A proboscis absent, but jaws usually present.
Proboscis present, but short.
The stomach may be drawn out into the manubrium, forming a proboscis (" Magenstiel ") of considerable length.
Shell turriculated and siphonated, thick, each whorl with varices; foot broad and truncated anteriorly; pallial siphon well developed; proboscis present.
It then often retains its vitality for a long time, apparently crawling as if it were itself a worm, a phenomenon which is at least partially explained by the extraordinary development of nervous tissue, equally distributed all through the walls of the proboscis, and either united into numerous longitudinal nerve-stems (Drepanophorus, Amphiporus) or spread out into a uniform and comparatively thick layer (Cerebratulus, sp.).
Shell ventricose,with elongated aperture, and short spire; proboscis and siphon long;operculum with marginal nucleus.
This very effective and elaborate innervation, which has been directly traced to the brain, whence strong nerves (generally two) enter the proboscis, renders it exceedingly probable that the most important functions of the proboscis are of a sensiferous, tactile nature.
In Nemertines the everted proboscis is retracted in the same way as the tip of a glove finger would be if it were pulled backwards by a thread situated in the axis and attached to the tip. The comparison may be carried still further.
The central thread just alluded to is represented in the Nemertean proboscis by that portion which is never everted, and the tip of the glove by the boundary between the evertible and non-evertible portion of the proboscis - a boundary which in the Metanemertini is marked by the presence of a pointed or serrated stylet.
Is a proboscis) - with rare exceptions these forms have a siphonate its whole length, except in Adeorbis and Valvata; in the latter alone it is bipectinate.
Supposing the tube to be completely introverted and to commence its eversion, we then find that eversion may take place, either by a forward movement of the side of the tube near its attached base, as in the proboscis of the Nemertine worms, the pharynx of Chaetopods and the eye-tentacle of Gastropods, or by a forward movement of the inverted apex of the tube, as in the proboscis of the Rhabdocoel Planarians, and in that of Gastropods here under consideration.
The acrembolic proboscis or frontal introvert of the Nemertine worms has a complete range.
B, The same, partially everted by eversion of the sides, as in the Nemertine proboscis and Gastropod eye-tentacle = pleurecbolic.
23 the proboscis is seen in an everted state; it is only so carried when feeding, being withdrawn when the animal is at rest.
- A, Triton variegation, to show the proboscis or buccal introvert (e) in a state of eversion.
Shell turriculated, with elongated spire; proboscis short; siphon rudimentary.
They have a well-developed proboscis which is used as a suctorial organ; some are abyssal, but the majority are either commensals or parasites of Echinoderms.
Heteronemertini, in which the dermal musculature is in three layers, an external longitudinal, a middle circular, an internal longitudinal; the nervous system lies between the first and second of these layers; the outer layer of longitudinal muscles is a new development; there is no intestinal caecum; no stylets on the proboscis and the mouth is behind the level of the brain.
The proboscis, which is thus an eminently muscular organ, is composed of two or three, sometimes powerful, layers of muscles - one of longitudinal and one or two of circular fibres.
Upper margin of the end of the proboscis developed into a distinct finger-like process, much longer than the lower margins, and the whole trunk uniformly tapering and smooth.
From their position in the proboscis the larvae can easily enter the blood of man the next time the mosquito bites (Low, Brit.
The parasitic actinula is found attached to the proboscis of the medusa; it thrusts its greatly elongated hypostome into the mouth of the medusa and nourishes itself upon the food in the digestive cavity of its host.
A distinctive feature is the position assumed in resting; Culex has a humpbacked attitude, while in Anopheles the proboscis, head and body are in a straight line, and in many species inclined at an angle to the wall, the tail sticking outwards.
In the female of Culex the palpi are much shorter than the proboscis; in Anopheles they are of the same length.
The other structural characters of the Order may be briefly summarized as: - mouth-parts adapted for piercing and sucking, or for suction alone, and consisting of a proboscis formed of the labium, and enclosing modifications of the other usual parts of the mouth, some of which, however, may be wanting; a thorax fused into a single mass; and legs with five-jointed tarsi.
The Pupipara are also termed Eproboscidea (although they actually possess a well-developed and functional proboscis), and by some dipterists the Eproboscidea are regarded as a suborder .and contrasted as such with the rest of the Diptera, which are styled the suborder Proboscidea.
As in all such introand e-versible organs, eversion of the Gastropod proboscis is effected by pressure communicated by the muscular body-wall to the liquid contents (blood) of the body-space, accompanied by the relaxation of the muscles which directly pull upon either the sides or the apex of the tubular organ.
The condition usually spoken of as a " proboscis " appears to be derived from the condition of a simple rostrum (having the mouth at its extremity) by the process of incomplete introversion of that simple rostrum.
So too the acrembolic eye-tentacle of the snail has a complete range of movement, and also the pleurembolic proboscis of the Rhabdocoel prostoma.
One of the best examples of the introversible mouth-cylinder or proboscis which can be found is that of the common whelk (Buccinum undatum) and its immediate allies.
No buccal appendages or suckers; a very long evaginable proboscis; a quadriradiate terminal branchia.
NEMERTINA, or Nemerteans (Nemertea), a subdivision of worms,' characterized by the ciliation of the skin, the presence of a retractile proboscis, the simple arrangement of the generative apparatus, and in certain cases by a peculiar pelagic larval stage to which the name " pilidium " has been given.
Protonemertini, in which there are two layers of dermal muscles, external circular and internal longitudinal; the nervous system lies external to the circular muscles; the mouth lies behind the level of the brain; the proboscis has no stylet; there is no caecum to the intestine.
With the mouth into a single exterior opening), there is a terminal opening, the rhynchostome (subterminal in Valencinia), at the foremost tip of the body, out of which the proboscis is seen shooting backwards and forwards, sometimes with so much force that both its interior attachments are severed and it is entirely expelled from the body.
_This stylet is thus situated terminally when the proboscis has reached its maximum eversion.
This aggressive character has a different aspect in several genera which are destitute of a central stylet, but in which the surface that is turned outwards upon eversion of the proboscis is largely pro- P. vided with nematocysts, sending the urticating rods of different sizes in all directions.
This retractor-muscle, indeed, serves to pull back with great rapidity the extruded proboscis, and is aided in its action by the musculature of the head.
Proboscis is everted Partial extrusion lessening the resistor rhynchostome.
It is worthy of notice that in those Nemertines which make a very free use of their proboscis, and in which it is seen to be continually protruded and retracted, the walls of the proboscidian sheath are enormously muscular.
At the circular insertion of the proboscis in front of the brain the muscular fibres belonging to the anterior extremity of the body and those connected with the proboscis are very intimately interwoven, forming a strong attachment.
In the latter a pallial siphon, a welldeveloped proboscis and an unpaired oesophageal gland are always present, in the former they are usually absent.
There is no reason in the actual significance of the word why the term " proboscis " should be applied to an alternately introversible and eversible tube connected with an animal's body, and yet such is a very customary use of the term.