Leptosastra Topsent 1904
Abstract
Leptosastra Topsent, 1904, (Hemiasterellidae) is a poecilosclerid with hemiasterellid traits Leptosastra Topsent is a monotypic demosponge genus with morphological characteristics diagnostic for a placement into different orders (see Hooper 2002a). Leptosastra forms thin, plaque-like crusts on hard substrates, characterised by erect acanthostyles embedded in basal spongin, which contribute to a hymedesmioid skeleton. It strongly resembles the choanosomal skeletons of Poecilosclerida, to which Topsent (1904) initially classified it, alongside the current Myxillidae, Coelosphaeridae and Hymedesmiidae (subfamily Dendoricinae). In contrast, Leptosastra’s ectosomal skeleton consists of a dense, cortex-like crust of oxyspheraster euasters, reinforced with thin rhabds (or tornotes) in sparse bundles (see inset in Figure 1). The presence of euasters suggests a phylogenetic position that is distant from Poecilosclerida. Since Dendy (1922), asterose microscleres have been regarded as a distinct character indicating deep splits in demosponge classifications, leading to the subsequent separation of “tetractinomorph” (aster-bearing) from “ceractinomorph” orders, which included Poecilosclerida (for a historic overview, see Boury-Esnault 2006; Erpenbeck et al. 2012a). Consequently, Hooper (2002a) tentatively placed Leptosastra into the family Hemiasterellidae, but noted the need for further data to elucidate its correct phylogenetic position. This classification has been held upright by several subsequent works on heteroscleromorph classifications (e.g., Morrow & Cardenas, 2015). To confirm the phylogenetic placement of Lepostastra, we analysed molecular material collected in 2005 from a box core sampling on the Rockall Bank, where two specimens were collected (ZMA Por.21277b and ZMA Por.21276b). Unfortunately, the holotype for L. constellata (MNHN DT 1033), type species of Leptosastra, was not available for this study (see also Hooper 2002a), but SEM analysis clearly identify the examined specimens as L. constellata (see inset in Figure 1). For both specimens 28S D3-D5 (634 bp), and CO1 (584 bp, for ZMA Por.21276b only) were amplified and sequenced. Phylogenetic reconstructions of both markers recover Leptosastra distant from Hemiasterellidae (or other taxa of its order Tethyida) but support its placement within the order Poecilosclerida. The internal classification of Poecilosclerida is still awaiting revision after its suborders were abandoned (Morrow & Cárdenas 2015). However, our CO1 (Fig. 1) and 28S D3-D5 reconstructions (Supplementary Data A) suggest Leptosastra as member of a clade containing predominantly hymedesmiid taxa. Here, Leptosastra falls in a clade of sequences from hymedesmiid Phorbas, Duchassaing & Michelotti, 1864, Kirkpatrickia Topsent, 1912, Hamigera Gray, 1867, Hemimycale Burton, 1934, Plocamionida Topsent, 1927, and Spanioplon Topsent, 1890. It also contains members of Family Crellidae (Crella Gray, 1867), a potential sister to Hymedesmiidae (see Van Soest 2002). This clade is furthermore consistent with 18S rDNA data published by Redmond et al. (2013). Consequently, Leptosastra can be classified as a poecilosclerid, with its hymedesmoid skeleton being homologous to that of other hymedesmiids. The euaster microscleres, in turn, resemble other asterose skeletal elements found in several poecilosclerids, which are considered to be convergent developments due to their occurrence with chelae microscleres, an autapomorphic feature of Poecilosclerida. Notable examples of this include the astroclone desma corpuscles found in Crambe tuberosa Maldonado & Benito, 1991 and C. chilensis Esteves, Lôbo-Hajdu & Hajdu, 2007. Additionally, there are mace-shaped tylostyle pseudoasters that bear remarkable similarities to euasters in Discorhabdella Dendy, particularly in D. pseudaster Vacelet & Cárdenas, 2018 (see discussion in Vacelet & Cárdenas 2018), and the strongly modified, aster-like spined chelae in Acanthancora Topsent. Based on the genetic analysis, we hereby transfer L. constellata to the Order Poecilosclerida.
Authors 11
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany & GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Affiliation as printed
Mar-Tec Computer Trading & Service GmbH, Allee der Kosmonauten 38, 12681 Berlin
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Affiliation as printed
Museum fu ̈ r Naturkunde, Leibniz-Institut fu ̈ r Evolutions- und Biodiversita ̈ tsforschung, Invalidenstrasse 43, 10115 Berlin, Germany
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany
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Bayerische Staatssammlung für Paläontologie und Geologie · Ludwig-Maximilians-Universität München
Affiliation as printed
Department of Earth- and Environmental Sciences, Palaeontology & Geobiology, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany & GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner Str, 10, 80333 Munich, Germany & Bavarian State Collection of Palaeontology and Geology, Richard-Wagner Str, 10, 80333 Munich, Germany
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Affiliation as printed
Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, the Netherlands
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