Phylum Porifera
Latin name pore-bearing
Animals of Phylum Porifera are commonly known as sponges.
This Phylum contains
about 5,000 - 9,000 living species.
• Poriferans (sponges) are the simplest metazoans
(multicellular animals).
• Their bodies are composed of loose assemblage of
cells (cellular level of organization).
• They do not possess germ layers
• They lack true tissues, organs or appendages.
• Digestion intracellular; Excretion and respiration by diffusion
Defining characteristic:
Microvillar collars surround flagella, with units arising from
either single cells or syncytia
Phylogeny
Porirefans (sponges) are believed to have evolved from
Choanoflagellates.
Choanoflagellates are the freshwater colonial protozoans
(Phylum Choanozoa), having only protoplasmic level of
organization.
They bear very definite morphological similarities to the
simplest sponges.
•
An early branching event in the history of animals
separated the sponges from other metazoans.
• They are offshoots of the main evolutionary paths seen in the
animal kingdom; (they represent an evolutionary dead-end).
• Phylogenically poriferans are distinct from other eumetazoans. ie.
Cellular layers possess by poriferans are not homologous to the
germ layers of the Eumetazoa; they do not possess a developmental
patterns in line with the other eumetazoa.
• Therefore, many Zoologists in the past have grouped
Poriferans in a separate Subkingdom- Parazoa –
almost/besides animals)
• Fossil sponges are among the oldest known animal
fossils, dating from the Late Precambrian to early mid
Cambrian (~530-570 million years ago).
Phylum Porifera, Class Demospongia
Early MidCambrian (~525 million years ago)
• Recent molecular evidence show that,
Poriferans are more closely related to other
metazoans (Eumetazoa) than any other living group.
• Based on molecular data, poriferans are now
considered to represent the ancestral body plan of
all animals:
• Sponges are aquatic animals (exclusively aquatic)
-most (98%) living in marine (salt water)
They are present in all seas and at all depths.
• -about 100 species (2%) live in fresh water habitats.
Spongilla
• Adults are sessile. They are attached to surfaces of rocks,
dead coral, or other suitable substrates.
• They are either solitary or branched to form colonies.
• Shape, colour and size of the sponge body vary greatly.
Loggerhead sponge – a colony
2m
• Generally they are asymmetrical and vase-shape.
• There are several types of cells found in poriferan body.
1. pinacocytes
2. porocytes
3. choanocytes are found only in poriferans
4. amoebocytes (archaeocytes)
• Each cell type possess specialized functions
(division of labour).
• Porocytes are pore (ostia) bearing cells through which
water enters into the central cavity called spongocoel.
• Therefore, porocytes make the body wall perforated.
Pinacocytes are flat cells that form the outer body
layer.
Choanocytes are flagellated cells (collar cells) that
line the inner cavity/chamber (spongocoel).
In between these two cell layers is the mesohyl (non
living).
(assemblege of cells embedded in a gelatinous
matrix, and supported by a skeleton of minute
needle like spicules and protiens -spongin)
The beating of the flagella of choanocytes draws water
into the animal and it expels through a large opening,
the osculum.
• Small food particles suspended in the water current are
captured by the action of the collars on the choanocytes.
• The particles are ingested by phagocytosis .
• Digestion is intracellular.
• Nutrients are distributed around the body by mobile cells
called Archaeocytes(amoebocytes).
• Sponges have three different types of body plans;
• Asconoid
• syconoid and
• leuconoid,
• This is in order of increased degree of evagination of the
choanocytes from the spongocoel, increasing the extent
of flagellated surface area enclosed by the sponge.
1. Asconoid
FLAGELLATED SPONGOCOELS – simplest type
-small, tube shaped sponges
• water enters through microscopic dermal pores
(ostia)into large cavity (spongocoel) lined with
choanocytes.
• water expelled through single large osculum
eg. Leucosolenia
Leucosolenia
2. Syconoid
FLAGELLATED CANALS
• larger than asconoids (but similar shape - tubular)
body wall thicker and folded
• water enters through dermal pores (ostia), to incurrent
canals, then RADIAL canals lined with choanocytes, and
empty into spongeocoel (not lined with choanocytes)
• water expelled through single large osculum
eg. Scypha (Sycon)
• Scypha (Sycon)
3. Leuconoid
• FLAGELLATED CHAMBERS
• most complex organization.
• They form large colonial masses; each member of the
colony having its own osculum
-water enters through dermal pores, to incurrent canals,
to chambers lined with choanoytes
-water discharged to excurrent canals, lead to osculum
-MANY oscula
-NO SPONGOCOEL
ex Euspongia
*Greatest surface area: volume
Loggerhead sponge
• Mesohyl is rich in protein (spongin) – a collagenous fibers
and spicules.
• Sponge body is supported by this hard skeleton
• Spicules are made of silicon dioxide(siliceous), calcium
carbonate (calcareous)).
Sponges are placed into three taxonomic classes based
on the chemical composition of their spicules/skeletons.
Class Calcarea
Class Demospongiae
Class Hexactinellida
Class Calcarea - (Calcispongiae) (calcareous sponges)
spicules made of CaCO3 Mono, three or four rayed
Small sponges
marine
vase/tube like body
All asconoids- Leucosolenia
Some syconoids – Schypa
Some leuconoids
Class Demospongiae - (demosponges)
skeletons made from protein (spongin) fibers
or SiO2 (Si dioxide) – not 6 rayed
or both sponging & SiO2
Only leuconoids
eg. Euspongia- marine,
Spongilla - fresh water
Class Hexactinellida – (Hyalospongiae)
skeletons composed of silicon dioxide (glass sponges)
6 rayed siliceous spicules
Deep sea sponges
syconoids and leuconoids
eg. Euplectella –syconoid/leuconoid arrangement
The Venus’ flower basket
Oscular sieve
(Fused siliceous spicules)
Ledges of Si
spicules project
out from cylinder
forming parietal
gaps
Curved,
cylindrical thin
body
Inside is spongocoele
Root spicules
• Reproduction
1. Fragmentation and regeneration:
• Sponges can reproduce asexually when they are fragment
by water disturbances or by predator actions and pieces
of the sponge grow into new individuals.
2. Gemmule formation (Internal budding)
3. Sexual reproduction
• Most are hermaphrodites and a single individual
releases eggs and sperm.
• A ciliated larval stage (amphiblastula) develops from
the zygote and is free swimming, allowing dispersal
of the species from one location to another.
It is little more than a developed blastula and looks
very different from the mature sponge that it will
produce.