Animals: Chapter 2: Mollusks, Arthropods, and Echinoderms

Mollusks The Octopus—Mollusk Without a Shell Examples: clams, snails, slugs, octopus Phylum Mollusca 2nd largest number of species found in phyla Importance: Used for food, making things, others are parasites

The Octopus—Mollusk without a Shell Eight arms/tentacles Each with a suction disk to grasp Able to regenerate tentacles Hunts for food but otherwise timid Moves by gliding along on arms Rapid movement by forcing water through siphon (muscular tube) May also release black inky substance for quick get away Soft/Flexible body Special skin pigments used for camouflage or may also reflect stimulation

The Clam—Mollusk with a Shell Bivalves: two shells Ex. Clams, muscles, scallops, Univalve: one shell Ex. Snail, cochs, Mantle-think skin that covers soft body; manufactures material for shell Adds layers as it gets older/grows Foot- hatchet shaped muscle that moves the clam Filter Feeders: food found in water Process: Sends two siphons into the water One siphons water into the shell Inside the shell the water is filtered for food Second siphon sends water and waste out of the shell

siphons Muscular foot

Arthropods More species than any other animal phylla Insect class is the largest Importance: pollinators, decomposers, crop eaters, disease carriers, and parasites Exoskeleton-hard non-living outer covering Jointed appedages (legs, antennae)

A Typical Insect’s Body 3 parts: head, thorax, abdomen 3 pairs of legs—total 6 Most have 2 pairs of wings Compound eyes

Arthropods Insect Life Cycles Incomplete metamorphosis-several molts-looks the same-sheds old exoskeleton Incomplete-egg-nymph-adult Ex. Grasshopper, cockroaches, water-bug, stinkbugs Metamorphosis-a ‘change in body form’

Complete metamorphosis-4 stages-egg-larva-pupa-adult Larva-active stage (caterpillars, maggots, grubs) Pupa-resting stage (cocoon, chrysalis, puparium) Each stage looks different

Arthropods Other Interesting Arthropods Barnacles, crabs, lobsters, shrimp, pill bugs, centipedes, millipedes, scorpions, spiders Different number of segments and legs Centipedes-flattened bodies with one pair of legs per segment; hunt for food Millipedes- rounded bodies with two pair of legs per segment; eat decaying matter

Echinoderms Sea stars, sea cucumbers, sea urchins Body supported by hard flat plates under skin Plates may have sharp spines Radial symmetry Starfish can regenerate rays

Water-vascular system key to movement Rows of tube feet at bottom of each ray Movement: Attaches tube feet and then pulls body to that location Eat: Climbs on top of clam and uses tube feet to pull apart shell When clam tires the shell opens Starfish turns its stomach inside out and digestive juices dissolve clam Starfish then withdraw its stomach from the shell

See Flow Charts for Classes of Mollusks Classes of Arthropods