TECTIBRANCHIATA. 



407 



Section 2. Aplysioidea. 



The shell is reduced or absent. The head is without cephalic disc and has 

 two pairs of tentacles. The epipodia arise from the sides of the body, and 

 are not direct continuations of the ventral surface of the foot. The visceral 

 commissure is much shortened (except in Aplysia), and the nervc^ganglia are 

 closely aggregated. There is a , 



second commissure connecting the 



pedal ganglia called the parapedal I ~~==^S^v 

 commissure, in addition to the 

 ordinary one ; the aorta passes 

 between the two. The osphradium 

 and its ganglion (supplied by a 



Md 



M 



FIG. 319. Larva of Cavolinia (Hyaleu) 

 tridentata (after Fol). Ms velum; P 

 foot; P' the two lateral (epipodial) 

 lobes of the foot ; A anus ; M retractor 

 muscle; Md stomach. 



R 



FIG. 320. Creseis acicula, dorsal view, after 

 Gegenbaur (hind end omitted). A anus ; At 

 auricle ; SI blind sac of stomach ; F tentacle ; 

 Fl fins ; G gonad ; Gg cerebral ganglion ; M 

 stomach ; Mn mantle-nerve ; N kidney ; U 

 mouth; Oe opening of kidney into mantle- 

 cavity ; Oes oesophagus ; P median lobe of 

 foot; R retractor; Ve ventricle; Ws ciliated 

 shield. The terminal part of intestine passes 

 ventral to anterior, not! dorsal as here repre- 

 sented. 



nerve from the supraintestinal) is 

 placed at the base of the gill, 

 between the openings of the genital 

 organ and the kidney. There is 

 a seminal groove leading from the 

 former to the penis, which is on 

 the right side of the head. 



The Aplysiidae and the Pteropoda Gymnosomata are included in this section. 

 The Aplysiidae have a widely open mantle-cavity, ctenidium, and an internal 

 shell, all of which are absent in the other families. Pneumoderma, however, is 

 said to retain the ctenidium in the lateral gill. 



Fam. 1. Aplysiidae. Shell internal, but the sac in which it lies opens by 

 a pore in the centre of the dorsal surface. With a mantle-cavity and ctenidium. 

 Aplysia L., Sea-hare; Aplysiella Fischer; Phyllaplysia Fischer, shell absent; 

 Notarchus Cuvier, epipodia fused, dorsally to the visceral sac ; Dolabella, Lmk. 



The following families, formerly included under Pteropoda Gymnosomata, are 

 without mantle or shell. The head is well developed and bears two pairs of 



