摘要:

The external features of a shortened, apluteal development (lacking a pluteus larva) are described. Some features are unusual for echinoids. The large egg is distinctively marked by dark and pale coloured yolk. The sperm entry point is marked by a dark yolk spot and the first cleavage plane in most embryos is through the meridian on which the sperm entry point lies. Dark yolk in the animal hemisphere segregates largely to one blastomere in the two‐cell embryo and pale yolk segregates to the other as a result of yolk movements during the first cell cycle. Progeny of the pale‐yolk blastomere form adult oral structures and progeny of the dark‐yolk blastomere form adult aboral structures. There is no feeding planktonic pluteus larva. The gastrula develops into a demersal vestibula larva with bilateral symmetry. The plane of symmetry is coincident with the Carpenter axis that defines a plane of symmetry through the madreporite in adult echinoderms. The coincidence shows that the anterior ambulacrum is vegetal with respect to egg polarity and the interradius originating at the madreporite is animal. The bilateral symmetry of the vestibula offers insight into the origin of radial symmetry in echinoderms and the body plan of an echinoderm anc

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1995.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We present a cladistic analysis of the Cirripedia Thoracica using morphological characters and the Acrothoracica and Ascothoracida as outgroups. The list of characters comprised 32 shell and soft body features. The operational taxonomic units (OTUs) comprised 26 well‐studied fossil and extant taxa, principally genera, since uncertainty about monophyly exists for most higher ranking taxonomic units. Parsimony analyses using PAUP 3.1.1 and Hennig86 produced 189 trees of assured minimal length. We also examined character evolution in the consensus trees using MacClade and Clados. The monophyly of the Balanomorpha and the Verrucomorphasensu strictois confirmed, and all trees featured a sister group relationship between the ‘living fossilNeoverrucaand me Brachylepadomorpha. In the consensus trees the sequential progression of ‘pedunculate‘sister groups up to a node containingNeolepasalso conforms to current views, but certain well‐established taxa based solely on plesiomorphies stand out as paraphyletic, such as Pedunculata (= Lepadomorpha); Eolepadinae, Scalpellomorpha and Chthamaloidea. The 189 trees differed principally in the position of shell‐less pedunculates,Neoverruca,the scalpelloidCapitulum,and the interrelationships within the Balanomorpha, although the 50% majority rule consensus tree almost fully resolved the latter. A monophyletic Sessilia comprising both Verrucomorpha and Balanomorpha appeared among the shortest trees, but not in the consensus. A tree with a monophyletic Verrucomorpha includingNeoverrucahad a tree length two steps longer than the consensus trees. Deletion of all extinct OTUs produced a radically different tree, which highlights the importance of fossils in estimating cirripede phylogeny. Mapping of our character set onto a manually constructed cladogram reflecting die most recent scenario of cirripede evolution resulted in a tree length five steps longer than any of our shortest trees. Our analysis reveals that several key questions in cirripede phylogeny remain unsolved, notably the position of shell‐less forms and the transition from ‘pedunculate‘to ‘sessile‘barnacles. The inclusion of more fossil species at this point in our understanding of cirripede phylogeny will only result in even greater levels of uncertainty. When constructing the character list we also identified numerous uncertainties in the homology of traits commonly used in discussing cirripede evolution. Our study highlights larval ultrastructure, detailed studies of early ontogeny, and molecular data as the most promising area

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1995.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The phylogenetic relationships of the Amphitritinae (Polychaeta: Terebellidae) were studied using parsimony analysis of 22 external morphological characters. To choose outgroups to polarize the characters, I carried out a preliminary analysis of the relationships of the four terebellid subfamilies and the Trichobranchidae. The single most parsimonious tree from the analysis supports monophyly of the Terebellidae by the presence of ventral glandular shields. However, this character is homoplasious within the Terebellomorpha, and further evaluation of the Terebellidae is recommended.ArtacamaandThelepuswere chosen as outgroups for the analysis of amphitritine genera. The generic level analysis yielded seven equally parsimonious trees, which are consistent in their topologies except for the relationships among seven genera in one large clade. In all trees,Artacamais the sister taxon to a large clade within the Amphitritinae; the Artacaminae is therefore synonymized with the Amphitritinae, which is diagnosed by the presence of double rows of uncini. Within the Amphitritinae, the status of several monotypic genera is questioned; plesiomorphic character states indicated by the analysis are discussed. The results presented are offered as working hypotheses of the relationships among amphitritine genera. The large number of homoplasies indicated by the analysis emphasizes the need to further evaluate these hypotheses using additional characters. With a robust phylogenetic hypothesis of amphitritine relationships, a re‐classification of the group based on apomorphic character states can be undertaken, and questions regarding the evolution of morphological characters, reproductive modes, or biogeographical patterns can be properly addresse

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1995.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Book reviewed in this article:Vertebrate Zoology. An experimental field approach,by Nelson G. Hairston Sr.Animals of Sandy Shares.Naturalist Handbook 21; Peter J. Hayward.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1995.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY