Download ch outline platyhelminthes mollusca annelida fl2011

Flatworms
Flatworms have bilateral symmetry. They also have three germ layers. They
are acoelomates.
Free-Living Flatworms
Freshwater planarians are small, literally flat, worms. They have an
excretory
and a nervous system.
Parasitic Flatworms
The parasitic flatworms include the tapeworms and the flukes.
Tapeworms
Tapeworms are endoparasites of various vertebrates, including
humans.
They attach to the intestinal wall of the host and
feed.
Flukes
Flukes are all endoparasites of various vertebrates. They are
named for the type of vertebrate organ they
usually
inhabit.
Rotifers
Rotifers are related to the flatworms and both are trochozoans. Rotifers have
a crown of cilia, known as the corona, on their heads.
Molluscs
Molluscs include chitons, limpets, slugs, snails, abalones, conchs,
nudibranchs, clams, scallops, squid, and octopuses. They have a true
coelom, bilateral symmetry, three germ layers, the organ level of
organization, and a complete digestive tract.
Unique Characteristics of Molluscs
All molluscs have a body composed of at least three parts: the visceral
mass, the foot, and the mantle.
Gastropods
Gastropods include nudibranchs, conchs, and snails. The foot is
ventrally
flattened.
Cephalopods
Cephalopods include octopuses, squid, and nautiluses. The foot has
evolved into
a funnel or siphon about the head.
Bivalves
Bivalves include clams, mussels, oysters, and scallops. Their shells
have two
parts.
The Visceral Mass
a
The clam has an open circulatory system and a heart. It also has
nervous system and a digestive system.
Comparison
Refer to Table 30.2 for a comparison of a clam, squid, and land snail.
Annelids
Annelids are segmented, have a hydrostatic skeleton, and specialization of
the digestive tract.
Polychaetes
Marine annelids are the Polychaeta, which refers to the presence of
many setae. Setae are bristles that anchor the worm or help it move.
Oligochaetes
The oligochaetes, which include earthworms, have few setae per
segment.
Segmentation
Segmentation is evidenced by body rings, coelom divided by
septa, setae on most segments, ganglia and lateral nerves in
each segment, nephridia in most segments, and branch blood
vessels in each segment.
Reproduction
Earthworms are hermaphroditic.
Comparison with Clam Worm
The comparison of the marine clam worm with the terrestrial
earthworm highlights the manner in which earthworms are
adapted to life on land.
Leeches
Leeches have no setae and each body ring has several transverse
grooves. Among their modifications are two suckers.