Phylum: Annelida - segmented worms Class: Oligochaeta Class: Polychaeta Class: Hirudinea
Oligochaeta
Class: Polychaeta Bristle worm is poisonous and attacks sea anemones
Class: Hirudinea
Christmas tree worm
Class: Polycheata
P O L Y C H A E T C L A S S
Yikes!!
Characteristics of Phylum :Annelida—Little rings True coelom Each compartment is surrounded by peritoneum which forms dorsal and ventral mesenteries that covers all the organs Hydrostatic skeleton Closed circulatory system
True coelom
*Centralized Nervous System* Brain Double ventral nerve cord Pair of ganglia in each segment Lateral nerves
*Centralized Nervous System*
Sensory organs Taste buds Statocysts - balance sensory receptor Photoreceptor eyes with lenses in some
Circulatory System Blood flows entirely in closed vessels Some spp. have hearts Blood contains hemoglobin, which increases oxygen carrying ability Phylum Annelida
Excretory system Pair of nephridia in each segment
Respiration By gas exchange through Skin Gills Parapodia - fleshy paired appendages
Body plan Bilateral Metameric-repeating segments (metamerism allows for budding) Setae-small hairs or sometimes parapodia, i.e. small appendages
Body plan Setae (“bristles”) of chitin “anchors” for earthworm “paddles” for polychaete Enlarged as jaws in leeches, some polychaetes
Reproduction Sexes are usually separate with gonads occurring in each segment Some species have gonad specific segments Breeding is usually seasonal (spring or fall) As gametes mature they fill the coelom and are released by the nephridia Fertilization can be internal or external Trochophore larvae develop, which are remarkably similar to the Molluscs
Skin Contains glands to secrete mucous and setae
Nutrition Eat any dead organic material Consume up to one half their body weight every day
Nutrition Annelids range from carnivores, herbivores, scavengers, deposit feeders, and filter feeders With very few defenses, many remain in a burrow or secreted tube Carnivores can capture prey with strong jaws and quickly drag it back to its burrow Can use a muscular pharynx = eversible proboscis
Digestion mouth esophagus crop intestines gizzard Mechanical –grinding in the gizzard Chemical in the intestines Extracellular and intracellular digestion
Environmental role Can be found in fresh water, salt water, soil Helps aerate/renutrify gardens Medicinal purposes
Classes How do we classify these segmented worms into different classes?
Class: Polychaeta (many setae or hairs) 20+ setae per segment Well differentiated head Specialized sense organs Parapodia No clitellum Mostly marine predators, e.g. “Barry” the seaworm
Class: Polychaeta (many setae or hairs)
Class: Oligochaeta (Few long hairs) Clitellum Few long, short or straight setae; 2-4 clusters per segment Land or marine, some parasites
Class: Oligochaeta (Few long hairs)
Class: Hirudinea Flattened dorsalventrally Mostly freshwater, some marine Fluid feeder (blood) Clitellum Setae have developed suckers Specialized proboscis
Class: Hirudinea Class Hirudinea pair of bladelike “jaws” posterior “suction cup” Predators External parasites, “bloodsuckers” Secrete anticoagulants Medicinal use
Blood Sucker The salivary glands excrete hirudin which prevents the blood from coagulating May also secrete an anaesthetic and substance to dilate small blood vessels Blood is broken down by symbiotic bacteria that is then used by the leeches Leeches were commonly used in the 19th century for bloodletting Recent medical uses are to relieve pressure after vascular tissue is damaged Snake bites or the reattachment of a finger or ear Phylum Annelida