;/. TYPES m DETAIL iyiTH THEIR SUBORDINATE GROUPS. 33 



a beak at the anterior end. Ab- 

 domen much reduced. Seven 

 pairs of legs (or fewer), containing 

 the reproductive organs and diver- 

 ticula of the stomach. Special 

 respiratory organs wanting. 



X Phoxichilidium. 



Tardigrada Minute fresh-water animals, known 



as ' ' water bears, ' ' with four pairs 

 of very short legs bearing hooks; 

 hermaphroditic, and without spe- 

 cial organs of circulation or respi- 

 ration. X Macrobiotus. 



Pentastomidea (Linguatulina). . .Worm -like parasites found in the 



lungs and nasal cavities of reptiles 

 and mammals. They resemble 

 Platyhelminthes, but their devel- 

 opment is like that of the Arach- 

 noidea. Legs reduced to two pairs 

 of hooks about the mouth. 



X Pentastomum. 



TYPE VI. ECHINODERMATA. 



A type of marine animals which, in the larval stage, are bilateral 

 and pelagic, but which, after a short larval life, attain through a 

 singular metamorphosis a pentamerous radiate structure. The adults 

 are characterized by the presence of calcareous elements in their in- 

 tegument which show all degrees of development from that of minute, 

 scattered plates to a complete test or shell in which the separate 

 plates are large and in close contact with one another. Locomo- 

 tion is effected by a water-vascular (ambulacral) system which com- 

 municates with the exterior and contains sea-water. 



Class I. HOLOTHUROIDEA Oval or vermiform Echinoderms 



covered by a leathery integument 

 in which are imbedded minute cal- 

 careous plates and spicules. 



