The ultrastructure of some Ordovician graptoloid prosiculae

• Autorzy: Bates D E B
• Języki publikacji: EN

Abstrakty

EN

The graptoloid prosicula (conus and cauda) forms the first part of the growing colony, and was probably secreted during a single continuous episode of growth. The wall is composed of a central unit of criss-cross fibrils (fusellar fabric), interlaced with parallel fibrils whose grouping appears as the spiral line (spiral line fabric). The conus is lined with a granular or felted sheet (sheet fabric). The diaphragm, at the apex of the conus, appears to be formed of fusellar fabric. The cauda is formed of fusellar and spiral fabrics with a central cavity apparently not open to the conus interior. An outer layer (diamond, mesh fabric) of fibrils forming a diamond mesh covers both conus and cauda, and is itself overlain by longitudinal rods. The apex of the cauda is formed of a second domed diaphragm of criss-cross fibrils, covered by a sheet fabric. The nema is extended distally as a series of finger-shaped increments, overlain by bandages. An outermost layer of clustered fibrils (stellate fabric) is occasionally present, lying on, or formed by a modification of, the diamond mesh fibrils of the conus.

PL

Prosicula graptolitów jest najwcześniej tworzoną częscią rabdozomu i była najprawdopodobniej budowana przez pierwszego zooida tuż po jego metamorfozie ze swobodnie żyjącej larwy. Przedmiotem niniejszej pracy jest ultrastruktura prosicul z późnoordowickiego wapienia Viola Springs. Prosicule z tej formacji skalnej zapewne należą do dwuseryjnych grapiolitów, których najpospolitszym występującym tam gatunkiem jest Geniulograptus typicalis. Na przełamach ścianek prosiculi obserwowanych w skaningowym mikroskopie elektronowym ukazuje się ich trójwarstwowa budowa, z wysciółką wewnątrz o nieregularnie orientowanych włóknach, środkową ścianą z wplecionymi włóknami tworzącymi linię spiralną oraz zewnętrzną warstwą o włóknach krzyżujących się w rombowy splot. Środkowa warstwa ściany tworzona była zapewne w jednorazowym akcie sekrecji ale jej struktura nie różni się istotnie od fuzellarnych elementów rabdozomu. Nema powstawała jako seria palcowatych przyrostów okrytych przez bandaże; jej wnętrze jest lite, nie pozostawia miejsca na jakiekolwiek miękkie tkanki.

Słowa kluczowe

PL

szkielet promienisty; ordowik; skamienialosci; graptolity; paleontologia; formacje skalne; rabdozomy; ultrastruktura; wapienie; Geniculograptus typicalis; prosicule

• Wydawca: -
• Czasopismo: Acta Palaeontologica Polonica
• Rocznik: 1996
• Tom: 41
• Numer: 1
• Opis fizyczny: s.39-57,fot.,bibliogr.

Twórcy

autor

Bates D E B

• lnstitute of Earth Studies, University of Wales Aberystwyth, Aberystwyth, Dyfed SY23 3DB, U.K.

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