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Most fossil forms had multiple columns of ambulacral plates, rather than the two rows found in all living species of sea urchin. They also lacked a perignathic girdle around the mouth.
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assemblage of stem forms, united only by their lack of more advanced features, rather than a true taxonomic
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seas. However, the great majority of species died out during the
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sea urchins became common. Today, only a single order, the
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542:Extant Ordovician first appearances
537:Middle Ordovician first appearances
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485:. You can help Knowledge by
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200:is a subclass of primitive
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291:Barnes, Robert D. (1982).
204:that were abundant in the
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231:The group is probably a
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312:"Palaeozoic Echinoidea"
212:, as the more advanced
16:Subclass of sea urchins
477:This article about a
431:Paleobiology Database
293:Invertebrate Zoology
384:Perischoechinoidea
370:Perischoechinoidea
340:Perischoechinoidea
244:Perischoechinoidea
198:Perischoechinoidea
174:Perischoechinoidea
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364:Wikispecies
202:sea urchins
178:McCoy, 1849
532:Echinoidea
526:Categories
479:sea urchin
285:References
271:Megalopoda
214:euechinoid
206:Palaeozoic
170:Subclass:
164:Echinoidea
251:Cidaroida
242:Subclass
218:Cidaroida
190:See text
140:Kingdom:
134:Eukaryota
349:Wikidata
227:Taxonomy
210:Mesozoic
150:Phylum:
144:Animalia
130:Domain:
355:Q149430
184:Orders
160:Class:
449:160731
423:669478
397:157822
317:20 Dec
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276:Order
269:Order
262:Order
255:Order
249:Order
481:is a
444:WoRMS
436:86958
237:clade
483:stub
410:7626
405:NCBI
392:ITIS
319:2009
297:ISBN
35:PreꞒ
379:ADW
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280:†
273:†
266:†
259:†
90:N
80:K
75:J
70:T
65:P
60:C
55:D
50:S
45:O
40:Ꞓ
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