Aschelminthes

1. Aschelminthes Chapter 11

2. Aschelminthes • Seven different Phyla fall under two categories in this group • Lophotrochoazoan- those that DON’T molt • Ecdysozoan- those that DO molt

3. Phylum Rotifera-Characteristics Lophotrochoazoan Triploblastic Bilateral Unsegmented Pseudocoelomate Complete digestive tract (separate mouth and anus) Anterior end often has a ciliated organ called a corona

4. Phylum Rotifera-Characteristics Posterior end with toes and adhesive glands Well developed cuticle Protonephridia with flame cells Males generally reduce in number or absent Parthenogenesis common- reproduction from unfertilized eggs

6. External Features • Cuticle covers a rotifer’s external surface • In many species, the cuticle thickens to form an encasement called a lorica • Cuticle or lorica are the main support element for a rotifer • Hydrostatic support from pseudocoelom is secondary support

7. Feeding and Digestion Coronal cilia brings food to mouth Food enters the pharynx that contains a muscular organ that grinds food called mastax Food passes through a ciliated esophagus to ciliated stomach Some species have a ciliated intestine that becomes a cloacal bladder. Cloacal bladder opens to the outside via an anus

8. Excretory System Protonephridia empty into the cloacal bladder for osmoregulation Exchange gases and dispose of nitrogenous wastes across body surface

9. Nervous System Two lateral nerves Bilobed, ganglionic brain on the dorsal surface of the mastax Sensory structures on either one or more short antennae or the corona One of five photosensitive eyespots may be on the head

10. Reproduction and Development • Varies with specific Class • Asexual • Parthenogenesis- when an embryo develops from an egg without fertilization • Sexual • Females: Ovary and vitellarium fuse to form an egg • Males: Testes produce sperm

11. Reproduction and Development • Amictic Eggs- are produced by mitosis, are diploid, cannot be fertilized, and develop directly into amictic females • Mictic eggs- are produced by meiosis and are haploid- if: • Unfertilized: develop quickly into males • Fertilized: they secrete a thick shell and become dormant for several months before developing into amictic females.

13. Phylum Nematoda- Characteristics Ecdysozoan Triploblastic Bilateral symmetry Vermiform- resembling a worm in shape Pseudocoelom Unsegmented Covered in layered elastic cuticle

14. Characteristics Juveniles molt Complete digestive tract Most with unique excretory system comprised of one or two renette cells or a set of collecting tubules Body wall has only longitudinal muscles used for locomotion by thrashing movements

16. External Features • Noncellular, collagenous cutitcle • Can molt 4 times during maturation • Maintains internal hydrostatic pressure • Mechanical protection • Resists digestion by the host • Sensory organs • Amphids- chemoreceptors along cuticle • Phasmids- chemoreceptors near anus

17. Internal Features Pseudocoelom Fluid-filled cavity containing visceral organs Hydrostatic skeleton Round shape from body muscles contracting against the fluid in the pseudocoelom

18. Feeding and Digestion Herbivores, carnivores, omnivores, saprobes, or parasitic Mouth with teeth, jaws, or stylets  buccal cavity  pharynx intestine short rectum  anus

19. Nervous System Anterior nerve ring Nerves extend anteriorly and posteriorly Neoroendocrine secretions are involved in growth, molting, cuticle formation, and metamorphosis

20. Reproduction and Development • Dioecious • Female • Paired convoluted ovaries • Oviduct swollen at end to form seminal receptacle • Oviduct becomes tubular uteris • Two uteri united to form a vagina that opens to the outside through a genital pore

21. Reproduction and Development • Male • Single testis • Vas deferens expands into a seminal vesicle • Posterior flap of tissue called a bursa • Bursa aids the male in the transfer of sperm to the female