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Chapter 13

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.

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Chapter 13

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  1. Chapter 13 Annelida: The Merametric Body Form

  2. 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

  3. 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

  4. 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

  5. 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

  6. Annelid Groups • Two characteristics used to classify Annelids: • Number of setae on each segment • Presence of parapodia • Marine Worms • Earthworms • Leeches

  7. Marine Worms • Class 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

  8. Class Clitellata- No parapodia; few to no setae • Subclass Oligochaeta- Earthworms 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

  9. 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

  10. Class Clitellata • Subclass 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

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