INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 2 - H.Y. Shcherbak - 1996

PHYLUM ARTHROPODA (ARTHROFODA)

SUBPHYLUM TRILOBITOMORPHA

These are marine animals that flourished at the beginning of the Paleozoic era (Cambrian and Ordovician periods) and completely died out by its end. Trilobitomorphs were generally small in size (ranging from a few millimeters to 10 cm), though some species reached up to 75 cm in length. To date, over 10,000 fossil species have been described.

Representatives of this subphylum are characterized by a combination of highly specialized features (significant cephalization, uniramous appendages) and primitive traits (unspecialized mouthparts, homonomous trunk segmentation, anamorphosis, etc.).

Trilobitomorphs are characterized by the division of the body into a HEAD and a trunk. The head bears a pair of antennae and four pairs of mouthparts that do not differ from the trunk appendages. The trunk consists of a variable number of segments (from 4 to 44), each carrying a pair of appendages. Often, several posterior segments fuse with the pygidium to form a tail region.

Trilobitomorphs, especially trilobites, serve as index fossils used to determine the age of sedimentary rocks and their assignment to a specific period of the Paleozoic era.

Four classes are known; we will examine one of them—Trilobita—which includes over 90% of all described trilobitomorph species and is the most thoroughly studied.