76 
T H E I'ASM A NIA N N ATU RA LI ST. 
form an arrangement somewhat like a lantern, and it is, therefore, often 
•called Aristotle's lanterns. 
A common sea urchin, near Hobart, found often thrown up on the 
beaches is Salmacis , while a very common large one on the Last Coast 
i s Strongvlocen tro tus erith rogra n m us. 
Some sea urchins are, instead of globular, heartshaped (heart 
urchins); there is a common one in the waters of the Derwent (Echino - 
cardium). Others are so flattened as to become pancake-like (‘cake’ 
urchins). 
The members of the class Ophiuroidea , including brittle-stars, also 
exist plentifully around Hobart (Fig. 12). They are much like starfishes 
but their arms are much longer and can move about fairly quickly 
•to allow them to creep over the sea bottom. When caught, most of 
them have a habit of breaking off their arms. If placed in fresh water 
however they die painlessly without injury. They never have more than 
five arms. 
Class Crinoidea , or feather stars, consist of animals which were much 
•more common in past geological ages than now. ’They look like a brittle- 
star or starfish whose arms have been very much branched. They are 
not common in the Derwent. 
In the Derwent are found a number of peculiar animals known as 
Holothuroidea or sea cucumbers (Fig. 11). They are easily recognised 
by their cucumber-like shape. They are related to the starfishes and sea 
urchins, but to a young field naturalist the relation would not be very 
evident. The commonest is probably the beche-de-mer. 
There are a number of different sea cucumbers in the Tasmanian 
joom of the Hobart Museum, all of which have been found in the 
Derwent or close to it. 
Fig. 12. — 
A brittle Star. 
Fig. 13.— 
Nereis (head end). 
Every field naturalist knows that it is hardly possible to move a 
rock on the shore or dig in the sand without finding a number of worms 
besides crabs and other Crustacea; these worms are among the 
•commonest inhabitants of the shore. Perhaps the easiest to obtain is 
the common ‘sand 1 worm or ‘ lob* worm (Nereis)) and a description of 
this will serve to introduce the reader to other more complicated species. 
