BIOL 2325 Chapter Notes - Chapter 12: Nematomorpha, Ventral Nerve Cord, Hydrostatic Skeleton
Document Summary
Protostomes- proceeds through blastula and gastrula stage. Cuticle-nonliving external layer secreted by the epidermis. 4 quadrants separated by 4 epidermal cords. Use hydrostatic skeleton and cuticle to perform antagonistic muscle function. Movement efficiency increased via increase in hydrostatic pressure. Gut: mouth, muscular pharynx, non-muscular intestine, short rectum, anus. Anterior pharynx muscles open mouth and suck food inside. Relaxation on pharynx pushes food through intestines. Ring of nerve tissue and ganglia around pharynx give rise to small nerves to anterior end and one dorsal and one ventral nerve cord. Males bear copulatory spicules to open vulva of females and iad in transmission of sperm. 4 juvenile stages marked by shedding of cuticle. Possess lorica which is like a protective armour. Forepart of body can be retracted into lorica. Head, neck, and trunk with 11 segments. Possesses scalids on head as in loricifera. Burrow in sand by extending head, anchoring scalids and moving body forward until head is retracted.
