BIOL 1604 Lecture Notes - Lecture 8: Schistosomiasis, Cysticercosis, Schistosoma
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Aceolomate Bilateral Animals
Three major evolutionary advances
Triploblastic
o Presence of three tissue levels
Cephalization
o Concentrating sense organs in the head regions
Bilateral symmetry
o Active, directed movement
Aceolomates do not have an extra cavity – only the gut cavity. They are flat
Packing tissue contains more cells and fibers and less extracellular matrix than dos the mesoglea
of cnidarians
Characteristics
Dorsoventrally flattened
Triploblastic, aceolomates with bilateral symmetry
No coelom
Muscular system primarily a sheath form of mesodermal origin. Layers of circular
longitudinal and sometimes oblique fibers beneath the epidermis
No respiratory, circulatory, or skeletal systems
Nutrition and digestion
In general, mouth and pharynx present
Incomplete gut or no gut
o Extracellular and intracellular digestion (enzymes and phagocytosis)
Osmoregulation
o Canals with tubules that end in protonephridia (flame cells). Excretion
Nervous system and sense organs
Vary in complexity
Simple nerve net to centralized nerve net
Pair of anterior ganglia with longitudinal nerve cords connected by transverse nerves in
most forms
Neurons: sensory, motor, etc.
Sense organs
o Statocyst
o Ocelli
o Rheoreceptors
o Auricles
Reproduction
Asexual: fragmentation, transverse fission
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Sexual: most forms are monoecious. Complex reproductive systems and internal
fertilization
Direct development or indirect with different larval stages
Phylum Platyhelminthes
Class Turbellaria
o Freshwater planarians
o Free living
o Mainly marine
o Terrestrial
o Predators, scavengers, herbivores
o Very few commensals or parasites
Digestive cavity varies from none to simple to highly branched
Epidermis is ciliated.
Locomotion
Muscular and ciliary movement
o Cilia
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