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An Introduction to Invertebrates

Chapter 33

1 million species of animals…

95% are invertebrates!

34-36 phyla of the AnimalKingdom

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Lower Invertebrates

5,500 species, mostly marine sponges Parazoans

2 layers unspecialized cells, no tissues Asymmetrical Suspension (filter) feeders Sessile Hermaphroditic, but cross fertilize Regenerative abilities

Phylum Porifera

: CaCO3 skeletal fibers

: opening

~10,000 species (jellyfish, sea anemones)

Live in shallow coastal marine waters

Eumetazoa Organized into tissues

Diploblastic – 2 germ layers Radially symmetrical Carnivorous

Have stinging tentacles called cnidocytes

Gastrovascular cavity Digestive system (only one opening)

Phylum Cnidaria

Life Cycle

Class Hydrozoa: hydra

Class Scyphozoa: sea nettle

Class Cubozoa: box jelly

Class Anthozoa: brain coral

3. Phylum Ctenophora

All Marine (100 species) Comb Jellies

Resemble Cnidarians Lack stinging cells; have sticky cells

to capture prey

Phylum Platyhelminthes

Bilaterally symmetrical Triploblastic (all germ layers) Gastrovascular cavity (both ends) Sexual and asexual reproduction Complex tissues: nerves and brain Acoelomate Mostly parasitic

Class Turberellaria: planaria

Class Trematoda: liver fluke

Class Monogenea: Dermophthirius

Class Cestoda: tapeworm

Phylum Rotifera

Mainly freshwater Pseudocoelomate Complete digestive system Use cilia to draw water into mouth

“wheel bearer” Parthenogenesis: sexual-female

dominate

Phylum Braciopoda

Bilateral symmetry Coelomates Triploblastic Marine Lophophores for feeding

Horseshoe-shaped/circular crown of ciliated tentacles surrounding mouth

Phylum Nemertea

Bilateral symmetry Triploblastic Acoelomate Mostly marine Proboscis used to probe environment Simple circulatory system – no heart, blood

movement through body contractions Complete digestive system

Phylum Nematoda

25,000 species Bilateral Symmetrical Organized into Tissues Complete digestive tract Sexual reproduction Pseudocoelomic

Phylum Annelida Protostome Coelomates Segmented Complete digestive

system Closed circulatory

system Nervous system

• cerebral ganglia and ventral nerve cord

Hermaphrodites • cross fertilized - clitellum

http://bill.srnr.arizona.edu/classes/182/LophPhor2.gif

Class Polychaeta: bristle worms

Class Oligochaeta: earth worms

Class Hirudinea: leeches

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Higher Invertebrates

Phylum Mollusca

Protostomes Coelomates Body plan – 3 parts

1. Muscular head-foot (soft-bodied) for locomotion

2. Visceral miss – internal organs3. Surrounded by mantle (CaCO3)

Some molluscs also have: Mantle cavity – contains gills,

anus, excretory pores Radula for scraping food from

surfaces Most dioecious

Class Gastropoda: snails

Class Polyplacophora: chitons

Class Cephalopoda: octopus Class Bivalvia: clams

Phylum Arthropoda 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 Largest phylum (1,000,000 species) Coelomates Protostome

Segmentation allows for specialization of body parts

1. Head2. Thorax3. Abdomen

Hard exoskeleton Cuticle made with chitin Prevents water loss: move onto land Organisms must molt (ectdysis)

Jointed appendages allows for specialization

1. Walking2. Feeding3. Copulation

Subphylum Cheliceriformes: spiders, horseshoe crabs, scorpions, ticks, mites

Subphylum Myriopoda:centipedes, millipedes

Subphylum Crustacea: crabs, lobsters, crayfish,

shrimp

Subphylum Hexapoda: insects

Phylum Echinodermata

Radial symmetry Deuterostomes Coelomates Sessile or sedentary

marine forms Well developed

organs and systems Have an internal

skeleton Water vascular system

tube feet that function for locomotion, feeding, and gas exchange

Dioecious

Class Asteroidea: sea stars

Class Ophiuroidea: brittle stars

Class Echinoidea: sea urchins

Class Crinoidea: sea lilies

Class Holothuroidea: sea cucumbers

Class Concentriclodea:

sea daisies