Phylogenetic Analysis of Thecosomata Blainville, 1824 (Holoplanktonic Opisthobranchia) Using Morphological and Molecular Data

Abstract

Thecosomata is a marine zooplankton group, which played an important role in the carbonate cycle in oceans due to their shell composition. So far, there is important discrepancy between the previous morphological-based taxonomies, and subsequently the evolutionary history of Thecosomata. In this study, the remarkable planktonic sampling of TARA Oceans expedition associated with a set of various other missions allowed us to assess the phylogenetic relationships of Thecosomata using morphological and molecular data (28 S and COI genes). The two gene trees showed incongruities (e.g. Hyalocylis, Cavolinia), and high congruence between morphological and 28S trees (e.g. monophyly of Euthecosomata). The monophyly of straight shell species led us to reviving the Orthoconcha, and the split of Limacinidae led us to the revival of Embolus inflata replacing Limacina inflata. The results also jeopardized the Euthecosomata families that are based on plesiomorphic character state as in the case for Creseidae which was not a monophyletic group. Divergence times were also estimated, and suggested that the evolutionary history of Thecosomata was characterized by four major diversifying events. By bringing the knowledge of palaeontology, we propose a new evolutionary scenario for which macro-evolution implying morphological innovations were rhythmed by climatic changes and associated species turn-over that spread from the Eocene to Miocene, and were shaped principally by predation and shell buoyancy.

Flashback and foreshadowing—a review of the taxon Opisthobranchia

“…Exploring and using morpho-anatomical characters, other authors investigated phylogenetic relationships within major subgroups (Edlinger 1980;Willan 1987;Jensen 1996 Gosliner 1980Gosliner , 1989Gosliner , 1995Gosliner , 1996Haszprunar 1985c;Gosliner and Kuzirian 1990;Gosliner and Willan 1991;Millen and Nybakken 1991;Johnson 1994, 1999;Kolb and Wägele 1998;Valdés and Bouchet 1998;Fahey and Gosliner 1999;Garavoy et al 1999;Garovoy et al 2001;Gosliner 1999, 2001;Fahey and Gosliner 2000;Dorgan et al 2002;Valdés 2002a, b;Bertsch et al 2009;Corse et al 2013; and many others). Based on some of these studies, new taxa were erected, e.g.…”

“…Subsequently, multilocus analyses appeared utilizing a variety of nuclear and mitochondrial markers to unravel phylogenetic relationships within Opisthobranchia and subgroups (e.g. Wägele et al 2003;Grande et al 2004a, b;Vonnemann et al 2005;KlussmannKolb and Dinapoli 2006;Händeler and Wägele 2007;Händeler et al 2009;Malaquias et al 2009;Klussmann-Kolb 2010a, b, 2011;Maeda et al 2010;Pola and Gosliner 2010;Moore and Gosliner 2011;Johnson and Gosliner 2012;Pola et al 2012;Corse et al 2013;Carmona et al 2013, and many more) (Fig. 3a, b) or phylogenetic relationships of opisthobranch taxa within Euthyneura (Grande et al 2004b;Klussmann-Kolb et al 2008;Jörger et al 2010;Göbbeler and Klussmann-Kolb 2011;Dayrat et al 2011;Schrödl et al 2011a; (Fig.…”

Pteropodos thecosomados en el Pacifico suroriental frente a Caldera, Chile (Mollusca, Opistobranchiata: Euthecos tomata y Pseudothecostomata)

“…Se capturaron 2021 individuos, correspondientes a 18 especies nominales, distribuidas en 8 géneros y 3 familias de moluscos holoplanctónicos, según la clasificación taxonómica propuesta por Van der Spoel & Boltovskoy (1981), Mass et al (2013) y Corse et al (2013). De acuerdo a esto, el número de especies conocidas para aguas chilenas aumenta a 25 especies y cinco familias, de las cuales 11 especies constituyen nuevos registros para la zona (Tabla 2).…”

“…La determinación de los pterópodos se realizó utilizando claves y literatura especializada (Van der Spoel, 1976;Boltoskoy, 1981;Wrobel & Mills, 1998;Mass et al, 2013). El status taxonómico de algunas especies se revisó y actualizó con base en los trabajos de Mass et al (2013), Corse et al (2013) y Gofas (2014.…”

The Miocene “Pteropod event” in the SW part of the Central Paratethys (Medvednica Mt., northern Croatia)

“…Pteropods are divided into two orders: Thecosomata de Blainville, 1824 ("sea butterflies") and Gymnosomata de Blainville, 1824 ("sea angels"). Thecosomata include mainly forms with aragonitic shell in the adult stage, but in Gymnosomata a shell is only present in the larval stage (e.g., Herman 1998;Janssen & Little 2010;Corse et al 2013;Janssen & Peijnenburg 2014 and references therein).…”