LECTURE NOTES AND STUDY GUIDE IN ZOOLOGY

Module 3. ARTHROPODS, TARDIGRADES, PENTASTOMIDS, ONYCHOPHORANS

Content Module 3.2. Tardigrades, Pentastomids, Onychophorans

Topic 3.2.1. Phylum Tardigrada

General characteristics of the phylum. Origin, evolution, paleontological records, contemporary diversity, geographic distribution, and their role in nature and human life. Overview of major taxonomic groups significant to human life and the functioning of natural ecosystems. Class Tardigrada.

Cosmopolitan microscopic (0.05 - 1.4 mm) inhabitants of terrestrial moisture-rich habitats, freshwater bodies, and marine environments. They possess a poorly segmented body with an indistinctly demarcated HEAD bearing four pairs of unjointed legs. The Digestive System is complete. Respiratory and circulatory Organs are absent. The Nervous system is of the arthropod type. Gonochoristic. Development is direct, with growth accompanied by molting. They share certain features with both polychaetes and Arthropods; however, specific anatomical and embryological characteristics indicate that they represent an independent and highly distinctive phylum within the animal kingdom.

Class Tardigrada.

Inhabiting numerous aquatic and terrestrial biotopes, the active life of all terrestrial species is strictly dependent on the Presence of Water. Over 400 species, with 50 found in Ukraine. The body is short, cylindrical, and stout, with a slightly flattened ventral side and no visible segmentation. It is believed to consist of five segments. The first segment (fused with the head lobe) lacks appendages, while the subsequent four bear a pair of legs each; three pairs are positioned laterally, and the fourth is located at the posterior end of the body. The legs are short, unjointed, and tubercle-like body outgrowths tipped with movable claws. The animals are nearly colorless or even transparent, occasionally yellowish-green, plum-green, purple, or reddish. They exhibit a constant Cell number (eukaryy) in certain Tissues and organs, such as the integument, Muscles, and midgut, which consist of a precisely determined, fixed number of Cells throughout the animal's lifetime in specific species.