Key words
cilium
gamete
life cycle
osculum
substrate
Kingdom Animalia:
Porifera
Typical poriferan
Colony of ascon-type sponges: external view
Invertebrates
●
osculum
The Porifera or sponges are a primitive
group of invertebrates. In many ways
they look like plants in that they
cannot move themselves and spend
most of their life cycle attached to a
firm substrate. There is some
differentiation within the body,
although they do not show the range
of cell types present in higher animals
Ascon-type sponge: partially sectioned
osculum
spicule
choanocyte
Body structure
The outer surfaces of Porifera are
covered with thin, flattened cells called
pinacocytes. Porocytes (cells with
pores) located all over the body allow
water into the sponge. Because their
bodies are hollow, their structure is
supported by a soft network of fibers
called spongin and/or by hard particles
called spicule, which protect the
animal. Between the outer body and
the spongocoel (the central cavity) is a
gelatinous layer called the mesohyal.
● Within the sponge, choanocytes, cells
fringed with cilia, force water through
the spongocoel, bringing in nutrients
and removing waste. Ameobocytes
take food to other cells. Water leaves
the sponge through a large pore,
usually at the top of the body, called
the osculum. The mechanism is very
efficient, with some sponges
processing 20,000 times their own
volume of water in 24 hours.
●
Reproduction
© Diagram Visual Information Ltd.
●
Sponges reproduce sexually and
asexually. Male gametes are released
into the inner space and pass out
through the osculum. These
sperm are collected by other
sponges, and female gametes are
fertilized internally. Sponges can also
reproduce asexually through the
production of buds.
porocyte
spongocoel
pinacocytes
mesohyal
amebocyte
pinacocytes