. The Cambridge natural history. Zoology. FAMILIES OF OPERCULATA 91. (Fig. 62, HI) derived partly from the external hypodermis and partly from the lining of the mantle. The hard parts of the shell usually also contain spaces and canals (C). The various forma of Acorn-barnacle may be classified accord- ing to the number of pieces that go to make up the skeleton ; thus starting with the typi- cal number eight (Fig. 63, A), we find that in various degrees a fusion between neigh- bourinc pieces has ^^'^''^ ^'^'—Diagrams of sliells of Operculata. A, C'ato- , , . phragmus (Octomerklae) ; B, Balamis,
. The Cambridge natural history. Zoology. FAMILIES OF OPERCULATA 91. (Fig. 62, HI) derived partly from the external hypodermis and partly from the lining of the mantle. The hard parts of the shell usually also contain spaces and canals (C). The various forma of Acorn-barnacle may be classified accord- ing to the number of pieces that go to make up the skeleton ; thus starting with the typi- cal number eight (Fig. 63, A), we find that in various degrees a fusion between neigh- bourinc pieces has ^^'^''^ ^'^'—Diagrams of sliells of Operculata. A, C'ato- , , . phragmus (Octomerklae) ; B, Balamis, Coronula, etc. taken place m the (Hexameriilae) ; C, Tefmdita (Tetrameridae). 0, different families carina ; , carino-lateral ; L, lateral ; R, rostriim ; , rostro-lateral. Fam. 1. Verru- cidae.—The ancient genus Verruca, which is still widely dis- tributed in all seas, and is found fixed upon foreign objects on the sea-bottom at various depths, is interesting on account of the asymmetry of its shell, which bears a different aspect accord- ing to which side one regards it from. This asymmetry is brought about by the skeletal pieces (carina, rostrum, and paired terga and scuta) shifting their positions after fixation has taken place. Fam. 2. Octomeridae.—In this family the eight plates com- posing the shell are separate and unfused (Fig. 63, A). The majority of the species come from the Southern hemisphere, the members of the genera Gatophragmns and Octomeris, but Pachylasma giganteutn occurs in deep water in the Mediter- ranean, where it has been found fixed upon Millepore corals. Fam. 3. Hexameridae.—This family includes by far the greater number of the Acorn-barnacles, in which only six plates are present, the laterals having fused with the carino-laterals (Fig. 63, B). The very large genus Balanus belongs here, the common B. tintinnctlndum of our coasts being found all over the world, and occurring under a number of inconstant varietaj forms. Especial in
Size: 2311px × 1081px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
