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larva. The bilateral shell grew into two valves as the rostroconch entered adulthood. Adult rostroconchs differ from bivalves because they have no functional hinge. Unlike the shell of a bivalve, which was able to move or articulate, the shell layers of a rostroconch โ the layers of rigid calciteโ
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Approximately 3 dozen genera and an even greater number of species have been described. Generally, rostroconchs are small, less than two centimeters in length, but larger forms, found in United States
Devonian limestones, can grow to a length of 15 cm.
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The posterior of the shell contains a flattened tube that is called the rostrum. The rostroconch probably burrowed itself into sediment, anterior first, leaving the rostrum above the sediment to be used as a water filtration system.
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and rostroconchs probably had an extendable muscular foot, indicated by a prominent anterior gape in the rostroconch's shell. It seems, however, that the internal anatomy and morphology of the foot were closer to that of the
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continue across the whole dorsal area of the rostroconch. The two valves would have been rigidly fixed in place, and would have to have been broken periodically to allow the rostroconch shell to grow.
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317:, a more advanced rostroconch, the outer shell layers do not cross the entire margin, suggesting independent steps towards the bivalve flexible hinge.
302:. True Rostroconchs appeared during the Ordovician, heavily competing with the bivalves until their decline in the end-early Ordovician turnover.
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228:, but were later given their own class. They have a single shell in their larval stage, and the adult typically has a single, pseudo-bivalved
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https://web.archive.org/web/20090302181354/http://www.palaeos.com/Invertebrates/Molluscs/BasalMollusca/Rostroconchia/Rostroconchia.html
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Pojeta, J., Runnegar, B., Morris, N. J., Newell, N. D. (1972). Rostroconchia: a new class of bivalved mollusks.
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part of the shell probably pointed downward and had a gap from which the foot could probably emerge.
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had a hinge in which all shell layers covered the dorsal region resulting in a very rigid shell. In
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Rostroconchs began their life as a small, bilaterally symmetrical, univalved protoconch
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Some evidence suggests that the conocardoid rostroconchs were the predecessors to the
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lifestyle. There were probably more than 1,000 species of members of this class.
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is the earliest, very primitive, rostroconch genus dating from the Late
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Kouchinsky, A. V. (1999). "Shell microstructures of the Early
Cambrian
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382:Learn how and when to remove this message
345:This article includes a list of general
264:Externally, rostroconchs look much like
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305:Early, primitive rostroconchs such as
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224:. They were initially thought to be
462:PALAEOS, 2002, Rostroconchia. URL:
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428:10.1111/j.1502-3931.1999.tb00537.x
351:it lacks sufficient corresponding
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762:Prehistoric protostome classes
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466:. Accessed November 16, 2008.
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742:Prehistoric mollusc taxonomy
453:10.1126/science.177.4045.264
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747:Cambrian first appearances
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126:Scientific classification
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16:Extinct class of molluscs
260:Morphology and lifestyle
366:more precise citations.
236:and muscular foot. The
216:dating from the early
696:Paleobiology Database
289:Evolutionary history
752:Permian extinctions
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683:Open Tree of Life
597:Taxon identifiers
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447:(4045): 264โ267.
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27:Temporal range:
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117:Technophorus
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629:Wikispecies
541:Cephalopoda
500:Classes of
364:introducing
314:Conocardium
169:Subphylum:
767:Conchifera
731:Categories
551:Scaphopoda
536:Gastropoda
412:Watsonella
408:Anabarella
347:references
328:References
322:Scaphopoda
278:planktonic
271:scaphopods
173:Conchifera
308:Ribeiroia
246:sedentary
149:Kingdom:
143:Eukaryota
662:11186032
620:Q1422647
614:Wikidata
546:Bivalvia
502:Molluscs
266:bivalves
250:infaunal
238:anterior
226:bivalves
218:Cambrian
214:molluscs
163:Mollusca
159:Phylum:
153:Animalia
139:Domain:
31:Cambrian
688:5295954
442:Science
416:Lethaia
360:improve
220:to the
211:extinct
190:Pojeta
179:Class:
119:sharpei
35:Permian
714:849233
349:, but
234:mantle
194:, 1972
192:et al.
709:WoRMS
670:IRMNG
649:7NVXD
248:semi-
230:shell
207:class
205:is a
701:8123
675:1502
657:GBIF
410:and
201:The
41:Pre๊
644:CoL
449:doi
445:177
424:doi
209:of
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398:^
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91:Pg
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578:โ
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493:e
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183:โ
96:N
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81:J
76:T
71:P
66:C
61:D
56:S
51:O
46:๊
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