Invertebrate Invertebrate Phylum'sPhylum's

Invertebrate Basics:• Animals with no backbones

• Multi-cellular, cells have no cell walls

• Most can move

• Most have symmetry, meaning that if cut in half the two sides will look about the same.

• Consumers, meaning they cannot make their own food.

Main Groups

• Porifera=Sponges• Cnidaria=Anemone, coral & jellyfish• Arthropod=Insects, spiders, crustraceans• Platyhelminthes=Flat worms• Nematoda=Round worms• Annelida=segmented worms• Mollusca=Clams, octopus, squid• Echinodermata=Star fish, sand dollars, sea

cucumbers

Phylum Porifera

• Sponges – Characteristics:

• Sessile, they are attached to a solid surface underwater. • Most live in salt water, although some live in fresh water. • diploblastic; that is, the body wall is made of two layers of cells with

a jellylike mesoglea between them; • The body wall is perforated with pores (hence the name Porifera)

through which water containing food particles is filtered. The water is drawn in through the pores by collar cells like those found in choanoflagellates. (Some sponges can process a volume of water more than 100,000 times their own volume in the course of a day!)

• dispersed by small, free-swimming larvae; • about 10,000 species known• No definite symmetry• Simplest invertebrate with no nervous system

Phylum Cnidarians

• Jellyfish, Sea Anemones, Corals– Characteristics:

• two layers of cells — ectoderm and endoderm — with a jellylike mesoglea between them

• predominantly radial symmetry: body parts (e.g., tentacles) arranged in whorls.

• cnidoblasts: specialized cells that secrete a stinging capsule called a nematocyst.

• Food is taken through a mouth into the gastrovascular cavity. There is no anus.

• Sexual reproduction produces a free-swimming, ciliated larva called a planula.

• The phylum contains about 10,000 species distributed in 3 classes

Phylum Platyhelminthes

• Flatworms (Planarian, Flat Worms, Turbellarians)– Characteristics:

• This phylum contains some 20,000 species • Flattened body• bilaterally symmetrical body.• They have three embryonic layers (triploblastic): the

endoderm, the mesoderm, and the ectoderm.• Flat worms have no other body cavity than the digestive cavity

(acoelomates).• Asexual reproduction occurs through fragmentation or fission. • Flat worms have one digestive opening that branches to all

parts of the body. Turbellarians have a muscular pharynx to up food.

• Parasitic classes rely on the host for digestion.• They have a blind gut, meaning they have a mouth, but no

anus.

Phylum AnnelidaPhylum Annelida• Examples: Annelids (Earthworms, clam

worm, leeches)– Characteristics:

• segmented; that is, their body is made up of repeating units.

• Has a nervous system • There are about 12,000 species known• Bilaterally symmetrical and vermiform. • Body has more than two cell layers, tissues

and organs. • Body possesses a gut, mouth, and anus. • Has a true closed circulatory system. • Has no true respiratory organs. • Reproduces sexual, gonochoristic, or

hermaphoditic. • Feed on a wide range of material. • Live in most environments.

Phylum Mollusca• Examples: Mollusks (clams,

mussels, oysters, scallops, snails, slugs, octopus, squid, chambered nautilus, tooth shells, chitons)– Characteristics:

• Over 70,000 living species • 6 classes—Bivalvia, gastropoda,

cephalopoda, scaphopoda, Amphineura, and Monoplacophora

• Bilaterally symmetrical• Body is in 2 sections, the head-foot and

the visceral lump• They have a closed circulatory system

with a heart

Phylum Nematoda

• Examples: Roundworms (Hookworms, Pin worms, filarial worms, guinea worm)– Characteristics:

• A one-way digestive tract running from mouth to anus.

• A cavity between the digestive tract and the body wall.

• Some 25,000 species have been identified but this may be less than 10% of the true number.

• Most are free-living; found in soil where they are important decomposers.

• Most are small although one that lives in whales can reach 30 feet!

Phylum Arthropoda• Examples: Insects, Arachnida, Scorpions, Spiders,

Crustaceans, Horseshoe Crabs, Centipedes, millipedes, Shrimp – Characteristics:

• Incredible diversity. Over a million living species have been identified so far — more than all the other species of living things put together — and this is probably only a fraction of them, they make up 80% of all described living things..

• Live in every possible habitat: fresh water, salt water, soil, even in the most forbidding regions of Antarctica and high mountains.

• A jointed external skeleton • Segmented. • Pairs of jointed appendages (legs); one pair to a

segment — used for locomotion, feeding, sensation, weaponry.

• Bilateral symmetry. • Main nerve cord runs along the ventral side. • They molt, or shed their skeleton

Phylum Echinodermata

• Examples: Starfish, sea urchins, brittle stars, sand dollars, sea cucumbers, sea daisies – Characteristics:

• Five rayed symmetrical body• Radial symmetry• Body has two layers of cells,

tissues, and organs• A water vascular system that

moves its tentacles• Open circulatory system