invertebrates a survey of invertebrates. trends in invertebrate evolution common ancestors of...
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Germ Layers The ectoderm (outer layer) will develop into skin and other body coverings, glands, and nervous system tissues The endoderm (inner layer) grows into tissues and organs of the digestive tract and respiratory systemTRANSCRIPT
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Invertebrates
A Survey of Invertebrates
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Trends in Invertebrate Evolution Common ancestors of multicellular
animals had already evolved two distinct cell layers called germ layers, separated by a jelly-like middle layer
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Germ Layers The ectoderm (outer layer) will
develop into skin and other body coverings, glands, and nervous system tissues
The endoderm (inner layer) grows into tissues and organs of the digestive tract and respiratory system
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Germ Layers Middle layers varies by animal Sponges and jellyfish only have a
primitive layer of jelly-like cells Higher animals have an actual
third cell layer called the mesoderm which develops into skeletal, muscle, and circulatory tissues, and reproductive system
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Trends in Invertebrate Evolution Second trend – existence of
mesoderm-lined cavity called coelom
Provides space for organs to grow and function without being twisted or squeezed by body movements
Fluid within coelom helps to carry food, wastes, dissolved gases
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Coelom Acoelomates = animals without a
coelom, like the hydra Pseudocoelomates = have a
body cavity between mesoderm and endoderm, like roundworm
Coelomates = have a true coelom that houses digestive tract and organs, like annelids (earthworm)
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Trends in Invertebrate Evolution Third trend is the evolution of a
body plan, built of several compartments
Compartments called segments, allow for increase in body size
In higher animals, segments are specialized and more complex
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Trends in Invertebrate Evolution Many organisms also have
symmetry Radial symmetry = body parts
repeated around an imaginary line drawn through center of the body
Bilateral symmetry = left and right sides are identical
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Trends in Invertebrate Evolution Organisms with bilateral symmetry
also show cephalization, which means that they have a distinct front end and back end (anterior and posterior)
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Invertebrate Phyla Phylum Porifera (sponges) Phylum Cnidaria (cnidarians) Phylum Platyhelminthes (flatworms) Phylum Nematoda (nematodes or
roundworms) Phylum Mollusca (mollusks) Phylum Annelida (annelids) Phylum Echinodermata (echinoderms) Phylum Arthropoda (arthropods) Phylum Chordata (invertebrate chordates)
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Phylum Porifera (sponges) Simplest multicellular animals Asymmetric Mostly independent, but can live
together Mostly marine, some in freshwater
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Phylum Cnidaria (cnidarians) Jellyfish, corals, sea anemones,
hydras Mostly marine, few freshwater Radial symmetry
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Phylum Plathyhelminthes (flatworms) Bilateral symmetry Show cephalization Mostly parasitic
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Phylum Nematoda (nematodes AKA roundworms) First to show a tube-like digestive
system (mouth at one end, anus at the other end)
Some are microscopic, some can be a meter long
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Phylum Mollusca (mollusks) Clams, snails, squids Can live everywhere, even on land Many have outer shells for protection Sea snails secrete chemicals to avoid
predators Clams, mussels, oysters, scallops are
bivalves (double shells) and can shut when in danger
Squids and octopuses also emit dark ink to confuse predators
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Phylum Annelida (annelids) AKA segmented worms Many are detritus feeders Live on land and in water
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Phylum Echinodermata (echinoderms) Star fish, sea cucumbers, sea
urchins) Live entirely in water Spiny skin Have five-part radial symmetry
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Phylum Arthropoda (arthropods) Most successful animals - largest
and most diverse phylum Jointed-leg animals Exoskeletons Divided into three groups
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Phylum Arthropoda (arthropods) Subphylum Chelicerata includes
spiders and scorpions Named by mouth parts (chelicerae) Mostly carnivorous, can be posionous
Class Crustacea includes lobster, shrimp, crab
Class Insecta contains ½ of all arthropods
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Phylum Chordata Invertebrate chordates Link between invertebrates and
vertebrates Endoskeleton with notochord, to
which muscles are attached Ex: Sea squirt