The sub-class is now divided into two orders: the Aspidobranchia in which the branchia or ctenidium is bipectinate and attached only at its base, and the Pectinibranchia in which the ctenidium is monopectinate and attached to the mantle throughout its length.
17, d), we find right and left of the two renal apertures a right and left gillplume or ctenidium, which here as in Haliotis and Pleurotornaria retain their original paired condition.
It will be remembered that, according to Spengel, the osphradium of mollusca is definitely and intimately related to the gill-plume or ctenidium, being always placed near the base of that organ; further, Spengel has shown that the nerve-supply of this olfactory organ is always derived from the visceral loop. Accord ingly, the nerve-supply FIG.
- A, Section in a plane vertical to the surface of the neck of Patella through a, the rudimentary ctenidium (Lankester's organ), and b, the olfactory epithelium (osphradium); c, the olfactory (osphradial) ganglion.
(After Spengel.) B, Surface view of a rudimentary ctenidium of Patella excised and viewed as a transparent object.
A single bipectinate ctenidium on left side.
Shell spirally coiled; a single ctenidium; eyes perforated; a horny operculum; lobes between the tentacles.
Shell with very low spire, without umbilicus, internal partitions frequently absorbed; a single ctenidium; a cephalic penis present.
No ctenidium, but a pulmonary cavity; heart with a single auricle, not traversed by the rectum.
No ctenidium, but a pulmonary cavity; operculum with an npophysis.
Br, Ctenidium (gill-plume).
This organ has, without reason, been supposed to represent the second ctenidium of the typical mollusc, which it cannot do on account of its position.
The Pectinibranchia the pedal nerves are br, Ctenidium (branchial distinctly nerves given off from the pedal plume).
U, The otocyst attached to the Ctenidium (gill-plume).
No ctenidium, pallial cavity transformed into a lung; aperture of shell circular; terrestrial.
To the left of the ctenidium a pulmonary sac, separated from it by an incomplete septum, am phibious.
Mantle with two posterior appendages; ctenidium large and capable of protrusion from pallial cavity.
Shell turriculated, with carinated br, Ctenidium (branchial whorls, the carinae tuberculated or plume).
Ctenidium of typical form Pleurocera.
I, Ctenidium (gill-plume).
34.-Female Janthina, with egg-float (a) attached to the foot; b, egg-capsules; c, ctenidium (gill-plume); d, cephalic tentacles.
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.
(All from Lankester.) by the mantle-skirt, is the ctenidium with its free end turned backwards.
The heart lies in front of, instead of to the side of, the attachment of the ctenidium - hence Opisthobranchia as opposed to " Prosobranchia," which correspond to the Streptoneura.
Many Opisthobranchia have by a process of atrophy lost the typical ctenidium and the mantleskirt, and have developed other organs in their place.
The gill-plume,which in A plysia is the typicalMolluscan ctenidium, is seen in fig.
The ctenidium (branchial plume).
There is a ctenidium, except in some Thecosomata and Gymnosomata, and an osphradium.
The pallial cavity is always well developed, and contains the ctenidium, at least in part; ctenidium, except in Lophocercidae, of folded type.
Cephalic shield continuous with dorsal integument; no shell; ctenidium projecting from mantle cavity.
Peraclis, ctenidium present.
Each gill has the structure of a typical molluscan ctenidium, consisting of an axis bearing an anterior and posterior row of filaments or lamellae.
The single pair of branchiae are placed symmetrically right and left of the anus, and each has the structure of a ctenidium bearing a row of lamellae on each side as in the Polyplacophora.
E, Of Paludina: i, intestine running parallel with the axis of the ctenidium and ending in the anus a; br., rows of elongate processes corresponding to the two series of lamellae of the upper figures.
The afferent vessel of the' ctenidium receives blood from the vena cava or principal blood-sinus of the body, the efferent vessel opens into the auricle of its own side.
Near the base of the ctenidium is a patch of sensory epithelium innervated from the branchial nerve, forming a sense-organ called the osphradium, whose function is to test the water entering the branchial cavity.
It consists of the anus in the middle, a renal organ and renal aperture on each side of this, and a ctenidium outside or anterior to the renal organ, an osphradium being situated at the base of the ctenidium.
Each auricle forms the terminal enlargement of the efferent vein of the ctenidium of its own side.
The Molluscan ctenidium is typically a plume like structure, consisting of a vascular axis, on each side of which is set a row of numerous lamelliform or filamentous processes.
Arca and Pectunculus) the lateral processes which are set on the axis of the ctenidium are not lamellae, but are slightly flattened, very long tubes or hollow filaments.
II, A a portion of four filaments of a ctenidium of the sea-mussel (Mytilus) is represented, having precisely the same structure as those of Arca.
The filaments of the gill (ctenidium) of Mytilus and Arca thus form two closely set rows which depend from the axis of the gill like two parallel plates.