152 CTENOPHORA 



Key to the orders of Tentaeulata : 



Oj Bodj' more or less jilobose or cjiindrical. 



&i Long tentacles present 1. Cydippida 



&o No tentacles in adult animal ; oral lobes present 2. Lobata 



Cj Body compressed and ribbon-like 3. Cestida 



Order 1. CYDIPPIDA. 



Body spherical or ejdindrical or compressed in the plane transverse 

 to the tentacular axis; tentacles very long, on opposite sides of the 

 body, springing each from a deep pocket: several families. 



Family PLEUEOBEACHIIDAE. 



Body spherical or ovoid, with the 8 ribs of eqnal 

 length: 4 genera. 



1. Pletjrobrachia Fleming. Body but very little 

 compressed ; combs rather long but not reaching the oral 

 or aboral areas: about 8 species. 



P. pileus (Fabricius) (P. rJiododactyla Agassiz; P. 

 bachei A. Agassiz) (Fig. 249). Body about 20 mm. long 

 and 18 mm. wide, and veiy transparent; tentacles about 

 15 cm. long and white or rose-colored, Avith long pinnae: 

 from the south side of Long Island to Greenland; breeds 

 in August and September; Europe; Pacific T3oast. 



P. brunnea Mayer. Body 12 mm. long, ovoid ; stom- 

 ach of an opaque yellowish-brown color; each tentacle 

 with a knob-shaped end: coast of New Jersey; rare. 



2. Mertensia Lesson. Body much compressed, the 

 tentacular axis being the Avider; the 4 subtentacular 



combs longer than the 4 subventral ones: 1 American species. 



M. ovum (Fabricius). Body about 5 cm. long and ovoid in outline; 

 tentacles, combs, and sense organ liglit pink in color: Arctic Ocean to 

 New Jersey; rare south of Cape Cod. 



Pleurohrachia 

 pileus 

 (Mayer). 

 T, tentacles ; 

 C, combs ; 

 other refer- 

 ences as in 

 Fig. 248. 



Order 2. LOBATA. 



Body ovate, compressed in tlie plane transverse to tliat of the stom- 

 ach; mouth wide, with a large and prominent oral lobe on each side of 

 it; at the base of each lobe is a pair of long i)rojections called auricles; 

 tentacles of the ordinary kind wanting in the adult, but numerous, deli- 

 cate, filamentous tentacles may fringe the margin of tlie mouth and 

 the auricles; aboral sense organs sunk in a pit; a larval eydippiform 

 stage present, which has a pair of tentacles issuing from pockets and 

 in certain genera may have sexual reproduction : several families. 



