New insights into Lithocodium aggregatum Elliott 1956 and Bacinella irregularis Radoicic 1959 (Late Jurassic-Lower Cretaceous): two ulvophycean green algae (?Order Ulotrichales) with a heteromorphic life cycle (epilithic/euendolithic)

摘要

The Late Jurassic-Lower Cretaceous microorganisms incertae sedis Lithocodium aggregatum Elliott and Bacinella irregularis RadoiiA double dagger are taxonomically studied based on material from the Lower Aptian of the western Maestrat Basin (Spain). This study is supplemented with detailed photographs from Elliot's type-material. Given that the original description of Lithocodium aggregatum is ambiguous, a detail from the holotype is chosen as an epitype to serve as an interpretative type (article 9.7 ICBN). Lithocodium is re-interpreted as a filamentous-septate heterotrichale ulvophycean alga (?order Ulotrichales) exhibiting a heteromorphic life cycle consisting of two phases: an epilithic gametophytic and a euendolithic sporophytic (Gomontia stage). Bacinella irregularis is interpreted and redescribed as a purely euendolithic ulvophycean alga which bores into either Lithocodium aggregatum or the substrate below Lithocodium crusts. A small microendolith boring into Lithocodium crusts capable of cryptobiotically stretching within its filamentous network is tentatively assigned to the siphonal chlorophyte Ostreobium Bornet and Flahault. Another associated microfilamentous boring chlorophyte with characteristic long thin hairs (setae) is described as Phaeophila? sp. The euendolithic community comprises a variety of micro- and macroborings that affect the thalli of Lithocodium. Finally, the filaments of the outer zone of the Lithocodium crust are infested by calcimicrobes (cyanobacteria, ?fungi). The description made by Elliott in his original work of the "inner layer" of Lithocodium aggregatum as "confused" is explained here as a complex multitaxon chlorophyte-calcimicrobial assemblage overprinted by multiple bioerosion ichnofabrics.