clearly most of the animals out there are invertebrates I say that approximately 1.3 million species of animals have been uh described uh clearly it's more than that uh but it's interesting to note that 95% of them are the invertebrates and I go on to say many yet to be described documented scientifically most of the animals are aquatic as obviously most of the planet happens to be water let's talk about the first group when we talked about these as as far as the parazoa that they are truly basal animals porifera you look at porifera literally meaning pore bearing and if you look at sponges they obviously are porous they have holes in them they're sessile sessile meaning attached and again with porous bodies and choanocytes we're going to take look at the collar cells of choanocytes that line the sponges and again they're an extremely interesting group uh unique development in simple anatomy if you ask the average person what is a sponge they probably would be perplexed and say oh that's something you buy at the store uh would they know it's an animal well they'd say that some of them were synthetic okay they might understand that some of them are are found in the ocean but beyond that if you press them if they were animals or what form they are I think most most people would be uh probably challenged by that unique development we're going to see that later on that they really have this bizarre larvae called it an amphiblastula and uh simple anatomy I think you'll agree there's not another animal that has the anatomical form quite like a sponge again you don't actually have to know numbers but I want to show this is is a fairly large group 5,500 species mostly marine uh there's probably at this point maybe 200 species or so fresh water I do want you to know uh the genus Spongilla which represents a freshwater genus of sponges we've said this many times lack true tissues and again contain only two layers of loosely uh uh two layers that are loosely associated with unspecialized cells um I will go back to this for a second but if we can take a look at this anatomy here you see the simplicity of the sponge uh and again some of the vocabulary the uh spongocoel the uh central cavity sometimes called the atrium the excurrent opening the osculum pores and then the cells these barrel shaped cells called porocytes with the the openings or pores epidermis which is these flattened layer of cells and you see the two layers of of uh cells we're talking about you've got your epidermis and then the inner layer referred to as the collar cells or choanocytes with an intervening layer that's gelatinous that we refer to as the mesohyl uh do not mistaken mesoderm and mesohyl remember these lack true tissues so ecto meso and endoderm don't fit into this okay uh and uh we're going to talk about spicules and amoebocytes in a minute but I I wanted to show you this very very simple anatomy for for now we will go back to this um as far as the size range is 1 centimeter you're going to look at a very tiny sponge in lab called Lucosolenia the genus is Lucosolenia that may very well be one of the tiniest sponges in the world 2 meters the giant barrel sponge of the Caribbean so you've got quite a diversity in sponges from fresh water to salt water and as far as sizes of sponges interesting to note that they are all suspension or filter feeders again taking water in and basically phagocytising particles which is their form of food we do believe that they perhaps evolve from uh organisms that we refer to as colonial choanoflagellates let me show you that association there and this is the interesting point we want to make if you look at the colonial choanoflagellates each one of these is an individual bound to a single stock they're all basically doing their own thing they are individuals that are doing their own thing now it's interesting to note when we look at the uh in the sponge called the choanocyte choanocyte sometimes called the collar cell it has got the exact anatomy as this colonial protist this microbial eukaryote exactly which got zoologists thinking that maybe over time it may have been a situation where perhaps perhaps these things grew together um maybe one grew together and then a couple of them grew together and then perhaps there was a membrane that evolved around them such that we wind up with what appears to be something that's like a sponge there may have been a great advantage if you could kind of coordinate your effort together and be protected with an so just a thought because you've got these cells that are almost point for point identical and it's strange that the sponges are lined with the identical cells that we find there so perhaps the choanoflagellates truly were uh ancestors of not just sponges but all of the animals just a hypothesis again we're going to go through more of the anatomy here as far as the collar cells or choanocytes that we were talking about uh basically water enters through the pore into the porocyte and then these flagellated cells begin to beat here's an individual uh collar cell or choanocyte and basically this collar right here covered with mucus particles go down and then when they reach the base they are phagocytised they're engulfed by this choanocyte uh a food vacuole forms around it and then these wandering cells that we find within the mesohyl called amoebocytes then can uh take up these uh particles either digest them right there with obviously lysosomes or they can move about the uh sponge distributing food particles slash energy