THE TASMANIAN NATURALIST 
75 
these the starfish moves. By a special contrivance in the interior of the 
animal the tube foot can be lengthened in any direction until they meet 
some firm body, the suckers then take hold, the tube leet shorten and so 
the animal is pulled along. The starfish is enclosed in a firm skeleton 
made up of a number of plates fitting together so that the whole body 
is flexible. Most of these plates have spines connected with them, 
especially along the tube feet grooves. The stomach of the starfish can 
be protruded through the mouth to enclose any piece of food and then 
withdrawn into the body. 
Asterina exigua is a small starfish, common on the rocks along the 
Domain near Government House. 
Another common starfish near Hobart is Asterina calcar , which 
has eight arms instead of five. 
Fig. 11.— 
A Sea Cucumber. 
Fig. 10.— 
A Starfish, from the lower side. 
The second class includes the sea urchins class, Echinoidea. These 
are also common about Hobart These differ from the starfishes in 
being globular in shape. They are covered with spines. When we 
remove the spines we have a somewhat ball-shaped body left called the 
corona, which is perforated by two large holes, a lower larger one, the 
mouth, and an upper smaller one. The corona is formed of plates 
tightly fitted together. Altogether there are twenty rows of these plates, 
each row extending round the corona, from the lower to the upper 
opening. All the plates are studded with rounded elevations or tubercles, 
to which the spines are fitted by ball and socket joints. If we carefully 
examine the plates we find that some of them are perforated by minute 
holes. These holes are for the protrusion of tube fee*. Two rows of 
these perforated plates are together, then occur two rows of unperforated 
plates, then two rows of perforated plates, and so on. Thus there are 
five perforated regions and five unperforated regions. 
Another peculiar feature about the sea urchins is the presence of a 
set of five teeth the points of which are seen to project through the 
mouth in the living specimen. These teeth are not firmly attached to 
the skeleton of the animal but may be easily removed if the shell be 
broken. The five teeth together with the small bones connecting them. 
