Pac, Pallial cavity.
F, Gill lamellae (not ctenidia, but organs of the pallial complex, having two kidneys, in some cases two branchiae, and two auricles.
In these there are neither branchia nor osphradium, and the pallial chamber which retains its large open ing serves as a lung.
Upon the surface of the visceral dome, and extending special pallial growths, comparable with those of Pleurophyllidia).
(Lankester.) the animal into the large anterior region of the sub-pallial space.
Shell with pointed spire; a short pallial siphon.
Pallial cavity transformed into a lung; operculum horny; shell narrow and elongated.
Epipodial fila L ments present; one or two pallial tentacles.
Cephalic shield continuous with neck; twelve to fourteen stomachal plates; a posterior pallial filament passing through a notch in shell.
With sinistral spiral; pallial cavity dorsal.
Adult without shell; a sub-epithelial pseudoconch formed by connective tissue; pallial cavity ventral.
Shell not coiled, symmetrical; pallial cavity ventral.
Median pallial nerve of dorsal each side, just below the lobe of mantle.
The pallial line, which is the line of attachment of the mantle parallel to the edge of the shell, is not indented by a sinus at the posterior end.
The chief points in which they vary are - (1) in the structure of the ctenidia or branchial plates; (2) in the presence of one or of two chief muscles, the fibres of which run across the animal's body from one valve of the shell to the other (adductors); (3) in the greater or less elaboration of the posterior portion of the mantle-skirt so as to form a pair of tubes, by one of which water is introduced into the sub-pallial chamber, whilst by the other it is expelled; (4) in the perfect or deficient symmetry of the two valves of the shell and the connected soft parts, as compared with one another; (5) in the development of the foot as a disk-like crawling organ (Arca, Nucula, Pectunculus, Trigonia, Lepton, Galeomma), as a simple plough-like or tongueshaped organ (Unionidae, &c.), as a re-curved saltatory organ (Cardium, &c.), as a long burrowing cylinder (Solenidae, &c.), or its partial (Mytilacea) or even complete abortion (Ostraeacea).
The pallial cavity, with its organs, is by this torsion moved up the right side of the larva to the dorsal surface, and thus the left organs become right and vice versa.
Pac, Pallial cavity.
In some cases each pleural ganglion is connected with the opposite branch of the visceral commissure by anastomosis with the pallial nerve, a condition which is called dialyneury; or there may be a direct connective from the pleural ganglion to the visceral ganglion of the opposite side, which is called zygoneury.
They are termed pallial gills.
(From Gegenbaur, pi, Pallial nerve.
Acmaea, without pallial branchiae, British.
Scurria, with pallial branchiae in a circle beneath the mantle.
No ctenidia but pallial branchiae in a circle between mantle and foot.
Patella, pallial branchiae forming a complete circle, no epipodial tentacles, British.
Neither ctenidia nor pallial branchiae.
Without shell and operculum, but with pallial cavity and ctenidium.
Pectinibranchia.-In this order there is no longer any trace of bilateral symmetry in the circulatory, respiratory and excretory organs, the topographically right half of the pallial complex having completely disappeared, except the right kidney, which is FIG.
In the latter a pallial siphon, a welldeveloped proboscis and an unpaired oesophageal gland are always present, in the former they are usually absent.
Pallial cavity transformed into a lung; pedal centres concentrated; a deep pedal groove.
Mantle with two posterior appendages; ctenidium large and capable of protrusion from pallial cavity.
Shell turriculated and siphonated, thick, each whorl with varices; foot broad and truncated anteriorly; pallial siphon well developed; proboscis present.
Foot with anterior transverse groove; a posterior pallial tentacle; generally burrowing.
Where the modification is carried to its extreme degree, not only the shell but the pallial cavity, ctenidium and visceral hump disappear, and the body acquires a simple elongated form and a secondary external symmetry, as in Pterotrachaea and in Doris, Eolis, and other Nudibranchia.
39 projecting from the branchial sub-pallial space.
When the shell of an A plysia enclosed in its mantle is pushed well to the left, the sub-pallial space is fully exposed as in fig.
The pallial cavity is always well developed, and contains the ctenidium, at least in part; ctenidium, except in Lophocercidae, of folded type.
Posteriorly the mantle forms a large pallial lobe FIG.
Under the pallial aperture.
Foot without parapodia; no pallial cavity, but always a single ctenidium situated on the right side between mantle and foot.
Mc, Sub-pallial chamber.
1, The lamelliform sub-pallial gills, which (as in Patella) replace the typical Molluscan ctenidium.
In both Oncidiidae and Pecten the pallial eyes have probably been developed by the modification of tentacles, such as coexist in an unmodified form with the eyes.
All have an osphradium, except the Auriculidae, which are terrestrial, and it is situated outside the pallial cavity in those forms in which water is not admitted into the lung.
Visceral mass and shell conical; tentacles atrophied; head expanded; genital apertures contiguous; marine animals, with an aquatic pallial cavity containing secondary branchial laminae.
Visceral mass and shell conical; head flattened; pallial cavity aquatic, but without a branchia; genital apertures separated.
Visceral mass and shell sinistral; inferior pallial lobe very prominent, and transformed into a branchia.
Shell conical, not spiral; inferior pallial lobe transformed into a branchia.
(I) Animal removed from its shell, a probe g passed into the sub-pallial chamber through the excurrent siphonal notch.
H, Anterior (pallial) adductor muscle of the shells.
T, Pallial tentacles.
U, The thickened muscular pallial margin which adheres to the shell and forms the pallial line of the left side.