where they may be needed notice we've got the word amoebocyte referring to the fact that they are wandering cells they've got uh pseudopods and what's interesting about the uh amoebocytes as you see here they do a number of different things they function in food uptake like we just talked about from the choanocytes we just showed you that just talked about the fact that they can be involved in food digestion talked about the fact that they are involved in nutrient distribution to other cells and the formation of skeletal fibers when we look at sponges they are characterized by having kind of these spikes that are associated with their structure we call them spicules spicules can be of two substances and we've used the the terminology the compounds before they spicules can be made out of CaCO3 uh which we call calcium carbonate or spicules may be made out of SiO2 silica or silicon dioxide right uh let me put the chemical formula down first SiO2 silica or as we've said before silicon dioxide which is glass okay uh so we can talk about some of the spicules being what calcareous and some of them are siliceous let me write up here the word calcareous okay um some sponges uh may be fibrous made out of collagen uh we look at um the uh commercial bath sponge you don't want to take a bath with something that's made out of glass spicules or calcium carbonate spicules commercial bath sponge contains fibers that are made out of spongin uh which is a proteinaceous like substance it's kind of like collagen okay uh and uh let's see if we can get some more anatomy down here and again I want to emphasize the the mesohyl this gelatinous material uh that's between the epidermis and the choanocytes as far as sponges are concerned most are hermaphrodites again we use the word monoecious mono meaning one ecious meaning house one house for both sex organs but they usually cross fertilize okay um as far as sponges are concerned and kind of represent this and uh you've got your porocytes you've got your uh eggs that are in the mesohyl and then in a in kind of a very crude way we'll show obviously sperm being carried up into the water column going through obviously uh the pore and then porocyte and then basically exchanging sperm uh fertilization takes place here embryos obviously wind up in the atrium or the spongocoel right and then ejected uh upon fertilization and then your zygote develops into a flagellated larvae okay and as we said uh escapes with the excurrent water through the osculum surviving larvae settle on the substrate and develop in most cases the larvae turns inside out during metamorphosis here is your amphiblastula your very very unusual embryology refer to as an amphiblastula so again we've got basically cross fertilizing hermaphrodites the formation of this amphiblastula and then basically ejected uh to the outside sponges do possess very extensive regenerative ability uh as a a form of asexual reproduction we can show their regenerative ability if we take a screen a very very fine mesh screen take that sponge and basically take the sponge and push it through the mesh every little piece that comes through that mesh and even finer than that right every little piece that comes through that mesh can undergo mytosis to be to produce an entire sponge so sexual reproduction yes asexual reproduction yes next group are the Cnidarians you know them better as corals and jellyfish and sea anemones let's erase some of this you've got the cnidocytes for which they're named these happen to be the stinging cells radial symmetry gastrovascular cavity and these cnidocytes the fact that they have a one opening serving as a mouth and anus they've got a very very interesting what we refer to as an incomplete digestive system incomplete digestive system which we'll talk about 10,000 species so this is a fairly large group most of which are marine watch your ecology uh if I say most or all or some okay uh and again hydras jellyfish sea anemone and obviously coral animals uh radial symmetry we say that they belong as we've talked about they belong to the Radiata they exhibit radial symmetry diploblastic two germ layers Ecto Endo no meso and a simple sack like body they are dimorphic not always but typically dimorphic meaning that they come in two forms and the two forms happen to be the polyp form and the medusa form here's the polyp form and again you see that uh single mouth anus opening so basically the prey items happen to be stung by the tentacles the tentacles force the prey item obviously into this this uh gastrovascular cavity where digestion takes place and then undigested material gets expelled out the same mouth anus opening if you look at the body plans basically if you were to take a polyp and turn it inside out you'd wind up with a medusa so it's kind of a variation on the same theme this is basically a polyp that has been turned inside out and again I called you to the fact that this is diploblastic that it's got two germ layers uh again do not confuse this gelatinous layer mesoglea with the term uh mesoderm polyp is one form uh asexual the medusa you know better as the jellyfish which is sexual and we go through an alternation of generations like we see in plants and then zoologists ask which is the dominant form which one does it spend most of its life as and if it's as we see in a minute quote the group we call the jellyfish this is the dominant form the medusa that it spends most of its life as so let's go back uh the largest of the Cnidarians is uh Cyanea capillata what