BIO2231 Lecture Notes - Lecture 3: Ctenophora, Scyphozoa, Bilateria
30 May 2018
School
Department
Course
Professor
Phylum Cnidaria: Jellyfishes, anemones, corals
• Radial symmetry, body plan= saclike, diploblastic (epidermis from ectoderm and gastrodermis
from endoderm, separated by mesoglea), single opening serving as both mouth and anus (have
digestive cavity)
• Nervous system in for of a nerve net
• Hydrostatic skeleton
• Characteristic= Cnidocytes; contain stinging organelles called nematocysts
• Nematocysts occur in all cnidarian groups. The nematocyst is one of three types of nidae. There
are at least 30 different types of nematocyst. They often bear spines or barbs, may inject toxins
into prey and have thick walls. All toxic nidae are nematocysts, but not all nematocysts are
venomous
• Mostly marine, few freshwater (shallow areas, warm tropical regions)
• Mostly sessile, some free swimming
• Polymorphic; polyp/hydroid- adapted to sedentary or sessile form
- tubular bodies, mouth surrounded by tentacles (oral end), aboral
end is usually attached to substratum by a pedal disc
- can reproduce asexually by budding, fission, pedal laceration
- if bud detaches= polyp, if attached= colony
- polymorphism; hydranths=feeding, gonangia= reproductive
-medusa/jellyfish form- adapted for floating/free swimming, bell/umbrella shaped
- statocysts (sensory structure)
- dioecious, reproduce sexually
• Reefs are found only in clear, shallow water because reef corals contain symbiotic zooxanthellae
that require light
• Extracellular and intracellular digestion
• General life cycle; zygote -> motile planula larva -> settles onto hard surface -> metamorphoses
into a polyp (can make other polyps asexually) -> medusae by budding or strobilation
• Myofibril- equivalent to longitudinal muscles
• Usually have external fertilization
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The nematocyst is one of three types of nidae. There are at least 30 different types of nematocyst. They often bear spines or barbs, may inject toxins into prey and have thick walls. All toxic nidae are nematocysts, but not all nematocysts are venomous: mostly marine, few freshwater (shallow areas, warm tropical regions, mostly sessile, some free swimming, polymorphic; polyp/hydroid- adapted to sedentary or sessile form. Tubular bodies, mouth surrounded by tentacles (oral end), aboral end is usually attached to substratum by a pedal disc. Can reproduce asexually by budding, fission, pedal laceration. If bud detaches= polyp, if attached= colony. Medusa/jellyfish form- adapted for floating/free swimming, bell/umbrella shaped. The mouth is usually centred on the concave side of the umbrella. and is located at the end of the tube-like manubruim. Sea anemones move food into the gastrovascular cavity by ciliary action in the siphonoglyph.
