Five new species of Homoscleromorpha (Porifera) of four genera, Oscarella, Plakortis, Plakina and Corticium, are described from vertical walls of reef caves at depths ranging from 23 to 28 m in the Caribbean Sea. Oscarella nathaliae sp. nov. has a leaf-like thinly encrusting, flat body, loosely attached to the substrate and a perforated, not lobate surface. Oscarella nathaliae sp. nov. contains two bacterial morphotypes and is characterized by two mesohylar cell types with inclusions. Plakortis myrae sp. nov. has diods of two categories: abundant large ones (83–119 mm long) and rare small ones (67–71 mm long) with sinuous, S-bent centres; triods Y- or T-shaped (18–5 mm long), and abundant microrhabds (5–12 mm long). Plakortis edwardsi sp. nov. has diods of one category with thick, sinuous, S-bent centres (110 to 128 mm long); triods T-shaped (actines 28–59 mm long). It is the only species of this genus showing small diods (22–31 mm long). Plakortis dariae sp. nov. has diods of two categories: large ones (67–112 mm long) and small, rare, irregular ones, slightly curved, often deformed with one end blunt (30–59 mm long); triods rare and regular (actines 20–44 mm long long). Corticium diamantense sp. nov. has oscula situated near its border, regular non-lophose calthrops of one size class, very rare tetralophose calthrops and candelabra with the fourth actine ramified basally in 4–5 microspined rays. In addition, a re-description of Plakina jamaicensis Lehnert & van Soest 1998 is based on newly collected material and the type specimen. P. jamaicensis has a convoluted brainlike surface; well developed sub-ectosomal cavities; irregular sinuous diods, triods, calthrops, rare monolophose calthrops, rare dilophose calthrops, rare trilophose calthrops and common tetralophose calthrops. Molecular ‘barcoding’ sequences for mitochondrial cob are given for Plakortis edwardsi sp. nov., P. dariae sp. nov., Plakina jamaicensis and Corticium diamantense sp. nov. An identification key for all western Atlantic Homoscleromorpha is provided.
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In Upper Cretaceous chalk sequences, the widespread occurrence of flint, as well as a possible astronomical pacing of their often-encountered rhythmic distribution, remains poorly constrained. The Campanian-Maastrichtian Hallembaye chalk succession (Maastrichtian type area, northeast Belgium) is characterized by the gradual evolution from no flint bands at its base to the regular presence of well-developed flint bands at its top. Here, the Hallembaye section is investigated to gain more insights into the underlying processes behind flint inception. A relationship is found between the amount of detrital material (i.e., clays) present in the chalk and flints, and the extent of silicification and flint development. Several astronomical cycles are identified within the succession using both a lithology-based flint proxy and high-resolution μXRF-based element data from chalk samples. A combined imprint of precession and obliquity is documented in the chalk Ti/Al profile. The flint bands display a predominant obliquity imprint with an increasing contribution of precession and eccentricity up-section. Two consistent stratigraphically integrated astronomical age models are preferred. The first model is a floating age model that is based on the minimal tuning of the short obliquity cycle in the Ti/Al signal. The second model is a numerical age model that is based on flint occurrences, tuned to a combined tuning target consisting of both the inclination and long eccentricity metronomes. Temporal variations in the hydrological cycle and consequent changes in eolian, fluvial and dissolved Si input to the European Basin appear astronomically controlled. In addition, flint nodules and bands are paced by Milankovitch timescales, reflecting astronomical control on the Si cycle and paleoenvironmental conditions governing conditions favorable towards flint formation.
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RBINS Staff Publications 2025
