Limits...
Plated Cambrian bilaterians reveal the earliest stages of echinoderm evolution.

Zamora S, Rahman IA, Smith AB - PLoS ONE (2012)

Bottom Line: Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution.Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta.This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeontology, The Natural History Museum, London, United Kingdom.

ABSTRACT
Echinoderms are unique in being pentaradiate, having diverged from the ancestral bilaterian body plan more radically than any other animal phylum. This transformation arises during ontogeny, as echinoderm larvae are initially bilateral, then pass through an asymmetric phase, before giving rise to the pentaradiate adult. Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution. Here we report new fossils from the early middle Cambrian of southern Europe that are the first echinoderms with a fully bilaterian body plan as adults. Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta. This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.

Show MeSH

Related in: MedlinePlus

Courtessolea moncereti Domínguez-Alonso, 1999 (MNHN F.A45783).Cambrian Series 3, Stage 5, Ferrals-les-Montagnes, France. Dorsal view and interpretive diagram (note that the theca shows a small degree of post-mortem distortion). Abbreviations: ap (anal pyramid), LL (adoral left plate), M (marginal plate), mf (marginal frame), Mp (posterior marginal plate), RL (adoral right plate), stp (spiny ctenidial plates), sp (suroral plate), tcp (tessellate ctenidial plates), ui (upper integument).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3368939&req=5

pone-0038296-g006: Courtessolea moncereti Domínguez-Alonso, 1999 (MNHN F.A45783).Cambrian Series 3, Stage 5, Ferrals-les-Montagnes, France. Dorsal view and interpretive diagram (note that the theca shows a small degree of post-mortem distortion). Abbreviations: ap (anal pyramid), LL (adoral left plate), M (marginal plate), mf (marginal frame), Mp (posterior marginal plate), RL (adoral right plate), stp (spiny ctenidial plates), sp (suroral plate), tcp (tessellate ctenidial plates), ui (upper integument).

Mentions: Courtessolea (Figure 6) is similar to Ctenoimbricata, except in having a complete dorsal and ventral ctenidium of large spinose plates and a much-reduced band of tessellate plates dorsally (probably homologous with the imbricate roof of Ctenoimbricata). It is bilaterally symmetrical with a single ring of marginal frame plates, and its periproct opens through the dorsal plated membrane immediately in front of the posterior marginal plate and on the anterior-posterior axis. There are four marginal plates at the anterior forming part of the ctenidium, three marginal plates (M2, M3, M4) along each side and a single plate bounding the tapering posterior part (Mp).


Plated Cambrian bilaterians reveal the earliest stages of echinoderm evolution.

Zamora S, Rahman IA, Smith AB - PLoS ONE (2012)

Courtessolea moncereti Domínguez-Alonso, 1999 (MNHN F.A45783).Cambrian Series 3, Stage 5, Ferrals-les-Montagnes, France. Dorsal view and interpretive diagram (note that the theca shows a small degree of post-mortem distortion). Abbreviations: ap (anal pyramid), LL (adoral left plate), M (marginal plate), mf (marginal frame), Mp (posterior marginal plate), RL (adoral right plate), stp (spiny ctenidial plates), sp (suroral plate), tcp (tessellate ctenidial plates), ui (upper integument).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3368939&req=5

pone-0038296-g006: Courtessolea moncereti Domínguez-Alonso, 1999 (MNHN F.A45783).Cambrian Series 3, Stage 5, Ferrals-les-Montagnes, France. Dorsal view and interpretive diagram (note that the theca shows a small degree of post-mortem distortion). Abbreviations: ap (anal pyramid), LL (adoral left plate), M (marginal plate), mf (marginal frame), Mp (posterior marginal plate), RL (adoral right plate), stp (spiny ctenidial plates), sp (suroral plate), tcp (tessellate ctenidial plates), ui (upper integument).
Mentions: Courtessolea (Figure 6) is similar to Ctenoimbricata, except in having a complete dorsal and ventral ctenidium of large spinose plates and a much-reduced band of tessellate plates dorsally (probably homologous with the imbricate roof of Ctenoimbricata). It is bilaterally symmetrical with a single ring of marginal frame plates, and its periproct opens through the dorsal plated membrane immediately in front of the posterior marginal plate and on the anterior-posterior axis. There are four marginal plates at the anterior forming part of the ctenidium, three marginal plates (M2, M3, M4) along each side and a single plate bounding the tapering posterior part (Mp).

Bottom Line: Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution.Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta.This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.

View Article: PubMed Central - PubMed

Affiliation: Department of Palaeontology, The Natural History Museum, London, United Kingdom.

ABSTRACT
Echinoderms are unique in being pentaradiate, having diverged from the ancestral bilaterian body plan more radically than any other animal phylum. This transformation arises during ontogeny, as echinoderm larvae are initially bilateral, then pass through an asymmetric phase, before giving rise to the pentaradiate adult. Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution. Here we report new fossils from the early middle Cambrian of southern Europe that are the first echinoderms with a fully bilaterian body plan as adults. Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta. This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.

Show MeSH
Related in: MedlinePlus