chapter 37-2 annelida. phylum: annelida annelid: means “little rings” many body segments can...

CHAPTER 37-2

Annelida

Phylum: Annelida

Annelid: means “little rings” Many body segments

Can include marine species Earthworms Leeches

Characteristics and Classification

Bilateral Symmetry Coelomates Segmented (important evolution) Developed organ systems External Bristles and Fleshy Protrusions

Setae #

Parapodia Presence or absence

Determine which class division Oligochaeta, Polychaeta, Hirudinea

Oligochaeta

Live in soil or fresh water Look for adaptations

for burrowing Have no parapodia Name means “few

bristles” Have few Setae

Most familiar member is the Earthworm

Oligochaeta – Structure and Movement

Earthworm body divided in more than 100 virtually identical segments

Locomotion method Worm anchors some middle segments by

setae Contracts muscles in front of those segments

This increases pressure on coelomic fluid Elongates the animal and pushes anterior end

forward Anterior setae then grip ground, pulling the

posterior segments forward

Oligochaeta – Feeding and Digestion

Ingest soil as they burrow through Sucked into mouth by the pharynx Esophagus – crop – gizzard – intestine - anus

Play an important role to maintain soil fertility Decomposition Release nutrients Oxygen penetration Loosen soil

Oligochaeta – Circulation

Closed circulatory system Blood travels to posterior end through

ventral blood vessel Blood returns to anterior end through

dorsal vessel Aortic arches link the two blood vessels at

the anterior end

Oligochaeta – Respiration and Excretion

No specialized respiratory organs Oxygen and CO2 diffuse

directly through skin Gas exchange only happens if

skin is moist Secrete mucus and have a thin

cuticle Eliminate cellular waste and

excess water Excretory tubules called

nephridia Each segment (except first 3

and last 1) contain a pair

Nephridia

Oligochaeta – Neural Control

Nervous system Chain of ganglia connected by a ventral nerve

cord Most segments contain a single ganglion

Nerves branch from each ganglion Several ganglia fused to form “brain” (cerebral

ganglia) Main function is to process simple info from sensory

structures Present in all segments, but concentrated at

anterior

Oligochaeta – Reproduction

Hermaphrodites (Cannot self fertilize) Mating: 2 worms press ventral surface

together, anterior pointing in opposite directions Held together by:

Setae & Mucus Secreted by clitellum (thickened section)

Sperm moves through mucus to seminal receptacle

Oligochaeta – Reproduction Cont’d

The worms separate After several weeks the clitellum secretes a

tube Made of mucus and chitin Tube slide forward and picks up eggs and sperm

Fertilization occurs within tube Young worm develops inside for 2-3 weeks

before hatching

Polychaeta

2/3 of all annelids “many bristles” Mostly marine Have antennae and specialized

mouthparts

Hirudinea

Smallest class, about 300 species

Leeches Mostly freshwater No setae or parapodia Sucker at each end of body Some are carnivores, but

many are parasitic Suck blood from host Secrete anesthetic and anti-

clotting substance