Contrasting modes of construction of Retiolite - type Rhabdosomes
Treść / Zawartość
Investigation of retiolite-type rhabdosomes has so far revealed two contrasting types of construction: 1. In a morphological series including Reteograptus geinitzianus, Gothograptus nassa, Holoretiolites spp. and 'Retiolites' sp. it is possible to demonstrate that sclerotization of the periderm secreted between the zooid and its mantle evagination became progressively localized, culminating in the formation of the highly specialized and sparse framework of Holoretiolites and 'Retiolites' sp. 2. In Retiolites geinitzianus (Barrande) the same kind of peridermal secretion combined with localized sclerotization to produce a superficially similar type of rhabdosome to some of those in the above morphological series, but with a quite different relationship to the secretary tissues of the zooids. Secretion and sclerotization of fibrous strips or 'bandages' seems to have occurred in many normal graptoloids, but resulting in the formation of a continuous cortex. The restriction of the sclerotized 'bandages' in the retiolites, so as to produce a sparse but resilient framework, suggests that their function was mechanical rather than protective.
- CROWTHER, P. and RICKARDS, B. 1977 Cortical Bandages and the Graptolite Zooid. - Geol. Palaeont., 11, 9-46.
- HOLM, G. 1890. Gotlands Graptoliter: Svenska Vetenskaps. - Akad. Handl., Bihang, 16, ser. 4, no. 7, 1-34.
- KIRK, N. H. 1972. Some thoughts an the construction of the rhabdosome in the Graptolithina, with special reference to extrathecal tissue and its bearing on the theory of automobility. - Geol. Dept. Publ., Univ. Coll. Wales, Aberystwyth, 1, 1-21.
- - 1973. Some thoughts on the construction and functioning of the rhabdosome in the Retiolitidae. - Ibidem, 3, 1-26.
- - 1974. More thoughts on the construction of the rhabdosome in the Dendroidea, in the light of the ultrastructure of the Dendreidea and of Mastigograptus. - Ibidem, 6, 1-11.
- - 1975. More thoughts on the construction and functioning of the rhabdosome in the Graptoloidea in the light of their ultrastructure. - Ibidem, 7, 1-21.
- URBANEK, A. and TOWE, K. M. 1974. Ultrastructural studies on graptolites., I. The periderm and its derivatives in Dendroidea and in Mastigograptus. - Smith. Contr. Paleobiol., 20, 1-20.
- - and - 1975. Ultrastructural studies on graptolites. 2. The periderm and its derivatives in the Graptoloidea. - Ibidem, 22, 1-24.