SUPPORTING LECTURE NOTES IN ZOOLOGY

Module 2. SUWKINDOM MULTICELLULAR ANIMALS (METAZOA). SECTION PRIMITIVE MULTICELLULAR ANIMALS (PROMETAZOA). LOWER MULTICELLULAR ANIMALS (EUMETAZOA)

Content Module 2.5. Annelids, Kamptozoa, Echiurans, Sipunculans

Topic 2.5.4. Phylum Sipunculida

General characteristics of the phylum. Origin, evolution, paleontological records, modern diversity, geographical distribution, and their role in nature and human life. Overview of the main taxonomic groups essential to human life and the functioning of natural ecosystems. Class Sipunculida.

Marine benthic animals, with the exception of the species Phascolosoma lurco (found in damp soil along sea coasts). Inhabiting various depths (down to 5,000 m); the highest species diversity is concentrated on the continental shelf (the coastal zone of the World Ocean floor down to a depth of 200 m) of tropical seas. Sluggish, dwelling in mollusk shells, tubes of sedentary polychaetes, crevices of coral skeletons, or burrowing in the substrate. Over 300 species. Only two species are found in the Black Sea. The body consists of a thickened trunk and an elongated introvert (proboscis). A well-developed integumentary-muscular sac. Unsegmented coelom. The Mouth is located at the tip of the introvert. The intestine is loop-shaped, with the anus opening on the dorsal side near the Base of the introvert. Excretory Organs are nephromixia; the Circulatory system is absent; Respiration occurs through the body surface. Dioecious, external Fertilization, development with metamorphosis, hatching into a trocophore larva. The phylum Sipunculida comprises a single class of the same name.

Class Sipunculida. Ranging in size from 1.5 to 60 cm. The introvert does not exceed the length of the trunk but is significantly narrower, capable of being retracted into the trunk and everted outwards. The anterior end of the introvert bears the mouth, surrounded by tentacles covered with ciliated epithelium.