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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.

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Presentation on theme: "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."— Presentation transcript:

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 cerebral ganglion 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 Septa- Internal body walls separate the segments through which nutrients and other materials pass Coelom- Coelom- Large, fluid-filled cavity located completely within mesoderm

5 Characteristics of Annelids Organ systems include: Closed circulatory system nephridia Excretory structures called nephridia Different regions of gut for different functions Setae Setae- External bristles paired on each segment provide traction for crawling Found on most Parapodia 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 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 hydrostatic skeleton 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 Clitellum- Contains male and female gametes; develops into cocoon after fertilization Seminal vescicles- store earthworms 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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