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

Body Cavities• Most bilateral

animals have a coelom and a complete gut

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.

Unique Cnidarian Weapons

• Nematocysts– Used to capture

prey and for defense

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

Echinoderms• Sea stars, sea urchins, sea

cucumbers, etc.– Invertebrates of the

deuterostome lineage– Exoskeleton with spines,

spicules, or plates of calcium carbonate

– Water-vascular system with tube feet

– Adults are radial, but bilateral traits appear in larval stages and other features