Porifera-Reviewer

PORIFERAP

- Sponges are a conspicuous and colorful component of many seascapes.

- Sponges have expanded their surfaces to catch the organic food particles suspended in seawater.

Filter Feeding – the separation of suspended food particles from water by passing them through a mesh that strains out the food.

- constant rearrangement of tissues -> amoeboid movement of cells

- dynamic tissues and totipotent cells – suggest that sponges are an intermediate form between protozoan colonies and other metazoans in which tissue and cell specializations tend to be permanent.

- Porifera is considered to be the sister taxon of the remaining Metazoa(Eumetazoa)

- Body symmetry may be radial (sphere, cone, cylinder) but ASSYMETRY predominates.

Indeterminate Growth – enlargement without a fixed upper sized growth.

FORMS: Massive(thick), erect, branching or encrusting.

- Colors results from cell pigments or endosymbionts.

FORM

Three anatomical designs: Asconoid, Syconoid, Leuconoid

Asconoid – simplest; hollow cylinder attached by its base to the substratum

        Pinacoderm – (= platter skin) monolayer of flat cells that cover the the body surface

             Atrium – (spongocoel) hollow interior lined with a monolayer of flagellated collar cells called choanoderm (= collar skin)

         Ostia – small pores that perforate the cylinder wall.

        Osculum – larger opening situated at the upper, free end of the body

        Aquiferous system – circulatory system of choanoderm, pores and chambers

* All asconoid sponges are small and have cylindrical or tubular bodies which typically do not exceed a diameter of 1mm.

* Asconoid design limits body size because growth in diameter produces an unfavorable area to volume ratio.

Leucoselenia sp. – may be single tube or cluster of tubes joined at their bases

Clathrina sp. – form a network of tubes

Syconoid – increased surface area and reduced atrial volume by forming alternating inpockets and outpockets of the body wall.

        Choanocyte chambers – (radial canals) outpockets of the choanoderm

        Incurrent canals – inpockets of the pinacoderm; discharge into the choanocyte chambers via numerous small openings known as prosopyles (=front gates)

Water flow in the Syconoid Aquiferous System: Ostia – Incurrent Canals – Prosopyles – Choanocyte chambers – Atrium – Osculum.

* Syconoid sponges generally are larger than Asconoid sponges.

* Species in genera Grantia and Sycon (formerly known as Scypha)

Leuconoid – largest body sizes

• aquiferous system is a complex network of water vessels that permeate a solid, spongy body; consists of spherical choanocyte chambers that lie at the intersection of incurrent and excurrent canals

Excurrent canals and often multiple oscula – relace the relatively voluminous atrium and single osculum of asconoid and syconoid sponges.

- Water exits each choanocyte chamber through an apopyle (= back gate) and then flows through the excurrent canals, which become progressively larger in diameter as they join with other excurrent canals.

Microciona prolifera – approx. 10,000 chambers/mm3, each 20 to 39 um in diameter and containing approx.. 57 flagellated cells (choanocytes)

* Leuconoid sponges achieve large body size because water pumping is decentralized

FORMS: Crusts, Mounds, branches, fingers, plates, tubes and vases

BODY WALL

 - thin in asconoid sponges, thick in most leuconoid sponges, intermediate in syconoid sponges

*Glass Sponges (Hexactinellida)

*Demospongiae and Calcarea

 - in demosponges and calcareous sponges, the body wall is cellular, but the glass-sponge boyd wall is a syncytium.

Syncytium – large or extensive multinucleated cytoplasm enclosed by an external membrane but not divided into cells by internal membranes.

Cellular

Two types of tissue: Epithelioid & Connective

Epithelioid – resembles epithelium, but it lacks epithelium’s intercellular junctions amd hemidesmosomes and is not underlaid by a basal lamina.

• Pinacoderm
• Exopinacoderm – covers outer surface of the body
• Endopinacoderm – lines the incurrent and excurrent canals
• Flagellated choanoderm – forms the atrial lining (asconoid) and the lining of the choanocyte chambers (syconoid & leuconoid)

Mesohyl – (= middle wood) connective tissue layer between pinacoderm and choanoderm

• forms a bushy, fibrous network that is especially obvious in bath sponges.
• Only layer of the sponge body wall that typically is not bathed with environmental water.
• Sole internal compartment of the body.
• Composed of proteinaceous, gel like matrix that contains differentiated and undifferentiated cells as well as skeletal elements.

Pinacocyte – (= platter cell) flattened (squamous) cells that abut each other edge to edge to form a skinlike cellular pavement over the body surface and line the incurrent and excurrent canals.

• generally lack flagella, except for species Plakina and Oscarella

Porocyte – form the ostia of all asconoid as well as many syconoid and leuconoid sponges.