Phylum Annelida

division of a body into serially repeated sections along the anterior/posterior axis, externally and internally
- ea. segment has excretory, circulatory, nervous, etc.structures

modification of body regions for specialized functions such as feeding, locomotion, reproduction

-built-in redundancy enhances overall survival chances of the animal
- creates hydrostatic compartments that help in support and locomotion
- permits tagmatization

-Marine, freshwater and terrestrial - range widely in size
-Generally detritus feeders or filter feeders; some carnivorous or parasitic (leeches)
Currently grouped with the Lophotrochozoa
Closely related to Mollusca, based on common trochophore larvae
Traditionally thought to be related to Arthropoda, although this is not well supported now

triploblastic, bilateral symmetry
- trochophore larva
- coelomate with schozocoelous development
- Paired epidermal setae

thick hair-like structures in the annelids. Epidermal.

-Complete digestive system
-Partitioned into functional units
-Pharynx pumps food from mouth into…
-Esophagus, which expands into…
-Stomach (partially digestive, partially storage), crop (storage), and/or gizzard (grinding)
-Calciferous glands remove excess calcium
-Intestine is the site of digestion and absorption

-Respiratory gases diffuse across body wall
-O2 carried by RESPIRATORY PIGMENTS (red, green, or colorless) in blood plasma, not heme, as in humans
Closed circulatory system with dorsal and ventral blood vessels (one-way flow) and connecting capillaries
-Contractile tissue in vessels pumps blood (supplementary “hearts” in earthworms)

-Paired, large ganglia in head region
-Ventral nerve cord with paired segmental ganglia in each segment
-Coordinates swimming and crawling
-Allows escape response of segments
-Eyes present in some polychaetes; lacking in earthworms and leeches
-Receptors to light, chemical, and mechanical stimulation on body surface
- Sensory organs tend to be diminished in Annelida except in polychaetes.

Excrete ammonia (aquatic worms) or urea (terrestrial worms)
-Ammonia excretion is primarily across the body wall in aquatic worms
-Primitive annelids have protonephridia; most annelids have METANEPHRIDIA, one pair per each body segment
-Many also have CHLORAGOGEN TISSUE

In Phylum Annelida, tissue that breaks down amino acids and serves like a primitive liver

- "Poly" many; "chetae" bristles
- major majority marine, usu sea floor dwellers - fan worms are sessile, too.
- May live in shells, rocks, or burrows, some form tubes

-Mobile species have PARAPODIA with setae or CHAETAE (a.k.a. bristles)
These are lateral extensions of the body wall used for locomotion; also assist in gas exchange by increasing surface area
- Move by (a) walking with parapodia, (b) crawling by undulating body, or (c) swimming
Some are sedentary and live in tubes -- chaetae/setae in sessile species are often modded into hooks for attachment

-Greater cephalization than other annelids, but mainly in mobile forms
-PROSTOMIUM is a lobe dorsal and anterior to the mouth containing numerous sensory organs, including antennae and eyes
-Eyes vary from simple receptors to complex eyes w lens & cornea

- Some predate w extensible proboscis
- Some possess poison glands
- Others are herbivores, scavengers, or detritivores
-Fan worms filter feed
-Some polychaetes absorb 20-40% of energy across body wall (V. unusual)

- All polychaetes can regenerate lost segments
-May have natural break pts if grabbed by predators (process called AUTOTOMY)
-Some reproduce by fission or budding
-Most are dioecious w external fertilization & trochophore larvae
-Swarming occurs in some species, where lg numbers of individuals join together to release gametes.

-Epitoky occurs in some species, where reproductive form (EPITOKE) is different from non-reproductive form (ATOKE)
-In some species the epitoke breaks free from the atoke, which stays in the burrow
-In others, the epitoke is formed as part of the body, and the whole animal leaves to mate

-Have a clitellum used in cocoon formation
-All are monoecious
-Have few or no setae
- mostly terrestrial, few aquatic
- burrow & feed on detritus/vegetation
- Lack parapodia
-Few setae, which can be extended & retracted
-Low degree of cephalization

undulation by antagonistic contractions of circular and longitudinal muscles that bulge and then lengthen the body in waves.
- tiny setae are anchor points
- Small conical prostomiumacts like a wedge while burrowing, and soil is swallowed as worm moves fwd

- Monoecious, reproduce sexually via reciprocal fertilization (exchange sperm)
-Cocoon of mucous and chitinous materials produced by CLITELLUM
-Eggs, sperm, and food (albumen) deposited in cocoon where fertilization takes place
-Young worms hatch from cocoon (no larvae)

-parasitic or feed on small invertebrates
- most freshwater, a few are marine
- no parapodia and setae are absent in most
- lo degree of cephalization
- suckers on anterior and posterior ends
- repro similar to oligochaetes, with clitellum only present during mating times
- saliva has anesthetic and anticoagulants

- Have lost metameric partitioning, resulting in single body cavity
- Coelomic sinuses replace blood vessels in most leeches
-Complex musculature (four types of muscles)
-Move in looping motion or swim with undulations

natural breaking points in the body of an annelid that might prevent a predator from eating the entire animal