Invertebrates

Page
7

Slide 61

Annelid: Earthworm

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

Slide 62

Leeches

Members of class Hirudinea are blood-sucking parasites, such as leeches.

Leeches secrete a chemical called hirudin to prevent blood from coagulating.

Slide 63

Leech

Slide 64

Concept 33.4: Ecdysozoans are the most species-rich animal group

Ecdysozoans are covered by a tough coat called a cuticle.

The cuticle is shed or molted through a process called ecdysis.

The two largest phyla are nematodes and arthropods.

Slide 65

Fig. 33-UN4

Calcarea and Silicea

Cnidaria

Lophotrochozoa

Ecdysozoa

Deuterostomia

Slide 66

Nematodes

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.

They have an alimentary canal, but lack a circulatory system.

Reproduction in nematodes is usually sexual, by internal fertilization.

Slide 67

A free-living nematode - round worm

25 µm

Slide 68

Juveniles of the parasitic nematode Trichinella spiralis encysted in human muscle tissue

Encysted juveniles

Muscle tissue

50 µm

Slide 69

Arthropods

Two out of every three known species of animals are arthropods.

Members of the phylum Arthropoda are found in nearly all habitats of the biosphere.

The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages, and dates to the Cambrian explosion (535–525 million years ago).

Early arthropods show little variation from segment to segment.

Slide 70