Zool Annelida

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Annelida
Major Groups

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Class Polychaeta
Class Clitellata
- Subclass Oligochaeta
- Subclass Hirudinea
Class Echiura

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Annelida
Apomorphy

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Chitinous bristles (setae/chaetae)

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Annelida
General

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- 12,400 described species.
- Marine, FW and terrestrial
- Freeliving, commensal and parasitic

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Annelida
Body Wall

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Anterior prostomium, then peristomium and a posterior pygidium
- Thin flexible, permeable outter layer
- Circular and Longitudinal muscles
- peritoneum (lines coelom)

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Annelida
Body Cavity

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- Metameric
- Segments seperated by septa
- Compartmentalized coelom
- Isolated coelomic fluid in each segment
- Idependent movement of segments

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Annelida Metamerism

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- External rings or "annuli"
- Repeated structures/ serial homology
- Internal septa (connective tissue inbetween each peritoneum)
- Digestive tract is NOT metameric

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Annelida
Nervous system

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- Anterior cluster of ganglia
- Pair Longitudinal cords with giant nerve fibers
- Cerebral ganglion (brain)
- Suboesophageal ganglion (under esophagus)

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Annelida
Circulatory System

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- Closed circulatory system
- Major dorsal and ventral vessel for anterior and posterior transport.
- Capillaries connect vessels
- No "heart"
- Vessels with contractile properites and one way valves, to act as heart
- Fluid transports oxygen via hemoglobin, hemoerythrin, and chlorocruorin (green)

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Annelida
Excretory System

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- Metanephridia (open tubes that drawns fluid to outside)
- Funnel opening in one segment and pore to outside in next segment
- Tubes involved in osmoregulation

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Annelida
Locomotion

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- Selective contraction of regions (Peristallic waves)
- Coelomic fluid creates hydrostatic skeleton
- Squeeze and push animal forward
- Chaetae act as brace for motion

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Class Clitellata
Subclass Oligochaeta
Characteristics

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- Earthworm
- 3500 described ssp
- FW, Marien and Terrestrial
- Scavengers and deposit feeders

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Oligochaeta
Body form

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- cylindrical body
- few lateral projections
- no parapodia
- setae present
- no head
- no tentacles
- few photoreceptors
- aquatic species have long setae

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Oligochaeta
Clitellum

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- Series of segments in anterior portion, swollen with glandular tissue
- Secrete mucous and cocoon to hold eggs
- Role in copulation

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Oligochaeta
Internal

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- Divided by septa
- well developed circular muscles

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Oligochaeta
Locomotion

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Earthworm
- wave of contraction of circular muscles.
- Chaetae anchor body

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Oligochaeta
Gas exchange

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- No specilized structures
- Diffusion across moist cuticle
- Hemoglobin in circulatory flid

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Oligochaeta
Reproduction

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- Gonads are discrete tissue
- Only in few segments
- Hermaphroditic, dont self breed.
- Copulation w/o intromission
- Male opening seg 14, spermatheca (storage) in seg 10-11
- Simultaneous transmission
- Some asexual
* Different form Polychaetes

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Oligochaeta
After Fertilization

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- Cocoon secreted by clitellum
- Eggs deposited from female gonopore
- Then sperm from spermatheca
- Kind of external fertilization
- Cocoon deposited in soil
- Direct development (No larval stage)

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Class Polychaeta

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- Marine segmented worms
- 70% annelids
2 groups = Errant and Sedentary

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Class Polychaeta
Apomorphy

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Parapodia = lateral extensions of the body wall modified for different functions in different parts of the body.

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Errant Polychaetes

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- Mobile
- Well-developed parapodia and sensory structures
- Homonomous

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Sedentary Polychaetes

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- Tube or burrow dwelling
- Reduced parapodia
- Heteronomous
- Gills, feeding tentacles
- Use sand grains and mucous to construct burrows

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Polychaetes
Obtaining food

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- Raptorial feeders (hunters) w/ eversible pharynx sclerotized jaw and toxic saliva
- herbivores, omnivores or scavangers
- Non-selective deposit feeders (process sand on beach)
- Selecive deposit feeders
- Filter feeders

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Polychaeta
Reproduction

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- Gonochoristic/dioecious
- No discrete gonads, gametes produced by peritoneal tissues
- 6 segments
- External fertilization
- Trochophore Larva

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Family Siboglinidae
Characteristics

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- 150 species
- benthic marine
- sedentary tube dwellers
- No digestive system
- Closed circulatory system
- Two groups: Perivates and vestimentiferans

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Siboglinidae
Apomorphy

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-Trophosome: filled with chemosynthetic bacteria
- Segmentation in posterior portion ONLY

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Siboglinidae
Group Perviates

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Absorb nutrients across body wall, resemble threads

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Siboglinidae
Group Vestimentiferans

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- Regions of hydrothermal vents
- Dense species rich communities

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Siboglinidae
Bacteria

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- Bodies too big and dense for diffusion so...
- Trophosomal bacteria, oxidize hydrogen sulfied or methane
- Generate ATP and synthesize carbohydrates.
- Worms deliver compounds to bacteria, worms use organics produced by bacteria.

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Siboglinidae
Reproduction

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- Gonochoristic
- Spiral cleavage
- Trochophore larva

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Class Echiura
Characteristics

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- Burrows, spoon worms
- No segmentation as adults
-160 species
- Deposit feeders
- No specilized sensory system
- Proboscis for feeding

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Class Echiura
Apomorphy

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Anal sacs with funnels protrude into coelom.

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Echiura
Reproduction

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Gonochoristic with no distinct gonads.
- Peritoneal lining
- Trochophore larva

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Subclass Hirudinea
Characteristics

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Leeches
- 700 species
- FW or terrestrial, few marine
- Highly muscular
- Clitellum

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Hirudinea
Apomorphy

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Posterior sucker**

Has two suckers, one on each end. Mouth is in anterior sucker, but is the only class with posterior sucker as well.

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Hirudinea
Morphology

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- Fixed number of postoral segments (32 + 2 preoral)
- Lack setae
- No coelomic space or septa
- Replaced by mesenchymal tissue
- Not true cosed circulatory system.

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Hirudinea
Locomotion

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- Inchworm movement with alternate attachment of suckers
- Undulations while swimming
- * No peristalisis

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Hirudinea
Reproduction

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- Hermaphroditic
(usually protandric hermaphrodites)
- Chitinous cocoons
- No larval stage
- Few segments with gonads.
- Internal fertilization (spermatophores penetrate skin)

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Hirudinea
Blood feeding

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- 3 Toothed jaws
- Specilized anticoagulant (Hirudin)
- Ectoparasitic and host-specific
- Macrobdella decora attacks humans.
- After blood meal, hemoglobin split into globin and heme.

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Hirudinea
Modern Uses

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- Anticoagulant hirudin (dissolves clots)
- Anesthetics, antibiotics
- Relieve fluid pressure following tissue damage