Phylum Porifera (the sponges)

Terminology

1) coelom = body cavity in tripoblastic animals; lined with a mesodermal peritoneum.

2) sponges coelom (spongocoel) = central cavity in sponges (not really true coelomic cavity because sponges and all other lower metazoans have diploblastic germ layers.

3) triploblastic = animals in which embryo has three distinct germ layers; ectoderm (outer) , mesoderm (middle) , endoderm (inner).

4) diploblastic = animals with two distinct layers (endoderm and ectoderm). Phylum Porifera (sponges).

5) Mesenchyme = embryonic, connective tissue that is irregular in shape and amoebocytic (amoeba-like) cells. Usually embedded in organic, gelatinous matrix called the mesoglea. It will undergo development and differentiation (become specialized) and form and endoderm and ectoderm of diploblastic organism.

 

General Characteristic of sponges - pore bearing

1) Filter feeders

2) Sessile (immobile) usually attached to substrata.

3) Use water currents to bring in food particles and /or soluble in nature.

4) System of canals which carry food, water, and oxygen into body and also transports wastes to be excreted out of the body.

5) Massive cells embedded within gelatinous matrix (mesoglea) makeup bulk of sponge body.

6) Support of main body by very stiff "skeletal" elements spicules which are also used for protection - inorganic material in form calcium carbonate or silica; or organic material in form collagenous (hair-like) protein substance called spongin.

7) No true organs or systems and only very simple tissues (very low level of tissue-grade organization).

8) Size ranges from a few mm to 2 meters in length.

9) Some are pigmented.

10) Radial symmetry (some spp. somewhat irregular and amorphic).

11) Mostly marine organisms but some fresh water spp.

12) Embryo mobile (some free floating and some free swimming).

 

Form and function (structure/function relationship)

a) Pores - openings in body wall of organism

1) ostia - many tiny openings (pores) for intake of water, soluble, and particular nutrients.

2) oscula - few, larger openings in body wall used for water outlet and excretion of water.

b) Canals- system of tubular "pathways" connecting ostia, spongocoel, and oscula

1) All the pores and spongocoel are connected by "system" of canals.

Some canals are lined with flagellated, specialized collar cells. The specific, specialized collar cells having flagellum called choanocytes.

These choanocytes line specific areas of certain canal systems; the movement of flagella of the many choanocytes results in the creation of water currents which flow through the sponge. Water enters the canals through tiny, incurrent pores (ostia : dermal ostia) then entering spongocoel; finally passing out of the organism through the osculum.

c) Canal systems - general group of sponges and not true taxonomic group or category.

1) Asconoid : simple type of organization whereby water enters dermal ostia directly to spongocoel; have here very simple tubular (canal-like) structure leading to spongocoel; are not choanocytes within tubular spongocoel. Allows creation of water currents in simple sponges.

2) Sysconoid : canal system where water enters through small dermal ostia into flagellated (choanocytes) radial canals (true canals leading to spongocoel); water leaves through single osculum (excurrent pore). Water currents generation originate within radial canals due to presence of choanocytes. Intermediate level canal organization and complexity.

3) Leuconoid : most complex canal system whereby water enters through dermal ostia into flagellated chambers making up complex systems of canals. Choanocytes therefore line chamber regions of leuconoid canal system to create water currents necessary for moving water and materials eventually into spongocoel.

d) Digestion : water currents bring particulate and soluble "food" into spongocoel where

1) particulate material is phagocytized "engulfed" by specialized digestive cells and "food" is digested intracellularly rather than extracellularly.

2) soluble nutrients are taken up by specialized digestive cells by either simple diffusion (passively) through cell membrane and into cell where they are future metabolized enzymatically; or actively taken up by active transport through cell membrane and into cell for further metabolized.

Transport of metabolized nutrients occurs intercellularly from one cell to another.

e) Reproduction - both sexual and asexual.

1) asexual : bud formation (external; internal) and by regeneration following fragmentation. Free living for short time; will eventually find new location and become sessile.

2) sexual : fusion of "gametes" (gamete-like sex cells) sponges mostly monoecious, having both female/male sex cells within same individual. Sperm (male sex cells) arise from transformation of certain choanocytes into motile sex cells which can fuse with a female sex cell and produce a zygote. Fertilization can occur either internally within individual from which male sex cells were produced, or male sex cells can "swim" to different individual and fertilize female sex cells internally or fertilization can occur externally by release of both male and female sex cells from individuals. Female sex cells usually originate from specialized archeocytes called amoebocytes transformation (primitive cell) cytes = egg (female sex cell).

f) Regeneration and sometic embryogenesis

1) Regeneration : forming two new individuals after cutting one individual into multicellular pieces.

2) Sometic embryogenesis : forming new individual from one cell without sexual fusion of gametes or sex cells. Usually archeocytes will transform developmentally into a immature embryo which undergoes embryo development. Mature embryos will become larvae which are free-swimming and motile; they will find a new location and become sessile.

g) Classification : classes of Porifera phylum

1) Calcarea class : taxon characterized by presence of calcium carbonate spiccules; making up primitive skeletal system.

2) Hesactinellida class : taxon characterized by presence of silicateous spicules (silia containing). Six-rayed.

3) Demospongiae class : silicateous spicules which are not six-rayed (more linear, pointed projection). Some organic material present and holds spicules together (spongin)

4) Sclerospongiae class : massive calcareous skeleton (coral) = coralline sponges.