Biology 320 Invertebrate Zoology Fall 2005 Chapter 5 – Phylum Porifera

Phylum Porifera The sponges Name Porifera means “pore bearers” First metazoan phylum we will discuss Posses epithelioid and rudimentary connective tissue Lack true muscle and nervous tissues Not considered to be eumetazoans

Approximately 8000 spp. of sponges Mostly marine, with approx. 150 described freshwater spp. Primitive, sessile filter feeders Most are asymmetrical, but some display radial symmetry Can be erect, branching, or encrusting on substratum

Body Design Three main forms of sponges, classified according to complexity Asconoid Syconoid Leuconoid Asconoid sponges Simplest body plan Resemble a hollow tube, with the base attached to the substrate Possesses one large spongocoel lined with a single layer of choanoderm Choanocytes beat and draw water through ostia in the epidermis

Asconoid sponges cont… Water exits spongocoel through a single large osculum Smallest of all sponges (1mm in diameter) Thinnest body walls Leucosolenia Growth is limited by spongocoel diameter If asconoid sponges had larger diameters, body volume would exceed pumping capacity of choanoderm Therefore, a only a change in this simple body plan would permit the evolution of larger body sizes in sponges

Syconoid Sponges Body wall contains pockets, known as choanocyte chambers, that are lined with choanoderm Increases choanoderm surface area Decreases spongocoel volume Larger than asconoid sponges (one cm – a few cm) Body walls are thicker than in asconoid sponges Grantia and Sycon (formerly Scypha)

Leuconoid sponges Contains thousands of choanocyte chambers, thereby further increasing the choanoderm SA Spongocoel is further reduced Therefore, these are the largest sponges (few cm to one meter, or more) Thickest body walls May possess more than one osculum

Body Wall Composition The body walls of sponges are classified as either being cellular or syncytial Cellular sponges have two primitive primary tissues Epithelioid – resembles epithelium Mesohyl – connective tissue middle layer There are two specific types of epithelioid tissue Pinacoderm – lines inside (except where choanoderm is present) and outside Choanoderm – choanocytes posses a flagellum and collar of microvilli

All mesohyl cells are totipotent and amoeboid Mesohyl is a fibrous (proteinaceous) ECM containing cells and skeletal elements All mesohyl cells are totipotent and amoeboid Archeocytes – can differentiate into any type of sponge cell. Aide in digestion (via phagocytosis) and internal transport Lophocytes – secrete and maintain collagen fibers Spongocytes – responsible for producing thick skeletal fibers known as spongin

Mesohyl cells cont… Sclerocytes – secrete spicules, interesting skeletal elements made of silica or calcium Myocytes – essentially muscle cells; usually concentrated around osculum. Constrict or dilate to control water flow Germ cells – reproductive cells

Syncytial sponges DO posses cells, but not at the same level of organization as cellular sponges Cytoplasm is continuous and lacks membranes that compartmentalize separate cells Lack pinacoderm Lack choanoderm. Posses collar bodies instead; these are located in collar body chambers, individually rather than in epitheliod sheets Mesohyl is present and contains archeocytes, sclerocytes, and germ cells

Syncytial sponges cont… Body wall resembles a 3D cobweb-like pattern and is called a trabecular syncytium Each strand of the trabecular syncytium encloses an axis of mesohyl Collagen and spicules are present

Taxonomy Two subphyla Subphylum Symplasma (Hexactinellida) Subphylum Cellularia Subphylum Symplasma consists of glass sponges that posses syncytial tissues Most sponges belong to Subphylum Cellularia, which is divided into two main classes, both possessing cellular tissues Class Demospongiae – have siliceous spicules and spongin Class Calcarea – have calcareous spicules

Skeleton Any cell, organism, etc. needs some form of support Mesohyl acts as an endoskeleton Diversity of mesohylar structure Fine collagen fibers only May be supplemented with spicules, spongin, or both Incredible diversity of spicules; and some can project through mesohyl to protect the outside of the sponge

Water Pumping Most pump a volume of water equal to their body volume, every 5 seconds Can slow / stop water flow to avoid taking in silt Can control rate of water flow via Contracting or relaxing myocytes, which controls osculum diameter Closing ostia Adjusting flagellar beat of choanoderm / collar bodies

Locomotion Some have limited capacity for locomotion Can move 1 to 4 mm per day Result of collected amoeboid movement of cells Osculum contraction Whole body contraction

Nutrition Filter feeders Typically phagocytize particles of 50µm or less Particle size determines which cells phagocytize All cells can phagocytize Choanocytes transfer particles to vacuoles for digestion Archeocytes remove wastes / inorganics from system

Feed on dinoflagellates, bacteria, viruses, debris, etc. Some are carnivorous (don’t filter); trap small animals such as crustaceans

May posses photosynthetic endosymbionts Cyanobacteria Dinoflagellates Chlorophytes Symbionts may cause sponge to be brightly colored Sponges must live in shallow water to photosynthesize Some obtain up to 80% of nutrients from photosynthate

Internal Transport Gas / waste transport is carried out via simple diffusion Sponges are “leaky,” so water penetrates almost the entire animal Sheets of cells are only one cell layer thick Mobile amoeboid cells Ammonia is the main metabolic waste Almost always the case for animals in aqueous environments Uric acid or urea in terrestrial habitats Archeocytes transfer wastes / nutrients Some individual cells posses contractile vacuoles

Nervous Tissue Lack nerve cells Some have localized impulses responsible for myocyte contraction Glass sponges can generate action potentials that travel all across their syncytium at a rapid rate Used to arrest flagellar beating

Ecology Many produce toxins to prevent predation Some animals are spongivores Nudibranchs Fish Turtles – Hawksbill turtle feces can be up to 95% siliceous spicules Some release chemicals that kill competing sessile organisms, such as corals

Some animals such as shrimps and brittle stars live in sponges Decorator crabs may place sponges on their carapaces Cliona breaks down calcareous shells. Bores into shells for protection

Reproduction Sponges are excellent regenerators Reproduce clonally through several methods Fragmentation – usually due to wave damage or grazing Budding Gemmules (winter bodies) – spore-like structures that are essentially a mass of nutrient-laden archeocytes that are surrounded by a shell. Undergo diapause

Sponges frequently reproduce sexually Sponges are hermaphrodites (monoecious) Germ cells occur throughout mesohyl Choanocytes can also release sperm, and form eggs

Sperm are broadcasted into water column Choanocytes phagocytize incoming sperm, but don’t digest They differentiate into an amoeboid cell and deliver sperm head to egg Most eggs are fertilized through phagocytosis (therefore, most sponge sperm lack an acrosome)

Some sponges are oviparous, and release zygotes into water column Most are viviparous, and retain zygotes in their body, later releasing larvae Sponge larvae are very diverse

Larvae are short lived Varied lifespans Settle within a few days Creep across substrate until a suitable spot is found Metamorphose into a juvenile Varied lifespans May live one to a few years in temperate zones Tropical or deep sea spp. May live 200 years or more Some only grow 0.2 mm/yr, and could be 5000 years old if that growth rate is constant