Marine Biology Phylum Porifera (means pore-bearer)
I.
Characteristics and Structure
A. General Characteristics
1. Sponges - animals with many pores, which contain no definite symmetry and they do not contain
organs or true tissues.
a. Intracellular digestion occurs in Food Vacuoles.
b. There are no Respiratory or Excretory organs, these functions are performed by simple diffusion,
(which means that substances (food, oxygen, or waste products) move from areas of higher
concentration to areas of lower concentration).
c. Sponges are the most primitive multicellular animals.
d. There bodies are a mass of cells embedded in a gelatinous matrix, and stiffened by tiny skeletal
structures called Spicules
2. Sponges are at least 500 million years old, dating back to the Cambium Period or before.
Aristotle was the first to recognize sponges as animals, but it was not until the microscope
that we really knew more about them
3. All adult members of the Porifera Phylum are sessile (Attached to the substratum), they are all
aquatic, and most live in the marine environment.
4. Classification - sponges are classified by the skeletal system (types of spicules) which is the only
true system they contain.
a. They normally need a hard substrate to attach, but some can burrow into the sand and mud bottoms
to grow
b. They are most commonly found in shallow water
c. They can grow on other living organisms, like mollusk shells, coral, crabs (decorator crabs will put a
piece of sponge on their carapace to grow and help camouflage them)
5. There are 2 important purposes the sponges serve:
a. They serve as habitats (hiding places) for all types of larval forms. (This is a commensalistic
symbiotic relationship, where one organism benefits and the other organism neither benefits nor
is harmed)
b. They filter and clean the water as they pull it in and through their bodies
B. Structure - They vary greatly in size, shape, and color
1. Some have radial symmetry, but most are irregularly shaped
2. They conform to the substrate: Some stand erect, some lobed or branched, some are encrusting, and
some bore holes into shell or rocks
3. Colors include greens, yellows, reds, purples, and blues, in shallow waters, and mostly gray and
brown in deeper water
4. There are different shapes and colors even within the same species
II. Form and Function
A. Body openings - The only body openings of these unusual animals are pores
1. Dermal Ostia (Incurrent Pores) - Water enters the animal through a multitude of these tiny pores.
2. Oscula (Osculum, singular) ( Excurrent pore(s) for water outflow. One to many, and larger than the
incurrent pores.
3. Spicules - the skeletal structures of the sponge, act like skeleton to give the sponge support
a. These structures prevent the collapse of the canals of the sponge
b. Depending on species, spicules or the support system of sponges can be one of the following, or a
combination of all of these:
● needlelike Siliceous Spicules,
• Calcareous spicules –Calcium carbonate
• a meshwork of organic Spongin fibers,
4. Spongocoel - The inner chamber(s) of the sponge. This is where food and oxygen are extracted from
the water
B. Types of Cells –
Mesohyl (also called Mesoglea or Mesenchyme): Most sponge cells are loosely arranged in this
gelatinous matrix The Mesohyl is the "connective tissue" of sponges.
1. Pinacocytes (Epidermal cells) - These are thin, flat cells that cover and protect the
exterior and some interior surfaces.
a. Some are "T" shaped, with their cell bodies extending into the Mesohyl
2. Myocytes - Contractile Pinacocytes
a. Are usually arranged in circular bands around the Dermal Ostia and Oscula
b. They help regulate the rate of water flow into and out of the sponge
3. Choanocytes - (Flagellated "Collar Cells") - Ovoid cells with one end embedded in the Mesohyl and
the other exposed to the water: They main two functions are dealing with water circulation and food
gathering.
a. The exposed end bears the flagellum surrounded by a collar
b. The openings in the sponge are connected by a system of canals, some of which can be lined with
these cells.
c. The Flagella maintain a current of water through the canals
d. Micro fibrils connect each choanocyte so that the collar forms a fine filtering device for straining food
particles from the water: The beating flagellum pulls water through the sieve like collar, and forces it
out through the open top of the collar so that food can gathered and passed on to neighboring
Archaeocytes (Amoebocytes) for digestion.
e. Particles too large to enter the collar cells become trapped in secreted mucus and slide down the collar
to the base where they are Phagoctized.
4. Archaeocytes (Amoebocytes) - The "Workhorses" of the sponge
a. Archaeocytes are located in the mesohyl, (gelatinous matrix), along with other specialized sponge
cells including collenocytes and structural elements called spicules. They move about within the
mesohyl with amoeba-like movements performing a number of important functions.
b. Cellular differentiation is an essential function of the archaeocyte.
c. All specialized cells within the sponge have its origins with the archaeocyte. This is especially
important in reproduction as the sex cells of the sponge in sexual reproduction are formed from
these amoeboid cells.
d. Similarly in asexual reproduction amoebocytes result in the formation of Gemmules which are
cyst-like spheres containing more amoebocytes as well as other sponge cells including the
phylum specific choanocyte.
e. They can Phagocytize particles at the external epithelium and receive particles for digestion from
the Choanocytes.
f. They carry food and oxygen to the Epidermal cells (Pinacocytes), and Pore cells (Myocytes)
g. They can also differentiate (change) into any of the following types of more specialized cells in
the sponge:

Sclerocytes - secrete they skeletal structures (Spicules)

