SUPPORTING LECTURE NOTES IN ZOOLOGY

Module 4. MOLLUSCS, CHAETOGNATHS, PHORONIDS, BRYOZOANS, BRACHIOPODS, POGONOPHORANS, HEMICHORDATES, ECHINODERMS

Content Module 4.1. Molluscs, Chaetognaths, Phoronids, Bryozoans, Brachiopods, Pogonophorans

Topic 4.1.6. Phylum Pogonophora

General characteristics of the phylum. Origin, evolution, paleontological data, modern diversity, geographical distribution, and their role in nature and human life. Overview of major taxonomic groups important for human life and the functioning of natural ecosystems. Class Frenulata. Class Afrenulata.

The phylum Pogonophora was established in the mid-20th century. Found in all seas and oceans with normal Water salinity. Over 150 species. They inhabit the sea floor inside chitinous tubes that are open at both ends and vary in Structure. Throughout their lives, they never leave their tubes, though they can move freely up and down within them. The length of the tubes exceeds the body length. The tube material is secreted by numerous multicellular glands whose ducts open onto the body surface. Most known species are colorless or whitish and translucent. Blood Vessels are visible through the body wall, especially on the tentacles, giving the tentacles a bright red color. The body is thread- or cord-like, cylindrical, with a length exceeding its thickness by 100–500 times. The body consists of four regions that differ somewhat in structure among representatives of Frenulata and Afrenulata, or Vestimentifera; the first region bears tentacles (ranging from one or two to many thousands). The body, including the tentacles, is covered with a cuticle, beneath which lies a single-layered epithelium with unicellular glands. Under the epithelium is a layer of circular and longitudinal Muscles. The muscles are lined on the inside by a peritoneal epithelium that bounds the well-developed secondary body cavity. Pogonophores completely lack a Digestive System in the adult stage. They feed on METABOLISM/21.html">Chemosynthesis products through Symbiosis with sulfur-oxidizing Bacteria or by absorbing Amino Acids from sea water. Excretory Organs, when present, are coelomoducts located in the first body region. The Circulatory system is well-developed, closed, and blood flow is directed. The blood is red due to the presence of Hemoglobin. There are no specialized respiratory organs; gas exchange occurs primarily through the tentacles. The Nervous system is primitive (a nerve plexus featuring concentrations of Nerve Cells and fibers—the so-called Brain, located on the ventral side of the first body region and innervating the tentacles—and a longitudinal nerve cord extending along the entire body). It lies entirely within the epidermal layer. Gonochoric; Sexual Dimorphism has not been detected. Pogonophores are an ancient group of animals; their tubes, described under the name Sabellitida, are known from the Late Precambrian.