Thuy B and Stöhr S (2016), A New Morphological Phylogeny of the Ophiuroide...

ECB-ART-48271

PLoS One 2016 May 04;115:e0156140. doi: 10.1371/journal.pone.0156140.

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A New Morphological Phylogeny of the Ophiuroidea (Echinodermata) Accords with Molecular Evidence and Renders Microfossils Accessible for Cladistics.

Thuy B , Stöhr S .

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Ophiuroid systematics is currently in a state of upheaval, with recent molecular estimates fundamentally clashing with traditional, morphology-based classifications. Here, we attempt a long overdue recast of a morphological phylogeny estimate of the Ophiuroidea taking into account latest insights on microstructural features of the arm skeleton. Our final estimate is based on a total of 45 ingroup taxa, including 41 recent species covering the full range of extant ophiuroid higher taxon diversity and 4 fossil species known from exceptionally preserved material, and the Lower Carboniferous Aganaster gregarius as the outgroup. A total of 130 characters were scored directly on specimens. The tree resulting from the Bayesian inference analysis of the full data matrix is reasonably well resolved and well supported, and refutes all previous classifications, with most traditional families discredited as poly- or paraphyletic. In contrast, our tree agrees remarkably well with the latest molecular estimate, thus paving the way towards an integrated new classification of the Ophiuroidea. Among the characters which were qualitatively found to accord best with our tree topology, we selected a list of potential synapomorphies for future formal clade definitions. Furthermore, an analysis with 13 of the ingroup taxa reduced to the lateral arm plate characters produced a tree which was essentially similar to the full dataset tree. This suggests that dissociated lateral arm plates can be analysed in combination with fully known taxa and thus effectively unlocks the extensive record of fossil lateral arm plates for phylogenetic estimates. Finally, the age and position within our tree implies that the ophiuroid crown-group had started to diversify by the Early Triassic.

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Species referenced: Echinodermata
Genes referenced: acp7 LOC579609 otp

