CHAPTER VII 



THE LEPTOSTRACA 



SERIES LEPTOSTRACA, Claus (1880). 



DIVISION PHYLLOCARIDA, Packard (1879). 



Order Nebaliacea. 



Definition. To the characters mentioned on p. 148 as distinctive 

 of the series the following may be added : Carapace present ; all 

 the thoracic somites distinct ; eyes pedunculate ; mandible with- 

 out lacinia mobilis ; no oostegites ; first four pairs of abdominal 

 appendages biramous, with appendix interna, last two pairs reduced ; 

 hepatic caeca few ; heart elongated ; development embryonic, young 

 set free at a late stage. 



Historical. The first-known member of the Leptostraca was 

 the Cancer bipes of 0. Fabricius, described from Greenland. Leach, 

 who in 1815 established the genus Xebalia, placed it among the 

 Macrura, but H. Milne-Edwards, while admitting its affinities with 

 Mysis, ranked it as a Phyllopod, and this view was long and widely 

 held. Metschnikoff in 1865, from a study of its development, 

 replaced the genus among the Malacostraca as a " phyllopodiform 

 decapod." Claus, in a series of memoirs ending with his exhaustive 

 monograph of 1889, vindicated the title of Nebalia to rank as a 

 Malacostracan, and placed it in a group Leptostraca, alongside the 

 Arthrostraca and Thoracostraca. The resemblance of certain fossil 

 Crustacea to Nebalia had long been recognised, and Packard in 

 1879 proposed the name Phyllocarida for the group, including the 

 living and fossil genera. Sars has called attention to the similarity 

 in general form between Nebalia and certain Copepoda, but Claus 

 showed this resemblance to be merely superficial. 



MORPHOLOGY. 



The carapace (Fig. 87) is compressed laterally so as to form a 

 bivalved shell (though without any definite hinge-line), loosely 

 enveloping the thorax and more or less of the abdomen, and quite 



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