On the nature and development of graptoblasts

• Autorzy: Mierzejewski P

Warianty tytułu

PL

O naturze i rozwoju graptoblastow

• Języki publikacji: EN

Abstrakty

EN

Two specimens of graptoblasts, which provisionally may be assigned to 'Graptoblastoides' sp. and 'Graptoblastus' sp., are described from the early Llandovery of Anticosti Island (Québec, Canada). Previous reports of Silurian graptoblasts were restricted to a single specimen from Poland. One of the new specimens is morphologically distinct from all known graptoblasts - both chambers of the inner cavity contain numerous incomplete septae, here referred to as hemiseptae. SEM observations show distinct two-layered character of the transverse septum, whereas the hemiseptae show no trace of layering. Hemiseptae and the transverse septum are derivatives of the inner lining of the graptoblast. The 'genera' Graptoblastus Kozłowski, 1949 and Graptoblastoides Kozłowski, 1949 are interpreted as stages in graptoblast development, and are consequently replaced by the purely descriptive terms 'graptoblastus' and 'graptoblastoides'. The following stages of graptoblast development are recognized: (1) pre-graptoblastoides stage, (2) early graptoblastoides stage, (3) late graptoblastoides stage, (4) early graptoblastus stage, and (5) late graptoblastus stage. A graptoblast s.s. (i.e., devoid of a blastotheca) and its developmental stages strikingly resemble the earliest stages of the astogeny of the modern pterobranch Rhabdopleura. These observations support A.Urbanek's hypothesis that zooids became encysted within graptoblasts and rejuvenated by a process of metamorphosis.

PL

Z wapieni wczesnego landoweru wyspy Anticosti (Kanada, Quebec) opisano dwa graptoblasty. Jest to pierwsze znalezisko sylurskich graptoblastów na obszarze pozaeuropejskim. Reprezentują one oba dotychczas znane parataksonomiczne "rodzaje", a mianowicie Graptoblastus Kozłowski, 1949 i Graptoblastoides Kozłowski, 1949. Zbadany graptoblastus No. 1 ma we wnętrzu swoich obu komór nieznane dotąd niepełne przegrody, dla których wprowadzono nazwę hemiseptae. Wyrażono pogląd, że formy graptoblastoides i graptoblastus reprezentują kolejne stadia w rozwoju osobniczym graptoblastów. Zwrócono uwagę na uderzające podobieństwo graptoblastów do najwcześniejszych stadiów rozwojowych larwy współzesnej Rhabdopleura Allman, 1869 (Pterobranchia, Rhabdopleurida). Zdaniem autora, w graptoblastach zachodził proces metamorfozy pączka terminalnego do swobodnie poruszającej się larwy, wydostającej się na zewnątrz poprzez cryptopyle.

Słowa kluczowe

PL

graptoblasty; Graptoblastoides; Kanada; Graptoblastus; paleontologia; wyspa Anticosti

• Wydawca: -
• Czasopismo: Acta Palaeontologica Polonica
• Rocznik: 2000
• Tom: 45
• Numer: 3
• Opis fizyczny: s.227-238,rys.,fot.,bibliogr.

Twórcy

autor

Mierzejewski P

• Instytut Paleobiologii PAN, ul.Twarda 51-55, 00-818 Warszawa

Bibliografia

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