74 
THE TA SM AN I AN N ATU R A LIST. 
which are capable of producing a somewhat painful sensation as many 
surf-bathers know to their cost 
Fig. 7. — Vertical section of sea anemone showing mouth (w) ; gullet (jj) ; internal 
cavity (*■), and a tentacle (/). 
Fig. 8 . —Cross section of sea anemone showing the twelve vertical partitions (///) inside. 
Up one side of each of these runs a muscle which serve to contract the 
body of the animal. 
Fig. 9. — A Jellyfish. 
Rather different externally from the rest of the phylum are the 
members of the group Scyphozoa^ or jelly fishes. Here the animal is 
like a zooid which has become flattened out and curved into an umbrella 
shape (Fig. 9). In centre of underneath surface of the umbrella is the 
mouth which leads as in all other Coclenterata to an internal digestive 
cavity. The tentacles hang round the margin of the umbrella. The 
margin of the umbrella is turned in to form a flange or rim which 
contracts rhythmically and causes the jelly fish to move through the water. 
The next Phylum is that including a great number of flat worm-like 
animals called the Platodes (flat-worms). This group includes certain 
peculiar worms found in the sea, on damp ground, and as parasites in or 
on various animals, but as they are not of great importance from the 
point of view of the young field naturalist we will not discuss them 
further. 
A very important, large and common group of animals is included 
in the Phylum Echinodermata (spiny skinned animals). In this group 
we include starfishes, brittle-stars, sea-urchins (‘sea eggs’) feather-stars 
and * sea cucumbers.’ 
Each of these groups of animals forms a part of the phylum 
Echinodermata known as a class. We will consider first the class 
Astcroidea (star fishes). 'These are very common in the Derwent Estuary, 
two of the commonest being Pentagon as ter australis and Asterina exigua, 
found at low water mark nearly everywhere. For description we will 
take the former (there are some specimens in the Tasmanian Museum). 
The starfish is a flat, five-armed animal, which creeps on the surface of 
rocks, stones, &c. In the middle of the creeping surface is the mouth, 
and from this opening radiate five grooves along the centre of each arm. 
If one of these grooves be examined in a living starfish it will be found 
to contain two rows of moving tube-like processes, each ending in a 
swollen sucker-like extremity. These are the tube feet. By means of 
