Worms and Mollusks Characteristics of Worms All worms

  • Slides: 8
Download presentation
Worms and Mollusks

Worms and Mollusks

Characteristics of Worms • All worms are invertebrates that have long, narrow bodies without

Characteristics of Worms • All worms are invertebrates that have long, narrow bodies without legs • Body structure: – Bilateral symmetry; they have head and tail ends, all tissues, organs and body systems. • Nervous System: – Simplest organisms with a brain; brain controls most of its body functions – Can detect objects, food, mates and predators quickly • Reproduction: – Some reproduce asexually by dividing into two separate organisms (genetically identical) – most reproduce sexually • Some are hermaphrodites, but still exchange sperm to fertilize egg

Flatworms • Flatworms are flat and soft as jelly • Some are a parasite:

Flatworms • Flatworms are flat and soft as jelly • Some are a parasite: an organism that lives inside or on another organism – robs food from its host and makes host weak – may injure the host’s tissues or organs, but rarely kill • Others (Planarians) are free living flatworms – scavengers: they feed on dead or decaying material – predators; feeds like a vacuum cleaner • Tapeworms: one kind of parasitic flatworm – Absorbs food from the host’s digestive system – Most live in more than one host in their lifetime (some even live in human hosts-see figure 15)

types of flatworms tapeworms planarian

types of flatworms tapeworms planarian

Roundworms • Can live in nearly any moist environment; most abundant animals on Earth;

Roundworms • Can live in nearly any moist environment; most abundant animals on Earth; cylindrical bodies (unlike flatworms) • Have a digestive system that is like a tube, open at both ends: food enters at mouth, and exits through an opening (anus) • One-way digestive system is efficient; like an assembly line enables the animal’s body to absorb a large amount of food

Segmented Worms • Earthworms, leeches, and some sea-floor worms are segmented worms • Body

Segmented Worms • Earthworms, leeches, and some sea-floor worms are segmented worms • Body structure – Segmented worms have bodies made up of many linked sections called segments – Have well-developed organ systems; ex. Nervous system that includes a brain and a nerve cord that runs the length of the worm’s body – One-way digestive system, like roundworms (see figure 17) • Closed circulatory system: blood

Characteristics of Mollusks • Mollusks: invertebrates with soft, unsegmented bodies that are often protected

Characteristics of Mollusks • Mollusks: invertebrates with soft, unsegmented bodies that are often protected by a hard outer shell • In addition to a soft body often covered by a shell, a mollusk has a thin layer of tissue called a mantle that covers its internal organs, and an organ called a foot • Body structure – have bilateral symmetry – unlike segmented worms, body parts aren’t usually repeated – digestive system with 2 openings • Open circulatory system – blood is not always in blood vessels; sloshes around inside body • Obtaining oxygen – gills: organs that remove oxygen from the water and carry carbon dioxide out of blood

Diversity of Mollusks The three major groups of mollusks are… Gastropods -include snails and

Diversity of Mollusks The three major groups of mollusks are… Gastropods -include snails and slugs -single shell or no shell -herbivores, scavengers, or carnivores -all use a radula to obtain food (flexible organ with tiny teeth) Bivalves -mollusks that have two shells held together by hinges and strong muscles -do not have radulas: use filter feeders -most are herbivores -don’t move quickly Cephalopods -ocean-dwelling mollusk whose foot forms tentacles around its mouth -only mollusks with a closed circulatory system -Carnivores: use muscular tentacles to capture prey -large brains