protostomes 2 - More eucoelomate protostomes(Annelids and...

More eucoelomate protostomes ( Annelids and Mollusks )
Porifera Cnidaria Platy- Nematoda Arthropoda Annelida Mollusca Echino- Chordata
helminthes dermata
levels of cell & tissue organization
fundamental symmetry and number of germ layers
development pattern
the nature of the body cavity
presence or absence of a body cavity
Protostoma
Deuterostoma
Eucoelomates Pseudocoelomates
other Bilateria Acoelomates
Protistan ancestor
Eumetazoa
Parazoa
Bilateria
Radiata
phylum Annelida (little rings; segmented worms)
About 15,000 described species in most habitats (marine,
freshwater, terrestrial; primarily free-living).
Structurally diverse but all share several common features:
• Organ system level of organization, cephalization ,
bilateral symmetry; complete gut
• circulatory system (overcomes diffusion limitations)
• hydrostatic skeleton, circular and longitudinal
muscles (good control of movement) -- nematodes have
only longitudinal muscles and are restricted to a ‘thrashing’
motion.
• Segmentation , segments separated by septa (each segment has
replicated functions such as nerve ganglia and excretory organs, but is
coordinated with the rest of the animal).
septum
segments
Coelom
Gut, lined with mesoderm
Functional attributes
of annelid body plan:
• Segmentation, hydrostatic skeleton, nerve net, and bidirectional
antagonistic muscles --> better movement control than in nematodes.
• coelom permits internal storage of specialized organs.
• no cuticle , so vulnerable to water loss and restricted to aquatic and
moist terrestrial habitats.
phylum Annelida (little rings; segmented worms)
Three major classes:
Oligochaeta , mainly freshwater and moist terrestrial
habitats (example: earthworms)
• small setae (spines) in pairs in each segment
• small and unspecialized head
• Segments relatively undifferentiated
Abundant, ecologically important,
especially in soil. Generally
hermaphroditic and egg-laying;
hatchlings like miniature adults
(no distinct larval stage).
Gippsland giant earthworm
(Australia)
phylum Annelida (little rings; segmented worms)

Polychaeta , mainly marine; very diverse structurally
• well-developed head, often with elaborate feeding organs or
tentacles.
• parapodia (fleshy flaps or extensions) on each segment, as well as
setae -- spines, often large (top view):
Parapoida function in locomotion (swimming, crawling, burrowing)
and gas exchange (large surface area)
Feeding organs
on head
Parapodia with setae
phylum Annelida (little rings; segmented worms)
Polychaeta
• Generally sexual
• larval stage ( trochophore ) is
charcteristic. Very different from
adult; generally planktonic.
Ecologically diverse: scavengers, predators, filter-feeders; some
planktonic, others burrowing, others crawl around, some swim.
mouth
stomach
anus
intestine
band of
cilia
phylum Annelida (little rings; segmented worms)
Hirudinea (leeches), mainly freshwater and moist terrestrial
habitats. Highly modified (derived from oligochaetes):
• body flattened (but can expand to hold a large meal)
• no setae or parapoida
• segmentation reduced (and undifferentiated)