1. Class Hydrozoa
Water animals

10. • The Hydrozoa include solitary or colonial
cnidarians, which have a noncellular
mesoglea, lack tentacles within the
gastrovascular cavity, and have no gullet.
• It comprises 3 major orders containing
fewer than 3,000 species which are mosly
marine.

11. Order Hydroida
Phylum: CNIDARI
Class: HYDROZOA

12. • Two common hydroids in rockpools around Sydney.
Both are members of the Leptomedusae with the polyps
protected by hydrothecal cups. The triangular structures
in right colony are the cups protecting individual polyps.
Size: Left - each erect frond aprox 10mm. Right - each
branch approx 5mm.

13. • Marine hydroids usually exist as colonies,
the polyps are protected by a horny
perisarc which.
• The colony can either be a branching
sessile structure attached to the substrate
or it can have erect fern-like 'fronds' with
microscopic polyps arranged along the
individual branches.

14. There are two major suborders of hydroids:
S.O. Anthomedusae.
The polyp is not protected by the
exoskeleton which stops at the base of the
polyp. (Also known as 'gymnoblastic
hydroids' or Athecata)
S.O. Leptomedusae.
Both the polyp and specialised gonad
structures are protected by exoskeleton
cups. (Also known as 'Calyptoblastic
hydroids', Thecata).

15. • All hydroids are carnivorous animals,
catching prey in the water column with the
aid of stinging and grappling nematocysts.
• Aeolids and some dendronotaceans, such
as Doto, prey on most families of hydroids,
and in most cases each nudibranch
species specialises on one or a few
species of hydroid.

16. Order Siphonophora
• These are the pelagic colonies of
hydrozoa which either drift on the ocean
surface or pulsate through the midwater.
• The best known is Physalia, the Portugese
man-o-war. A modified free-floating polyp
develops into a large gas-filled float from
which other polyp and medusiod
individuals are produced by budding.

17. • These threads of tiny
hydroids can reach
lengths of more then
30 meters!
• Each individual is
approximately 1 cm.
Physalia, the Portugese man-o-
war

18. The Hydrocorals
• Are colonial hydrozoans that have a hard
calcified supporting skeleton.
• The millepore hydrocorals are commonly
known as fire or stinging corals (they can
inflict a serious sting).
• Hydrocorals are essentially warm water
animals
Order: MilleporinaStylasterina.

19. Distichopora violacea, Red Sea

20. Class Anthozoa
Flower animals

21. Anatomy of a polyp. These animals have an
almost plant-like appearance, being anchored in
place.

22. • Anthozoans are exclusively marine,
polypoid cnidarians.
• the largest class of cnidarians, containing
over 6,000 species.
• A gullet extends for a short distance into
the gastrovascular cavity, and septa are
present, which increase the surface for
digestion and absorption.
• Anthozoans are colonial or solitary
organisms.

23. Subclass Alcyonaria
• includes almost universally colonial
organisms in which each of the polyps, or
hydroid members, has eight feathery
tentacles.
• Most of them produce a skeleton, and
many make some contributions to
coral reefs.
• While some are found in temperate seas,
they are especially common in subtropical
to tropical regions.

24. • The organ pipe coral (Tubipora), a soft
coral (Alcyonium), the Indo-Pacific blue
coral (Heliopora), and the sea pens, which
have a stalk extending into the bottom
mud or sand, are some typical alcyonarian
corals. Horny corals, of the order
Gorgonacea, are perhaps the best known.

25. Sea-Pens

26. Subclass Zoantharia
• includes both solitary and colonial forms,
in which the polyp has more than eight
tentacles.
• The solitary sea anemones belong here,
in the order Actiniaria, characterized by
the lack of a skeleton.

27. • The stony corals so important in forming
coral reefs belong to the order
Madreporaria; they are especially
characterized by their calcium carbonate
exoskeleton, marked by many cups for the
polyps, each of which contains stony
septa dividing the gastrovascular cavity
into compartments.

28. • The shape of coral skeletons depends on
the pattern of growth of the colony.
Ufelina