On the Number of Rays in Starfish

Hotchkiss, Frederick H. C.

doi:10.1093/icb/40.3.340

Cited by 16 publications

(32 citation statements)

References 38 publications

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“…Indeed, the sixth arm appears in the C-D interradial in almost all cases. Moreover it appears on the dorsal (C) end of the hydrocoel crescent, and appears usually markedly earlier than its successors (if any) (Hotchkiss 2000). This was found for the six-rayed Leptasterias, as well as for Pycnopodia, Stichaster, Crossaster, Solaster, Patiriella, Acanthaster, and Heliaster.…”

Section: An Evolutionary and Developmental Modelmentioning

confidence: 77%

A hexamer origin of the echinoderms' five rays

Lussanet

2011

Evolution &Amp; Development

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Of the major deuterostome groups, the echinoderms with their multiple forms and complex development are arguably the most mysterious. Although larval echinoderms are bilaterally symmetric, the adult body seems to abandon the larval body plan and to develop independently a new structure with different symmetries. The prevalent pentamer structure, the asymmetry of Lovén's rule and the variable location of the periproct and madrepore present enormous difficulties in homologizing structures across the major clades, despite the excellent fossil record. This irregularity in body forms seems to place echinoderms outside the other deuterostomes. Here I propose that the predominant five-ray structure is derived from a hexamer structure that is grounded directly in the structure of the bilaterally symmetric larva. This hypothesis implies that the adult echinoderm body can be derived directly from the larval bilateral symmetry and thus firmly ranks even the adult echinoderms among the bilaterians. In order to test the hypothesis rigorously, a model is developed in which one ray is missing between rays IV-V (Lovén's schema) or rays C-D (Carpenter's schema). The model is used to make predictions, which are tested and verified for the process of metamorphosis and for the morphology of recent and fossil forms. The theory provides fundamental insight into the M-plane and the Ubisch', Lovén's, and Carpenter's planes and generalizes them for all echinoderms. The theory also makes robust predictions about the evolution of the pentamer structure and its developmental basis.

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Section: An Evolutionary and Developmental Modelmentioning

confidence: 77%

A hexamer origin of the echinoderms' five rays

Lussanet

2011

Evolution &Amp; Development

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“…In asteroids with more than five arms, Hotchkiss (2000) describes several species in which the extra primary podial buds are added in the region where the hydrocoele ring closes, which in the notation used here, is between radius I and radius II, although in this region, the timing and pattern in which extra arms are added is variable (Hotchkiss 2000).…”

Section: Match With the Skeletal Platesmentioning

confidence: 99%

On the sites of secondary podia formation in a juvenile echinoid: growth of the body types in echinoderms

Morris

2009

Dev Genes Evol

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The growth of the adult echinoderm body is addressed here in the echinoid Holopneustes purpurescens in a study of the early development of the secondary podia along the five radial canals of the adult rudiment. At a stage when the first four secondary podia have formed along each radius oral to the primary podium, two podia are on one side of the radius and two are on the other side, all at a different distance from the primary podium. The pattern of the connexions of these secondary podia to the radial canals changes in successive radii in a manner similar to Lovén's law for skeletal plates and matches the reported sequence in the times at which the first ambulacral skeletal plates form in the adult echinoid rudiment. A similar pattern is described for the reported origins of the secondary podia in apodid holothurians. A common plan for the growth of the body types is described for echinoids, asteroids, holothurians and concentricycloids. The five metameric series of secondary podia formed in echinoderms have a coelomic developmental origin like the single metameric series of somites formed in the axial structures of chordates.

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“…Perhaps the most striking of these is the five‐fold body symmetry of adult echinoderms. The origin and nature of echinoderm pentamerism has been well debated (see, for example, Nichols, 1967a, b; Stephenson, 1967, 1974, 1979; Lawrence, 1988; Lawrence & Komatsu, 1990; Hotchkiss, 1998a, b, 2000) but remains contentious, particularly because a number of early taxa (e.g. carpoids: Smith, 2005; helicoplacoids: Sprinkle & Wilbur, 2005) were not pentaradial.…”

Section: Echinoderm Symmetry and Palaeozoic Multiradiate Asteroidsmentioning

confidence: 99%

“…Asteroids and, to a lesser extent, ophiuroids are the exception: although most species are five‐rayed, many deviations are encountered, across both time and taxa. Of 34 extant asteroid families, 20 include only five‐rayed forms, nine have both five‐rayed and multiradiate species, and five families are exclusively multiradiate (Hotchkiss, 2000). As most of the multiradiate forms have ray numbers indivisible by five, questions are raised about the nature of pentamerism, both in starfish and across the echinoderms as a whole.…”

Section: Echinoderm Symmetry and Palaeozoic Multiradiate Asteroidsmentioning

confidence: 99%

“…In a paper describing two Mississippian species, Blake & Guensburg (1989) examined the palaeobiological implications of supernumerary rays, while Hotchkiss (2000) provided a comprehensive review and analysis of the possible origins of multiradiate asteroids. These studies apart, there has been very little work on the origin and ecological significance of early multiradiate taxa.…”

Section: Introductionmentioning

confidence: 99%

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Evolutionary and ecological significance of Lepidaster grayi, the earliest multiradiate starfish

Herringshaw

Smith

Thomas

2007

Zoological Journal of the Linnean Society

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Lepidaster grayi Forbes, 1850, from the Much Wenlock Limestone Formation (Silurian: Wenlock) of England, is the earliest species of starfish (Echinodermata: Asteroidea) to deviate from pentaradial symmetry, having 13 rays rather than five. Based on the patterns of supernumerary ray development seen in extant multiradiate asteroids, two possible models are evaluated for the origin of the eight additional rays seen in L. grayi . In the 'all-in-one' model, all rays were added in the same interradius, whereas in the 'quadrants' model generations of rays would have been added in each of four interradii. The smallest specimen of L. grayi , apparently having only nine rays, suggests that the 'quadrants' model is most probable for the species. The presence of supernumerary rays in Silurian starfish, coupled with the existence of numerous other Palaeozoic multiradiate taxa, shows that asteroids have been able to deviate from pentamerism for most of their evolutionary history, and the variety of methods of supernumerary ray addition indicates that the multiradiate condition is homoplastic. The ecological significance of multiradiate Palaeozoic starfish is reviewed: the mouth frame of L. grayi had considerably greater flexibility than that of contemporaneous fiverayed species and, in combination with its supernumerary rays, enabled L. grayi to manipulate and consume larger food items. It is probable that Silurian starfish utilized a similar range of trophic guilds as those exploited by extant taxa.

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On the Number of Rays in Starfish

Cited by 16 publications

References 38 publications

A hexamer origin of the echinoderms' five rays

A hexamer origin of the echinoderms' five rays

On the sites of secondary podia formation in a juvenile echinoid: growth of the body types in echinoderms

Evolutionary and ecological significance of Lepidaster grayi, the earliest multiradiate starfish

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