The Cambridge natural history . h three rather large teethin a row, generally unicuspid, jaw in two pieces, stomach withhorny plates, anus generally on the left side. The Thecosomata feed on Protozoa and the lower Algrae; ^ It appears more convenient to treat the whole group together, rather than dealwith the two sections separately. 436 PTEROPODA THECOSOMATA they have no proboscis, and the intestine is flexured. The finsare always closely connected with the head, or what answers toit. About 42 species are known, belonging to 8 genera. Fam. 1. Limacinidae.—^Fins very large, branchial chamberdo
The Cambridge natural history . h three rather large teethin a row, generally unicuspid, jaw in two pieces, stomach withhorny plates, anus generally on the left side. The Thecosomata feed on Protozoa and the lower Algrae; ^ It appears more convenient to treat the whole group together, rather than dealwith the two sections separately. 436 PTEROPODA THECOSOMATA they have no proboscis, and the intestine is flexured. The finsare always closely connected with the head, or what answers toit. About 42 species are known, belonging to 8 genera. Fam. 1. Limacinidae.—^Fins very large, branchial chamberdorsal, anus on right side; shell spiral, sinistral (ultra-dextral,see p. 249), operculate. Genera : Liviacina, shell helicoid,deeply umbilicated (Z. helicina swarms in Arctic seas andfurnishes food for many Cetacea) ; Peraclis, spire turreted,aperture large, elongated, produced anteriorly, no umbilicus;operculum sinistral, in spite of the shell being ultra-dextral. Fam. 2. Cavoliniidae.—Fins large, branchial chamber Fig. 290.—Illustrations of Pteropocla Thecosomata: A, Limacina australis Eyd.; B,Cleodora cuspidata Bosc. (shell only) ; C, Cuvierina columnella Piang ; D, Crescisvirgida Rang ; E, Clio balantium Rang ; /, /, fins ; I, liver; o, ovary ; sh, sliell.(After Souleyet.) shell a non-spiral cone, angular or round, very thin, emljryonicportion distinct, or formed of two separate plates. In Cavolinia ( = Hyalaea, Fig. 5, B, p. 10) the shell consists oftwo plates, the ventral being convex, with one to three sharpspines at the posterior end, the dorsal flatter, without apertm-e is broad, contracted dorso-ventrally. Two longpointed prolongations of the mantle project from the lateral slitsof the shell, and probably serve to balance the bulky body whenswimming. Fins trilobed at the margin. Cleodora has onlyrudimentary lateral pi-olongations, fins bilobed, shell triangular,angles greatly produced, aperture very wide, dorsal side Cuvierina the s
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
