SUPPORTING LECTURE NOTES IN ZOOLOGY

Module 3. ARTHROPODS, TARDIGRADES, PENTASTOMIDS, ONYCHOPHORANS

Content Module 3.2. Tardigrades, pentastomids, onychophorans

Topic 3.2.2. Phylum Pentastomida (Tongue Worms)

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 of significance to human welfare and natural ecosystem functioning. Class Pentastomida.

A small group (about 70 species) of thermophilic endoparasites inhabiting the Respiratory system of vertebrates; their precise systematic position remains unresolved. The body is elongated, typically tapering toward the posterior end. Externally, it is covered by a thin cuticle and exhibits superficial annulation. A diagnostic feature is the presence of four sclerotized hooks at the anterior end near the oral opening. Muscles are striated. The Digestive System is a straight, complete tube. Excretory, respiratory, and circulatory systems are absent. Male and female reproductive systems are complex. Embryonic development is poorly understood. The life cycle involves alternation of hosts.

Class Pentastomida, or Tongue Worms (Pentastomida or Linguatulida).

Most adult pentastomids are lung parasites of reptiles; a few species of the genus Linguatula parasitize the nasal sinuses of canids and felids, while one species (Reigardia sternae) has been found in the Ovaries of gulls and terns. The body shows varying degrees of annulation and is indistinctly divided into anterior and posterior regions, sometimes emphasized by structural differences in their integument. The posterior end of the body is bifurcated in some species. The four hooks, located on the ventral side of the anterior end, may be simple (single) or double, positioned on cuticular tubercle-like body outgrowths or

retracted into cuticular pockets. The hooks are operated by powerful muscles, enabling the animals to anchor securely to host Tissues. Adult forms completely lack appendages.



Last update: 13/08/2026

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