Anjali Chacko, Michelle Fernandez, Rose Zhang Cnidarians Phylum: Cnidaria Anjali Chacko, Michelle Fernandez, Rose Zhang

Cnidarians – Phylum Cnidaria Marine Specialized Cells Cnidocytes – stinging organelles Solitary or Colonial

Two Body Shapes of Cnidarians Polyp Dorsal mouth with tentacles Ex: Hydra Medusa Mouth on lower oral surface Ex: Jellyfish

Fig. 33-5 Figure 33.5 Polyp and medusa forms of cnidarians

3 Classes of Cnidarians: Hydrozoa EX: Hydras, Hydroids, Portuguese Man-of-War Polyp dominant/ alternation Some Colonies Scyphozoa EX: Jellyfish Medusa dominant Free Swimming Anthozoa EX: Sea Anemones, Corals No medusa Sessile

Examples:

Anatomy of Cnidarians Radial symmetry Hollow sac with mouth and surrounding tentacles at one end Mouth leads to gastrovascular cavity (digestive) Mouth – ingests food, expels waste

Anatomy of Cnidarians Continued… Epidermis Protective covering Gastrodermis Lines gut, digestive Mesoglea Gelatinous, acellular Separates epidermis + gastrodermis

Feeding in Cnidarians (hydra) Paralyze prey with Nematocysts Nematocysts Stinging cells In cnidocytes Stimulated – release coiled, hollow thread Sticky or long and coil around prey or barbs/spines Prey then pushed into mouth Lastly, gastrovascular cavity for digestion Body motion helps circulate contents

Gas exchange/Excretion Through diffusion No cell far from surface

Response in Cnidarians Nerve nets Nerve cells that connect sensory cells in body wall to contractile and gland cells Cells contacted and entire body responds by crunching in

Reproduction in Cnidarians Asexual Budding – good conditions Colony – buds remain on parent Sexual Fall or stagnant water Become males and females Female – ovary – single egg Male – testis - sperm Zygote – may become covered with shell for winter

Fig. 33-8-3 Figure 33.8 The life cycle of the hydrozoan Obelia