An Introduction to the Invertebrates (part 4?!) Annelida & Nematoda. Reference: Chapter 33.3, 33.4

Transcription

1 An Introduction to the Invertebrates (part 4?!) Annelida & Nematoda Reference: Chapter 33.3, 33.4

2 More Relationships Slime molds Tubulinids Entamoebas Nucleariids Fungi Choanoflagellates Animals Excavata SAR clade Archaeplastida Unikonta

3 Lophophorates: Phyla Ectoprocta and Brachiopoda v Characterized by a lophophore, a crown of ciliated tentacles around their mouth Lophophorates have a true coelom v Two lophophorates we haven t talked about yet: phyla Ectoprocta and Brachiopoda

4 Lophophorates: Phyla Ectoprocta and Brachiopoda v Phylum Ectoprocta (also called bryozoans) Sessile colonial animals that superficially resemble hydrozoans- but have lophophore instead of feeding tentacles A hard exoskeleton encases the colony, and some species are reef builders

5 Lophophorates: Phyla Ectoprocta and Brachiopoda v Phylum Brachiopoda Superficially resemble clams and other hinge-shelled molluscs BUT the two halves of the shell are dorsal and ventral rather than lateral as in clams- and they have a true lophophore for filter feeding Brachiopods are marine and attach to the seafloor by a stalk Lophophore

6 Phylum Annelida ( little rings ) v Annelids are segmented worms Bodies are composed of a series of fused rings v Annelids are true coelomates v The Phylum Annelida is divided into two Classes Polychaeta (polychaetes) Clitellata Subclass Oligochaeta (earthworms and their relatives) Subclass Hirudinea (leeches)

7 Hydrostatic Skeleton v Hydrostatic Skeleton Except in leeches, coelom is filled with fluid and serves as a hydrostatic skeleton Fluid volume remains constant Contraction of longitudinal muscles causes body to shorten and expand Contraction of circular muscles causes body to narrow and lengthen By separating this force into sections, widening and elongation move the whole animal Alternate waves of contraction, or peristalsis, allow efficient burrowing Swimming annelids use undulatory movements

8 Annelida Class Polychaeta v Members of class Polychaeta have paddle-like parapodia that work as gills and aid in locomotion v Most polychaetes are marine

9 Polychaete Christmas Tree Worm Highly modified parapodia!

10 Polychaeta - Osedax v Bone-eating snotflower v Feeds on whale carcasses

11 Polychaeta - Osedax Video, Osedax worms on whale falls (~ 2 min):

12 Annelida Class Clitellata v The Class Clitellata includes several sub-classes Subclass Oligochaeta are named for relatively sparse chaetae (setae), bristles made of chitin Earthworms eat through litter and soil, extracting nutrients as the organic and mineral material moves through the alimentary canal Earthworms are hermaphrodites but do not self-fertilize Some can reproduce by parthenogenesis Rarely, some groups can regenerate if chopped at certain segments Can lose tail section and still survive but rare, usually wind up with 2 halves of one dead earthworm

13 Figure Epidermis Circular muscle Cuticle Coelom Septum (partition between segments) Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Nephrostome Fused Ventral vessel nerve cords Clitellum Skin Metanephridium Giant Australian earthworm Pharynx Esophagus Crop Intestine Cerebral ganglia Mouth Subpharyngeal ganglion Circulatory system vessels Gizzard Ventral nerve cords with segmental ganglia

14 Annelida Subclass Hirudinea - Leeches v Most species of leeches live in fresh water; some are marine or terrestrial v Leeches include detritivores, predators of invertebrates, and parasites that suck blood v Parasitic leeches secrete a chemical called hirudin to prevent blood from coagulating Once used in blood-letting not such a good idea. Now important in treating certain injuries

15 Video, phylum Annelida (~ 13 min):

16 Superphylum Ecdysozoa v The most species-rich animal group v Ecdysozoans are covered by a tough coat called a cuticle v The cuticle is shed or molted through a process called ecdysis v The two largest phyla are Nematoda and Arthropoda

17 Phylum Nematoda ( roundworms ) v Everywhere! Free-living and parasitic (on both plants & animals) Aquatic habitats, soil, moist tissues of plants, and in body fluids and tissues of animals v Triploblastic, pseudocoelomate, protostomes Possess an alimentary canal with mouth and anus Rudimentary nervous system Lack a circulatory system v Reproduction in nematodes is usually sexual, by internal fertilization v Caenorhabditis elegans is a model organism in research

18 Parasitic Nematodes v Eggs may be infective stage Pinworms (Enterobius vermicularis) v Larvae may be infective stage Hookworm (Necator americanus) Trichinella spiralis: trichinosis

19 Nematodes: Eggs Infective for Humans

20 Nematodes: Larvae Infective for Humans Figure 25.26

21 Figure Encysted juveniles Muscle tissue 50 µm

22 More Relationships Slime molds Tubulinids Entamoebas Nucleariids Fungi Choanoflagellates Animals Excavata SAR clade Archaeplastida Unikonta