Background: The identification of free-living marine nematodes is difficult because of the paucity of easily scorable diagnostic morphological characters. Consequently, molecular identification tools could solve this problem. Unfortunately, hitherto most of these tools relied on 18S rDNA and 28S rDNA sequences, which often lack sufficient resolution at the species level. In contrast, only a few mitochondrial COI data are available for free-living marine nematodes. Therefore, we investigate the amplification and sequencing success of two partitions of the COI gene, the M1-M6 barcoding region and the I3-M11 partition. Methodology: Both partitions were analysed in 41 nematode species from a wide phylogenetic range. The taxon specific primers for the I3-M11 partition outperformed the universal M1-M6 primers in terms of amplification success (87.8\% vs. 65.8\%, respectively) and produced a higher number of bidirectional COI sequences (65.8\% vs 39.0\%, respectively). A threshold value of 5\% K2P genetic divergence marked a clear DNA barcoding gap separating intra-and interspecific distances: 99.3\% of all interspecific comparisons were 〉0.05, while 99.5\% of all intraspecific comparisons were 〈0.05 K2P distance. Conclusion: The I3-M11 partition reliably identifies a wide range of marine nematodes, and our data show the need for a strict scrutiny of the obtained sequences, since contamination, nuclear pseudogenes and endosymbionts may confuse nematode species identification by COI sequences.
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Moderately diverse trace fossil assemblages occur in the Eocene Tambak Member of the Tanjung Formation, in the Asem Asem Basin on the southern coast of South Kalimantan. These assemblages are fundamental for establishing depositional models and paleoecological reconstructions for southern Kalimantan during the Eocene and contribute substantially to the otherwise poorly documented fossil record of birds in Island Southeast Asia. Extensive forest cover has precluded previous ichnological analyses in the study area. The traces discussed herein were discovered in newly exposed outcrops in the basal part of the Wahana Baratama coal mine, on the Kalimantan coast of the Java Sea. The Tambak assemblage includes both vertebrate and invertebrate trace fossils. Invertebrate traces observed in this study include Arenicolites, Cylindrichnus, Diplocraterion, Palaeophycus, Planolites, Psilonichnus, Siphonichnus, Skolithos, Thalassinoides, Taenidium, and Trichichnus. Vertebrate-derived trace fossils include nine avian footprint ichnogenera (Aquatilavipes, Archaeornithipus, Ardeipeda, Aviadactyla, cf. Avipeda, cf. Fuscinapeda, cf. Ludicharadripodiscus, and two unnamed forms). A variety of shallow, circular to cylindrical pits and horizontal, singular to paired horizontal grooves preserved in concave epirelief are interpreted as avian feeding and foraging traces. These traces likely represent the activities of small to medium-sized shorebirds and waterbirds like those of living sandpipers, plovers, cranes, egrets, and herons. The pits and grooves are interpreted as foraging traces and occur interspersed with both avian trackways and invertebrate traces. The trace fossils occur preferentially in heterolithic successions with lenticular to flaser bedding, herringbone ripple stratification, and common reactivation surfaces, indicating that the study interval was deposited in a tidally influenced setting. Avian trackways, desiccation cracks, and common rooting indicate that the succession was prone to both subaqueous inundation and periodic subaerial exposure. We infer that the Tambak mixed vertebrate-invertebrate trace fossil association occurred on channel-margin intertidal flats in a tide-influenced estuarine setting. The occurrence of a moderately diverse avian footprint and foraging trace assemblage in the Tambak Member of the Tanjung Formation illustrates that shorebirds and waterbirds have been using wetlands in what is now Kalimantan for their food resources since at least the late Eocene.
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RBINS Staff Publications 2024
