Intro to the Invertebrates

What is an Animal?

Basic Definitions

• What is an animal? – a multicellular eukaryotic heterotroph

whose cells lack cell walls.

• What is an invertebrate?– an animal that does not have a backbone.

What is an Invertebrate?

Simple to more complex

The Phlya of Invertebrates

• Porifera

• Cnidaria

• Platyhelminthes

• Nematoda

• Annelida

• Arthropoda

• Echinodermata

Phylum ExamplesEvolutionary

Milestone

Porifera sponges multicellularity

Cnidaria jellyfish, hydra, coral tissues

Platyhelminthes

flatworms bilateral symmetry

Nematoda roundworms pseudocoelom

Mollusca clams, squids, snails coelom

Annelida earthworms, leeches segmentation

Arthropodainsects, spiders, crustaceans

jointed appendages

Echinodermata

starfish deuterostomes

Chordata vertebrates notochord

 

Vocabulary• Radial Symmetry: having body parts

that repeat about an imaginary line through the center of the body.

• Bilateral Symmetry: having body parts that repeat on either side of the body.

• Cephalization (cephalo = head): the gathering of sense organs and nerve cells into the head region.

• Ganglia- Clusters of nerve tissue• Hermaphrodite: having both sexes in one animal.

Symmetry

Embryonic Development:

Zygote = fertilized egg

Blastula = a hollow ball of cells

Blastopore = the blastula folds in creating an opening

Protostome = mouth is formed from blastopore

Deuterosome = anus is formed from blastopore

Different Body Plans

• Coelom: body cavity that is completely lined with mesoderm.

• A coelomate is an animal with a coelom. • An acoelomate is an animal without a

coelom.

Body Plans

Phylum Porifera

Sponges

Sponges (Phylum Porifera)

• Sponges have no specialized tissues.

• Many holes called pores, or ostia.• Osculum – large opening at the

top. Water is taken into the sponge through its many pores and circulated out through the osculum. This is how they ‘breathe’

• They have no muscle or nervous system.

• Sponges are sesslie – which means they do not move.

• Sponges filter food out of the water as it flows through the ostia. Special cells called collar cells pick up the food and start digestion.

• Sponges can regenerate lost body parts.

Sponge Anatomy

Phylum Cnidaria

Jellyfish, Coral, Hydra, Sea Anemone, Portuguese-man-of-war

Cnidaria• “Stinging Cell” animals with raadial symmetry.• They have Nematocysts – stinging cells in the

tentacles, activated by touch. Provides protection and helps capture food.

• Some are sessile, some can ‘swim’.• They are hermaphrodites (contain both male

and female reproductive structures in the same body.

• They have 3 layers– Ectoderm – outer cell layer– Endoderm – inner cell layer– Mesoglea – jelly-like layer separating ectoderm and

endoderm. Within the mesoglea is a nerve net. There is no brain.

• They contain a central cavity called the gastrovascular cavity, or enteron. Digestion takes place here and the contents are absorbed by the endodermal cells. The undigested food is expelled through the mouth.

2 Body forms in Cnidaria

Polyp Form

Medusa Form

Phylum Platyhelminthes

Planarians, Flukes, and Tapeworms

Platyhelminthes or Flatworms (the simplest bilateral animals)

• Three classes• Planarians are mostly free-living, non-parasitic,

and marine• Flukes are parasites• Tapeworms are parasites (with hooks and suckers

that anchor the worm inside the intestines of a host animal)

Anatomy of a Flatworm

Ever see the ALIEN movies?

Phylum Nematoda

Roundworms and Rotifers

Nematodes

• Roundworms can be parasitic (hookworm, pinworm, threadworm) or non-parasitic, they can also be decomposers. They have pointed heads and tapered tails with a complete digestive tract.

• Rotifers are tiny animals, with a crown of cilia and a complete digestive tract. They are common in freshwater.

Nematode Anatomy

Phylum Annelida

Earthworms, Leeches and Polychaetes

Christmas Tree WormChristmas Tree Worm

Annelids

• Segmented bodies; Bilateral symmetry • True body cavity (coelom). The organs of the

digestive, nervous, and circulatory systems run the length of the body.

• Complex digestive and circulatory systems.• Earthworms are hermaphrodites. • Small brain located near the pharynx. A ventral

nerve cord extends from the brain and runs the length of the body. In each segment it swells to form structures called ganglia.

• Their muscular system contains both circular and longitudinal muscles. As these muscles contract and relax they shorten and elongate the body making it move. Setae, small bristle-like hairs, extend from the body walls and act as anchors as the worm moves.

• They have a hydrostatic skeleton (water-filled tube).

• No respiratory organs; worms breathe through their moist skin.

Earthworm Anatomy

Phylum Mollusca

Clams, Squid, Octopus

Can you see the Giant Clam in this photo?Can you see the Giant Clam in this photo?

Mollusks

• Mollusks have bilateral symmetry. • Their body is covered with a thin membrane called the

mantle. This structure may secrete the shell. • Three body parts: head, muscular foot, and the visceral

hump (contains the internal organs). • Breathing occurs through the gills or the lining of the

mantle cavity.• Squid and octopus are the most intelligent

invertebrates. They are about as smart as a house cat.• Reproduction is sexual.• They are true coelomates.

Check out the complex anatomy of a clam

Giant squid- an amazing mollusk

Giant squid

• Head: houses a complex brain.Eyes: largest in the animal kingdom. They can grow to 25 cm (10 in.) in diameter--about the size of a volleyball.Fins: relatively small in this species. They help balance and maneuver the huge animal as it swims.Mantle: the main body. This muscular sac contains most of the organ systems.Arms (8): studded with two rows of suckers.Feeding tentacles (2)

• Funnel: a multipurpose tube used in breathing, jetting, squirting ink, laying eggs, and expelling waste.