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; 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.
Stylifer, the operculum is lost, animal fixed by a large proboscis which forms a pseudopallium covering the whole shell except the extremity of the spire, parasitic on all groups of Echinoderms. Entosiphon, visceral mass still coiled; shell much reduced, proboscis very long forming a pseudopallium which covers the whole body and projects beyond in the form of a siphon, foot and nervous system present, eyes, branchia and anus absent, parasite in the Holothurian Deima blakei in the Indian Ocean.
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.
No operculum, except in Actaeonidae and Limacinidae.
Pseudo-sinistrally; operculum i, Mouth of the shell.
An operculum is present only in Amphibola; a contrast being thus afforded with the operculate pulmonate Streptoneura (Cyclostoma, &c.), which differ in other essential features of structure from the Pulmonata.
The Pulmonata have a straight visceral nerve-loop, usually no operculum even in the embryo, and a multidenticulate radula, the teeth being equi-formal; and they are hermaphrodite.
The shell of the Pulmonata, though always light and delicate, is in many cases a well-developed spiral " house," into which the creature can withdraw itself; and, although the foot possesses no operculum, yet in Helix the aperture of the shell is closed in the winter by a complete lid, the " hybernaculum," more or less calcareous in nature, which is secreted by the froot.
Thus the whole of the Pulmonata (which breathe air, are destitute of gill-plumes and operculum and have a complicated hermaphrodite reproductive system) are either snails or slugs.
The land-snails which have no gill-plume in the mantle-chamber and breathe air, but have the sexes separated, and possess an operculum, belong to the orders Aspidobranchia and Pectinibranchia, and constitute the families Helicinidae, Proserpinidae, Hydrocenidae, Cyclophoridae, Cyclostomatidae and Aciculidae.
The first pair of foliaceous appendages in each animal is the genital operculum; beneath it are found the openings of the genital ducts.
The agreement of the grouping of the somites, of the form of the parapodia (appendages, limbs) in each region, of the position of the genital aperture and operculum, of the position and character of the eyes, and of the powerful post-anal spines not seen in other Arthropods, is very convincing as to the affinity wise suppressed praegenital somite.
VIIgo, The genital somite or first somite of the mesosoma with the genital operculum (a fused pair of limbs).
--Diagrams of the meta-sternite st, who showed that with genital operculum op, and the first lamellithe statements of gerous pair of appendages ga, with uniting von Graber were sternal element st of Scorpio (left) and Limulus erroneous, and (right).
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.
Though there are indications of lamelliform respiratory appendages on mesosomatic somites following that bearing the genital operculum, we cannot be said to have any proper knowledge as to such appendages, and further evidence with regard to them is much to be desired.
The appendages of the 1st and 2nd mesosomatic somites persisting as the genital operculum and pectones respectively, those of the 3rd, 4th, 5th and 6th somites (?
The meeting of the coxae of all the prosomatic limbs in front of the pentagonal sternum; the space for a genital operculum; the pair of pectens, and the absence of any evidence of pulmonary stigmata are noticeable in this specimen.
Intromittent organ of male beneath the genital operculum (=sternum of the 1st somite of opisthosoma).
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.