MOLL USCA—S YSTEMA TIG RE VIE W 



11 



a. Pteropoda thecosomata. — These are nearly related to the Ccphalaspidca, 

 and possess a mantle, mantle cavity, and shell. The head is not distinct, and has 

 only one pair of tentacles. The fins, at their anterior edges, are fused over the mouth ; 

 the anus lies to the left. Fam. Limacinidse. An external calcareous shell, with 

 left-handed or sinistral twist, and a spiral ojierculum. Anus to the right (Lima- 

 cina [Fig. 16], Pcradis). Fam. Cavoliniidse. External symmetrical shell {Clio, 

 Cavolinia). Fam. Cymbuliidae. Internal cartilaginous shell {Cymhulia, Cymhidi- 

 opsis, Glcba). The Thecosomata feed chiefly on small Protozoa and Algfe. 



ex. 



Fig. 1(5.— Limacina Lesueuri (dorsal aspect, 

 after Pelseneer). l, Penis ; 2, tin (parajjo- 

 (lium) ; 3, seminal furrow ; 4, mantle process 

 ("balancer"); 5, visceral <lome ; 6, head with 

 two tentacles and the seminal furrow 3. 



Fig. 17. — Pneumoderma (diagram from the 

 right, after Pelseneer). 1, right evaginated 

 process bearing hooks (hook sac) ; 2, proboscis ; 

 :i, right buccal tentacle ; 4, position of the right 

 nuclial tentacle ; 5, right flu (parapodium) ; 6, 

 seminal furrow ; 7, genital aperture ; 8, position 

 of the jaw ; 9, ventral proboscidal papilla ; 10, 

 right buccal appendage provided with suckers ; 

 11, head ; 12, aperture for penis ; 13, right an- 

 terior pedal lobe ; 14, anus ; 15, posterior pedal 

 lobe ; 16, ctenidium ; 17, posterior adaptive 

 gill ; (?, r, a, p denote dorsal, ventral, anterior, 

 and i)Osterior. 



4a 



b. Pteropoda gymnosomata. — These are nearly related to the Anaspidae. 

 Tliey have no mantle, mantle cavity, nor shell. The head is distinct, and carries 

 two pairs of tentacles. The fins are separate ; the anus lies to the right. Fam. 

 Pneumodermatidse. One ctenidium to the right {Dcxiohranchcca, Sjwnc/iobraiichcea, 

 Piu'iimoderma [Fig. 17]). In the last two genera there is an adaptive posterior gill 

 as well. Fam. Clionopsidse and Notobranchseidse. No ctenidium, but a posterior 

 adaptive gill. Fam. Clionidae. Xeither ctenidium nor adaptive gill. All (Jymnoso- 

 mata are carnivorous, feeding principally on Thecosomata. 



Sub-Order 2. Ascoglossa. 



This sub-order is characterised by the fact that the worn-out teeth of the long 

 narrow radula, which consists of a single row of dental plates, are preserved in a sac 



