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Lecture 11

Lecture 11 - Cnidarians.docx

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Biology (Sci)
BIOL 111
Suzanne Gray

October 11 , 2011 CNIDARIANS & PLATYHELMINTHES Embryonic development: Zygote is a multicellular organism (2n); diploid cell resulting from union of two haploid gametes; 1 cell of 2 generation Embryo is a young animal or plant while it is still contained within a protective structure (i.e. seed coat, egg sell or uterus) Two major processes occur during embryonic development: 1. Cleavage: cell division (process forming many cells from one cell) 2. Gastrulation: in-folding (process forming embryonic tissue layers ~2 to 3, from one layer of cells) cleavage zygote 2-cell stage 8-cell stage gastrulation morula (solid ball) (hollow ball) early gastrula late gastrula Germ Layers: Gastrula: layers of embryonic cells (include ectoderm, endoderm, mesoderm) Ectoderm: epidermis, nervous system (outer) Endoderm: lining digestive and respiratory system (inner)  Organisms with 2 germ layers are diploblastic Mesoderm: most internal organs; muscles; skeletal system, heart and stomach  Organisms with 3 germ layers are triploblastic Archenteron: digestive space (gut cavity)  Contains blastopore; mouth or anus Tissues are important because they enable body organization, while the gut enables extracellular digestion. Body from symmetry: 1. Asymmetrical: no axis divides body into equal halves (ex. Sponges) 2. Radial Symmetry: along one axis, as long as one cuts through center, body can be divided into equal or symmetrical halves from many angles (ex. Cnidarians) NOTE: have to be looking down and going through the center of the body 3. Bilateral Symmetry: single axis divides body into equal halves, midsagittal plane; between eyes (ex. Platyhelminthes) 4 • ~11,000 species – mostly marine – microscopic to many metres – carnivorous a. Based on internal systems, a human is not bilateral (heart on the left) • nervous and muscular tissue Cnidarians:  Jellyfish, sea anemones, corals, hydrozoans  ~11,000 species; mostly marine, microscopic to many meters, carnivorous  Diploblastic  Nervous and muscular tissue Generalized mouth (from blastopore) Body Plan Mouth also functions as the DIPLOBLASTIC anus. gastrovascular cavity(“blind gut”) mesoglea (from archenteron) Cnidarian Body Forms gastrodermis 1. pplypermis (from ectoderm) (from endoderm) Body Forms: sessile Cnidarian 1. Polyp (ex. Sea anemone) Forms sea anemone 10 1. pplypely sessile Most life cycles include both body plans sessile Body Forms sea anemone 2. Medusa (ex. Jellyfish)a Body Forms motile How do jellyfish Cnidarians obtain energy?edusa  Carnivorous, using cnidocysts to capture prey, inject prey with venom and stick to prey How do Cnidarians obtaining  Extracellular digestion in gastrovascular cavity 11  Corals can obtain a large proportion of their energy from symbiotic algae motile  Cnido=nettles jellyfish • arnivorous, using cndocystts tto captture prey, inject prey with venom & stick to prey 11 • xtracellular digestion in gastrovascular • Little to no integration or processing of signals • Provide direct lines of commuuniaton between th sensors and effectors October 11 , 2011 (muscles)IANS & PLATYHELMINTHES Cnidarians have simple nervous system:  Little to no integration or processing of signals  Provide direct lines of communication between sensors and effectors (muscles) Sexual Reproduction cleavage & gastrulation Asexual reproduction • budding Obelia (a marine hydrozoan) See fig. 31.19 for another example Cnidarian Diversity:  Class Hydrozoa (i.e. hydra): polyp dominant phase, most species alternate between two body shapes
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