Phylum Porifera Sponges Ancient group of animals that dates back to the late Precambrian about 600 million years ago

Phylum Porifera (sponges) Sessile, aquatic, benthic, suspension feeders on bacteria and protists Mainly marine (~7000 species), but some in freshwater (~300 species). ~27 freshwater species in North America.

Defining Characteristics of Phylum Cellular level of organization No true tissues No true embryological germ layers Cells are not connected to each other by basement membrane as seen in true tissues Adults asymmetrical or radially symmetrical; no fixed body shape Cells are totipotent Can change form and function Unique flagellated cells – choanocytes drive water through pores, canals and chambers constituting the aquiferous system

Defining Characteristics of Phylum Adults are sessile (immobile) suspension feeders (a few are carnivorous) Larval stages are motile Mesohyle - middle layer: variable, but always includes motile cells and usually some skeletal material. Skeletal elements Spicules composed of calcium carbonate, silicon dioxide and/or collagen fibers (protein = spongin)

Phylum Porifera Bauplan

Two Unique Characteristics Aquiferous System Water current channels Choanocytes Cells are totipotent Most able to change many times Reproductive cells and those that make spicules differentiate irreversibly These two features define sponges and have played major roles in poriferan success. Sponge diversity is largely derived from these two characteristics.

Compensating for Simplicity of Form in Sponges Increasing size/surface area comes from folding body wall in variety of patterns. Plasticity of form and totipotency of sponge cells compensate for lack of tissues and organs Aquiferous system Brings water close to the cells responsible for food gathering and gas exchange. Removes excretory and digestive wastes and reproductive products are expelled 1 x 10 cm Leucosolenia filters 22.5 liters daily

What is “A” Sponge Old idea: individual sponge was one cell Later – one choanocyte chamber = one sponge Currently two ideas: Each excurrent opening (osculum) = one sponge Preferred: each “sponge” in its entirety = individual Any and all sponge material bounded by a continuous outer cellular covering.

Bauplan - Body Structure Outer squamous surface cells make up the pinacoderm (single cell thick) Cell = Pinacocyte Pinacoderm is perforated by small holes Incurrent pores = dermal pores or ostia Pinacocytes lining internal canals are endopinacocytes vs. exopinacoderm Inner surface is the choanoderm (single cell thick) Cell = Choanocyte

Sponge Anatomy

Bauplan - Body Structure Between pinacoderm and choanoderm is the mesohyle Various thicknesses Contains amoeboid cells, collagen, spicules Plays roles in digestion, gamete production, transport of nutrients and waste products (via amoeboid cells) and secretion of the skeleton Water movement is driven by beating of choanocyte flagella Pump large volumes of water at low pressure = water current (aquiferous) system

Bauplan - Body Structure Body covered in holes (ostia) Pores lined with porocytes Pores - hence the name Porifera “Pore bearer” Skeleton made of spicules Silica CaCO3 Or Spongin – protein

Sponge Anatomy

Porifera Bauplan Cell Types

Pinacocytes (“tablet cells”) - form the pinacoderm, the outermost layer of sponge; equivalent of epidermis

Water enters thru prosopyle, exits thru apopyle Porocytes (pore cells) - line the pores (or ostia) of the sponge; provide channels to spongocoel Water enters thru prosopyle, exits thru apopyle prosopyle apopyle

Sponge Cell Types Microvillae form collars around flagella of Collar cells = Choanocytes Functions of choanocytes Generate currents that maintain water flow throughout sponge. Capture small food particles on sticky contractile collar. Capture sperm for fertilization/may produce sperm nucleus microvillus Flagellum Collar

Choanocytes - flagellated collar cells that pump water through the sponge, capture prey, capture sperm

Choanocytes –, form the choanoderm. Similar to choanoflagellates. Collect food matter on sticky contractile collar; may also produce sperm.

Sponge Cell Types Amoebocytes (or Archaeocytes) are amoeba-like cells that are totipotent, in other words each is capable of transformation into any other type of cell. Have important roles in feeding, reproduction and in clearing debris that blocks the ostia. Store, digest and transport food, excrete wastes, secrete skeleton Amoebocytes wander through the central jelly or mesohyle Form gametes May give rise to buds in asexual reproduction. Several different types.

Amoebocytes

Functions of Amoebocytes Transfer food from cells that do the feeding to cells that have other functions Produce spicules, collagen and other mesyhyle components. Replace missing cells Act as immune response cells Become gametes

Amoebocyte Types Large Amoebocytes- distribute food to other cells of sponge; move by way of pseudopods Archeocytes- undifferentiated sponge cells that can give rise to more differentiated cells such as pinacocytes, porocytes or oocytes. Play major role in digestion, transport excretory activities. Chromocytes – pigmented amoebocytes Trophocytes – nurse cells (provide nutrients) involved in gemmule formation Sclerocytes - produce spicules - the mineralized spicules that form the skeletons of many sponges and in some species provide some defense against predators. Calcoblasts – make calcium carbonate spicules Silicoblasts – make silicious spicules

Other types of cells within the mesohyl Lophocytes – are amoeba-like cells that move slowly through the mesohyl and secrete collagen fibers. Collenocytes – are another type of collagen-producing cell. Rhabdiferous cells – secrete polysaccharides that also form part of the mesohyl. Thesocytes - resting archaeocytes in gemmules of freshwater sponges Myocytes ("muscle cells") regulate the opening and closing of the ostia and osculum . "Grey cells" act as the equivalent of an immune system for the sponge. Oocytes and spermatocytes are reproductive cells.

Other types of cells within the mesohyl In addition to or instead of sclerocytes, demosponges have spongocytes that secrete a form of collagen that polymerizes into spongin, a thick fibrous material that stiffens the mesohyl. No specialized cellular communication. Cells signal each other by diffusion of chemical messages Cell aggregation – cells can reaggregate after mechanical disruption. Can identify self from non-self If two different species’ cells are mixed, each species reaggregates only with its own cells.

Mesohyl Middle layer of sponge Acellular matrix Contains archaeocytes Gelatinous Nonliving Acellular Contains archaeocytes Contains spicules and spongin

Sponge Skeletal Materials Spicules and spongin fibers are Structural Used in defense against predators Also important for identification of sponges

Sclerocytes - derived from amoebocytes; produce spicules

Growth of a sponge spicule Sclerocytes - derived from amoebocytes; produce spicules Spicule Founder cell Thickener cell

Additional spicule shapes Figure 4.2 Additional spicule shapes

Massive calcium carbonate supports evolved several times independently in the Demospongiae and the Calcarea. Massive calcium carbonate supports evolved several times independently in the Demospongiae and the Calcarea

Generalized Sponge Anatomy Osculum H2O inhalant pore (ostium) spongocoel(atrium)

Cell Layers Pinacoderm made of pinacocytes Ostia lined by porocytes Mesohyle with amoebocytes Choanoderm with choanocytes

Mesohyle

Sponge Body Plans Asconoid Syconoid Leuconoid See handout for details of water flow and anatomy for practice, label the following diagrams

            Asconoid Syconoid Leuconoid Choanocytes Mesohyl Pinacocytes Water flow

Leucosolenia Pinacoderm

Leucosolenia Asconoid sponge

Leucosolenia

Asconoid Body Plan Simplest body type Found only in the Calcarea Choanoderm is simple and continuous Water: enters through pores and flows into spongocoel then out through osculum.

Structure and organization of an asconoid sponge. Spicule Pinacoderm Porocyte Osculum Spongocoel Mesohyl Amoebocyte Choanocyte in choanoderm Inhalant pore

Syconoid Body Plan More complex body type Choanoderm is folded into many radial canals Water: enters through pores and travels through radial canals to spongocoel then out through osculum. radial canals spongocoel

Grantia = Scypha = Sycon See following slides for anatomy

Grantia = Scypha = Sycon

Structure and organization of a syconoid sponge. Spongocoel Spicule Osculum Pinacoderm Incurrent Pore Choanocyte Incurrent Canal Radial Canal Amoebocyte Internal water canal Mesohyl

Sycon (Grantia, Scypha) Asconoid sponge

Grantia longitudinal section; water flow shown by arrows

Amphiblastula larva

apopyle

prosopyles

Grantia cross section; water flow shown by arrows.

Grantia Details of radial canal

Structure and organization of a leuconoid sponge

Leuconoid Body Plan Most common and most complex type of sponge body Water: flows in through pores into inhalant canals. It then enters choanocyte lined chambers… …and finally travels the excurrent canals to the osculum.

Detailed organization of the leuconoid sponge Apopyle Prosopyle

Hexactinellida

Hexactinellida

Hexactinellida Live in deep water Habitat favored possibly because body structures are so fragile.

Hexactinellida Glass sponge community in Antarctica's eastern Weddell Sea, in an area not covered by ice shelves

Syncitia Hexactinellid sponges No pinacoderm covering body wall and lining aquiliferous system Instead the tissue is arranged in three-dimensional cobweb-like strands called a trabecular syncitium or network No choanoderm, have a choanosyncitium instead Collar bodies (no nucleus) rise of the surface of the choanosyncitium. Each group of collar bodies occupies a syconoid- like pocket supported by the trabecular network. Each group of collar bodies comes from out growths of stem cell - choanoblast

Flagellated cells lack nuclei, and are called collar bodies. Choanosyncitium Trabecular Syncitium Major components of the body are the trabecular syncytium and Choanosyncitium. Flagellated cells lack nuclei, and are called collar bodies.  Produced by nucleated choanoblasts.

Trabecular Syncytium Is the largest example of a syncytium known in the animal kingdom. Comes from fusion of early embryonic cells. Embryos are cellular until gastrulation SO - Hexactinellid sponges may have evolved from cellular sponges

Possesses multiple nuclei Is bilayered Choanosyncitium Trabecular syncitium Syncytium Is Cytoplasmic Lacks cell walls Possesses multiple nuclei Is bilayered Extends through the entire body of the sponge. Syncytium Connects through cytoplasmic bridges to various cells in the sponge, such as choanoblasts and archaeocytes.

Trabecular Syncytium Choanosyncitium encloses and supports the collar bodies and the choanoblasts Trabecular syncitium branches from the primary reticulum and forms a kind of barrier around the collars of the collar bodies.  Nuclei are scattered within the two reticula. Water is drawn through openings, or prosopyles, and moves through the microvilli of the collar bodies then through the excurrent canals to the outside through apopyles. Some water passes directly through the prosopyles into the flagellated chamber

prosopopyle

Collar body

Syncytia Cytoplasm within the syncytium flows bidirectionally. Food products may be distributed through the sponge via the syncytium and not via cellular transport as in other sponges.