15/1/14 Early metazoans: Porifera & Placozoa Parazoa: Characterized ...
15/1/14 Early metazoans: Porifera & Placozoa Parazoa: Characterized by lack of true tissue = Porifera/placozoa Eumetazoa: everything else on the tree this division is more fluid now. Sponges may in fact have true tissue General characteristics of porifera Porebearing w/ simple morphology o Water goes into small pores (ostium) and out of the larger holes (osculum) o Sponges are basically water processing machine and haven’t really changed for millions of years o Some have a chimney structure for more efficient water exit “Super osculum” for hydrodynamic efficiency Skeleton: o Hard skeleton have spicules: stick together w/ collagen (arrangement dictates the shape/identity of the sponge) Class Hexactinelid: siliceous spicules eg. Euplectella ie. Venus’ flower basket has spicules w/ fiber optic properties (industrial interest in this) Can also be calcerous (CaCO3) o Spongin: flexible like bath sponge (Genus spongia) Asymmetric growth: o Fresh water sponges: have a symbiotic association with algar (not obligate, but facultative) Algae gets a growing edge to live and expand on, and sponge gets nutrients (?) Together in plantless lakes they can fir the functional niche of a macrophyte Eg. Eunaplus gragilis: Warfare between invasive species and native species. Sponges overgrow zebra mussels in Great Lake system and can compete with zebra mussels because of the asymmetric growth. Both species have marine ancestry. o Some sponges show radial symmetry “Super osculum” last exit pore for all the water coming in through the sides. The larger sponge the more beneficial this hydrodynamic efficiency will be eg. Xestospongia: Barrel Sponge Oldest multicellular animals o Eg. Archeocyatha: very successful and abundant but then disappeared Seems like a good arrangement to process water (efficient) Calcareous (as seen a bunch in Burgess Shale faunaw/spicules) o Eg. Paleophragmodictya: Very strong surface reticulatioin o Eg. Hydnoceras: orthogonal reticulation, grown in the same envr as hexactinellids and similar spicule arrangement o Early Vendian fossils: captures particular cell types in these fossils
Amebocytes: freely moving cells that gather and process food Clerocytes: excrete the spicules o Oldest evidence: Fossil steroids that only come from sponges No true tissues or organs o Fresh water sponges: not true skin, but close? They have no genes that code for the blocking of molecules, but they seem to be able to be stopped by the sponge. So, there is some type of “skin” that can block certain molecules not as permeable as we once believed o Maybe it does have tissue? Skin is the first organ that will have evolved. No nervous system o Sponges can move and react to stimulus that suggests some sort of nervous pathway? o Tiny sponge with ink injected. Over the course of 30 minutes, it will have a mini sneeze that will clear the sponge of the dye —> there must be some communication between cells. Using contractile filaments that are reacting to a common chemical signal. This isn’t a nervous system, but it’s kind of a nervous reaction o Rhythmic contraction or “breathing of the sponge may enhance filtration/feeding Generally sessile o Sponge may want to move to adjust their position on a reef in reaction to changing current, or to avoid a spatial competitor —> we’ll call them sessile but “sedentary” may be a better term Distinctive cell type: Choanocyte o Layer of cells on the inside of a cavity. o They create a current with their flagellum. The shape of the sponge will exchange that through nozzle effect Filterfeeders o except Cladorhizidae: Passive predators still suspension feeder. These species don’t have choanocytes or the water pumping design Asexual and sexual reproduction o Sponge produces sperm and spray them out from the osculum. The sperm are sucked into another sponge and the eggs are fertilized inside o Sponges in fresh water and intertidal can form gemmules (not so much deepsea sponges). Gemmules germinate when water is the current temperature. All the gemmules germinate at once coordinatedly and can fuse because they’re the same genetic material Body plans o Asconoid: like a tube o Syconoid: More surface area to take in more water o Leuconoid: Choanocyte chambers that act as pumping stations. There is more surface of choanoderm to process more water —> most successful form
Sponge Diversity:
15/1/14 Most common: Demonspongiae, Hexactinellida, Calcarea Stromatoporoids: only one know extant species (?) Homoscleromorpha: Have protenaceous structures in their cells that are more similar to the rest of the metazoa than other sponge groups
Placozoa: Ciliated freeliving metazoans that are ciliated Feed through the base (ventrally), similar to ediacaran fauna See slides for details
Amebocytes: freely moving cells that gather and process food Clerocytes: excrete the spicules o Oldest evidence: Fossil steroids that only come from sponges No true tissues or organs o Fresh water sponges: not true skin, but close? They have no genes that code for the blocking of molecules, but they seem to be able to be stopped by the sponge. So, there is some type of “skin” that can block certain molecules not as permeable as we once believed o Maybe it does have tissue? Skin is the first organ that will have evolved. No nervous system o Sponges can move and react to stimulus that suggests some sort of nervous pathway? o Tiny sponge with ink injected. Over the course of 30 minutes, it will have a mini sneeze that will clear the sponge of the dye —> there must be some communication between cells. Using contractile filaments that are reacting to a common chemical signal. This isn’t a nervous system, but it’s kind of a nervous reaction o Rhythmic contraction or “breathing of the sponge may enhance filtration/feeding Generally sessile o Sponge may want to move to adjust their position on a reef in reaction to changing current, or to avoid a spatial competitor —> we’ll call them sessile but “sedentary” may be a better term Distinctive cell type: Choanocyte o Layer of cells on the inside of a cavity. o They create a current with their flagellum. The shape of the sponge will exchange that through nozzle effect Filterfeeders o except Cladorhizidae: Passive predators still suspension feeder. These species don’t have choanocytes or the water pumping design Asexual and sexual reproduction o Sponge produces sperm and spray them out from the osculum. The sperm are sucked into another sponge and the eggs are fertilized inside o Sponges in fresh water and intertidal can form gemmules (not so much deepsea sponges). Gemmules germinate when water is the current temperature. All the gemmules germinate at once coordinatedly and can fuse because they’re the same genetic material Body plans o Asconoid: like a tube o Syconoid: More surface area to take in more water o Leuconoid: Choanocyte chambers that act as pumping stations. There is more surface of choanoderm to process more water —> most successful form
Sponge Diversity:
15/1/14 Most common: Demonspongiae, Hexactinellida, Calcarea Stromatoporoids: only one know extant species (?) Homoscleromorpha: Have protenaceous structures in their cells that are more similar to the rest of the metazoa than other sponge groups
Placozoa: Ciliated freeliving metazoans that are ciliated Feed through the base (ventrally), similar to ediacaran fauna See slides for details
