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Ch. 35 Porifera Invertebrates Animals without a backbone 97% of all species Simplest is sponge Sponges Sponge *Phylum: porifera *Show transition from unicellular to multicellular life. *Have no tissue or organs. *Less cell specialization. * 10,000 species, most in salt water. * Adult form is sessile. * Attaches itself firmly to some surface. * Range from 1cm to 2 m. Body Plan ody wall is 2 layers with jellylike substance between. Surrounds hollow cylinder that is closed at bottom and open at top. Interior of cylinder is lined with collar cells. *they beat their flagella and draw water in through pores. Sponge Body Plan Body Plan Water pumped in is pumped out through osculum. Skeleton is made up of spongin (protein fibers) or spicules (calcium carbonate) or both. Feeding and Digestion Filter feeders. *filter food out of water that is pumped through pores by collar cells. Food is bacteria, protozoa and unicellular algae. Food digested by collar cells then nutrients passed on to amebocytes which are crawling cells which take nutrients to all cells. Waste materials are then carried out by water through osculum. Feeding and Digestion Reproduction Asexual by buds. *Buds fall off and live separately. Gemmules are formed during droughts or cold weather. *Food filled ball of amebocytes. *When conditions improve, sponge cells emerge from gemmules and grow into new sponge. Reproduction Regeneration *Grow missing parts. *Sponges can regenerate complete sponges. Sexual (see transp. 145) *Sperm released into water from 1 sponge enters pore of another sponge. *Collar cells in second sponge engulf sperm, transfer it to amebocyte which takes it to an egg. *Egg fertilized, develops into larva, larva attach to an object and grows into adult sponges. Hermaphrodites Some species have separate sexes but most species produce both egg and sperm. These are known as hermaphrodites. They do not self fertilize. This is most common in invertebrates that are sessile, move slowly or live in low-density populations.