Spongocytes - secrete spongin fibers of the skeleton

Collenocytes - secrete fibrillar collagen
C. Types of Canal Systems - Most sponges fall into one of the three types, based on their canal Systems Asconoid, Syconoid, or Leuconoid
1. Asconoid - Simplest type of organization. Small and tube shaped
a. water enters through microscopic dermal pores into a large cavity
called the Spongocoel, which is lined with Choanocytes
b. water is pulled in through pores by choanocyte flagella and expelled
through single Osculum
c. slender tubular individuals grow in groups attached by a common
stolon (stem) in shallow water
d. found only in class Calcarea
2. Syconoid - Larger but looks much like the Asconoids: Tubular body and
single Osculum
a. Body wall much thicker and more complex than the Asconoids
b. Receive water through incurrent canals that deliver it to the
choanocyte lined radial canals, which empty into the
Spongocoel
c. Spongocoel is lined with epithelial type (Pinacocytes) cells
rather than Choanocytes
d. Found in class Calcarea
3. Leuconoid - Most sponges are of the Leuconoid type, and they
occur in all classes
a. Possession of the Leuconoid plan makes possible a much larger body due to an increase in
complexity and efficiency of the water pumping system
b. Most Leuconoids form large colonial masses, each
member of the mass having its own Osculum
c. Clusters of flagellated chambers are filled from incurrent
canals and discharge waster into excurrent canals that
eventually lead to the Osculum
D. Sponge Feeding - Sponges feed primarily on particles suspended in the water pumped through their
canal systems
1. When this a large amount of suspended food in the water, sponges will close up pores for digestion
2. Detritus particles, planktonic organisms, and bacteria are consumed nonselective
a. Pinacocytes may phagocytize particles at the surface, but most of the larger particles are consumed
in the canals by Archaeocytes that move close to the lining of the canals
b. The smallest particles are phagocytized by the Choanocytes
3. Intracellular digestion occurs within food vacuoles, performed by Archaeocytes
4. Pinocytosis - sponges consume a significant portion of their nutrients in the form of organic matter
dissolved in the water circulated through the canal system
5. All life activities of the sponge depend on the current of water flowing through their body:
a. Feeding
b. Respiration (obtaining oxygen)
c. Waste removal
d. Sexual reproduction
E. Reproduction and Development - All sponges are capable of both sexual and asexual reproduction.
1. Most are Monoecious (Hermaphroditic) and have both male and female sex organs in one
individual
2. Some are Dioecious and have separate sexes
3. Sexual Reproduction a. Ova are fertilized by motile sperm in the Mesohyl
b. In the Mesohyl the zygotes develop into flagellated larvae, which break loose and are carried away
by the currents
c. The ciliated larvae swim with the other Meroplankton, then settle, become attached, and grow into
adults
4. Asexual Reproduction – Asexual budding is the most common form of reproduction. The external
buds that can detach or remain to add on to the colony
5. Gemmules - packets of 3 types of cells (encapsulated Archaeocytes) which can be produced during
unfavorable conditions
a. More common in freshwater species, some marine
b. These internal buds are produced asexually
c. They can survive periods of drought or freezing temperatures
d. Later, with favorable conditions for growth, the Archaeocytes in the Gemmules will escape and
develop into new sponges
III. Sponge Classes - They are classified according to the type of Skeletal structures (Spongin or Spicules)
they contain
A. Class Calcarea (Calcispongiae)
1. Have spicules of calcium carbonate that often form a fringe around the Osculum
2. Spicules are straight monaxons (needle-shaped) or three or four rayed
3. All three types of canal systems are seen in this class
4. All are marine, and tend to be small
5. Most are drab, but a some bright colors exist
6. Ex: Sycon, Leucosolenia, Clathrina
B. Class Hexactinellida (Hyalospongiae)
1. Glass sponges have six-rayed siliceous spicules extending at right angles from a central point
2. Spicules often united to form exquisite glasslike latticework (they differ dramatically in structure
from other sponges)
3. There body is often cylindrical or funnel shaped and adapted to the slow, constant current of the sea
bottom
4. There is little Mesohyl and they do not have Myocytes (contractile cells)
5. Flagellated chambers in simple Syconoid or Leuconoid arrangement
a. Archaeocytes have limited motility
b. Choanocytes have no nuclei
6. The Venus Flower Basket (Euplectella) is a classic example of this class
C. Class Demospongiae
1. Comprise approximately 80% of all sponge species including most of the larger sponges
2. Their skeletons may be siliceous spicules, spongin fibers, or both
3. All members of the class are Leuconoid, and all are marine except one family
4. Vary both in color and in shape: They can be encrusting, tall and fingerlike, or shaped like fans,
vases, cushions, or balls
5. Loggerhead sponges may grow several meters in height and diameter; They are the largest species of
sponges
6. Some are Boring Sponges, that penetrate and excavate molluscan shells and coral skeletons
7. The Bath sponges belong to the group called Horny sponges, which have only spongin skeletons
a. They can be cultured by cutting off part of the sponge, cleaning and drying
b. It takes many years for them to grow to a good market size
8. Ex: Cliona (boring sponge), Spongilla, Myenia, and all bath sponges
D. Class Sclerospongiae
1. Small group of sponges that secrete a massive basal skeleton of calcium carbonate, and are thus
often called Coralline Sponges
2. Leuconoid organization and siliceous spicules and spongin in most
3. Live in caves, crevices and other cryptic habitats on coral reefs or in deep water
4. Ex: Astrosclera, Calcifibrospongia