Chapter 13 Annelida: The Merametric Body Form. Phylum Annelida Segmented worms believed to have...
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Transcript of Chapter 13 Annelida: The Merametric Body Form. Phylum Annelida Segmented worms believed to have...
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 ganglioncerebral 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
SeptaSepta- Internal body walls separate the segments through which nutrients and other materials pass
Coelom-Coelom- Large, fluid-filled cavity located completely within mesoderm
Characteristics of AnnelidsOrgan systems include:
Closed circulatory systemExcretory structures called nephridianephridiaDifferent regions of gut for different functions
SetaeSetae- External bristles paired on each segment provide traction for crawling
Found on most
ParapodiaParapodia- Fleshy appendages on some
Annelid GroupsTwo characteristics used to classify Annelids:
Number of setae on each segmentPresence of parapodia
Marine WormsEarthwormsLeeches
Marine WormsClass Polychaeta- Parapodia with numerous setae
Largest group; live in ocean; eyes
Distinctive pair of paddle-like parapodia on each segment Ex: Nereis
Many burrow or are free-swimming, others live in protective tubes formed by gland secretions
Ex: Feather-dusters; tubes
Class Clitellata- No parapodia; few to no setae
Subclass Oligochaeta- Earthworms and some freshwater wormsNo parapodia and few setae on each segmentNo head region, nor eyesAortic archAortic arch- 5 tube-like heartsLight sensitive and touch sensitive organs at each end; sensory cells detect moistureConsume soil with pharynx which travels through one-way gutCrop-gizzard-intestine-anusWaste is called casting which fertilizes soil
EarthwormsFluid of coelem creates a hydrostatic skeletonhydrostatic skeletonEach segment has circular and longitudinal muscles which pull against this skeletonAlternately contract the two sets of muscles to moveClitellumClitellum- Contains male and female gametes; develops into cocoon after fertilization
Seminal vescicles- store earthworm’s own spermSeminal receptacles- Store the sperm of another worm
Class ClitellataSubclass Hirudinea- Leeches
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