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25:
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can be seen towards the apex of the shell. These were apparently counterweights for the soft body at the other end of the shell, and allowed the nautilus to swim in a horizontal position. Without these deposits, the apex of the buoyant shell would have pointed upwards and the heavier body downwards, making horizontal swimming difficult. The siphuncle of the
353:
In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral edge of the shell. In some fossil straight shelled nautiloids, cylindrical calcareous growths ("siphuncular deposits") around the siphuncle
334:
connecting ring. Connecting rings are strongly variable in morphology, from narrow homogenous tubes to bulbous, segmented cavities. Some are infolded, sending lobes or blades of calcite into the siphuncle. Connecting rings are typically continuous with the septal necks, and are difficult to
287:. The siphuncle itself is only rarely preserved, but its shape can be inferred from hardened structures which lie around it. Many fossils show the holes where the siphuncle passes through each septum. Around these holes, the rim of the septum is bent into a stout
228:, diffuse from the blood in the siphuncle into the emptying chamber. This is not a form of active pumping: the gas moving into the chamber is a passive process. Most energy is expended through the absorption of water from the chamber.
176:. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the
335:
distinguish without close examination. However, their developmental origin is wholly separate from the shell and septa, and they utilize calcite rather than aragonite as a biomineralized reinforcement.
254:
Generally, the siphuncle is unable to provide a way to change the density of shell rapidly and thus cause the animal to rise or sink at will; rather, the animal must swim up or down as required.
350:), longitudinal rods, and various other concretions. Endosiphuncular deposits are typically thin structures which may be homologous to parts of the septae or connecting rings.
208:
The siphuncle is used primarily in emptying water from new chambers as the shell grows. To perform this task, the cephalopod increases the saltiness of the
1080:
701:
1085:
603:
442:
Mutvei, Harry; Zhang, Yun-bai; Dunca, Elena (2007). "Late
Cambrian Plectronocerid Nautiloids and Their Role in Cephalopod Evolution".
888:
89:
61:
417:
265:
108:
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morphology. Many extinct cephalopods have a much more prominent connecting ring, with a very thick and porous inner
596:
844:
838:
247:, allowing them to keep a stable buoyancy with minimal effort. In the geologic past, many cephalopods grew to an
68:
832:
46:
511:"High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K"
873:
188:
for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a
75:
322:
layers secreted from the tissues of the siphuncle. This fragile and poorly-mineralized form is known as a
1200:
589:
275:
in cross section. Septal necks are preserved, but the thin connecting rings have been degraded and lost.
893:
883:
42:
318:. In living nautiluses, the connecting ring is a simple, thin-walled cylinder, with organic or thinly
57:
1075:
1070:
35:
248:
1177:
558:
Kroger, B; Yun-Bai, Zhang (2008). "Pulsed cephalopod diversification during the
Ordovician".
310:
have fully preserved septal necks and connecting rings outlining the shape of the siphuncle.
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522:
451:
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in the siphuncle, and the water moves from the more dilute chamber into the blood through
8:
1149:
914:
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In each chamber of the shell, the siphuncle is encased by a tubular structure known as a
181:
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of the shell, and thus the shell behaves as a flotation device comparable to the
16:
Strand of tissue passing longitudinally through the shell of a cephalopod mollusk
1106:
928:
919:
878:
743:
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535:
510:
225:
298:
154:. Only cephalopods with chambered shells have siphuncles, such as the extinct
1194:
1131:
681:
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257:
Cephalopods with a wider siphuncle have a higher rate of metabolic activity.
144:
1090:
989:
748:
648:
477:
Kröger, Björn (2003). "The size of the siphuncle in cephalopod evolution".
283:
cephalopods is assumed to have worked in the same general way as in living
236:
338:
Biomineralized structures which develop within the siphuncle are known as
1044:
799:
377:
367:
303:
342:(or simply siphonal deposits). These may include horizontal partitions (
1181:
1136:
948:
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372:
355:
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148:
131:
shell, showing a narrow siphuncle connecting the chambers of the shell
1169:
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24:
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1006:
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Removing water from the chambers of the shell reduces the overall
924:
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327:
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307:
232:
213:
172:
151:
1049:
280:
221:
794:
243:. Typically, cephalopods maintain a density close to that of
209:
204:
Simplified structure and mechanism of cephalopodic siphuncle.
200:
121:
251:(perhaps approaching ten meters in length) thanks to this.
240:
330:
layer. This more strongly-mineralized form is known as a
425:
New Mexico Bureau of Mines and
Mineral Resources, Memoir
358:also contained much of the organisms' body organs.
49:. Unsourced material may be challenged and removed.
184:(chambers). Some older studies have used the term
560:Palaeogeography, Palaeoclimatology, Palaeoecology
1192:
557:
441:
597:
604:
590:
551:
534:
508:
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109:Learn how and when to remove this message
297:
264:
199:
120:
509:King, Andy H.; Evans, David H. (2019).
