Phyla Cnidaria and Cnetophora Radiata Classification Cnidaria Five classes 1 Hydrozoa hydroids or hydrocorals fire coral have both polyp and medusa form mostly marine and colonial a Hydrocorals are not true coral they are huge number of nematocysts causing severe stinging pains chills and nausea they secrete a calcareous skeleton resembling rue corals b Siphonophores a colony of specialized cooperative and polymorphic polyps Ex Portuguese man of war colony 2 Scyphozoa Jellyfish conspicuous medusa alternates with inconspicuous polyps they are dioecious separate male female medusa 3 Staurozoa new class split off from scyphozoa solitary polyps top of polyp resemble a small medusa or ephyra it has 8 tentacles octomerous non swimming planula settles 4 Anthozoa sea anemones and corals both solitary and colonial marine species sea anemones are soft bodied the cylindrical body with tuft of tentacles in multiples of six or eight often have symbiotic photosynthetic algae called zooxanthellae exclusively polyp form NO MEDUSA STAGE colonial corals secrete hard calcareous skeletons that build up a coral reef both monoecious and dioecious species exist a Subclasses i hexacorallia sea anemones and hard corals and have hexamerous polymerous symmetry ii octocorallia soft corals sea fans sea pens sea pansies and have octomerous symmetry and secrete stiff but flexible gorgonin protein iii ceriantipatharia throny black corals tube anemones and have hexamerous or polymerous symmetry 5 Cubozoa box jellyfish medusa stage is prominent bell is squarish with tentacles off each corner potentially lethal stings for humans Body types polyps or medusa Polyps phase o Hydrozoa conspicuous colonial o Scyphozoa incospicious usually small o Staurozoa solitary o Anthozoa often large and conspicuous o Cuboza inconspicuous or unknown Medusa phase o Hydrozoa inconspicuous o Scyphozoa conspicuous often large o Staurozoa absent o Anthozoa absent o Cuboza predominant Phylum cnetophora comb jellies Many are bioluminescent marine about 150 species monoecious free swimming resemble a cone and use ctenes luminescent cilia for locomotion no nematocysts but have glue cells called colloblasts to capture prey Organization no organs organized at the tissue level cells work together Cnidaria diploblastic tissue layer with two germ layers Embryonic Development Cnidaria multicellular animals with true tissues derive their cells from cnidocyte cells Cnidocytes contain organelles called cnidae cnidum the most common are nematocysts Nematocysts a stinging cnidum ejects a harpoon like barbed and stinging toxin threads cellular organelle capped by an operculum within a cnidocyte cell a capsule with coiled inverted thread with spines and toxins tactile stimulations causes explosive thread eversion Functions of a cnidocytes capture prey defense adhesion movement and aggression Cnidae are grouped into three functional categories volvents whiplike and entangle prey glutinants sticky secretion that sticks to the prey penetrants nematocysts have barbs at their tips and penetrate the prey often injecting a toxin that causes paralysis The cnidocil is the hair trigger of the cnidocyte and is activated by physical contact causing the cell to burst open and extrude its contents The permeability of a cnidocyte can change with physical contact the water rushes in and pops operculum open and the inner coil thread is forced out If it is a nematocyst the barbed thread will burst out of the cell then the cnidocyte gets destroyed and replaced Symmetry radial symmetry Boral end with mouth Aboral end with anus opposite from mouth Skeleton Support Hydrostatic Skeleton it consists of a fluid filled gvc that works with an outer epitheliomuscular cell layer with longitudinal myofibrils and an inner gastrodemal nutritive muscular cell layer with circular lateral myofibrils The medusa stage swims by increasing and decreasing the diameter of the bbell through the contraction of myofibrils around the bell margin forcing water in and out of the subumbrellar surface No hard skeletal parts Cnidaria body walls consist of two tissue layers outer epidermis formed from the ectoderm and an inner gastroderm formed from the endoderm there is an acellular layer called mesoglea which separates both tissue layers the mesoglea is the jelly there is no mesoderm since it is diploblastic the body has an incomplete gastrovascular cavity gvc which communicates with the surrounding medium through a single opening which is the mouth the mouth anus is surrounded by tentacles that capture prey food Two body types polyps and medusa Polyps cylindrical attached to substrate sessile it can glide around the substrate with its pedal disc usually solitary or colonial the mouth is on top and it is surrounded by tentacles facing up it may secrete hard calcareous material Medusa umbrella shaped bell floats or swims by contraction tentacles surround the mouth that generally faces downward General cnidarian cell types Epitheliomuscular cells in epidermis with longitudinal myofibrils Nutritive muscular cells in gastrodermis with circular myofibrils Stem cell like interstitial cells give rise to sex cells cnidocytes sensory and nerve cells in both tissue layers Gland cells both tissue layers Movement Locomotion Cnidaria slow swimming or sessile attached to substrate Sensory Nervous Cnidaria primitive nerve net made up of cells from the gastrodermis and epidermis no organs or brain the nerve cells form synapses and interact with sensory nerves and muscles and cnidocytes the nerve net allows body movement locomotion in food capture Digestion Feeding Gastrovascular cavity GVC allows capture of larger prey tentacles are loaded with cnidocytes to capture prey and pass on to the opening of the GVC that is lined with cilated gastrodermal cells the digestive enzymes that are secreted into the GVC help break food into smaller particles which is extracellular digestion in GVC enables digestion of larger food then the food particles are absorbed and digested intracellularly by the gastrodermal cells that line the gut undigested food particles exit the 2 way GVC through the mouth anus mostly carnivorous Excretory Osmoregulation no specialized structures simple diffusion with the environment water Circulation Transport gastrovascular canals in scyphozoan medusae Respiration simple diffusion with the environment Reproduction both monoecious and dioecious species both sexual and asexual modes Polyps can reproduce
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