Chapter 17 Annelida: Segmented Worms Annelida: Segmented Worms

I. Dividing the Body  Cons of Coelom – muscle contraction pushed coelom fluid  Benefits of metamerism (segmentation)  Better at burrowing  Independent movements of segments  Fine control possibilities  More advanced nervous system required  Redundancy = safety factor  Evolutionary potential (specialization)  Cons of Coelom – muscle contraction pushed coelom fluid  Benefits of metamerism (segmentation)  Better at burrowing  Independent movements of segments  Fine control possibilities  More advanced nervous system required  Redundancy = safety factor  Evolutionary potential (specialization)

Annelida Annelida = seg. worms Annelida Annelida = seg. worms  15,000 species - Three major classes  Polychaeta (10,000+ sp.)  Bristleworms  Primarily marine worms  Oligochaeta (approx sp.)  Earthworms & relatives  Terrestrial & freshwater (few marine)  Hirudinea (<2000 sp.)  Leaches  Primarily freshwater with few marine & terrestrial sp.  15,000 species - Three major classes  Polychaeta (10,000+ sp.)  Bristleworms  Primarily marine worms  Oligochaeta (approx sp.)  Earthworms & relatives  Terrestrial & freshwater (few marine)  Hirudinea (<2000 sp.)  Leaches  Primarily freshwater with few marine & terrestrial sp.

II. Body Plan  Segmented  Anterior prostomium (head side)  Posterior pygidium (tail side)  New segments posterior end before pygidium.  Both circular & longitudinal muscles  Epidermis that secretes…  A non-chitinous cuticle (collagen)  Segmented  Anterior prostomium (head side)  Posterior pygidium (tail side)  New segments posterior end before pygidium.  Both circular & longitudinal muscles  Epidermis that secretes…  A non-chitinous cuticle (collagen)  Coelom (mesodermal)  Hydrostatic skeleton  Peritoneum  Line coelom; form mesenteries & septa  Mesodermal epithelium  Mesenteries  Secure organs  Septa  Divide segments

III. Polychaete Worms (many hairs)

IV. Oligochaeta (few hairs)  Most terrestrial, freshwater, few brackish & marine  Setae – needle-like, chitinous substance  short in earthworms, longer in aquatic oligochaetes  A. Earthworms A. Earthworms  2cm to 4m in length  Most terrestrial, freshwater, few brackish & marine  Setae – needle-like, chitinous substance  short in earthworms, longer in aquatic oligochaetes  A. Earthworms A. Earthworms  2cm to 4m in length

A. Earthworms  4 setae per segment  Setae are moved by muscles to anchor worm during locomotion  Movement by alternate contraction of circular & longitudinal muscles (peristaltic) Movement  1) Nutrition:  Scavengers - feed on decaying organic matter; mouth  buccal cavity  pharynx  esophagus  crop (storage)  gizzard (grinding)  intestine (typhlosole  SA)  anus  Chloragogen tissue produces glycogen & fat (like the liver)  2) Circulation and Respiration  Double circulatory system:  1) Coelom fluid  2) closed circulatory system  dorsal vessel is like its heart  Ventral vessel is like the aorta – delivering blood to organs  Hemoglobin (most annelids)  4 setae per segment  Setae are moved by muscles to anchor worm during locomotion  Movement by alternate contraction of circular & longitudinal muscles (peristaltic) Movement  1) Nutrition:  Scavengers - feed on decaying organic matter; mouth  buccal cavity  pharynx  esophagus  crop (storage)  gizzard (grinding)  intestine (typhlosole  SA)  anus  Chloragogen tissue produces glycogen & fat (like the liver)  2) Circulation and Respiration  Double circulatory system:  1) Coelom fluid  2) closed circulatory system  dorsal vessel is like its heart  Ventral vessel is like the aorta – delivering blood to organs  Hemoglobin (most annelids)

 3) Excretion:  blood fliltration  metanephridia: like kidneys  Capillaries surrounded by nephritic tubule  Nitrogenous waste (urea) is pulled out of blood  Excreted through external pore  4) Nervous system:  Central NS  cerebral ganglia=“brain”  Connectives  ventral nerve cords  Sensory NS:  Mechanoreception (touch)  Photoreception (light/dark) cells within the epidermis  Chemoreception (food etc.) receptor organs similar to taste buds interspersed throughout the epidermis  3) Excretion:  blood fliltration  metanephridia: like kidneys  Capillaries surrounded by nephritic tubule  Nitrogenous waste (urea) is pulled out of blood  Excreted through external pore  4) Nervous system:  Central NS  cerebral ganglia=“brain”  Connectives  ventral nerve cords  Sensory NS:  Mechanoreception (touch)  Photoreception (light/dark) cells within the epidermis  Chemoreception (food etc.) receptor organs similar to taste buds interspersed throughout the epidermis

