these notes provide a comprehensive summary of cnidaria in a clear and easily understandable way. These notes include information from past exam papers and will enable you to succeed at zol1501
Phylum Porifera: sponges
Most animals move to search for food, but a sessile sponge draws food and water into its body instead. A sponge
uses a flagellated collar cell, the choanocyte, to move water. The beating of many tiny flagella, one per choanocyte,
draws water past each cell, bringing in food and oxygen and carrying away wastes. Their body is designed as an
efficient aquatic filter for removing suspended particles from the surrounding water. Sponges clear many litres of
water and are primary consumers in their ecosystems. They are mostly marine and are abundant in all seas and at all
depths. Sponges vary in size. Many sponges are brightly coloured due to pigments in their dermal cells. Although
their embryos are free-swimming, adult sponges are always attached to a substrate, bored into sand or mud. Their
growth patterns often depend on the shape of their substratum, direction and speed of water currents and
availability of space.
Characteristics of Phylum Porifera:
Multicellular. Body made of many cell types, some of which are organised into incipient (beginning to develop) tissues
Body with pores, canals and chambers that form a unique system of water currents
Mostly marine, all aquatic
Radial or no symmetry
Outer surface of flat pinacocytes
Most interior surfaces lined with choanocytes that create water currents
Gelantinous protein matrix called mesohyl contains amebocytes and skeletal elements
Skeletal structure of fibrillar collagen (a protein) and calcareous or siliceous crystalline spicules, often combined
with modified collagen (spongin)
No organs or true tissues
Intracellular digestion
Excretion and respiration by diffusion
Sessile and attached to substratum
Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm. Free-swimming
flagellated larvae in most
Form and Function:
Feeding:
- Sponges feed mainly by collecting suspended particles from water pumped through internal canal systems
- Water enters canals through pores in the outer layer of cells, a pinacoderm
- Inside the body, water is directed past the choanocytes, where food particles are collected on the choanocyte
collar
- The collar has many finger-like projections, called microvilli
- The use of the collar as a filter is one form of suspension feeding
- Particles are taken in by phagocytosis
- Sponges may also absorb dissolved nutrients from the water
Types of canal systems:
Asconoids:
- Simplest organisation
- Sponge draws water in through microscopic dermal pores by the beating of many flagella on the choanocytes
- These choanocytes line the internal cavity, called the spongocoel
- As the choanocytes filter the water and extract food particles from it, used water is expelled through a single
large osculum
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