Conellae, enigmatic structures on cephalopod shells—shapes, distribution, and formation

Conellae, enigmatic cone-shaped structures which can be found on the surface of internal moulds of cephalopod shells (predominantly of ammonoids), are regarded herein as the product of remote (biologically induced) biomineralization formed in closed-off cavities during lifetime and might be primarily composed of vaterite, aragonite, or calcite. To date conellae have been interpreted in many different ways: (i) as organisms (gastropods, cirriped crustaceans, or disciniscid brachiopods), (ii) pre-diagenetic syn vivo features, i.e., biologically controlled or induced, the product of remote biomineralization, (iii) and diagenetic, i.e., abiogenic origin and post-mortem. The proposed processes of conellae formation seem insufficient to explain conellae related phenomena. Further, their assumed primary aragonitic or calcitic mineralogy are reviewed and based on new material critically assessed. The stratigraphic range of conellae extends from the Middle Ordovician and probably to modern Nautilus. Predominantly, conellae can be found on internal moulds along the keel, ribs or nodes, umbilical shoulder, at the transition between phragmocone and body chamber, and can be associated with repaired scars. However, conellae are also common on the smooth body chambers of large macroconchs of Jurassic ammonites. Conellae, which are located on ammonite body chambers, are filled with the same material found in the body chamber and can contain small burrows, sand grains, or coprolites. Some of these conellae are partially covered with nacreous shell material. Limonitic conellae were also found on the limonitic internal moulds of orthocone nautiloids. Moreover, disciniscid brachiopods found on inoceramid bivalves were re-identified herein as conellae. A short guide for conellae identification has been provided herein

The dorsal shell wall structure of Mesozoic ammonoids

The study of pristine preserved shells of Mesozoic Ammonoidea shows different types of construction and formation of the dorsal shell wall. We observe three major types: (i) The vast majority of Ammonoidea, usually planispirally coiled, has a prismatic reduced dorsal shell wall which consists of an outer organic component (e.g., wrinkle layer), which is the first layer to be formed, and the subsequently formed dorsal inner prismatic layer. The dorsal mantle tissue suppresses the formation of the outer prismatic layer and nacreous layer. With the exception of the outer organic component, secretion of a shell wall is omitted at the aperture. A prismatic reduced dorsal shell wall is always secreted immediately after the hatching during early teleoconch formation. Due to its broad distribution in (planispiral) Ammonoidea, the prismatic reduced dorsal shell wall is probably the general state. (ii) Some planispirally coiled Ammonoidea have a nacreous reduced dorsal shell wall which consists of three mineralized layers: two prismatic layers (primary and secondary dorsal inner prismatic layer) and an enclosed nacreous layer (secondary dorsal nacreous layer). The dorsal shell wall is omitted at the aperture and was secreted in the rear living chamber. Its layers are a continuation of an umbilical shell doubling (reinforcement by additional shell layers) that extends towards the ventral crest of the preceding whorl. The nacreous reduced dorsal shell wall is formed in the process of ontogeny following a prismatic reduced dorsal shell wall. (iii) Heteromorph and some planispirally coiled taxa secrete a complete dorsal shell wall which forms a continuation of the ventral and lateral shell layers. It is formed during ontogeny following a prismatic reduced dorsal shell wall or a priori. The construction is identical with the ventral and lateral shell wall, including a dorsal nacreous layer. The wide distribution of the ability to form dorsal nacre indicates that it is a plesiomorphic trait which either was passed on from gyrocone ammonoid ancestors or (re-)developed in post-Triassic ammonoids

Ultrastructure of calcareous dinophytes (Thoracosphaeraceae, Peridiniales) with a focus on vacuolar crystal-like particles.

Biomineralization in calcareous dinophytes (Thoracosphaeracaea, Peridiniales) takes place in coccoid cells and is presently poorly understood. Vacuolar crystal-like particles as well as collection sites within the prospective calcareous shell may play a crucial role during this process at the ultrastructural level. Using transmission electron microscopy, we investigated the ultrastructure of coccoid cells at an early developmental stage in fourteen calcareous dinophyte strains (corresponding to at least ten species of Calciodinellum, Calcigonellum, Leonella, Pernambugia, Scrippsiella, and Thoracosphaera). The shell of the coccoid cells consisted either of one (Leonella, Thoracosphaera) or two matrices (Scrippsiella and its relatives) of unknown element composition, whereas calcite is deposited in the only or the outer layer, respectively. We observed crystal-like particles in cytoplasmic vacuoles in cells of nine of the strains investigated and assume that they are widespread among calcareous dinophytes. However, similar structures are also found outside the Thoracosphaeraceae, and we postulate an evolutionarily old physiological pathway (possibly involved in detoxification) that later was specialized for calcification. We aim to contribute to a deeper knowledge of the biomineralization process in calcareous dinophytes

Form and formation of flares and parabolae based on new observations of the internal shell structure in lytoceratid and perisphinctid ammonoids

