Op., Operculum, or ventral lip. ov., Ovary.
Above the mouth is the lid (operculum), which varies in size from a small narrow process to a large heartshaped expansion.
But there are forms in which the involution is " hyperstrophic," that is to say, the turns of the spire projecting but slightly, the spire, after flattening out gradually, finally becomes re-entrant and transformed into a false umbilicus; at the same time that part which corresponds to the umbilicus of forms with a normal coil projects and constitutes a false spire; the coil thus appears to be sinistral, although the asymmetry remains dextral, and the coil of the operculum (always the opposite to that of the shell) sinistral (e.g.
Shell spirally coiled; a single ctenidium; eyes perforated; a horny operculum; lobes between the tentacles.
Shell spirally coiled; operculum horny; intertentacular lobes absent.
Shell spirally coiled; epipodial tentacles present; operculum thick and calcareous.
Shell flattened, not umbilicated, generally smooth; operculum horny.
Shell semi-globular, with short spire; operculum calcareous, not spiral.
No ctenidium, but a pulmonary cavity; operculum with an npophysis.
Cyclostoma, shell turbinated, operculum calcareous, British.
Pallial cavity transformed into a lung; operculum horny; shell narrow and elongated.
Head with two long labial palps; shell ovoid; operculum horny, semicircular, carinated.
Foot divided into two, posterior half bearing the operculum; a wide epipodial velum; shell turbinated.
Shell thin; operculum absent; tentacles bifid; foot secretes a float; pelagic. Janthina.
Shell ventricose,with elongated aperture, and short spire; proboscis and siphon long;operculum with marginal nucleus.
' Shell globular and ventricose; aperture oval and canaliculated; operculum spiral.
Shell ventricose, with short spire, and wide aperture; no varices and no operculum; foot very broad, with projecting anterior angles; siphon long.
Summit of spire heterostrophic; a projection, the mentum, between head and foot; operculum present.
Eulima, foot well developed, with an operculum, animal usually free, but some live in the digestive cavity of Holothurians.
Visceral sac and shell coiled in one plane; foot divided transversely into two parts, posterior part bearing an operculum, anterior part forming a fin provided with a sucker.
Shell fusiform and solid, aperture elongated, columella folded; no operculum; eyes on sides of tentacles.
Tentacles; operculum horny.
Foot broad, with two slender posterior appendages; operculum unguiculate.
Shell thick, with short spire, last whorl large and canal short; aperture wide; operculum horny.
Shell ovoid, with short spire and folded columella; foot small, no operculum; siphon short.
Foot very large; without operculum; shell with short spire and longitudinal ribs; siphon long.
Shell turriculated, with numerous whorls; aperture and operculum oval; eyes at summits of tentacles; siphon long.
Shell conical, with very short spire, and narrow aperture with parallel borders; operculum unguiform.
A few Euthyneura in which the shell is not much reduced retain an operculum in the adult state, e.g.
F, Foot; op, operculum; mn, anal papilla; ry, dry, two portions of unabsorbed nutritive yolk on either side of the intestine.
44 and 45), are less abnormal than Aplysia in regard to their shells and the form of the visceral hump. They have naked spirally twisted shells which may be concealed from view in the living animal by the expansion and reflection of the parapodia, but are not enclosed by the mantle, whilst Actaeon is remarkable for possessing an operculum like that of so many Streptoneura.
The operculum retains its op..
(iii.) In Umbonula of Cribrilina, showing the frontal membrane and parietal the entrance to the muscles of the young zooecium are like compensation - .sac on those of Membranipora, but they become the proximal side of the covered by the growth, from the proximal operculum (op).
(vi.) In Microporella the opening of the compensation-sac has become separated from the operculum by calcareous matter, and is known as the "median pore."
The operculum of the normal zooecium has become the mandible, while the occlusor muscles have become enormous.
In its least differentiated form the avicularium occupies the place of an ordinary zooecium ("vicarious avicularium"), from which it is distinguished by the greater development of the operculum and its muscles, while the polypide is normally not functional.
They occur in particular in relation with the orifice of the zooecium, and with that of the compensation-sac. This delicate structure is frequently guarded by an avicularium at its entrance, while avicularia are also commonly found on either side of the operculum or in other positions close to that structure.
Shelheleth), the celebrated odoriferous shell of the ancients, the operculum or "nail" of a species of Strombus or "wing shell," formerly well known in Europe under the name of Blatta byzantina; it is still imported into Bombay to burn with frankincense and other incense to bring out their odours more strongly; saffron (Heb.
Intromittent organ of male beneath the genital operculum (=sternum of the 1st somite of opisthosoma).
The praegenital somite, VII PrG, is still present, but has lost its rudimentary appendages; go, the genital operculum, left half; Km, the left pecten; abp 4 to abp 7, the rudimentary appendages of the lung-sacs.
The seventh, VII, is anterior to the genital operculum, op, and is the cavity of the praegenital somite which is more or less completely suppressed in subsequent development, possibly indicated by the area marked VII in fig.
Mesosomatic segments furnished with large plate-like appendages, the 1st pair acting as the genital operculum, the remaining pairs being provided with branchial lamellae fitted for breathing oxygen dissolved in water.