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Phylum Porifera: Sponges Chapter 6 Slide 2 Gemmules Large mass of archaeocytes Formed during harsh conditions Environmentally resistant When ready, archaeocytes are released form new sponges. Slide 3 Slide 4 FRESHWATER SPONGES PORIFERA: SPONGILLIDAE Slide 5 Slide 6 Slide 7 Ephydatia fluviatilis Slide 8 M G Ephydatia fluviatilis Gemmoscleres And Megascleres Slide 9 Ephydatia fluviatilis Gemmules Slide 10 Slide 11 Ephydatia fluviatilis Gemmule Slide 12 Ephydatia fluviatilis Gemmule Surface Slide 13 Ephydatia fluviatilis Gemmoscleres Birotulate Slide 14 Spongilla lacustris Slide 15 Slide 16 Spongilla lacustris Megascleres And Microscleres m M Slide 17 Spongilla lacustris Gemmules With Micropyle Mycropyle Gemmoscleres Slide 18 Spongilla lacustris Gemmoscleres Slightly Curved Amphistrongyla Covered With A Variable Number Of Recurved Spines Slide 19 Reproduction Sexual reproduction. Slide 20 All sponges reproduce sexually and produce motile larvae. 1) Viviparous or incubating- eggs develop in the sponge cells until the larval stage. 2) Oviparous release gametes (oocytes and spermatozoa) into the water and fertilization and larval development takes place in the open water. Slide 21 The spermatozoids are derived from choanocytes. The choanocytes (C) start reabsorbing the microvilli of their collars while the cell body fills out in the choanocyte chamber (Cch). Slide 22 The transforming choanocytes (C) divide many times, and detach themselves progressively from the inner wall of the chamber. Slide 23 Spermatic follicles (Fo) are disseminated among the choanocyte chambers (Cch) in the mesohyl. Slide 24 The origin of the oocytes in sponges remains uncertain. They may have a choanocyte origin or a archeocyte origin. At an early stage it has a central nucleus (N) and is partially surrounded by follicular cells (Cf). Slide 25 Throughout its maturation the oocyte grows and becomes very large. It accumulates enormous quantities of vitelline (Vg) in the cytoplasm. Slide 26 At the end of oocyte formation the cytoplasm is completely taken over by vitelline (Vg) reserves and the follicular envelop is a thin layer of flattened cells (Cf). Slide 27 Fertilization The Smoking Sponges Mature sperm and oocytes are released into the environment through the aquiferous system. Fertilization takes place in the water (ovipery). Slide 28 Fertilization in Viviparous Sponges After release the sperm is taken in to the aquiferous system. Indirect fertilization in viviparous sponges constitutes one of the most unusual phenomenon in the animal kingdom. Slide 29 Fig 6.14 The sperm never penetrates the oocyte directly, but instead it penetrates an intermediary cell usually a choanocyte. Slide 30 Fig 6.14 The choanocyte transforms itself by reabsorbing its collar and flagellum while the sperm enclosed in a vacuole is modified to become a nonflagellar sperm. This carrier cell assures the transport of the sperm to the oocyte Slide 31 After fertilization the fertilized egg begins to divide, and the cells begin digesting the vitelline (Vg) reserves. Slide 32 The Larva Three basic larval types have been described in sponges. 1) Coeloblastula larva 2) Parenchymula larva 3) Amphiblastula larva Slide 33 The Parenchymella larva is generally ciliated and solid. Slide 34 Parenchymella larva Slide 35 The amphiblastula larva is a hollow larva made up of two distinct areas: small ciliated cells at the anterior pole (Pa), and large cells at the posterior pole (Pp). The larva is located in one of the large tubular choanocyte chambers (Cch). It is released through the osculum, swims freely for a few days and attaches to a substrate. The anterior ciliated cells differentiate and become choanocytes. Slide 36 The Big Picture Sponges are one of the most primitive metazoans with cellular organization. It is their aquiferous system and totipotent nature of cells that allows them to achieve such large sizes and diversity of body sizes.