Chapter 37-2 Annelida

Phylum: Annelida Annelid: means “little rings” Can include 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 Have no parapodia 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