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An Introduction to the Invertebrates (part…4?!)

Annelida & Nematoda

Reference: Chapter 33.3, 33.4

More Relationships

SAR clade Archaeplastida

Unikonta

Excavata

Slime molds Tubulinids 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)

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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

Lophophore!

Polychaeta - Osedax

v “Bone-eating snotflower” v Feeds on whale carcasses

Video, Osedax worms on whale falls (~ 2 min): https://www.youtube.com/watch?v=URi8KccVkks

Polychaeta - Osedax 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

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Epidermis

Circular muscle

Cuticle

Longitudinal muscle

Dorsal vessel

Chaetae

Intestine

Nephrostome

Fused nerve cords

Ventral vessel

Clitellum

Esophagus Pharynx

Crop

Metanephridium

Coelom

Septum (partition between segments)

Anus

Skin

Metanephridium

Intestine

Gizzard

Ventral nerve cords with segmental ganglia Circulatory

system vessels Subpharyngeal ganglion

Mouth

Cerebral ganglia

Giant Australian earthworm

Figure 33.24 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

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Nematodes: Eggs Infective for Humans Nematodes: Larvae Infective for Humans

Figure 25.26

Figure 33.27

Encysted juveniles Muscle tissue 50 µm

More Relationships

SAR clade Archaeplastida

Unikonta

Excavata

Slime molds Tubulinids Entamoebas Nucleariids Fungi Choanoflagellates Animals