Annelida

Annelida General Info  Segmented worms  Contains 3 classes –Polychaeta –Oligochaeta –Hirudinea  Triploblastic protostomes with a coelom, closed circulatory system, and true segmentation

Class Polychaeta  Called: lugworms, clam worms, bristleworms, fire worms, palolo worms, sea mice, featherduster worms  They look the most diverse of the classes of Annelids  Some have fine, barbed hairs that will embed in skin if you touch them  Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin.

Class Oligochaeta  Earthworms  Eats its weight in soil each day –Suck in organic and other material by expanding pharynx, grinding up soil in the gizzard  Hermaphroditic-they use copulation  No eyes because they live underground igochaeta.jpg

Class Hirudinea  Leeches  Inhabit fresh water for the most part, some tropical  Flattened dorsoventrally (like a flatworm)  The coelom is not divided, unlike Oligochaeta and Polychaeta.  All have evolved suckers on one or both ends, some have evolved the ability to suck blood –Parasitic This is the picture from the Bio Book

Body Plan  3 body regions-prosomium, trunk, pygidium; head, thin body, small tail  Average length 1.36  Bilateral  Metameric (segmented)  Cylindrical body  Have a coelom

Feeding  Wide range  Detritus and algae; eat decomposing organic material, small organisms, and soil particles  Ingest soil-increases rate of the nutrient cycle  Castings-pass out what they don’t need (earthworms)  Filter feeders, scavengers  Complete digestion, extracellular, have a mouth and anus

Respiration  Not true respiratory organs  Diffusion, respiration can occur directly through body walls  Cutaneous (occurs due to rich vascularity under epidermis) or branchial  Gills if aquatic  vascular

Circulation  True closed circulatory system-blood circulates with in blood vessels and through heart  May have several hearts  First to have closed system, makes pumping more efficient  Blood usually contains hemoglobin

Excretion  Use nephridia: coiled tubules with an expanded funnel- shaped nephrostome for excretion  The nephrostome is attached to the septum dividing two segments and opens into the anterior segment. The tubule opens to the outside.  Filtration of the blood across the tubule wall occur through diffusion  Most annelids have metanephridia which depend on filter cells to filter blood twice  Primitive annelids have protonephridia which perform two filtrations  Aquatic annelids excrete ammonia  terrestrial annelids excrete urea

Response  Simple brain located in the anterior end  Ganglia: nerve cell bodies, located in every segment  One ventral nerve cord runs the length of the body connecting to the brain and paired ganglia of each segment  Sense light, moisture, chemicals, and physical stimulation  Some have eyes (polychaeta)

Movement  Hydrostatic skeleton-flexibility  Annelids contract various muscle groups around the segment that elongate one segment at a time. Then they contract muscles along the length to move forward  Terrestrial annelids have setae: chitin that help anchor them to the ground  Movement: –crawl using parapodia- outgrowths that look like bristles (lugworms) –Swim (leeches) –Crawl by folding segments (like earthworms)

Reproduction  Asexual Reproduction: –Budding: an outgrowth of the parent separates to form a new individual (not similar size) –Fission: parent separates into two or more individuals of equal size  Sexual Reproduction (following slides)

Polychaeta Sexual Reproduction  External fertilization in water  Lack gonads  Result in ciliated trochophore larvae  Swarming occurs in some species- individuals join together to release sperm and/or eggs

Oligochaeta Sexual Reproduction  Hermaphroditic  reproduce sexually by reciprocal fertilization where partners exchange sperm by joining their anterior ends during mating  After mating, the oligochaeta produces cocoons that take up eggs which are then fertilized by the sperm  Young worms hatch from cocoon (no larvae)

Works Cited  "All Tropical Fish - Bristleworms Class: Polychaeta." All Tropical Fish - Marine Fish, Corals, Invertebrates and Freshwater Fish. Web. 20 Apr  "The Annelids (Phylum Annelida)." The Earth Life Web. Web. 20 Apr  “Annelids-Easy Review.” Biology Questions. Web. 19 Apr  “Annelida-Worms and Leeches.” CSIRO Entomology Home. Web. 19 Apr  "Introduction to the Polychaeta." UCMP - University of California Museum of Paleontology. Web. 20 Apr  Ramel, Gordon. “The Annelids (Phylum Annelida).” The Earth Life Web. Web. 19 Apr  Raven, Peter, and George Johnson. Biology. 6. New York, New York: McGraw-Hill, Print.  Rouse, Greg W., Fredrik Leijel, and Damhnait McHugh Annelida..