Chapter 17 Annelids

metamerism

division of body into repeating units (= segments = metameres) along the anterior (older ones) -> to posterior axis (head and pygidium are not considered segments)

annuli

external rings on body of worms

septa

internal wall that divides the segments on the body

parapodia

paired, unjointed lateral appendages that are used for locomotion (respiration only in polychaetes), have chatea

setae (chaetae)

hair-like, chitinous bristle found on parapodia

metameric body plan advantage

if you cut the new piece off, the rest survives, efficent body organization, and flexibility due to individual segment control

earthworms and environment

Stimulate microbial activity
Mix and aggregate soil: bring up phosphorus & potassium; add nitrogen in soil (from digestion)
Increase filtration
Improve water holding capacity
Provide channels for root growth
Bury and shred plant material

earthworm reproduction

hermaphrodites
the worms 69, touch back ends and mucus secreted by clitellum holds them in place
mutually exchange sperm
worm secretes cocoon around sex organs, the C. has eggs from oviducts, albumin from skin, and new sperm, fertilization.
Cocoon is released, and direct development (no metamorph)

earthworm eating habits

pull soil particles into their mouth using a muscular pharynx by suction, then the food travels through esophagus, crop, gizzard(ingested small stones that break down food), and intestine

Oligochaetes

usually terrestrial, hempahrodites
no special head, few chaetes

Polychaetes

only marine
special head
yes parapodia with many chaetes
dioecious

typhlosole

large internal fold in intestine to maximize nutrient absorption surface area

clitellum

ring of secretory cells in epidermis – always visible in earthworms, but only visible during reproductive season in leeches

how do earthworms move?

-setae are bristles that keep it down
-longitudinal muscles contract, shorten, and push forward
-circular contract, decrease diameter, squeezes and longer

polychaetes Reproduction

•No permanent sex organs
•Usually dioecious
•Organs= simple and gonads appear as temporary swellings of the peritoneum and shed gametes into the coelom
•Fertilization is external and development proceeds through a trochophore larval stage
•Several species show epitoky:
•live most of the year as a sexually immature atoke, but during breeding season a portion of the body becomes sexually mature, swollen with gametes, and breaks off as an epitoke

Feeding in errant polychaetes

perdators (bacteria, worms, small animals, cnidarians)
sit and wait for pray to catch with jaws

Sedentaria feeding (live in burrows)

indirect deposit feeder: “capture” food particles in suspension in water with their motile grooved-tentacles
Suspension feeeding: straining particles from the water above using mucus and tentacles
direct deposit feeding: swallow large amounts of sediment to obtain organic matter and microbe

terminal portion

pygidium with anus, youngest segments

Fluid filled coelom

(pair in each segment) serves as hydrostatic skeleton

prostomium

first segment, ‘lips’

polychate anatomy

1) well differentiated head
2) parapodia
3) many setae

Digestiv esystem

complete system, regional specialization

respiratory system

gas exchange occurs primarily across the body wall. parapodia and gills in polychaetes

reproduction system

varies by group
poly=dioecious, but no perma organs
oligo= monoecious, perma organ called clitellium

circulatory system

closed in most (some joins with coelom)
dorsal (replaces heart pumping) and ventral vessel

nervous syste,

Dorsal cerebral ganglia, circumpharyngeal connectives, ventral nerve cord, segmental ganglia

Excretory system

Metanephridia in most; protonephridia in some polychaetes

Hydrostatic skeleton:

fluid filled metamere/coelom
circular + longitudinal muscles alternate contraction
peristaltic (terrestrial), ondulatory (marine)