29 terms

Phylum Platyhelminthes, Nematoda, Mollusca

Belong to the subregnum bilateria

20,000 species

Habitats: marine, freshwater, damp terrestrial habitats

Some free living, some parasitic
Subregnum Bilateria
The supergroup containing all animals except sponges, cnidarians and ctenophores
Flatworm Anatomy & Physiology
Bilateral symmetry




Organ system level of classification: distinct nervous system organized by ganglia

Incomplete digestive system

Reproduction: sexual and asexual

Excretory system
Flatworm: Excretory system
Most basic organism to possess this

Organized through flame cells

Osmoregulation, elimination of nitrogenous waste
Balance of salt and water within an organism
Class Turbellaria: The Planarians
Mostly free-living (not parasites) in fresh water

Mouth on ventral surface with extendable pharynx


Sexual - fertilization

Asexual - fission
Ciliated epithelium - integral part of locomotion

Triangular head

Eye spots - light sensitive structures

Auricle - Olfactory structures
Trematoda: The Flukes
All parasitic

Most adults are vertebrate endoparasites

Multiple species parasitize humans

Most go through 2-3 species throughout their life cycle

Have oral sucker to attach to host
The Flukes
Mouth that leads to pharynx, which divides into intestinal caeca of the gastrovascular cavity


Capable of sexual reproduction
Cestoda: The Tapeworms
All endoparasitic

So used to living in other organisms, lack their own digestive system

Usually have 2 organism life cycle
Cestoda: The Tapeworm Anatomy
Segments called proglottids

Scolex acts as a holdfast

Spread by releasing proglottids while most of the organism remains attached. These are full of eggs
Phylum Nematoda
Bilateral pseudocoelomates

25,000 - 500,000 species

Non-living cuticle

Have an organ system level of organization

Capable of sexual reproduction and infernal fertilization
Nematode: Pseudocoelomates
Have a body cavity

Room for organs

Complete digestive system

Allows for hydrostatic skeleton - gives nematodes great mobility
Round worms

Body covered with flexible cuticle made up of collaged

Dioecious: distinct male and female

Female larger than males

Males have spicules near anus

Ascaris lumbricoides common intestinal parasite in South East, US
Mature in small intestine

Larvae burrow through skin of new host, find way to intestine via heart, lungs and esophagus
Trichina Worms
Cause of trichinosis - usually caused by eating undercooked pork
Pin Worms
Most common nematode parasite in US

30% of children infected

Adults live in large intestine

Crawl out of anus at night and bite down, lay eggs
Filiarial Worms
Usually spread to vertebrates from mosquitoes

Microfilarids circulate in bloodstream until mosquito bites

Responsible for heart worm in dogs

Cause Elephantitis in humans
Phylum Mollusca
More than 90,000 species

Marine, freshwater & terrestrial

Evolved in Precambrian

Protostome coelomates

Triploblastic, true coelum

Bilateral symmetry

Organ-system organization

Sexual reproduction, usually dioecious

Covered with protective, muscular mantle
Class Polyplacophora: Chitons
Marine animals that live on rocks close to shore

Scrape algae and diatoms off or sufaces with radula

Hold onto rocks with suction from their muscular foot

Breath through lateral gills

Eight hard plates along dorsal surface for protection
Class Gastropoda
Orders: snails, slugs, whelks, conchs, sea hares
Gastropod Anatomy & Physiology
Torsion (twisting) of visceral mass has caused asymmetry

Most have univalve, coiling shell; many have hard operculum to cover the opening

Well developed head

Rough radula for feeding

Flat foot to feed on surfaces

Most are hermaphroditic

Breathe through gills and mantle

Have 2 or 3 chambered heart
Bivalva: Clams, Oysters, Scallops and Mussels
Marine and freshwater

Sedentary filter feeders

Lack distinct head

2 shell, laterally compressed and attached with a hinge ligament

Umbo is the bump at the base - growth origin

Inside of shell lined with nacreous layer
Bivalva Anatomy & Physiology
Mantle cavity contains gills and visceral mass

Water enters through incurrent siphon
Flows over the gills
Exits via the excurrent siphon

Circulatory system with 3 chambered heart

Separate sexes
Class Cephalopoda
Marine predators

Foot modified into tentacles and arms

Chitonous beack

Siphon for expelling water

Well-developed eyes

Large brains for invertebrates