we call Lion's mane jellyfish or Arctic jellyfish sometimes called sea blubber I've got it here as you know genus species subspecies sometimes it breaks it down into two separate species Cyanea arctica and Cyanea capillata I basically want you to know this part of it Cyanea capillata uh the Arctic jellyfish Lion's mane uh diameter can be 6 feet across and weigh several hundred pounds from the Arctic regions to basically uh Massachusetts Bay uh they're huge uh I'm not saying that they could kill you but the sting would be quite a horrible thing at that at that large an animal okay um let's take a look at some other points about them obviously they are carnivorous uh we talked about tentacles around the mouth uh capturing the prey and obviously forcing them into the gastrovascular cavity um the tentacles are armed with stinging cells we call cnidocytes uh hence the name Cnidaria and again uh when we look at the cnidocytes uh they've got uh these pneumatocysts which are stinging uh capsules associated with them and I would note here that the simplest forms of muscles uh simplest forms of muscles and nerves really occur in the Cnidarians uh notice I say simplest forms it's probably not until we get to the planarians that we see true muscles as far as their uh nerves are concerned they've got an interesting nervous system that we refer to as a nerve net right coordinates movement but it is interesting to note that there is no brain let me show you the uh nerve net associated with Cnidarians and you see here uh again in the case of a Hydra which can be thought of as semi sessile because they are not totally attached they can move but notice how uh found in the tentacles these uh nerve cells so in the periphery it may not be a central nervous system but it is highly efficient at obviously finding and responding to stimuli in the uh periphery uh of the animal and as far as um breaking down Cnidaria two major clades Medusozoa and Anthozoa I would note that highly uh those uh clades Cnidarians that have a Medusa have a jellyfish stage we refer to as the Medusozoa and that includes which will go over Hydrozoa Scyphozoa and the Cubozoa the Box jelly okay uh so let's go over that right now the Anthozoa when we're talking about things like sea anemones we'll talk about them so let's go over the the the big clade Medusozoa under the Medusozoa or the Hydrozoa again alternation of generations alternation between polyp and Medusa and again we saw this in plants with sporophytes and gametophytes now we're talking about uh sexual Medusa asexual polyp although the polyp is the dominant stage right you look at the word you've got Hydrozoa you've got the word hydroid or polypoid that means the Hydra happens to be the dominant stage some of them are colonial and we're going to take a look at the genus Obelia and again it's a genus because it's italicized the genus Physalia the Portuguese man o' war and others are solitary like Hydra okay so Hydra is an interesting one very very unique in that it only has the polyp stage there is no Medusa stage so three points about Hydra that I want you to know one fresh water remember a lot of these Cnarians are marine or salt water the second point about Hydra they're solitary they don't form colonies and the and the uh the third point uh concerning these uh this group uh polyp only no Medusa polyp only no Medusa stage and again we'll talk further about uh Hydra in a minute as far as Obelia this is interesting they show a nice alternation of generations and as we said before the dominant stage is the polyp or hydroid stage with a very very transient very very temporary Medusa stage male and female Medusa external fertilization so if you go to some of these area lakes and you see little jellyfish it happens to be a Medusa from this colonial hydrozoan and the genus is Obelia although Obelia can be marine as well as fresh water uh and again you see a very very simple alternation generation where you've got now these medusae uh butting off the reproductive polyp male and female external fertilization a zygote forms mitotic cleavage with a ciliated planula larvae settling to the bottom developing into a mature polyp and then again your uh colonial uh situation with the uh polyps let me just go back for a second to Hydra I was talking about Hydra I just want to go back for a second sexual reproduction yes you've got male and female Hydra what's interesting to note is they can also reproduce asexually by a phenomenon we call budding in which basically the parental polyp clones an uh a identical individual off its side like this a little bud a little mini me and then that detaches and voila we've got obviously uh a uh developed Hydra here and again when the conditions go unfavorable like the water's getting too hot or too cold uh they can shift from this to sexual reproduction produce as much uh genetic variation as possible they go on to say that a resistant zygote is formed and they can remain dormant if the environmental conditions are harsh uh and then when they improve then they can engage obviously in um in back to uh budding again let's go to the next group Scyphozoa these are the jellyfish and again the Medusa is clearly the uh prevalent form uh the word planktonic meaning drifting or floating so when you see the word planktonic means drifting floating not to be confused with neptonic which means swimming under your own power planktonic usually means drifting uh within the currents of the ocean neptonic means swimming typically swimming under your