Ch. 26.3

Phylum CNIDARIA hydras, jellyfish, sea anemones, and coral Found all over the world Can live individually or in colonies

Soft bodies, carnivorous, stinging tentacles Simplest animals to have body symmetry Name comes from STINGING CELLS (cnidocytes) used for defense and capturing prey contain NEMATOCYST  poison-filled stinging structure that contains a coiled dart What is a Cnidarian

Only a few cells thick Tissues function for feeding and movement RADIAL symmetry Form and Function

Life cycle has 2 parts: POLYP – cylindrical body with armlike tentacles; mouth points upwards MEDUSA – motile, bellshaped body; mouth on the bottom Both have a body wall that surrounds the GASTROVASCULAR CAVITY Digestion takes place in the GASTRODERM

Pulls prey into its mouth after stinging them Food enters and wastes leave the body via the gastrovascular cavity Digestion is EXTRACELLULAR (outside of the cells) food can be absorbed in the GASTRODERM Feeding

Nutrients are transported via diffusion Respiration, Circulation, and Excretion

Specialized sensory cells (NERVE NET) Found throughout the body OCELLI – eyespots that detect light Response

HYDROSTATIC SKELETON – circular muscles and longitudinal muscles that enable movement via contraction and water pressure Medusas move by jet propulsion (from muscle contractions) Movement

Reproduce both sexually and asexually asexually by BUDDING (identical offspring) EXTERNAL FERTILIZATION in water Female releases eggs into the water; male releases sperm Zygote forms a free swimming larva and then develops into a polyp Reproduction

JELLYFISH – Class Scyyphozoa (cup animals) live as medusas HYDRAS – Class Hydrozoa. Use nematocysts to sting prey lack a medusa stage SEA ANEMONES and CORALS – Class Anthozoa (flower animal). Only have polyp stage Groups of Cnidarians

Coral live in areas based on temperature, water depth, and light intensity Corals in reefs need lots of light Rely on algae for survival (symbiosis) Coral reefs are being damaged from logging, farming, mining, water pollution, overfishing changes ecological balance Rising temperatures and global warming causes coral bleaching Ecology of Corals