MARINE BIOLOGICAL STATION AT PORT ERIN. 99 



CRUSTACEA. 



(Figs. XII. to XX.) 



Crustaceans are animals such as crabs and lobsters, 

 shrimps and prawns, sand-hoppers and barnacles, along 

 with innumerable smaller forms, " water-fleas " and the 

 like, which abound in almost all parts of our seas. They 

 all have segmented bodies and jointed legs, and a hard 

 shell or covering to the body. They are, then, " shell- 

 fish " of a kind, but they differ from the true shell-fish, 

 such as oysters and periwinkles, in having segments and 

 legs. Once the difference has been pointed out, no one 

 can mistake a shrimp-like shell-fish for a cockle-like shell- 

 fish : the former are Crustaceans and the latter Molluscs. 

 It is better to reserve the term shell-fish for the Molluscs. 

 Among the most abundant of lower Crustaceans are the 

 rock-barnacles or acorn shells {Balanus) which are so 

 abundant on rocks round our coast, and which by their 

 white limy shells closely placed on the dark grey rock of 

 Bradda Head give at low tide the appearance of a belt of 

 whitewash encircling the base of the cliff. The ship- 

 barnacle (Lcpas) is closely related to Balanus. Its home 

 is on the open sea, but specimens are occasionally drifted 

 in to Port Erin. Once we captured a floating ship's 

 bucket, which was covered inside and out with adhering 

 barnacles, some large and some small ; and on another 

 occasion two large logs came ashore in the bay bearing 

 great fringes of living ship's barnacles hanging from 

 their sides. 



Most of the lower Crustacea (or Entomostraca), unlike 

 the barnacles, are free-swimming; and from their small 

 size, somewhat insect-like appearance and legs, and their 



