. Outlines of zoology. s and nephridia is notcarried out, or only partially, Haliotis (ear-shell); Fissurella (key-hole limpet); Patella (limpet). Order 2. Azygobranchiata The originally left gill and the originally left nephridium have been lost. Heart with single auricle, one gill, one nephridium ; operculum present. Periwinkle {Littorind), buckie (Buccimim, Fig. 222), dog-whelk (Purpura), lanthina, and the majority of the marine Gasteropods with coiled shells, together with some fresh-water forms. The pelagic Heteropods are also included here -.^Atlanta, shell well developed ; Carinari
. Outlines of zoology. s and nephridia is notcarried out, or only partially, Haliotis (ear-shell); Fissurella (key-hole limpet); Patella (limpet). Order 2. Azygobranchiata The originally left gill and the originally left nephridium have been lost. Heart with single auricle, one gill, one nephridium ; operculum present. Periwinkle {Littorind), buckie (Buccimim, Fig. 222), dog-whelk (Purpura), lanthina, and the majority of the marine Gasteropods with coiled shells, together with some fresh-water forms. The pelagic Heteropods are also included here -.^Atlanta, shell well developed ; Carinaria,?with small shell; Ptero-trachea, with no shell. Branch B. Euthyneura The visceral loop does notshare in the torsion of thevisceral hvimp. Order The visceral loop is euthy-neural, as in snails; thesingle auricle lies behind theventricle; the shell andmantle are often absent. A. Tectibranchiata. Ashell is present,but may be rudi-mentary ; there isa well-developedmantle fold anda single gill, Fig. 229.—A Pteropod {Cymbiiliaferonii), showing the wing-like expan-sions (pteropodiallobes)of the mid-foot. MODE OF LIFE. 421 Bulla, Aplysia, Dolabella, Umbrella. The Tectibranchiataalso include the Pteropoda, the winged snails or sea-butter-flies, which have become much modified for pelagic have a secondarily acquired bilateral symmetry, and-swim by two large lateral lobes of the foot. They oftenswim actively in shoals, and occur in all seas. They affordfood for whales, etc., and the shells of some are abundant inthe ooze. They include—? (a) Thecosomata, with mantle fold and shell, diet ofminute animal or vegetable organisms, closely relatedto Bulla and its allies. Examples.—Hyalea, Cymbulia.{b) Gymnosomata, without mantle fold or shell in theadult. Closely allied to Aplysia and its carnivorous, Clio, Nudibranchiata. Shell, mantle fold, and true gill are absent;various forms of adaptive gills may be present, o
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
