PHYLUM ANNELIDA Segmented Worms

Triploblastic

Mouth and Anus

True coelum

Bilaterally symmetrical

External Parasite/Soil

Closed circulatory system

www.nsf.org www.homestead.com

Annelida

• Annelids have bodies composed of a series of

fused rings

• The phylum Annelida is divided into three

classes:

– Oligochaeta (earthworms and their relatives)

– Polychaeta (polychaetes)

– Hirudinea (leeches)

Annelida: Oligochaetes

• Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin

• They include the earthworms and a variety of aquatic species

• Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal

Earthworms are hermaphrodites but cross-fertilize

http://en.wikipedia.org/wiki/File:Mating_earthworms.jpg

Fig. 33-22

Epidermis

Circular muscle

Longitudinal muscle

Dorsal vessel

Chaetae

Intestine

Nephrostome

Fused nerve cords

Ventral vessel

Metanephridium

Septum (partition between segments)

Coelom Cuticle

Anus

Metanephridium

Crop

Intestine

Gizzard

Ventral nerve cord with segmental ganglia Blood

vessels

Subpharyngeal ganglion

Mouth Cerebral ganglia

Pharynx

Esophagus

Clitellum

Giant Australian earthworm

Annelida: Oligochaetes: Earthworm dissection

http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/animal%20diversity/protostomes/loph

otrochozoans/lophotrochozoans.htm

Members of class

Polychaetes have paddle-like

parapodia that work as gills

and aid in locomotion

Parapodia

Bristle Worms

Members of class

Hirudinea are blood-

sucking parasites, such

as leeches

PHYLUM NEMATODA

Cuticle surrounds body

Triploblastic

Mouth and Anus

Pseduocoelum

Bilaterally symmetrical

Internal Parasite/Soil

Tube within a tube

Lack a circulatory or respiratory system

“It’s a nematode world” E. O. Wilson

Nematodes, or roundworms, are found in most

aquatic habitats, in the soil, in moist tissues of

plants, and in body fluids and tissues of animals

EO Wilson on TED talks March 2007

There are more than 15,000 species of

roundworm named.

The pseduo-coelum is most likely a

secondarily derived character, and is

probably not a useful phylogenetic

characteristic and recent research shows

that they are most likely most closely

related to Arthropoda.

Wallace, Ricci, & Malone 1996 interactive key to the nematodes

They have an alimentary canal, but lack a circulatory

system

http://www.bumblebee.org/invertebrates/Nematoda1.htm

Reproduction in

nematodes is usually

sexual, by internal

fertilization and the sexes

are distinct.

Nematodes exhibit

Sexual Dimorphism –

our Ascaris are quite

large and therefore

female.

Ascaris lumbricoides is the most common human

nematode parasite but many other plague humans

around the world. Filariasis is a general name for

nematodes that reside in lymph and connective

tissue.

Both Loa Loa and

Onchoceriasis infect

the fluid inside the eye

Wucherieria bancrofti

block lymph nodes of

infected people and

cause edema.

Encysted juveniles Muscle tissue

Juveniles of the parasitic nematode Trichinella spiralis

encysted in human muscle tissue (LM)

If all the matter in the universe

except the nematodes were swept

away,

our world would still be dimly

recognizable...

-N.A. Cobb from Nematodes and

Their Relationships, 1915

The virtual nematode

Meet Mephisto - The worm that rules the

underworld - Discover magazine