Chapter 17Chapter 17

Annelida:Segmented Worms

Annelida:Segmented Worms

I. Dividing the BodyI. 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 = seg. wormsAnnelida = seg. worms 15,000 species - Three major classes Polychaeta (10,000+ sp.)

Bristleworms Primarily marine worms

Oligochaeta (approx. 3000 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. 3000 sp.) Earthworms & relatives

Terrestrial & freshwater (few marine)

Hirudinea (<2000 sp.) Leaches

Primarily freshwater with few marine & terrestrial sp.

II. Body PlanII. Body Plan Segmented Anterior prostomium

(head side) Posterior pygidium

(tail side) New segments form

@ 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 form

@ 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

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)IV. Oligochaeta (few hairs) Most terrestrial, freshwater, few

brackish & marine Setae – needle-like, chitinous substance

short in earthworms, longer in aquatic oligochaetes

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 2cm to 4m in length

A. EarthwormsA. Earthworms 4 setae per segment Setae are moved by muscles to anchor worm during

locomotion Movement by alternate contraction of circular &

longitudinal muscles (peristaltic) 1) Nutrition:

Scavengers - feed on decaying organic matter; mouthbuccal cavitypharynxesophaguscrop (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) 1) Nutrition:

Scavengers - feed on decaying organic matter; mouthbuccal cavitypharynxesophaguscrop (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. HirudineaV. Hirudinea Primarily freshwater Usually 2 - 6 cm. Some to 30 cm!

Text fig. 17 - 19 Colorful A. Form and Function

fixed number of segments. Suckers for locomotion lack coelomic compartments septa have disappeared

Primarily freshwater Usually 2 - 6 cm. Some to 30 cm!

Text fig. 17 - 19 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.