BIOL 204L Study Guide - Midterm Guide: Pedicellaria, Hemichordate, Chelicerae
Document Summary
Protein-based outer body covering (cuticle) that is periodically molted for growth (= ecdysis) Cuticular integument not acting as external skeleton (hydroskeleton) Caterpiller-like body, has changed little in 500 million year history. Single dorsal heart circulates fluids around internal organs. Metabolic activity is shut off, allowing them to live in extreme environmental conditions. 3 segmented thorax with 3 pairs of legs. Fusion of 2 segments 1 segment (millipedes) Each has 2 pairs of organs and legs. *remaining groups united by two apomorphies besides crinoidea: oral surface faces down, tube feet evolved suckers. Madreporite-skeletal plate that allows seawater to enter the system. Arms with ciliated grooves used for suspension and feeding. *ambulacral grooves runs from oral to the aboral poles. Around the mouth, tube feet modified into retractable oral tentacles. An excretory organ used for removing metabolic waste. Pharynx: part of the digestive tract between the mouth cavity and esophagus. Provides an axis for muscle attachment, can bend without shortening.
