X. Flatworms: Kingdom Animalia, Phylum
Platyhelminthes
Among bilateral organisms (meaning those that can be divided into an equal right and left
side by a single cut), the flatworms, Phylum Platyhelminthes, are the simplest. In this
short chapter, one species is described after a brief description of the Phylum.
Phylum Platyhelminthes, the Flatworms
•
•
•
•
•
leaf or ribbonlike animals
length ranges from 0.02 inches to 66 feet long (!!)
digestive tract incomplete (lacks an anus)
digestive cavity is only space within the body; otherwise lack an internal cavity
three major groups
turbellarians: free living forms
• dense nervous tissue clusters form a primitive brain
• a nerve cord pair joins the brain to the rest of the nervous system, which
extends throughout the body
• digestive system highly branched
• mouth on ventral side; a muscular tube projects from here during feeding
• use cilia located on ventral surface to move about
flukes: parasitic flatworms
• male is larger
• female invests much time located within a groove that traverses the
male’s length
• the thus mate readily and may produce more than 1000 eggs a day
• males and females possess suckers which attach to blood vessels in the
host’s intestine
• can cause severe diseases in humans; blood fluke disease occurs
extensively throughout South America, Asia, and Africa
• most have a complex life that involves stages in more than one host
tapeworms
• live in digestive tracts of vertebrates (reptiles, birds, and mammals)
• body is a series of repeated segments (very unlike flukes and flatworms)
• lack a digestive tract (absorb nutrients across body integument)
• head, the smallest body segment, is equipped with teeth and sucking
structures for attaching to grasp host tissues
• segment immediately behind head is youngest while posterior-most
segment is oldest
• repeated segments contain male and female reproductive parts
• the posterior-most segment gets filled with ripe eggs and breaks off to be
voided from the body in the feces
• life cycles are complex and generally utilize more than one host
•
some species can reach 66 feet in the human intestine
1. Flatworm, Kaburakia excelsa
Kingdom Animalia
Phylum Platyhelminthes
Class Turbellaria
Order Polycladida
Family Stylochidae
Genus Kaburakia
Occurrence ................................... •
•
Form/Function ............................. •
•
•
•
Reproduction ...............................
•
Predators/Prey ..........................
•
•
Noteworthy Facts ………………
•
Alaska to southern California
low intertidal
to 4 inches long and 2.8 inches wide when active
and extended
nuchal tentacles large, retractile, and bearing eyes
inside at the base
marginal eyes occurring around entire perimeter of
body
tan color, heavily imprinted with uniformly
distributed dark-brown, dash-like markings, which
gives the entire body a bluish hue
in Washington, gravid individuals have been
identified in March
150 – 160 golden eggs are laid in capsules as a
mono- or bilayer on rocks
carnivorous; feeds on ascidians, polychaete
worms, crustaceans, and mollusks
one of the largest coastal flatworms