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The Invertebrates• Animals are multicelled
heterotrophs that move about for at least part of their life cycle
• Animals develop in a series of stages– Ectoderm, endoderm,
and often mesoderm form in the early embryo
– Cells interact in functional units (epithelium and connective tissues)
Comparing Key Groups• Evolutionary trends
toward – Greater size – Compartmentalizat
ion (division of labor among cells, tissues, and organs)
– Integration of specialized activities that keep the organism alive
• Most animals are bilateral– Mouth– anus
Body Organization
• Cephalization – Sensory cells concentrated at the head
• Segmentation– Repetition of body units, front-to-back
Sponges (Phylum Porifera)• Sponges
– No symmetry, tissues, or organs – Flattened cells line the body wall
(many pores; spikes of silica and/or proteins)
– Skeleton of silicon, calcium, or spongin (protein fibers)
– Filter feeders (flagellated collar cells absorb food; amoeboid cells digest and distribute it)
– Hermaphrodites– Zygote develops into free-living
larva
Cnidarians (Phylum Cnidaria)• Jellyfishes, corals, and sea
anemones– Radial, tentacled carnivores
(bag like with only one opening– Gastrovascular cavity
(respiration and digestion)– True epithelial tissues with a
jellylike matrix in between (mesoglea)
– Simple nervous system (nerve net)
– Hydrostatic skeleton– Some are commercial, some
symbiotic with algae
Eaten by molluscs and flatworms for nematodes. Base of food web.
Flatworms (Phylum Platyhelminthes)
• Free-living turbellarians (planarians), parasitic tapeworms and flukes– Simplest animals
with organ systems– Bilateral protostomes – Paired nerve cords,
ganglia– Hermaphrodites
Annelids
• Segmented worms (earthworms, polychaetes) and leeches– Closed circulatory system– Digestive and excretory
systems, solute-regulating nephridia
– Nervous system, ganglia in each segment
– Muscles and fluid in chambers act as a hydrostatic skeleton
– Hermaphrodites
Mollusks (Phylum Mollusca)• Soft body with mantle.• Including gastropods (snails), bivalves
(scallops), chitons, nudibranchs, cephalopods – 100,000 named species
Cephalopods• Another class of
molluscs.• The fastest (squids),
largest (giant squids), and smartest (octopuses) invertebrates
• Have a mantle – Sheetlike part of
the body mass, draped back on itself