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225:, a door-like structure which is attached to the dorsal surface of their foot. In evolutionary terms, the appearance of an operculum occurred shortly after that of torsion, which suggests a possible link with the role of torsion, though there is not sufficient evidence for or against this hypothesis. The English zoologist
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which has one end attached to the left side of the shell and the other end has fibres attached to the left side of the foot and head. At a certain point in larval development this muscle contracts, causing an anticlockwise rotation of the visceral mass and mantle of roughly 90˚. This process is very
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species, ventilation is better with anterior positioning. This is due to the back and forth motion of the shell during movement, which would tend to block the mantle opening against the foot if it was in a posterior position. The evolution of an asymmetrical
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growth of the left hand side of the organism compared to the right hand side. This second stage is much slower and rotates the visceral mass and mantle a further 90˚. Detorsion is brought about by reversal of the above phases.
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During torsion the visceral mass remains almost unchanged anatomically. There are, however, other important changes to other internal parts of the gastropod. Before torsion the gastropod has an
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shell. Torsion allows repositioning of the shell, bringing the centre of gravity back to the middle of the gastropod's body, and thus helps prevent the animal or the shell from falling over.
268:(olfactory sense organs) to an anterior position means they are sampling water the gastropod is entering rather than leaving. This may help the gastropod locate food or avoid predators. In
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Whatever original advantage resulted in the initial evolutionary success of torsion, subsequent adaptations linked to torsion have provided modern gastropods with further advantages.
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The original advantage of torsion for gastropods is unclear. It is further complicated by potential problems that accompany torsion. For example, having the place where wastes are
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pressures on left and right hand side organs and as a result in some species there are considerable differences. Some examples of this are: in the
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positioning because sediment can be stirred up by the motion of the gastropod. Another possible advantage for aquatic species is that moving the
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rapid, taking from a few minutes to a few hours. After this transformation the second stage of torsion development is achieved by differential
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206:. Nevertheless, the diversity and success of the gastropods suggests torsion is advantageous, or at least has no strong disadvantages.
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end up at different heights. Because of differences between the left and right hand sides of the body, there are different
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There are two different developmental stages which cause torsion. The first stage is caused by the development of the
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The torsion or twisting of the visceral mass of larval gastropods is not the same thing as the spiral coiling of the
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180˚ with respect to the head and foot of the gastropod. This rotation brings the mantle cavity and the anus to an
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Page L. R. (2006) "Modern insights on gastropod development: Reevaluation of the evolution of a novel body plan".
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nervous system, where the visceral nerves cross over in a figure of eight fashion. As a result, the parietal
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or rotation towards the original position; this may be only partial detorsion or full detorsion.
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170:(equivalent to lungs or gills) in some species, one side may be reduced or absent; or in some
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235:, in which he argued with gentle humour in favour of the defence theory, including the lines
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head into its shell. Some gastropods can also close the entrance to their shell with a tough
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gastropods. By moving the mantle cavity over the head, the gastropod can retract its
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gastropods, anterior positioning of the mantle cavity may be useful for preventing
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One likely candidate for the original purpose of torsion is defence against
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Goodhart, C. B. (1987). "Garstang's
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getting into the mantle cavity, an event which is more likely with
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Were baffled now by tactics which their dining plans frustrated.
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With the tender morsel safe within and the horny foot without!
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shell allowed gastropods to grow larger, but resulted in an
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Their prey upon alarm collapsed, but promptly turned about,
78:, which is also present in many shelled gastropods.
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303:Hardy A.C. 1951. Introduction to Garstang W.
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242:foes, still drifting by in numbers unabated,
44:development. Torsion is the rotation of the
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252:Torsion can provide other advantages. For
194:positioned above the head could result in
421:. Sinauer Associates, Inc. Massachusetts.
399:Learn how and when to remove this message
27:Novel characteristic of larval gastropods
362:This article includes a list of general
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106:
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178:has been transformed into part of the
40:which occurs in all gastropods during
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154:down the body. Torsion results in a
427:Integrative and Comparative Biology
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417:Brusca, R.C.; Brusca, G.J. (1990)
368:it lacks sufficient corresponding
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819:Reproductive system of gastropods
67:) there is a degree of secondary
824:Respiratory system of gastropods
739:Circulatory system of gastropods
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764:Excretory system of gastropods
754:Digestive system of gastropods
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63:In some groups of gastropods (
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1:
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229:wrote a famous poem in 1928,
118:when the torsion is complete.
829:Sensory organs of gastropods
794:Nervous system of gastropods
440:Ruppert, E.E. et al. (2004)
319:Journal of Molluscan Studies
307:. Blackwell, Oxford. pp. 8-9
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860:Circumesophageal nerve ring
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232:The Ballad of the Veliger
146:, where the two visceral
60:position above the head.
383:more precise citations.
174:species the right hand
435:doi:10.1093/icb/icj018
331:10.1093/mollus/53.1.33
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103:(pc) prior to torsion.
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442:Invertebrate Zoology
784:Hypobranchial gland
732:Internal soft parts
656:External soft parts
180:reproductive system
186:Evolutionary roles
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901:Gastropod anatomy
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809:Oesophageal pouch
668:Caudal mucous pit
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16:(Redirected from
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799:Nidamental gland
723:Suprapedal gland
620:Other hard parts
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389:November 2009
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536:Periostracum
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325:(1): 33–36.
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305:Larval Forms
304:
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204:sense organs
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176:renal system
164:evolutionary
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124:asymmetrical
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38:synapomorphy
30:
29:
865:Trochophore
850:Pseudofeces
804:Odontophore
759:Diverticula
703:Pneumostome
546:Planispiral
381:introducing
270:terrestrial
141:euthyneural
126:velar/foot
91:Trochophore
82:Development
890:Categories
814:Osphradium
789:Nephridium
708:Rhinophore
698:Parapodium
627:Clausilium
566:Selenizone
556:Protoconch
506:Body whorl
364:references
288:References
279:unbalanced
275:conispiral
266:osphradium
240:Predaceous
219:vulnerable
112:Protoconch
101:protoconch
845:Epiphragm
749:Ctenidium
637:Operculum
632:Love dart
596:Umbilicus
561:Sculpture
541:Peristome
516:Columella
479:Gastropod
339:0260-1230
262:posterior
223:operculum
211:predators
160:ganglions
69:detorsion
35:gastropod
678:Cnidosac
496:Aperture
258:sediment
192:excreted
168:ctenidia
152:parallel
58:anterior
18:Untorted
875:Veliger
855:Torsion
481:anatomy
412:Sources
377:improve
254:aquatic
198:of the
196:fouling
31:Torsion
718:Siphon
688:Mentum
683:Mantle
673:Cerata
647:Radula
591:Suture
511:Callus
366:, but
337:
148:nerves
133:tissue
128:muscle
52:, and
50:mantle
42:larval
838:Other
693:Notum
642:Pearl
611:Whorl
606:Varix
601:Valve
581:Spire
551:Plait
531:Nacre
488:Shell
215:adult
200:mouth
76:shell
54:shell
33:is a
744:Crop
526:Lira
501:Apex
335:ISSN
202:and
150:run
521:Lip
327:doi
213:in
114:of
93:of
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333:.
323:53
321:.
296:^
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341:.
329::
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