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	Fig 1. Phylogenetic tree of the full morphological dataset inferred using MrBayes.Numbers at nodes indicate posterior probabilities in bold followed by bootstrap values inferred from parsimony estimates using TNT. For nodes which were not recovered by the parsimony estimate, bootstrap values were omitted (shown as â€œ-â€œ). Euryalids are marked in red, extinct species are marked by a cross.
	Fig 2. Phylogenetic tree with 13 ingroup taxa reduced to the LAP characters only.Numbers at nodes indicate posterior probabilities. Euryalids are marked in red, extinct taxa are marked by a cross, taxa treated as LAP-only records are underlined.
	Fig 3. Comparison between the morphology-based phylogenetic tree and the latest phylogenomic tree.(A) Schematic summary of the phylogenetic tree of the full morphological dataset as shown in Fig 1. (B) Schematic summary of the phylogenomic tree redrawn from Oâ€™Hara et al. [13]. Euryalids are marked in red, extinct taxa are marked by a cross.
	Fig 4. Phylogenetic tree of the full morphological dataset inferred using MrBayes with synapomorphy candidates mapped on the relevant nodes.Character acronyms and state numbers as given in S1 Appendix. Green characters occur only once according to our analysis whereas grey characters occur at least two times independently. Characters applying to single taxa are not shown. Cases of reversals within a particular clade are indicated as character acronym crossed in red. Characters M-DP-5 and M-OP-2 are omitted for the sake of clarity. Euryalids are marked in red, extinct taxa are marked by a cross.
	Fig 5. Ophiuroid skeletal characters identified as the potential synapomorphies.(A) Radial shield of Ophioderma longicauda (SMNH-133258). (B) Radial shield of Ophiarachna incrassata (MnhnL OPH001). (C) Radial shield of Ophiocoma echinata (MnhnL OPH002). (D) Radial shield of Ophiomyxa pentagona (SMNH-111006). (E) Radial shield of Ophiura ophiura, with entire rather than incised abradial edge (MnhnL OPH003). (F) Abradial genital plate of Ophiomusium lymani (SMNH-130500). (G) Abradial genital plate of Ophioderma longicauda (SMNH-133258). (H) Abradial genital plate of Ophiolimna bairdi (SMNH-127044). (I) Abradial genital plate of Ophiodoris malignus (MnhnL OPH004). (J) Abradial genital plate of Ophiothrix fragilis (SMNH-111046). (K) Abradial genital plate of Ophiotholia spathifer (MnhnL OPH005). (L) Detail of genital slit of Palaeocoma milleri showing papillae (Pap) on abradial genital plate (MnhnL OPH006). (M) Detail of genital slit of Ophionereis porrecta showing granules (Gran) on abradial genital plate (specimen now disarticulated). (N) Detail of ventral disc of Ophiura ophiura showing position of second oral tentacle pores (2nd otp) and arrangement of the respective papillae (MnhnL OPH007). Scale bars equal 0.25 mm in (A)-(K) and 1 mm in (L)-(N).
	Fig 6. Ophiuroid skeletal characters identified as the potential synapomorphies.(A) Detail of mouth of Gorgonocepahlus caputmedusae showing multiple rows of oral papillae (SMNH-131549). (B) Detail of mouth of Ophiomyces delata showing multiple rows of oral papillae (SMNH-123450). (C) Dental plate of Ophiarachna incrassata (MnhnL OPH008). (D) Dental plate of Ophiocten sericeum (MnhnL OPH009). (E) Dental plate of Ophioscolex glacialis (SMNH-111001). (F) Dental plate of Ophiodoris malignus (MnhnL OPH010). (G) Dental plate of Ophionereis porrecta (SMNH-111008). (H) Oral plate of Amphiura chiajei in abradial view showing rib-like branching structures (ribs) (SMNH-105100). (I) Oral plate of Ophiactis savignyi in abradial view (MnhnL OPH011). (J) Oral plate of Ophiomusium lymani in adradial view showing position of adradial muscle attachment area (ad amaa) (SMNH-130500). (K) Oral plate of Ophiodoris malignus in adradial view (MnhnL OPH012). (L) Oral plate of Asteronyx loveni in adradial view (MnhnL OPH013). (M) Oral plate of Ophiopholis aculeata in adradial view (MnhnL OPH014). (N) Ventral arm plate of Ophiomyces delata showing sockets for tentacle scales (tss) (MnhnL OPH015). (O) Ventral arm plate of Ophioderma longicauda showing spur on proximal edge (spur) (SMNH-133258). (P) Dorsal arm plate of Ophioderma longicauda showing spurs on proximal edge (SMNH-133258). (Q) Arm spine of Ophiarachna incrassata (MnhnL OPH016). (R) Vertebra of Ophiothrix fragilis in dorsal view (SMNH-67805). (S) Vertebra of Ophiodoris malignus in dorsal view (MnhnL OPH017). Scale bars equal 1 mm in (A)-(B), 0.25 mm in (C)-(G) and (N)-(S), and 0.5 mm in (H)-(M).
	Fig 7. Ophiuroid skeletal characters identified as the potential synapomorphies.(A) Vertebrae of Gorgonocephalus caputmedusae in lateral view (SMNH-131549). (B) Vertebra of Euryale aspera in distal view (SMNH-131557). (C) Vertebra of Ophionereis porrecta in proximal view (SMNH-111047). (D) Lateral arm plate of Ophiocopa spatula (SMNH-122912). (E) Lateral arm plate of Ophioleuce seminudum (SMNH-118750). (F) Lateral arm plate of Ophiodoris malignus (MnhnL OPH018). (G) Lateral arm plate of Ophiomyxa pentagona (SMNH-90260). (H) Lateral arm plate of Ophiactis fragilis (SMNH-67805). (I) Spine articulations of Gorgonocephalus caputmedusae (SMNH-131549). (J) Spine articulation of Ophiura ophiura (MnhnL OPH019). (K) Spine articulation of Ophiomusium lymani (MnhnL OPH020). (L) Spine articulation of Ophienigma spinilimbatum (SMNH-131562). (M) Spine articulation of Histampica duplicata (SMNH-131574). (N) Spine articulation of Ophiacantha bidentata (SMNH-45856). (O) Spine articulation of Ophiomyces delata (SMNH-123451). (P) Spine articulation of Ophiarachna incrassata (MnhnL OPH021). Abbreviations: mo: muscle opening; no: nerve opening; dl: dorsal lobe; vl: ventral lobe; sf: sigmoidal fold. All lateral arm plates in external view. Scale bars equal 0.5 in (A)-(C), 0.25 mm in (D)-(H) and 0.1 mm in (I)-(P).
	Fig 8. Ophiuroid skeletal characters identified as the potential synapomorphies.(A) Lateral arm plate of Ophiomusium lymani showing within-plate tentacle pore (to) (SMNH-130493). (B) Lateral arm plate of Ophiocten sericeum showing distalwards-pointing, between-plate tentacle opening (to) (MnhnL OPH022). (C) Lateral arm plate of Ophiactis savignyi showing knobs on the inner side (kn) (MnhnL OPH023). (D) Lateral arm plate of Ophiarachna incrassata (MnhnL OPH024). (E) Lateral arm plate of Ophiochondrus stelliger. (F) Lateral arm plate of Ophiotreta valenciennesi (MnhnL OPH026). (G) Lateral arm plate of Ophiochiton fastigatus (MnhnL OPH025). (H) Lateral arm plate of Ophiopholis aculeata (SMNH-111040). All lateral arm plates in internal view. Scale bars equal 0.25 mm.

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