own power you have to know the reproductive cycle of the jellyfish in this case it happens to be the genus Aurelia which we refer to as the moon jelly fish and again I emphasize when you see a moon jellyfish if you go to the coast uh you are looking obviously at the uh at the Medusa stage coastal species usually pass through a small polyp stage uh and again Aurelia would be a coastal form open ocean open ocean species that we call pelagic that's a good word pelagic meaning open ocean have eliminated the polyp entirely let me show you the reproductive cycle of Aurelia which is a coastal species now you see this small polyp we call a scyphistoma in the case of pelagic forms if you're 20 or 30 miles off the coast of Florida the water is way too deep for this scyphistoma or polyp to attach so it's eliminated it totally out of its reproductive cycle so here we got a Medusa we're only showing one individual they want you to know obviously you would have you know clearly you would have two you'd have the female and you'd have obviously the male right sexual reproduction external fertilization with the formation of an embryo that embryo then uh develops into a ciliated larvae called the planula the planula settles to the bottom uh and becomes a polyp that we call a scyphistoma so if I ask you for the technical name as seen under a microscope if it's a lab practical if you're taking it in person uh the technical name for the polyp in this case is the scyphistoma then what happens is the process of transverse fision takes place transverse fission in which now the polyp elongates and now under and and divides this way transverse vision and you wind up with a strobila phase uh the untechnical name is the mature polyp the technical name is strobila transverse fission takes place and now the process of strobilation takes place strobilation after transverse fission then each one of these saucer like structures coming like an assembly line one after another now develops into what we call the ephyra stage uh this is the uh you might write down the untechnical term would be immature medusa technically called the ephyra stage and then the cycle starts again the next group Cubozoa we were talking about the Box jellies 20 species or so and again because of their square uh like appearance we call them the box jellies we have some that come up from the Caribbean that wash onto Florida beaches but they're not nearly as dangerous as the sea wasp of Australia the Great Barrier Reef and I do want you to know a Chironex fleckeri uh which may very well be one of the most dangerous invertebrates on the planet extremely deadly and again there's signs all over the Great Barrier Reef beaches and that sort of thing to watch out for them the next big grouping of Cnidarians we call the Anthozoans this contains sea anemone and coral most of you know the sea anemone the salient point here is they occur only as polyps there is no medusa stage and again basically what happens with corals which you know that they are marine they basically take in that polyp uh take they take in saltwater right seawater they extract calcium carbonate CaCO3 to build their exoskeleton and then what happens is this when the polyp dies what's left behind is this calcarius exoskeleton which is the coral rock the coral that we know okay uh as far as corals are concerned uh you've got things like hard corals you've got soft corals you've got sea fans there's actually quite a bit of diversity uh in corals the ones we're most familiar with are what we refer to as the hermatypic corals these are the reef building corals reef building corals that everybody uh knows many of these coral reefs are endangered uh as far as climate change and bleaching and that sort of thing many of you know this already um okay next group the Ctenophores Ctenophora right now uh do not confuse these with the Cnidarians this is a separate group all together although they're very Cnidarian like this is the other group of diploblastic animals remember two germ layers Ecto Endo no mesoderm the group is uh called the comb jellies or sometimes called the sea walnuts for their spherical shape either comb jellies or sea walnuts of a common name again big characteristic ciliary plates and instead of stinging they've got these adhesive cells that we call colloblasts which uh gather uh prey they're exclusively marine there are no freshwater ctenophores and again we talked about the fact that they do resemble the medusae of of Cnidarians but again they're not Cnidarian some of them can be elongate and ribbon like here's one form that is elongate and ribbon likee and I do want you to know the the genus Cestum and notice it's italicize the common name is Venus's Girdle this is kind of atypical uh very interesting very very neat looking thing the Venus's girdle I want you to know that one most of them are are like um the one here the comb jelly uh and again eight comb rows these are fused cilia that we call Comb rows which are few cilia that they use in locomotion or some times called ctenes Ctenophore meaning bearing ctenes or bearing comb rows and again you've got this pair of retractable tentacles retractable tentacles so basically they hang down these Colloblasts are adhesive the prey sticks to them and then they can withdraw these uh retractable tentacles up to the mouth what is interesting is they do have a complete digestive tract separate mouth and anal pore unlike Cnidarians that have got a gastrovascular cavity these guys have got a complete digestive tract