Chapter 5; Porifera and Placozoa

Pinacoderm

2 differentiated cells Pinacocytes are flattened cells that abut each other edge to edge to form a skin like cellular pavement over the body surface and line the incurrent and excurrent canals. Generally lack flagella.

Choanoderm

flagellated color cells

Sponge Nutrition

All sponge cells can ingest particles by phagocytosis. Food-trapping filter are the incarnate canals which progressively decrease in diameter as they penetrate inward and choanocytes. Both choanocytes and archeocytes engulf and digest particles in vesicles but the choanocyte often transfers particles to the archeocytes for digestion. Carnivorous species occur in the demo sponge family Cladorhizidae. They trap crustaceans and other small animals on sticky cellular threads that extend out from the surface of the sponge. Two sources of wastes in sponges; indigestible products of intracellular digestion and inorganic mineral particles that enter the sponge in the water stream. Many harbor photosynthetic endosymbionts in their tissues and derive a nutritional benefit from the photosynthate.

Sponges

Evolved a multicellular body uniquely specialized for filter feeding, the separation of suspended food particles from water by passing them through a mesh that strains out the food. Body continuously remolds itself to fine-tune its filter-feeding system. Adult sponges are sessile and attached organisms, although some are capable of limited movement of the body or its parts. Approximately 8000 species of sponge Most marine

Lophocytes

Archeocyte-like ameboid cells that secrete collagen fibers from their trailing end as they move through the mesophyl. Produce and maintain the fine collagen fibers in the mesophyl.

Mesophyl

Connective tissue layer between the pinacoderm and the choanoderm.

Choanocytes

Flagellate collar cells that make up the choanoderm. Generate water flow through the sponges. Have an apical collar of long microvilli around single flagellum. The collar is in the form of a cylinder or an inverted cone. Basal part of most species bears as bilateral vane as in the choanoflagellates.

Placozoa

Flattened body that is enclosed in a layer of cells one cell thick that resembles a epithelium, particularly because typical intercellular junctions join the adjacent cells. Clonal reproduction by fragmentation. 4 cells - very simple metazoans. Rely on simple diffusion for transport. "intermediates between sponges and remaining metazoans" Trichoplax

Porococytes

Form the ostia of all asconoid as well as many syncanoid/leuconoid sponges. Each porocyte surrounds a pore, whose diameter is regulated by contraction of cytoplasmic filaments. Miniature sphincter valves.

Asexual Reproduction

Fragmentation, budding, and gemmules. Fragmentation primarily results from current or wave damage. Budding is uncommon but does occur in a few sponges. Many produce hundreds to thousands of spearlike gemmules typically in the fall

Water Pumping

Generally a sponge pumps a volume of water = to its body volume once every 5 seconds. Volume entering must be = to the volume exiting through the sponge at any moment Flow velocity is fastest through the osculum and slowest in the choanocyte chambers.

Leuconoid Design

Largest body sizes Aquiferous system is a complex network of water vessels that permeate a solid, spongy body. Consists of spherical choanocyte chamber that lie at the intersection of incurrent and excurrent canals. Water exits each choanocyte chamber through an apopyle (=back gate)

Trabecular Syncytium

Living tissue in hexactinellids 3D cobweb like strands

Archeocytes

Macro-phage like cells in the mesophyl that are are ameboid cells bearing a conspicuous nucleus and numerous large lysosomes. Totipotent an can differentiate into any other type of sponge cells. Also phagocytic and play a role in digestion and internal transport.

Syncanoid Design

Increases surface area and reduced atrial volume by forming alternating in pockets and out pockets of the body wall. Outpockets - choanocyte chambers Incurrent canals - inpockets ostia -> incerte canals -> prosophytes -> choanocyte chambers -> atrium -> osculum

Osculum

Larger opening, situated at the upper free end of the body. Exit

Sexual Reproduction

Mostly hermaphrodites. Sperm spawned from one sponge and transported by water currents to another, in which fertilization occurs internally. Most are viviparous, retaining zygotes in the parents body and releasing larvae. Sponges lack goons and germ cells occur in either simple clusters (sperm) or individuals (eggs) throughout the mesophyll. A coeloblastula larvae is produced by cancerous sponges. This larvae is a hollow sphere composed of a single layer of flagellated cells. A amphiblastula larva occurs in other calcareous sponges, and develops as a hollow ball composed of 2 types of cells; anterior flagellated cells and posterior non flagellated granular cells. A parenchymella larvae is characteristic of most demo sponges. The embryo develops directly into a solid mass of cells, forming a stereo blastula. Trichimella larvae typify glass sponges. They are stereo blastula that bear a band of flagellated cells around the equator of the larval body. The interior is occupied by yolk-bearing cells, schlerocytes, other cells, and choanocyte chambers.

Myocytes

Mule-like cells containing actin and myosin that aggregate around the osculate of some demo sponges. Regulate the size of the oscular aperture and thus help to control water through the cell.

Sponogocytes

Occur only in Demospongiae Resemble archeocytes, but secrete collagen that polymerizes into thick skeletal fibers known as Spongin.

Spicules

Occur principally in the mesophyll, the can project freely through the surface pinacoderm, thus affording the sponges some protection. Commonly guard the oscular and sometimes the ostia. Spongin and spicules occur together in most species of sponges. Siliceous (SiO2) or Calcareous (CaCO3) Megascleres typically form the principal skeletal framework, whereas the considerably smaller microscleres may support the pinacodermal lining of the canal system or in high density, toughen the body wall.

Oocytes and Spermatocytes

Reproductive cells that undergo gametogenesis in the mesophyl to form sperm and eggs.

Epitheloid Tissue

Resembles epithelium but lacks epithelium's intracellular junction. Pinacoderm

Schlerocytes

Secrete mineralized skeletal spicules of many sponges.

Ascanoid

Simplest anatomical design. Hollow cylinder attached to its base to the substratum.

Ostia

Small pores that perforate the cylinder wall. Entrance