A Family Level Analysis of Tardigrade Phylogeny

Abstract

In the present study a character data set suitable for cladistic analysis at the family level was developed. A data matrix consisting of 50 morphological characters from 15 families of tardigrades was analyzed by maximum parsimony. Kinorhynchs, loriciferans, and gastrotrichs were used as outgroups. The results agree with the currently accepted hypothesis that Eutardigrada and Heterotardigrada are distinct monophyletic groups. Among the eutardigrades, Eohypsibiidae was found to be a sister group to Macrobiotidae+Hypsibiidae, while Milnesiidae was the basal eutardigrade family. The basal heterotardigrade family was found to be Oreellidae. Echiniscoideans grouped with some traditional Arthrotardigrada (Renaudarctidae, Coronarctidae+Batillipedidae) suggesting that the arthrotardigrades are not monophyletic. The 18S rRNA gene sequence of Batillipes mirus Richters, 1909 and Calohypsibius schusteri Nelson & McGlothlin, 1996 were obtained and their addition to a previously published dataset supports the monophyly of Heterotardigrada and of Parachela versus Apochela within the Eutardigrada.

The 18S rDNA sequences support polyphyly of the Hypsibiidae (Eutardigrada)

“…Analyses of the 18S rDNA gene sequences taken from Genbank data correspond (as expected) with those presented by Garey et al (1999), Jørgensen & Kristensen (2004) and Nichols et al (2006) probably is Thulinius (see Garey et al 1999). Further, they inserted R. oberhaeuseri in the Macrobiotidae without any comment (see l.c., page 667, Tab.…”

“…Echiniscus viridissimus Péterfi, 1956 (AF056024) (Garey et al 1996), Halobiotus stenostomus (Richters, 1908) (AY582121) (Jørgensen & Kristensen 2004), Macrobiotus hufelandi group (X81442) (Giribet et al 1996), Macrobiotus areolatus group (U32393) (Garey et al 1996, named Macrobiotus tonolli Ramazzotti, 1956) Macrobiotus echinogenitus Richters, 1904 in the figures in Nichols et al 2006), Milnesium tardigradum (Doyère, 1840)(AY582120) (Aguinaldo et al 1997), Ramazzottius oberhaeuseri (Doyère, 1840), (AY582122) (Jørgen-sen & Kristensen 2004), Richtersius coronifer (Richters, 1903) (AY5821239) (Jørgensen & Kristensen 2004), and Thulinius stephaniae (Pilato, 1974) (AF056023) (Garey et al 1996; Thulinia renamed Thulinius by Bertolani 2003).…”

“…arthropod relationships were discussed in detail already by Marcus 1929) and elaborated with additional details in numerous subsequent articles (e.g., Dewel & Dewel 1997; for review see Schmidt-Rhaesa et al 1998). Within the Tardigrada the classes Heterotardigrada and Eutardigrada are well established by morphological characters (for review of the older literature see Marcus 1929) and the monophyly of both classes as well as the ancestral Apochela and the derived Parachela (see Schuster et al 1980) among the Eutardigada appears to be supported by molecular data (Garey et al 1999;Jørgensen & Kristensen 2004;Nichols et al 2006). Currently, relationships within and between the various tardigrade families, based mainly on morphological characters and cladistic analyses, exist for the Echiniscidae (Kristensen 1987;Jørgensen 2000) and Macrobiotidae (Guidetti & Bertolani 2001).…”

“…Currently, relationships within and between the various tardigrade families, based mainly on morphological characters and cladistic analyses, exist for the Echiniscidae (Kristensen 1987;Jørgensen 2000) and Macrobiotidae (Guidetti & Bertolani 2001). More recently Nichols et al (2006) studied morphological data and 18S rDNA to evaluate congruence of morphological and molecular data at the family level and Guidetti et al (2005) within the Macrobiotidae.…”

The past, the present and the future of eutardigrade taxonomy

“…These investigations have been directed both on phylogeny (Garey et al, 1996(Garey et al, , 1999Giribet et al, 1996;Jørgensen and Kristensen, 2004;Guidetti et al, 2005;Nichols et al, 2006;Guil and Giribet, 2011) and on species identification and distribution (Jørgensen et al, 2007;Schill and Steinbrück, 2007;Faurby et al, 2008;Cesari et al, 2009Cesari et al, , 2011Guil and Giribet, 2009;Bertolani et al, 2011). They will go on, will be more and more thorough and will help us to distinguish between sibling species so similar morphologically that they are now very difficult or even impossible to be distinguished one from another.…”