412 



CHARACTERS OF INVERTEBRATE ANIMALS 



Lobster {Palinurus vulgaris) (fig. 251), Norway Lobster {Nepkrops 

 Norvegicus), Prawn {Palcemon serratus), Shrimp [Crangon vul- 

 garis). The Crayfish {Astacus fluviatilis) is a fresh- water form. 



Fig. 251. — Kock-Lobster {Palinurus vulgaris] 



Another section, including forms intermediate between the 

 above and Crab, is formed by the Hermit-Crabs (fig. 252), which 



take up their abode in the empty shells of 

 various sea-snails, and possess a soft un- 

 symmetrical tail that has lost most of its 

 appendages except the last pair. These 

 have lost their original function of acting 

 as swimming organs, and are modified 

 into hook-like structures, by which the 

 hermit-crab holds on to its house. 



The last section of the Decapods 

 includes the true Crabs (fig. 2 50), in which 

 the cephalo-thorax is very broad, and the 

 tail so much reduced as to be useless 

 as a swimming organ. Among British 

 species may be noted the Edible Crab 

 {Cancer pagurus) and the Shore Crab {Carcinus mosnas). 



2. The Opossum-Shrimps (Schizopoda) are small marine forms 



Fig. 232.— A Hermit-Crab [Pagurus 

 Bernhardjts), removed from its dwelling 