The ultrastructure of pristine shells of Jurassic and Cretaceous lytoceratid and perisphinctid ammonoids indicates that flares and parabolae represent homologous structures. Both mark an interruption of shell growth. We dismiss earlier interpretations of parabolae as actual aperture, relics of resorbed apophyses or superstructure of the musculature associated to a semi-internal shell. Instead we propose an episodic growth model including several growth stops at the aperture during the formation of a frill-like aperture for parabolae and flares. Such an aperture is composed of the outer prismatic layer, the nacreous layer and an apertural prismatic coating. Here, we observed the apertural prismatic coating for the first time as an integral part of flares and parabolae. The apertural prismatic coating covers only the inner surface of the frill and was secreted by a permanent mantle cover indicating a prolonged period without the production of new shell material. Parabolae differ from flares by their general shape and the presence of ventro-lateral parabolic notches and nodes. The notches were formed by folding of the frill and had the potential to form semi-open spines. The corresponding parabolic nodes are caused by an outward swelling of the shell-secreting mantle tissue producing new shell material at the position of the folding. New shell material that belongs to the conch tube is attached to the base of flares and parabolae after withdrawal of the mantle edge representing the continuation of shell growth. Usually, the frilled aperture associated with flares and parabolae were removed during lifetime. This study reports on flares in Argonauticeras for the first time. In this genus they are typically associated with varices

Die Arten der Unterklasse Neritimorpha Koken, 1896 (Gastropoda) aus der Korallenfazies des oberen Kimmeridgiums (oberer Jura) von Saal bei Kelheim und dem Gebiet Nattheim (Süddeutschland)

Die Fundstellen der Gastropoden aus den Korallenriffkalken des oberen Kimmeridgiums von Saal bei Kelheim und dem Gebiet um Nattheim (Süddeutschland) werden beschrieben. Es wurden 15 Arten der Unterklasse Neritimorpha gefunden. Neu sind die Familie Parvulatopsidae, die (Unter-)Gattungen Dauterria, Parvulatopsis, Wallowiella (Plicaropsis) und Bipartopsis sowie die Arten Dauterria rotundata, D. variocostata, Pileopsella biconvexa, Parvulatopsis quinquecostatus, Wallowiella (Plicaropsis) compacta, Cassianopsis ratua, C. eversi, Hayamiella schaeferi und Bipartopsis robustus. Das Original der Neritites cancellatus.Stahl, 1824 wird als Holotypus wegen Monotypie gewertet, die Art zur Gattung Wallowiella (Plicaropsis) gestellt. Neritopsis quenstedti Brösamlen, 1909 wird in die Gattung Cassianopsis und Natica decussata Münster in Goldfuss, 1844 sowie Neritopsis semiplicata Brösamlen, 1909 in die Gattung Hayamiella versetzt. Für sie werden Lectotypen festgelegt. Die Cassianopsinae Bandel, 2007 sowie die Gattungen Wallowiella Frýda, Blodgett & Stanley, 2003, Cassianopsis Bandel, 2007 und Hayamiella Kase, 1984 werden neu definiert. Die Cassianopsinae sind von der oberen Trias bis in die Unterkreide nachweisbar. Sie erlebten vor der oberen Trias eine basale Aufspaltung. Die seit der oberen Trias fassbaren verschiedenen Entwicklungslinien wurden in der Folgezeit nur langsam umgestaltet unter Beibehaltung ihrer jeweiligen grundlegenden Merkmalskombination.Gründel J, Keupp H, Lang F.: Species of the subclass Neritimorpha Koken, 1896 (Gastropoda) from the coral facies of the Upper Kimmeridgian (Upper Jurassic) from Saal near Kelheim and the Nattheim area (southern Germany) Gastropods from the Upper Kimmeridgian coral reef-related limestones are described. The fossils occur at Saal near Kelheim and in the area of Nattheim (southern Germany). Fifteen species of the subclass Neritimorpha are reported. New are the family Parvulatopsidae, the (sub-)genera Dauterria, Parvulatopsis, Wallowiella (Plicaropsis) and Bipartopsis as well as the species Dauterria rotundata, D. variocostata, Pileopsella biconvexa, Parvulatopsis quinquecostatus, Wallowiella (Plicaropsis) compacta, Cassianopsis ratua, C. eversi, Hayamiella schaeferi and Bipartopsis robustus. The original specimen of Neritites cancellatus Stahl, 1824 is the holotype because of monotypy. This species belongs to the genus Wallowiella (Plicaropsis). Neritopsis quenstedti Brösamlen, 1909 is a member of the genus Cassianopsis. Natica decussata Münster in Goldfuss, 1844 and Neritopsis semiplicata Brösamlen, 1909 are transferred to the genus Hayamiella and lectotypes are designated. New definitions are given for the Cassianopsinae Bandel, 2007, as well as for the genera Wallowiella Frýda, Blodgett & Stanley, 2003, Cassianopsis Bandel, 2007 and Hayamiella Kase, 1984. The Cassianopsinae are known from the Upper Triassic to Lower Cretaceous. This subfamily had a basal split before the Upper Triassic. Since the Upper Triassic several different evolutionary lines have evolved. These lines are very conservative with only minor changes of their characteristic combination of structural features

Kieselschwämme (Hexactinellida und "Lithistida" aus den Cipit-Kalken der Cassianer Schichten (Karn, Südtirol)

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