 Niche  Aeration & enrichment of soil  C. Darwin study: Earthworms are able to consume their weight in soil every day.  Reproduction & Development  Hermaphroditic sexually mature when clitellum appears  Anterior ends emerge for copulation  Mating involves simultaneously releasing sperm from the sperm ducts (cross fertilization). Sperm cells travel via seminal grooves to seminal receptacles.  Sperm is then shed along with eggs into a mucous cocoon (produced by the clitellum) which provides a protective environment for the direct development of the juveniles.  Niche  Aeration & enrichment of soil  C. Darwin study: Earthworms are able to consume their weight in soil every day.  Reproduction & Development  Hermaphroditic sexually mature when clitellum appears  Anterior ends emerge for copulation  Mating involves simultaneously releasing sperm from the sperm ducts (cross fertilization). Sperm cells travel via seminal grooves to seminal receptacles.  Sperm is then shed along with eggs into a mucous cocoon (produced by the clitellum) which provides a protective environment for the direct development of the juveniles.

V. Hirudinea  Primarily freshwater  Usually cm. Some to 30 cm!  Text fig  Colorful  A. Form and Function  fixed number of segments.  Suckers for locomotion  lack coelomic compartments  septa have disappeared  Primarily freshwater  Usually cm. Some to 30 cm!  Text fig  Colorful  A. Form and Function  fixed number of segments.  Suckers for locomotion  lack coelomic compartments  septa have disappeared

 1. Nutrition  Pharynx & “teeth” (often chitinous) for feeding off the fluids of other organisms.  The gut is often modified to store large amounts of fluid.  Some leeches prey on the other invertebrates while others prefer vertebrate hosts.  Most parasitic leeches detach from their hosts in order to reproduce. Some species attach their cocoons to their host.  Many leeches feed on blood. They were once used to “bleed” people who were sick. They are still used medicinally to relieve congestion when venous circulation is compromised (inadequate blood return from tissues).  1. Nutrition  Pharynx & “teeth” (often chitinous) for feeding off the fluids of other organisms.  The gut is often modified to store large amounts of fluid.  Some leeches prey on the other invertebrates while others prefer vertebrate hosts.  Most parasitic leeches detach from their hosts in order to reproduce. Some species attach their cocoons to their host.  Many leeches feed on blood. They were once used to “bleed” people who were sick. They are still used medicinally to relieve congestion when venous circulation is compromised (inadequate blood return from tissues).

 2. Respiration  occurs through the skin except for the gills of some fish parasites.  3. Excretion  Leeches excrete through pairs of nephridia (10-17)  4. Nervous system  Their CNS consists of both anterior & posterior “brains” as well as 21 pairs of ganglia positioned along the ventral nerve chord.  Sensory modalities include photoreception by ocelli, subcutaneous mechanoreceptors, chemoreception, & thermoreception in at least some.  2. Respiration  occurs through the skin except for the gills of some fish parasites.  3. Excretion  Leeches excrete through pairs of nephridia (10-17)  4. Nervous system  Their CNS consists of both anterior & posterior “brains” as well as 21 pairs of ganglia positioned along the ventral nerve chord.  Sensory modalities include photoreception by ocelli, subcutaneous mechanoreceptors, chemoreception, & thermoreception in at least some.

Modern leech medicine

 5. Reproduction  Hermaphroditic  Cross-fertilize during copulation  Sperm are transferred by hypodermic impregnation.  The clitellum secretes a mucous cocoon to receive the sperm and egg.  The cocoons are buried in mud or damp soil, and development direct (oligochaetes). Some parasitic species attach their cocoon to a host.  5. Reproduction  Hermaphroditic  Cross-fertilize during copulation  Sperm are transferred by hypodermic impregnation.  The clitellum secretes a mucous cocoon to receive the sperm and egg.  The cocoons are buried in mud or damp soil, and development direct (oligochaetes). Some parasitic species attach their cocoon to a host.