On the Origin and Phylogeny of the Coelenterates

Hand, Cadet

doi:10.2307/2411883

Cited by 24 publications

(26 citation statements)

References 2 publications

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“…There is no consensus as to which of these two types of life history is ancestral. One view (figure 1) is that the medusa-only life cycle, seen today only amongst trachyline hydrozoans, represents the primitive condition which gave rise to the medusa-polyp alternation of generations characteristic of all other hydrozoans, scyphozoans and cubozoans (see, for example, Hyman 1940 ;Hand 1959 ;Brusca & Brusca 1990). Whilst this view regards the Anthozoa as having undergone secondary loss of the medusoid stage, another opinion is that this class is most representative of ancestral character states (i.e.…”

Section: Introductionmentioning

confidence: 99%

Internal and external relationships of the Cnidaria : implications of primary and predicted secondary structure of the 5'–end of the 23S–like rDNA

Odorico

Miller

1997

Proc. R. Soc. Lond. B

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SUMMARYSince both internal (class-level) and external relationships of the Cnidaria remain unclear on the basis of analyses of 18S and (partial) 16S rDNA sequence data, we examined the informativeness of the 5h-end of the 23S-like rDNA. Here we describe analyses of both primary and predicted secondary structure data for this region from the ctenophore Bolinopsis sp., the placozoan richoplax adhaerens, the sponge H meniacidon heliophila, and representatives of all four cnidarian classes. Primary sequence analyses clearly resolved the Cnidaria from other lower Metazoa, supported sister group relationships between the Scyphozoa and Cubozoa and between the Ctenophora and the Placozoa, and confirmed the basal status of the Anthozoa within the Cnidaria. Additionally, in the ctenophore, placozoan and sponge, noncanonical base pairing is required to maintain the secondary structure of the B12 region, whereas amongst the Cnidaria this is not the case. Although the phylogenetic significance of this molecular character is unclear, our analyses do not support the close relationship between Cnidaria and Placozoa suggested by previous studies.

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Section: Introductionmentioning

confidence: 99%

Internal and external relationships of the Cnidaria : implications of primary and predicted secondary structure of the 5'–end of the 23S–like rDNA

Odorico

Miller

1997

Proc. R. Soc. Lond. B

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“…The gastrula of many lower turbellarians is likewise a stereogastrula. This correlation, together with symmetry considerations to be discussed presently, has resulted in the postulation of various planuloid or gastruloid ancestors for the Metazoa (e.g., Hyman, 1940;Hand, 1959;Jagersten, 1955). While the arguments put forward in favor of such ancestors are cogent, the various lines of evidence mentioned below suggest that, whether or not they existed, no phylogenetic significance can logically be placed either on the ancestors or on the planuloid-type larvae.…”

Section: Planuloid Ancestorsmentioning

confidence: 99%

“…As Hanson (1958) points out, the sagittocysts of Acoela are reminiscent of nematocysts. One interpretation of such a distribution of these organelles is that Cnidaria and Ctenophora have a common ancestor which, in turn, is fairly closely related to the Protozoa (Hand, 1959). However, another interpretation might be that, aside from possessing these nematocyst-like structures, the organisms have nothing else in common which suggests a close relationship.…”

Section: Michael J Greenbergmentioning

confidence: 99%

“…Early acoelan cleavage is biradial. 1 Ento-1 It is often stated that acoelan cleavage is a modification of the spiral type (Dawydoff, 1928;Hyman, 1951;Hand, 1959). Actually, only the second and third cleavage appear to be spirally oriented in these forms.…”

Section: Cleavage Patternsmentioning

confidence: 99%

“…It is only in the Anthozoa that bilaterality finally appears but not in early cleavage. Hand (1959) notes that, on the basis of their drastically different symmetry and polarity, the platyhelminth and cnidarian lines must have diverged very early from the common planuloid ancestral type. That this is true is not to be doubted.…”

Section: Cleavage Patternsmentioning

confidence: 99%

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Ancestors, Embryos, and Symmetry

Greenberg¹

1959

Systematic Zoology

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Muscle and nerve net organization in stalked jellyfish (Medusozoa: Staurozoa)

Westlake

Page

2016

Journal of Morphology

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Staurozoan cnidarians display an unusual combination of polyp and medusa characteristics and their morphology may be informative about the evolutionary origin of medusae. We studied neuromuscular morphology of two staurozoans, Haliclystus 'sanjuanensis' and Manania handi, using whole mount immunohistochemistry with antibodies against FMRFamide and α-tubulin to label neurons and phalloidin to label muscles. All muscles appeared to lack striations. Longitudinal interradial muscles are probable homologues of stalk muscles in scyphopolyps, but in adult staurozoans they are elaborated to inwardly flex marginal lobes of the calyx during prey capture; these muscles are pennate in M. handi. Manubrial perradial muscles, like the manubrium itself, are an innovation shared with pelagic medusae and manubrial interradial muscles are shared with scyphozoan ephyra. Marginal muscles of M. handi displayed occasional synchronous contraction reminiscent of a medusa swim pulse, but contractions were not repetitive. The nerve net in both species showed regional variation in density and orientation of neurons. Some areas labeled predominantly by α-tubulin antibodies (exumbrellar epidermis), other areas labeled exclusively by FMRFamide antibodies (dense plexus of neurites surrounding the base of secondary tentacles, neuronal concentration at the base of transformed primary tentacles; gastrodermal nerve net), but most areas showed a mix of neurons labeled by these two antibodies and frequent co-labeling of neurons. Transformed primary tentacles had a concentration of FMRFamide-immunoreactive neurons at their base that was associated with a pigment spot in M. handi; this is consistent with their homology with rhopalia of medusae, which are also derived from primary tentacles. The muscular system of these staurozoans embodies characteristics of both scyphopolyps and pelagic medusae. However, their nerve net is more polyp-like, although marginal concentrations of the net associated with primary and secondary tentacles may facilitate the richer behavioral repertoire of staurozoans relative to polyps of other medusozoans. J. Morphol. 278:29-49, 2017. ©© 2016 Wiley Periodicals,Inc.

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On the Origin and Phylogeny of the Coelenterates

Cited by 24 publications

References 2 publications

Internal and external relationships of the Cnidaria : implications of primary and predicted secondary structure of the 5'–end of the 23S–like rDNA

Internal and external relationships of the Cnidaria : implications of primary and predicted secondary structure of the 5'–end of the 23S–like rDNA

Ancestors, Embryos, and Symmetry

Muscle and nerve net organization in stalked jellyfish (Medusozoa: Staurozoa)

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