Transcript Chapter 13 - PlanbookConnect

Chapter 13
Annelida: The Merametric Body
Form
Phylum Annelida
Segmented worms believed to have evolved
in the sea where two-thirds still live
Other one third are terrestrial
Fossils found up to 530 million years old
Range from 1 mm to 3 M long
Characteristics of Annelids
Each segment contains digestive, excretory,
circulatory, and locomotor organs while some are
modified for reproduction, feeding, or sensation
Anterior segment contains a cerebral ganglion
(primitive brain) which is connected to a ventral
nerve cord that runs along the underside of the
body
Delivers sensory info. To brain
Characteristics of Annelids
Septa- Internal body walls separate the
segments through which nutrients and other
materials pass
Coelom- Large, fluid-filled cavity located
completely within mesoderm
Characteristics of Annelids
Organ systems include:
Closed circulatory system
Excretory structures called
nephridia
Different regions of gut for
different functions
Setae- External bristles
paired on each segment
provide traction for
crawling
Found on most
Parapodia- Fleshy
appendages on some
Annelid Groups
Two characteristics
used to classify
Annelids:
Number of setae on
each segment
Presence of parapodia
Marine Worms
Earthworms
Leeches
Marine Worms
Class PolychaetaParapodia with numerous
setae
Largest group; live in
ocean; eyes
Distinctive pair of paddlelike parapodia on each
segment Ex: Nereis
Many burrow or are freeswimming, others live in
protective tubes formed by
gland secretions
Ex: Feather-dusters; tubes
Class Clitellata- No parapodia;
few to no setae
Subclass OligochaetaEarthworms and some
freshwater worms
No parapodia and few setae on
each segment
No head region, nor eyes
Aortic arch- 5 tube-like hearts
Light sensitive and touch
sensitive organs at each end;
sensory cells detect moisture
Consume soil with pharynx
which travels through one-way
gut
Crop-gizzard-intestine-anus
Waste is called casting which
fertilizes soil
Earthworms
Fluid of coelem creates a hydrostatic skeleton
Each segment has circular and longitudinal muscles which
pull against this skeleton
Alternately contract the two sets of muscles to move
Clitellum- Contains male and female gametes; develops
into cocoon after fertilization
Seminal vescicles- store earthworm’s own sperm
Seminal receptacles- Store the sperm of another worm
Class Clitellata
Subclass HirudineaLeeches
eye spots
Lack setae and parapodia
Flattened body; segments
not separated internally
Suckers at both ends of its
body
Most species are predators
or scavengers; some are
parasites