PoriferaCnidaria Ctenophora Phoronida Ectoprocta Brachiopoda Echinodermata Chordata Platyhelminthes Mollusca Annelida Arthropoda Rotifera Nemertea Nematoda “ Radiata ” Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate Phylum: Annelida

“segmented worms” bilateral symmetry, triploblasts, protostomes, coelomates main advance is segmentation (metamerism) body composed of series of fused rings segments (and coelom) separated by septa repeated structures and organs earthworms, bristle worms, leeches

Earthworm anatomy

Phylum: Annelida Class: Oligochaeta earthworms Named for relatively sparse “chaetae” (setae) or bristles found on eahc segment, made of chitin Includes earthworms and some aquatic species earthworms eat their way through the soil, extracting nutrients as soil passes through alimentary canal valuable to farmers till & aerate soil fecal castings improve soil texture

Phylum: Annelida earthworms, sandworms, leeches well-developed complete one-way (mouth to anus) digestive system, tube within a tube mouth- found on protostome (1st segment) pharynx- muscular, sucks in soil esophagus crop- stores food gizzard- muscular w/ small stones, grinds food intestine- chemical digestion, nutrient absorption anus

well-developed excretory system with repeated structures, two per segment metanephridia (primitive kidney) excretory tubule open at both ends network of small blood vessels closely associated nephrostome at one end of tubule ciliated funnel collects fluid from coelom excretory pore (nephridiopore) at other end of tubule dilute urine (urea) exits to outside body Phylum: Annelida Class: Oligochaeta earthworms

circulatory system closed with unidirectional flow of blood 5 aortic arches-muscular vessels that pump blood (“hearts”) dorsal blood vessel supplies blood to posterior ventral blood vessel returns blood to anterior hemoglobin dissolved in blood increases capacity to carry oxygen Phylum: Annelida Class: Oligochaeta earthworms

nervous system cerebral ganglia at anterior end comprise brain ventral nerve cord runs length of animal segmental ganglia originate from ventral nerve cord, 2 per segment Phylum: Annelida Class: Oligochaeta earthworms

Phylum: Annelida Class: Oligochaeta earthworms reproduction sexual most are hermaphrodites (monoecious) clitellum (thick band on epidermis) is site copulation sperm transferred from male pore on clitellum “cocoon” secreted by clitellum encases fertilized eggs that develop to juvenile worms one mating yields 2 pregnancies in hermaphrodites

locomotion circular and longitudinal muscles hydrostatic skeleton (fluid filled coelom, cuticle) setae on each segment chitinous bristles embedded in epidermis waves of muscular contractions shorten/lengthen animal secrete mucus to lubricate path Phylum: Annelida Class: Oligochaeta earthworms

Earthworm anatomy

Members of Phylum Annelida Class Oligochaeta means “few setae” (bristles) earthworms (Lumbricus terrestris) & relatives many terrestrial, some aquatic

Members of Phylum Annelida Class Polychaeta sandworms, bristle worms pair of parapodia w/ “many setae” (bristles) per segment parapodia are fleshy paddle-like extensions highly vascularized for gas exchange used as gills & for locomotion reproduction lack clitellum free-swimming trochophore larva mostly marine

Members of Phylum Annelida Class Hirudina leeches named for “hirudin”, the anti-coagulent secreted into host also secrete anesthetic that prevents host from feeling attachment feed on blood historical medical use in bloodletting not all bite, many feed on dead or dying tissues or animals, on open wounds terrestrial and aquatic species

Phylum Annelida: The Table- selected entries not covered elsewhere Cleavage/cells: radial and determinate; egg is small with little yolk Respiratory system: cutaneous breathing; skin must be kept moist for diffusion of oxygen; in Polychaeta parapodia act as external “gills” Relationship to other phyla: Mollusca- mesoderm origin, larval characteristics, cleavage pattern Arthropoda- segmentation, type of cuticle, nervous system Chordata- coelom segmentation