PORIFERA

Six Key Transitions in Animal Body Plan

Evolution of tissues
- exists as aggregates of cells with minimal intercellular coordination

Evolution of bilateral symmetry

- allows parts of the body to evolve in different ways
(organs develop in various locations of body); permits mobility for active lifestyle

Evolution of body cavity

- body cavity allows enlargement of digestive tract for
storage & efficient digestion (exposure to enzymes) ,
- storage for gonads provides for diverse modification of
breeding strategy

Evolution of segmentation
- efficiency in assembling a series of identical
parts; evolved several times in invertebrates

Evolution of molting
- gradual increase in mass is inhibited by hard exoskeletal
material; molting allows periodic shedding off of exoskeleton for growth

Evolution of deuterostome development

- exhibits the basic plan of development; deuterostome
evolved from protostomes

Origins of Porifera
• Animals (including Porifera) belong to Opisthokont that includes fungi and choanoflagellates
• Choanoflagellates, with solitary and colonial representatives, are considered as sister group of
animals
• Basis for relationship: choanocyte cells (= collar cells) resemble choanoflagellate cells
• Sponge is an aggregation of cells held by extracellular matrix

Uses of Sponges
o Cleaning agents
o Applicators of make-up, paint, etc.
o Insulators
o Insoles of foot with discomfort
oTectitethya crypta - source of two chemicals (spongothymidine
and spongouridine) that were used for the development of anti-cancer & anti-viral drugs
Phylum Porifera - Sponges
• Mostly marine, but include some freshwater inhabitants; usually found attached to the
substratum in shallow or deep water.
• They are sessile; permanently attached to the substrate
• Obtain their food by filter feeding

General Morphology
• Internal cavity is called the atrium or spongocoel
• Water is drawn into it through a series of incurrent pores or dermal
ostia present in the body wall into a central cavity and then flows out of the sponge through a
large opening at the top called the osculum.

Body layers
1.The pinacoderm - an outer layer of flattened
cells called pinacocytes
2. An inner lining containing flagellated cells (choanocytes) - draw water in through the pores
and move out through the osculum; also trap food particles that are suspended in the water.
• The water current is also used for gas exchange, removal of wastes, and release of the
gamete
3. Mesohyl - a gelatinous layer that contains several different kinds of wandering cells called
amoeboid cells

Types of Amoeboid Cells:

Archaeocytes - phagocytize food particles;
- can also undergo differentiation to form other cells (totipotent), including cells that produce
spicules and gametes
Myocytes - conducting and contractile cells

The Skeleton
Sclerocytes - cells in the mesohyl that produce the skeleton composed of tiny pointed
structures made of silica or calcium carbonate called spicules
- act as an internal scaffolding and function in protection
Spongocytes - produce skeleton consisting of spongin fibers made of
collagenous material
Collencytes - secrete collagen used as matrix

Types of Sponges (Canal Systems)

A. Asconoid Sponges
• Simple vaselike structure
- puts limitations on size; (increase
in volume without a corresponding increase in the surface area of the choanocytes)
B. Syconoid Sponges
• The flagellated choanocyte layer has undergone folding,
forming finger like projections - a single osculum with more
complex body wall
- water is received through
incurrent canals radial canals spongocoel
• Results in an increase in the surface area which allowed sponges to increase in the size

C. Leuconoid Sponges
• No atrium; several small chambers in which choanocytes are located
- a whole series of incurrent
canals lead to the choanocyte chambers; water is discharged through excurrent canals
• The leuconoid sponges exhibit a significant increase in surface area and are, therefore, among
the largest sponges

Sponge Reproduction
• Most are hermaphroditic or monoecious.
• Exhibit high regenerative capabilities •Sponges can reproduce sexually and asexually
Asexual Reproduction:
a. Regeneration – small fragments or squeezed out amoebocytes aggregate to for the sponge
b. Budding & branching - small outgrowths from aggregations of archaeocytes near surface
(budding); Stolons of sponge grow by branching and successive secondary branching
c. Fission and fragmentation – fission develops and cut off parts that grow into new sponge;
fragment along weak parts during unfavoratble environmental conditions
d. Reduction bodies - rounded balls produced by sponges after disintegration in adverse
environmental conditions
(consists of internal mass of amoebocytes, covered externally by
pinacoderm & spicules)
e. Gemmules – more common among freshwater sponges
(food laden archaeocytes aggregate into a mass and surrounded by archaeocytes; It is secreted
with thick hard chitinous inner layer covered with membrane on surface. Scleroblasts secrete
amphidisc spicules between 2 covering layers.)
- sponges die and disintegrate in autumn, leaving gemmules to
survive winter; gemmules hatch in summer when water is abundant

Gemmules are dormant stage; resistant to desiccation, freezing, and anoxia

Requires to undergo vernalization (period of low temperature)
before gemmules hatch into new sponge.

Sponge Reproduction (Sexual)

-Sex cells are produced by archaeocytes or choanocytes; egg
& sperm are produced at different times to avoid cross fertilization
-Sperm leaves a sponge via the osculum by the currents generated from the choanocytes. It
enters thru ostia and reach the mature ova in the mesohyl.
Fertilized eggs develop into ciliated free-swimming larvae
called parenchymula larvae

Sponge Taxonomy
Class Calcarea (Calcispongidae)
• Only sponges that possess spicules composed of calcium
carbonate.
• Spicules are straight or have 3-4 rays, and do not have hollow axial canals.
• Today, their diversity is greatest in the tropics, predominantly in shallow waters

Class Hexactinellida (Hyalospongiae)

• Glass sponges; characterized by siliceous spicules consisting of six rays
intersecting at right angles
• Widely viewed as an early branch within the Porifera

Class Demospongiae
• Greater than 90 percent of the 5,000 known living sponge
species are demosponges.
• Demosponge skeletons are composed of spongin fibers and/or siliceous spicules
• Siliceous spicules with one to four rays not at right angles, All members express the leuconoid
body form

Class Homoscleromorpha
• Recently separated from Class Demospongiae
• Inhabit marine waters, particularly cryptic areas, thus often overlooked; though common
nearshore
• Unique features:
a. Pinacoderm with true basement membrane
b. Cells are connected to each other
c. Cells are attached to the extracellular matrix through adherens cell junction
d. Has two clades:
- without spicules,
- with spicules that do not form
around a longitudinal axial filament
Class Homoscleromorpha
__________________________
Phylum Placozoa
• A multicellular, transparent, amorphous organism • Mobile: partly planktonic and
flagella-ameboid
• Flat bodied, consisting of 2 distinct layers

Types of Placozoan cells

-Ventral side consists of two cell types: cylinder cells (column-shaped, with cilia) gland cells
(associated with enzyme production)
-Dorsal side consists of cover cells (flattened, ciliated)
-Fiber cells (star-shaped), fill space between two tissue layers; form thin extensions to connect
with other fiber cells (coordinate movements)

- ventral layer of flagellated columnar cells, associated with glandular cells (=endoderm)
- upper layer is thin, with flagellated cells (= ectoderm) - a fluid-filled space containing a dense
network of
fibrous cells
• Feeding of Chlorella (Chlorophyta) involves direct digestion by enzymes (extracellular)
• Asexual Reproduction : budding, fragmentation, binary fission; high regeneration capability
• Sexual Reproduction: produces 1 oocyte and an embryo (occurs with high population density
causing
placozoa to degenerate)