Quick Refresher Anterior: head-end Posterior: tail-end Dorsal: top-side Ventral: bottom-side

Phylum Annelida many marine, freshwater, and terrestrial worms Ex) earthworms “segmented worms” Divided by rings or segments septa/septum (walls) separate segments setae: small, bristle-like appendages

Earthworm

Giant Gippsland Earthworm of Australia

External Anatomy

Mouth cavity brain pharynx Ventral nerve cord esophagus Seminal receptacle Lateral heart Ventral blood vessel Seminal vesicles nephridium crop Dorsal Blood vessel gizzard

Internal Anatomy

Musculature Cuticle- thin external layer Epidermis- outer cellular layer Circular muscle layer Longitudinal muscle layer

Obtain food by eating through and taking nutrients from soil Digestive System Obtain food by eating through and taking nutrients from soil

Digestive System Mouth- oral cavity (where soil enters) Pharynx- where food is swallowed Esophagus- Moves food down into the crop Crop: temporary food storage compartment  before moving to gizzard Gizzard:  food is ground using the rocks the earthworm also ingests Intestine: digestion and absorption (into surrounding blood vessels) Anus: Undigested material is removed from body

Respiratory System All annelids live in moist environments most are aquatic.  earthworms can survive only in damp soil.  Gas exchange occurs at body surface through diffusion NO LUNGS!

Circulatory System closed system 3 main vessels that supply the blood to organs within the earthworm → aortic arches, dorsal blood vessels, and ventral blood vessels five pairs of lateral hearts (aortic arches) surround esophagus and pump blood dorsal vessel- carry blood to front half Ventral vessel- carry blood to back half

Nervous System Cerebral ganglia acts as “brain” Prostomium: tongue-like lobe above mouth, allows earthworms to “feel” through soil

Reproductive System Earthworms are hermaphrodites male and female reproductive organs present in each individual Mates are introverted and attach with clitella to exchange sperm, then seperate sperm stored in two sperm receptacles cocoon forms (mucus from clitellum) -- earthworm will slide out of cocoon and the cocoon will pick up eggs and sperm from receptacles/pores embryos develop in cocoon

What happens when an earthworm is cut in half? Can it form two separate worms? most organs are in anterior can regenerate a new posterior posterior end cannot regenerate a new anterior so, no you don't get two new worms.