INVERTEBRATE ANIMALS. 67 



III. Sedentary. The Prawn parasite, Bopyrus, 

 may sometimes be detected under the carapace of a 

 prawn, where the Isopod probably feeds together with, 

 rather than upon, its host. 

 Estimated number of species: recent, 210; British, 42. 



IT Examples of Idotea entomon, from the Baltic, 

 the largest of the Isopods ; Serolis, from the 

 Falkland Islands, resembling a Trilobite. 



Group 165.— Orders L.EMODIPODA. Aai^oc, the throat ; 

 S»V, twice ; ttouV, a foot; and AMPHIPODA: oci/,<p), both- 

 ways ; .Troof , a foot. The species in the former order are 

 few, and possess heads indistinctly separated from the 

 thorax ; hence the first pair of limbs seem to be attached 

 to the throat. The order includes the Skeleton-screw, 

 Spectre-shrimp, and the Whale-louse, Cyamus. From 

 the Isopods the Amphipods differ in having pairs 

 of limbs set to the front and others to the rear. 

 Amongst them are the Sand-hoppers, Talltrus, which 

 occur in millions near the water's edge on sandy coasts, 

 incessantly leaping as if overflowing with the joy of 

 life (Paley). The Coast-screw, Gammarus ; the xylo- 

 phagous Chciura ; and the tube-inhabiting Ccraptis. 

 Estimated number of species : British, 110. 



Division PODOPHTHALMATA. ttovs, a foot; 

 d<f>6aAju,oj, an eye. Eyes on footstalks ; body protected 

 by a carapace. 



Group 166.— Order STOMAPODA. a-TOfxu, a mouth ; ttou?, a 

 foot. Gills external ; pairs of legs, generally seven. The 

 Opossum-shrimps, Mysis, so called from the pouch in 

 which the female carries her eggs, abound in some parts 



