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An Introduction to Invertebrates
Chapter 33
1 million species of animals…
95% are invertebrates!
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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
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