3 Worm Phyla (long, thin bodied animals) All eumatazoans (have true tissues) All have bilateral symmetry Develop a coelom → body cavity 1. Phylum Platyhelminthes (flatworms) 2. Phylum Nematoda (roundworms) 3. Phylum Annelida (segmented worms)

Phylum Annelida Annelida The segmented worms

Annelida (segmented worms) 16,500 species Name means “little rings” Most advanced of the worm groups Aquatic and terrestrial Size less than 1 mm up to 3 meters Bilateral symmetry Triploblasts Coelomates – tube within a tube body plan (mouth and anus) Segments Closed circulatory system

Classes 1. Oligochaeta (earthworms) 2. Polychaeta (diverse, tubeworms & sandworms) 3. Hirudinea (leeches)

Structures and functions Segments – chambers along the entire length of body Septa – divide the segments (connective tissue) Epidermis covered in chaetae Chaetae – bristles that cover the body Used in burrowing and movement (grip) Muscles – longitudinal and circular, used for movement Longitudinal muscle is outside, just under the epidermis Circular muscle is inside, just under the longitudinal muscle

Circulation and Respiration and Nervous systems Annelids have a closed circulatory system – blood travels in well developed vessels throughout the body Blood vessels (dorsal and ventral) Aortic arches (lateral vessels) – “heart” Made up of contracting vessels Marine worms and leeches have partially open circulatory systems Breathe through skin Cerebral ganglia – brain – located in head region Nerve cords carry messages (dorsal and ventral)

Oligochaeta (earthworms) Freshwater and terrestrial (burrowers) Reduced head Feed on dirt and soil Small, sparse chaetae Closed circulatory system

Digestive tract (complete gut) Mouth – takes in food Pharynx – forces food into esophagus Esophagus – removes calcium Crop – stores food Gizzard – contains small stones and pebbles to grind food Intestine – “digests” food with enzymes Nutrients diffuse into blood vessels Repeats in every segment Nephridium – excretory gland “kidney-like” Repeats in every segment Anus – passes undigested food out of the body

Reproduction Hermaphroditic – contain both male and female reproductive organs Testes and ovaries located between head and clitellum Clitellum – swelling along the body which makes the cocoon (egg capsule) cocoon Baby worms look like miniature adults

Interesting Facts One of the largest earthworms is the Giant Gippsland Earthworm found in Australia. It can reach lengths of 4 meters. If a worm’s skin dries out, it will die. Worms can eat their weight each day. Even though worms don’t have eyes, they can sense light, especially at their anterior (front end). They move away from light and will become paralyzed if exposed to light for too long (approximately one hour). In one acre of land, there can be more than a million earthworms.

Polychaeta (tubeworms/sandworms) Mostly marine Drift freely, burrow in sea floor, or build tubes from secretions (mucus) and/or bits of dirt and shells Have parapodia (“almost feet”) paddle like structures on each segment used for locomotion covered in chaetae In many species, parapodia are richly supplied with blood vessels (function as gills)

Hirudinea (leeches) Freshwater 1-30 cm Lack setae Reduced coelom and segmentation No septa Anterior and posterior suckers Some parasites (blood suckers), predators, and scavengerspredators

Blood suckers (leeches) Parasitic blood suckers Can consume up to 10 times own body weight in blood After gorging, leeches can go for months without feeding Specialized crop (for storing blood) No gizzard Methods of feeding: Secrete hirudin – chemical that keeps blood from coagulating So that blood can continue to flow throughout feeding Jaws (teeth) – to slit holes in the skin of host Enzymes – digest a hole in skin of host Ex. Tiger leechTiger leech

Leech anatomy

Leech reproduction Similar to earthworm reproduction Some leeches carry cocoons on their ventral side until the eggs hatch