Phylum Annelida Annelus = “ Little Ring” The Segmented Worms www.onacd.ca

Review Discuss 3 things you learned about unsegmented worms (Recall unsegmented worms are: Phylum Platyhelminthes (flatworms) Phylum Nematoda (roundworms)

Shape of Life Video: Annelids https://www.youtube.com/watch?v=9Q9gh1k99rY

3 Major Classes in Phylum Annelida Class Oligochaeta: the earthworms Class Hirudinea : The leeches Class Polycheata: The marine worms

Identifying Characteristics of the Annelids Group of soft-bodied animals commonly known as segmented worms Segments are separated internally into compartments by septa Segments are marked by little rings called annuli (annulus = little ring)

Identifying Characteristics of the Annelids Bilateral symmetry Triploblastic (three tissue layers) TRUE COELOM (body cavity which allows them to have true organ systems and muscular layers) Possess complex digestive & circulatory systems Nervous and excretory systems No developed respiratory system as they exchange O2 and CO2 via moist epidermis. Aquatic worms may exchange gases through gills.

Identifying Characteristics of the Annelids Mostly free-living heterotrophs Terrestrial, freshwater and marine environments Mostly aquatic or damp environments Many annelids are nocturnal Can range in size from less than 1 mm to over 3 meters (the seep tube worm)

Identifying Characteristics of the Annelids Reproduce sexually and some asexually by regeneration and fission Are hermaphroditic with cross fertilization

Example: The Earthworm https://www.youtube.com/watch?v=LhfcS7pbkKg Digestive system: one way tube including: mouth/pharynx, anus and specialization of digestive organs (esophagus, crop, gizzard, and intestines) Earthworm feces (castings) act as fertilizer

Typhlosole increases surface area for digestion Food moves through digestive tract from mouth to anus due to peristalsis (rhythmic muscular contractions)

Circulatory system Closed system (blood contained in vessels) Dorsal vessel, ventral vessel, ring vessels connect segments. Valves prevent backflow. Presence of a primitive heart (actually 5 aortic arches) to pump blood

Nervous system cephalization and primitive brain ventral nerve cord no defined sensory organs

Excretory system nephridia (primitive kidneys) which eliminate waste from blood and expel it from body (via nephridiopore). One pair of nephridia per segment.

Movement Hydrostatic skeleton Circular and longitudinal muscles Setae anchor the earthworm during movement

Response Most annelids are active animals with well developed nervous systems Brain sits on top of the gut at the anterior end Ventral nerve cord Earthworms have no defined sensory organs Light sensitive skin

Reproduction As always, variety seen within a large group of organisms! Most annelids reproduce sexual Some can reproduce asexually by budding or regeneration Most annelids are hermaphroditic Some species have separate sexes and external fertilization

Earthworm Reproduction http://www.youtube.com/watch?v=2fG-KkR3FZ8 Hermaphroditic: (produce both eggs and sperm) must still copulate in order to mix their gametes (cross-fertilization) Regeneration: capable of re-growing amputated segments of their bodies Mating Earthworms

Earthworm Reproduction When two earthworms do mate they release sperm to one another. Each earthworm’s seminal receptacle receives sperm from its mate’s seminal vesicles. Sperm and eggs are released into the cocoon secreted by the clitellum Fertilization is external

Worm Clitellum

Organization 3 Classes Class Polychaeta Class Hirudinea Marine worms Parapodia Paired appendages on each segment Trochophore larvae Class Hirudinea Leeches Mostly freshwater Free-living or ectoparasites

Organization Class Oligochaeta Ex. earthworms, etc. Freshwater or terrestrial Each segment contains 4 sets of bristles called setae Light sensitive epidermis Body adapted for burrowing Reduced head Streamlined body

Other Annelids: Class Polychaetes Marine worms Parapodia (pad-like appendages with bristles) Live in coral reefs, sand, mud, crevaces

Nervous systems in Marine species Sensory tentacles Chemical receptors Two or more pairs of eyes

Class Hirundinea: Leeches Mostly ectoparasites (external parasites) Drink blood and body fluids of host About 25% of leeches are free-living carnivores Eat snails, worms, insect larva

Take Two Leeches and Call Me in the Morning https://www.youtube.com/watch?v=O-0SFWPLaII

Kingdom of the Leeches https://www.youtube.com/watch?v=cKUAroimQrk

Ecological Importance of Annelids Form the base of many food chains House (carry) parasites such as Protozoa, Platyhelminthes and Nematodes Aerate & mix the soil and are constructive to mineralization and nutrient uptake by vegetation Certain species mix the nutrient-rich surface and mineral soil by traveling between the two Oligochaete Worm

Chemical Roles include: Biological Roles: composters help integrate dead organic matter to make fertile soil Chemical Roles include: help cycle nutrients and minerals through the soil through their casts (worm poop!) Increase the levels of nitrogen, phosphates and potash

Physical Roles include: burrowing and keeping the soil structure open (aerating the soil and providing a path for drainage)

Random Annelid Facts In the New Zealand Maori culture NOKE is an earthworm dish sold as a delicacy Lumbriculus and Aulophorus (species of annelids) are known to reproduce by the penis breaking into fragments and then forming whole new worms!

Australian giant earthworm

Annelids http://www.youtube.com/watch?v=NxeT_GDKv9g http://www.scivee.tv/node/2751 http://dsc.discovery.com/tv-shows/dirty-jobs/videos/worm-grunting.htm