Phylum Rotifera > 1,800 described species < 1 mm Complex, variety of body forms Solitary Pseudocoelomate Generally freshwater

Rotifer body Head, trunk, foot Ciliary organ on anterior end = corona Complete gut Protonephridia Tendency to constant cell number Pharynx modified with internal jaws

Posterior Elongate foot Cuticular annuli with telescoping action “toes” for attachment

Locomotion Some can change shape by “telescoping” action Some sessile as adults Hydrostatic skeleton Most rotifers swim and crawl Cilia

Digestion Complete digestive tract Mouth --> buccal tube -->Pharynx (mastax) -->Salivary gland -->Gastric gland -->Stomach -->Intestine -->Nephridioduct -->Cloaca -->Anus

Circulation, Gas Exchange No special organs for internal transport or gas exchange Coelomic fluid aided by muscles small size reduces diffusion and transport tissues

Osmoregulation one pair of flame bulbs protonephridia empties into cloaca

Nervous System and Sense Organs Bilobed mass of gangli Nerves connect to body Chemoreceptors, mechanoreceptors

Reproduction Parthenogenesis Development from egg w/o fertilization = most rotifers female Adaptation for freshwater habitats with severe disturbance If males exist -- copulation or hypodermic impregnation

Phylum Acanthocephala Spiny – head worms 1200 species All gut parasites of vertebrates

Phylum Acanthocephala Life cycle requires intermediate host – usually arthropod Fig Pechenik

Cyst eaten by ostracod Adult worm in turtle intestine Cyst out w/feces Ostracod eaten by snail Snail eaten by turtle

Phylum Acanthocephala Constant number of cells No respiration organs No digestive organs Pseudocoelom

Phylum Acanthocephala Proboscis for attachment to intestinal wall Dioecious Fertilized eggs develop in pseudocoelom of female To acanthor stage