1193:
611:
476:
415:
585:
884:Flotation devices ("secondary fins")
504:
502:
500:
411:
409:
407:
405:
47:adding citations to reliable sources
18:
143:passing longitudinally through the
13:
1176:) → Juvenile → Subadult → Adult •
306:nautiloid cephalopod fossils from
216:. At the same time gasses, mostly
14:
1212:
497:
402:
920:Hepatopancreas (digestive gland)
843:
837:
831:
464:10.1111/j.1475-4983.2007.00708.x
23:
889:Funnel–mantle locking apparatus
346:), stacked conical structures (
34:needs additional citations for
1076:Nuchal folds (occipital folds)
1071:Nuchal crest (occipital crest)
515:Swiss Journal of Palaeontology
470:
190:mollusc organ of the same name
1:
395:
260:
1182:Protoconch (embryonic shell)
572:10.1016/j.palaeo.2008.12.015
418:"Nautiloid shell morphology"
416:Flower, Rousseau H. (1964).
7:
361:
195:
10:
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536:10.1007/s13358-019-00186-4
125:A cross-section through a
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340:endosiphuncular deposits
479:Senckenbergiana Lethaea
311:
295:(or siphuncle notch).
276:
205:
132:
1163:Developmental stages:
1055:Spadix and antispadix
939:Nephridia ("kidneys")
301:
268:
203:
180:(walls) dividing the
124:
43:improve this article
1150:Squid giant synapse
527:2019SwJP..138...65K
456:2007Palgy..50.1327M
1201:Cephalopod zootomy
1081:Occipital membrane
954:Pericardial glands
649:Argonautid eggcase
491:10.1007/BF03043304
312:
277:
272:Nautilus pompilius
206:
133:
1188:
1187:
1120:
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1019:Suckers and hooks
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944:Nidamental glands
874:Dermal structures
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823:
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710:
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279:The siphuncle of
162:, and the living
119:
118:
111:
93:
1208:
1174:Doratopsis stage
1145:Squid giant axon
1064:Occipital region
975:
974:
915:Ctenidia (gills)
910:Branchial hearts
903:Internal anatomy
867:External anatomy
864:
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566:(1–2): 174–183.
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468:
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450:(6): 1327–1333.
439:
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324:nautilosiphonate
291:tube known as a
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107:
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27:
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1211:
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1141:Nervous system
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1086:Olfactory organ
1059:
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836:
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677:Belemnoid guard
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654:Nautiloid shell
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383:Orthoceratoidea
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332:calciosiphonate
316:connecting ring
302:These polished
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139:is a strand of
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1132:Chromatophores
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978:Brachial crown
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644:Ammonoid shell
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485:(1–2): 39–52.
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226:carbon dioxide
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1028:Buccal region
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934:Needham's sac
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697:Spirula shell
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692:Gladius (pen)
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682:Cirrate shell
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444:Palaeontology
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249:enormous size
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99:December 2008
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63:
60: –
59:
55:
54:Find sources:
48:
44:
38:
37:
32:This article
30:
26:
21:
20:
1162:
1091:Nuchal organ
990:Hectocotylus
879:Fins (wings)
809:
785:Body chamber
749:Periostracum
563:
559:
553:
521:(1): 65–85.
518:
514:
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237:swim bladder
230:
207:
185:
171:
136:
134:
126:
105:
96:
86:
79:
72:
65:
53:
41:Please help
36:verification
33:
1178:Egg fossils
1137:Photophores
1100:Other parts
1045:Odontophore
967:Head &
800:Phragmocone
378:Orthocerida
368:Phragmocone
293:septal neck
269:A shell of
58:"Siphuncle"
1112:Statocysts
949:Osphradium
687:Cuttlebone
613:Cephalopod
396:References
373:Orthoceras
356:Endocerida
344:diaphragms
304:orthocerid
289:aragonitic
285:nautiluses
281:fossilised
261:Morphology
168:cuttlefish
164:nautiluses
160:belemnites
149:cephalopod
69:newspapers
1170:Paralarva
997:Tentacles
810:Siphuncle
769:Umbilicus
754:Sculpture
659:Orthocone
545:1664-2384
389:Baculites
348:endocones
245:sea water
156:ammonites
137:siphuncle
1195:Category
1035:Aptychus
1007:Dactylus
778:Internal
729:Aperture
722:External
715:Features
670:Internal
637:External
362:See also
328:calcitic
320:calcitic
239:in bony
218:nitrogen
196:Function
128:Nautilus
1125:General
925:Ink sac
790:Camerae
764:Sutures
615:anatomy
523:Bibcode
452:Bibcode
431:: 1–78.
308:Morocco
233:density
214:osmosis
182:camerae
173:Spirula
152:mollusk
83:scholar
1050:Radula
1002:Carpus
859:funnel
856:&
854:Mantle
815:Whorls
739:Callus
702:Stylet
543:
224:, and
222:oxygen
186:siphon
170:, and
141:tissue
85:
78:
71:
64:
56:
1166:Spawn
1012:Manus
970:limbs
805:Septa
795:Nacre
759:Spire
744:Lirae
630:Types
622:Shell
421:(PDF)
210:blood
178:septa
147:of a
145:shell
90:JSTOR
76:books
1107:Eyes
1040:Beak
985:Arms
927:and
894:Tail
734:Apex
541:ISSN
241:fish
158:and
135:The
62:news
929:ink
568:doi
564:273
531:doi
519:138
487:doi
460:doi
45:by
1197::
1180:•
1168:→
562:.
539:.
529:.
517:.
513:.
499:^
483:83
481:.
458:.
448:50
446:.
429:13
427:.
423:.
404:^
220:,
192:.
166:,
1172:(
605:e
598:t
591:v
574:.
570::
547:.
533::
525::
493:.
489::
466:.
462::
454::
112:)
106:(
101:)
97:(
87:·
80:·
73:·
66:·
39:.
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