Animal Kingdom: Pseudocoelomates and Nematodes - Prof. Robert Okazaki, Study notes of Zoology

Download Animal Kingdom: Pseudocoelomates and Nematodes - Prof. Robert Okazaki and more Study notes Zoology in PDF only on Docsity! 72 CHAPTER 9 STUDY GUIDE 9.1 Introduction A. A World of Nematodes and Position in the Animal Kingdom 1. Nine distinct phyla of animals belong to the pseudocoelomates. 2. Phylogenetic analysis suggests there are at least two large superphyla within protostomes. 3. Molecular evidence divides Protostomia into two groups that diverged in the Precambrian: Lophotrochozoa and Ecdysozoa. 4. Ecdysozoa go through a series of molts; Lophotrochozoa possess a lophophore and trochophore larva. 5. Rotifera, Acanthocephala, and Entoprocta belong to Lophotrochozoa. 6. Ecdysozoan pseudocoelomates include Nematoda, Nematomorpha, Kinorhyncha, and Priapulida. 7. Rotifera and Acanthocephala are closely related to Gnathostomulida. 8. The original blastocoel of the embryo persists as a space or cavity between enteron and body wall. 9. Since it lacks the peritoneal lining of a true coelom, it is a pseudocoel. 10. This defines the pseudocoelomates , a Protostomia division of the bilateral animals. 11. More complex animals have a true coelom formed from mesoderm and lined with a peritoneum (Figure 9.2). 12. All have a body wall that is often syncytial, a dermis and muscles surrounding the pseudocoel. 13. Except in parasitic Acanthocephala, the digestive tract is complete. 14. Digestive tract, gonads and excretory organs are within the pseudocoel bathed in perivisceral fluid. 15. Eutely is a constant number of cells or nuclei per species, a property in several groups. B. Biological Contributions 1. The pseudocoelom may be filled with fluid or gelatinous material with mesenchyme cells. 2. It generally provides greater freedom of movement. 3. There is space for more development of digestive, excretory, and reproductive systems. 4. It is simpler to distribute materials throughout the body. 5. This provides a storage area for waste products to be later discharged. 6. It serves as a hydrostatic organ. 7. A complete digestive tract is found in most phyla. 9.2 Phylum Rotifera A. Characteristics (Figure 9.1) 1. Rotifers have a ciliated crown, the corona that beats like a rotating wheel. 2. Rotifers are highly diverse in color, size and shape; some are colonial. 3. Floaters are globular, creepers are elongated and sessile forms are vase-like. 4. Rotifers are found worldwide with over 2000 species known. 5. Most are freshwater species but a few are marine, terrestrial, parasitic, or epizoic. 6. Aquatic species are mostly benthic but some are pelagic. 9. A rotifer body has a head, trunk and tail; only the corona is ciliated. 10. The ciliated corona or crown surrounds a nonciliated central area with sensory bristles and a mouth. 11. Beating of the cilia help in feeding and locomotion. 12. The mastax is a muscular pharynx equipped with hard jaws for chewing. 13. The trunk contains visceral organs and a terminal foot. 14. A pair of protonephridial tubules have flame cells and empty into a cloacal bladder. 15. Sensory organs include eyespots, sensory pits, and papillae; they have a bilobed brain.. 16. Rotifers are dioecious; males are smaller than females. a. In some classes, males are unknown, and in others, males occur only briefly. b. Female systems may provide yolk to developing ova by cytoplasmic bridges . c. Ovaries and yolk glands may be combined as germovitallaria. d. Some species are parthenogenetic, producing diploid eggs that hatch into diploid females. e. Monogononta females produce diploid amictic eggs that form diploid females, or haploid mictic eggs that, if not fertilized, become haploid males. 9.4 Phylum Acanthocephala A. Characteristics 1. All spiny-headed worms are parasites in the intestines of vertebrates (Figure 9.3C). 2. Over 1,100 species are known; they occur worldwide and parasitize fish, birds and mammals. 3. Its proboscis has rows of recurved spines that penetrate and may rupture host intestines (Figure 9.3A,B). 4. Larvae develop in crustaceans or insects, they do not parasitize humans. 73 5. The body is somewhat flattened and molecular evidence indicates they are highly modified parasitic rotifers. 6. The body wall is syncytial and its surface has minute crypts to increase surface area. 7. About 80% of the tegument is a lacunar system of fluid-filled canals that may distribute nutrients and remove wastes from muscles. 8. If present, the protonephridia with flame cells perform excretory functions. 9. They lack a digestive tract and absorb all nutrients across the tegument, which bears some transport mechanisms. 10. Males have a protrusible penis ; during copulation, sperm are ejected into the vagina and travel into the pseudocoel. 11. Shelled embryos discharged in the feces do not hatch until eaten by an intermediate host, often an arthropod. 9.5 Clade Micrognathozoa A. Characteristics 1. The only micrognathozoan species, Limnognathia maerski, was collected from Greenland in 1994. 2. These interstitial are about 142 um long, with a two-part head, thorax, and abdomen with a tail. 3. Dorsal plates are present on the epidermis. 4. They move with cilia and a ventral ciliary adhesive pad. 5. The jaw consists of plates and teeth; the mouth leads into a simple gut. 9.6 Phylum Gastrotricha (Figure 9.4) A. Characteristics 1. Gastrotrichs are bristly microscopic animals, ventrally flattened, and lacking a corona and a mastax. 2. They live in the interstitial spaces between benthic particles of sand or mud. 3. They glide on plant or animal substrates using ventral cilia or attach with posterior adhesive glands. 4. About 460 species of gastrotrichs occur in fresh and saltwater. 5. Food includes algae, protozoa and detritus. 6. Gastrotrichs are hermaphroditic; some reproduce parthenogenetically. 7. Notice the potential new phylum Cycliophora with little creatures found on the mouthparts of Norway lobsters. (Figure __) 9.7 Phylum Entoprocta (Figure 9.5) A. Characteristics 1. About 100 species of Entoprocts occur worldwide, usually in marine environments. 2. They are less than 5 mm long and mostly microscopic, resembling hydroid cnidarians. 3. Urnatella gracilis is a common freshwater species in North America. 4. The body is cup-shaped and bears a circular crown of ciliated tentacles. 5. It attaches by a stalk with adhesive glands; tentacles and stalk are continuations of the body wall. 6. The gut is U-shaped with both mouth and anus opening within the circle of tentacles, hence its phylum name. 7. Long cilia on the sides keep a current bringing in particles; short cilia on the inner surfaces capture food and direct it to the mouth. 8. A pair of protonephridia is embedded in the gelatinous parenchyma. 9. There are no circulatory or respiratory organs. 10. Some are monoecious, some dioecious and some first produce sperm and later eggs. 11. Modified spiral cleavage leads to a trochophore-like larva. 12. Ectoprocts are still called bryozoans. 9.8 Phylum Nematoda: Roundworms A. Characteristics 1. About 12,000 species are described; perhaps a half million exist. 2. They live in virtually all habitats in all biomes; topsoil may contain billions per acre. 3. Nematode parasites exist in nearly all animal and many plant species; they are economically and medically important. B. Form and Function 1. Distinguishing Characteristics a. They have a cylindrical shape (Figure 9.6A) and most are under 5 cm long.. b. They have nonliving cuticle. c. They lack motile cilia or flagella. d. Muscles in the body wall only run longitudinally. 2. They lack protonephridia; one or more large glands or similar structures serve for excretion.