An Introduction to the Invertebrates (part…4?!) Annelida & Nematoda Reference: Chapter 33.3, 33.4 More Relationships Excavata SAR clade Archaeplastida Slime molds Tubulinids Unikonta Entamoebas Nucleariids Fungi Choanoflagellates Animals 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 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 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 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) 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 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 Polychaete – Christmas Tree Worm Highly modified parapodia! Polychaeta - Osedax v “Bone-eating snotflower” v Feeds on whale carcasses Polychaeta - Osedax Video, Osedax worms on whale falls (~ 2 min): https://www.youtube.com/watch?v=URi8KccVkks 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 Figure 33.24 Cuticle Coelom Epidermis Septum (partition Circular muscle between segments) Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Skin Fused Ventral vessel nerve cords Nephrostome Metanephridium Clitellum Esophagus Crop Pharynx Intestine Giant Australian earthworm Cerebral Gizzard ganglia Ventral nerve cords Mouth Subpharyngeal Circulatory with segmental ganglia ganglion system vessels 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 Video, phylum Annelida (~ 13 min): http://shapeoflife.org/video/phyla/annelids- powerful-and-capable-worms 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 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 Parasitic Nematodes v Eggs may be infective stage § Pinworms (Enterobius vermicularis) v Larvae may be infective stage § Hookworm (Necator americanus) § Trichinella spiralis: trichinosis Nematodes: Eggs Infective for Humans Nematodes: Larvae Infective for Humans Figure 25.26 Figure 33.27 Encysted juveniles Muscle tissue 50 µm More Relationships Excavata SAR clade Archaeplastida Slime molds Tubulinids Unikonta Entamoebas Nucleariids Fungi Choanoflagellates Animals .