Dendroidea sentence example
- There are two main groups, or sub-phyla: the Graptoloidea or Graptolites proper, and the Dendroidea or tree-like Graptolites; the former is typified by the unbranched genus Monograptus and the latter by the many-branched genus Dendrograptus.
- In the Dendroidea, as a rule, the polypary is non-symmetrical in shape and tree-like or shrub-like in habit, with numerous branches irregularly disposed, and with a distinct stem-like or short basal portion ending below in root-like fibres or in a membranous disk or sheet of attachment.
- Of the early development of the polypary in the Dendroidea little is known, but the more mature stages have been fully worked out.
- But in striking contrast to what obtains among the Graptoloidea in general, the budding orifices in the Dendroidea become closed,, and all the various cells shut off from each other.
- The classification of the Dendroidea is as yet unsatisfactory: the families most conspicuous are those typified by the genera Dendrograptus, Dictyonema, Inocaulis and Thamnograptus.Advertisement
- In the Dendroidea, as already pointed out, the bithecae were possibly gonothecae, but they have been interpreted by some as nematophores.
- As respects the mode of life of the Graptolites there can be little doubt that the Dendroidea were, with some exceptions, sessile or benthonic animals, their polyparies, like those of the recent Calyptoblastea, growing upwards, their bases remaining attached to the sea floor or to foreign bodies, usually fixed.
- The Dendroidea alone, however, have this extended range, the Graptoloidea becoming extinct at the close of Silurian time.
- Both groups make their first appearance together near the end of the Cambrian; but while in the succeeding Ordovician and Silurian the Dendroidea are comparatively rare, the Graptoloidea become the most characteristic and, locally, the most abundant fossils of these systems.