Phylum Porifera Porifera Characteristics Freshwater and marine Simplest

Phylum Porifera

Porifera Characteristics • Freshwater and marine • Simplest of all animals • Asymmetrical • No systems for repro, digestion, respiration, sensory, excretion

Porifera Characteristics • ~ 5, 500 extant species • Highest abundance in unpolluted littoral and tropical reefs • ~ 75% benthic biomass

Porifera Characteristics • Sessile (Adults) • Suspension-feeders (Adults) • Multicellular • Flagellated cells = choanocytes circulate water through water canals • No tissues • Cells totipotent

Porifera Characteristics • Outer and inner cell layers lack basement membrane • Middle layer (mesohyl) has motile cells and skeletal material • Skeletal elements (when present) are calcium carbonate, silicon dioxide and/or collagen fibers

Taxonomy and classification • Taxonomy based on skeletal elements • Now embryological, biochemical, histological, and cytological methods to diagnose sponge taxa

Three classes (Calcarea, Demospongiae, Hexactinellida) • Class Calcarea: Calcareous sponges • Shallow, tropical water, near shore Leucetta

Class Calcarea • Spicules = calcium carbonate • Calcarean spicules lack hollow canals = strong Clathrina

Class Hexactinellida (Glass sponges) – Silica spicules – Spicules join at right angles, sponge appears artificial

Class Demospongiae (Demosponges) • Largest and most diverse class of sponges, ~ 90 percent of sponges • Spicules either spongin, an organic substance; or silica, a mineralized substance Oscarella

Class Demospongiae • Genera Adocia, Halisarca, Myxilla

Aquiferous system • Brings water to cells • 1 x 10 cm sponge pumps 22. 5 l water daily • Large sponge filters body mass every 10 -20 s

Sponges are single individuals • Grow by continually adding cells that differentiate as needed

Body structure and aquiferous System Outer layer – Perforated by small holes - dermal pores or ostia • Choanoderm: innermost layer of flagellated cells = choanocytes • Mesohyl: middle layer

Body structure: 3 shapes

Asconoid sponges • Asconoid: one-cell thick choanoderm is simple and continuous – ~10 cm height – Thin walls enclose central cavity; atrium opens outside via osculum – Pinacoderm has specialized cells; porocytes – External opening of porocyte canal is ostium or incurrent pore

Asconoid sponges

Syconoid sponges • Syconoid: choanoderm folded – Mesohyl two layers thick: • Outer region is cortex (contains skeletal material)

Leuconoid Sponge • Leuconoid: choanoderm subdivided into separate flagellated chambers

Flow rate • Flow rate not uniform throughout • Water must move slowly over choanoderm – Exchange nutrients, gases, and wastes • Water leaving osculum must be carried far enough away to prevent fouling

Cells that line surfaces • Pinacocytes • Porocytes • Choanocytes

Cells that line surfaces • Porocytes – Form ostia – Cylindrical tube-like cells – Contractile - open and close pore to regulate diameter

Cells that line the surface • Choanocytes – = choanoderm – Create currents – Not coordinated in movement

Cells that secrete skeleton • Fibrillar collagen – Collencytes – Lophocytes – Spongocytes • Calcareous and siliceous spicules – Sclerocytes

Contractile cells • Myocytes – Contractile cells – Filament arrangement homologous with smooth muscle cell – Unlike neurons and true muscle fibers

Cell Aggregation • Atlantic sponge (Microciona prolifera) – Pieces pressed through fine cloth – Separated cells reorganize – 2 -3 weeks – Self-recognition

Support • Skeletal elements – Organic - collagenous – Inorganic – siliceous (hydrate silicon dioxide) • Sponges only animals that use hydrated silica as skeletal material

Sponge Harvest • Harvested for thousands of years • Greeks harvested sponges • Sponge fishery south of FL, Bahamas, Mediterranean – 1938: 2. 6 million lbs

Sponge Harvest • Hippospongia • Spongia

Spicules • Microscleres • Megascleres – Demosponges and Hexactinellids have both – Calcareous sponges have only megascleres

Nutrition, Excretion, and Gas Exchange • Intracellular digestion • Continuously circulate water – Size selective feeders • Food capture – Phagocytosis and pinocytosis

Excretion • Ammonia and gas exchange – Diffusion

Activity and Sensitivity • Respond to environmental stimuli: – Close ostia or oscula, canal constriction, backflow

Reproduction and Development • Sexual and asexual reproduction – All sponges capable of sexual and asexual repro – Processes unknown due to lack of distinct, localized gonads (gametes, embryos occur throughout mesohyl) – Asynchrony of reproductive activity w/in populations

Reproduction and Development • Asexual Reproduction – All sponges produce viable adults from fragments – Cellular reorganization “pinches off” branch ends which regenerate into new adults – branching species

Reproduction and Development • Asexual Reproduction – Common in Florida’s sponge farms - cuttings attached to cement structure – Other processes include formation of gemmules, budding

Reproduction and Development • Gemmules – Produced in winter as dormant bodies – Coat and supportive cells protects from freezing and desiccation

Reproduction and Development • Gemmules

Reproduction and Development • Budding – Squat or elongate club-shaped protrusions from sponge surface – Buds drop, carried by current, adhere to substratum – Marine species

Reproduction and Development • Sexual Processes – Majority are hermaphroditic; produce sperm and eggs at different times • = Sequential hermaphroditism – Protogyny or protandry may occur once or many times during life

Reproduction and Development • Sexual reproduction • Sperm from choanocytes; eggs from choanocytes and archaeocytes

Reproduction and Development • Sexual process (Demospongiae and Calcarea) • Sperm and oocytes released into environment via aquiferous system – Sperm release -”smoking sponges” – Fertilization in open water (oviparous) – Few viviparous: sperm into nearby sponge’s aquiferous system; sperm to oocyte for fertilization

Reproduction and Development Madsen sponge releasing sperm

Reproduction and Development • Release of larvae (vivipary) – Through aquiferous system or ruptured wall – Larvae swim hours or days, or crawl along substratum before settling – Larvae are lecithotrophic = use stored yolk

Reproduction and Development • Larval development

Distribution and Ecology • Calcareous sponges abundant in shallow waters < 200 m • Hexactinellids deeper • Demosponges at all depths

Distribution and Ecology • Sensitive to suspended sediments • Resistant to hydrocarbon and heavy metal contamination – Why?

Symbioses • Commensalism common (small inverts, fishes) • Protection, habitat, water currents for suspended food particles • Some organisms utilize sponge for camouflage, small piece on shell or carapace

Boring Demosponges - harmful to corals and mollusc shells • = bioerosion; chemical and mechanical removal of fragments by etching cells