8 



(c) Pulmonata — Gills aborted. Breathe air by a lung formed 

 by the. apposition of a part of the mantle to the side of the body. 

 Hermaphrodite, e.g. Helix (garden snail); Limnaeus (pond snail); 

 Limax (slug). 



(d) Heteropoda. — Well developed head and eyes. Foot fin- 

 like, and well developed, e.g. Atlanta. 



4. Ptehopoda ( Sea-butterflies). — Odontophora, in which the anterior 



portion of the foot surrounds the head, and the median part is con- 

 verted into a pair of flapping organs used as fins. Hermaphrodite. 

 e.g. Clio. 



5. (yBPHALOPODA (Cuttle-fishes). — Odontophora, with two large and 



highly organised eyes (the only invertebrate eyes which structurally 

 resemble those of the vertebrates). The anterior part of the foot 

 produced into long tentacular arms. The middle parts of the foot 

 fold over and unite, giving rise to a funnel-like tube (the siphon), 

 which serves as the chief organ of locomotion. 



(a) Tetrabranchiata. — Four gills. Two pairs of auricles. 

 Tentacles, short and numerous, without suckers. Funnel is 

 incompletely closed. Shell is external, divided into chambers 

 and coiled, e.g. Nautilus. 



(b) Dihranchiata. - — Two gills. Two auricles. Eight or ten 

 tentacular arms with numerous suckers. Funnel completely closed. 

 Ink bag always present, e.g. Sepia (cuttle-flsh), eight short and two 

 long arms, and internal shell; Octopus, eight arms, no internal shell. 



Class VII.— MOLLUSCOIDEA (Mollusc-like 



Animals). 



Characters. — Fixed, bilateral, unsegmented, A small group of unimpor- 

 tant mollusc-like forms. 



STJB-DIVISIONS. 



I. POLYZOA (Bryozoa). — Minute animals enclosed in a case ("ceU") 

 of horny or limy matter. The mouth of each animal is surrounded by a 

 circle of tentacles, both nutritive and respiratory in function. Nervous 

 system, a single ganglion between mouth and anus. The cells of different 

 iadividuals become connected to form colonies of a plant-like (sea-weed) 

 appearance, e.g. Sea-mat (Flustra), 



II. BEACHIOPODA. — Fixed, non-colonial forms. Body is covered 

 by two mollusc-like mantle lobes which secrete a Hmy bivalve shell, the 

 valves being dorsal and ventral (not lateral as in Lamellibranchs). Mouth 

 surrounded by two spirally coUed arms (nutritive and respiratory). Nervous 

 system — circum- oesophageal nerve ring and two small supra -oesophageal 

 ganglia. Worm-like excretory organs, e.g. Lamp-shells (Terebratula). 



