Reconciling Molecular Phylogeny with Morphological Taxonomy in an Under-Appreciated Taxon: Living Crinoidea (Echinodermata) Charles G
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Reconciling Molecular Phylogeny with Morphological Taxonomy in an Under-Appreciated Taxon: Living Crinoidea (Echinodermata) Charles G. Messing1, Mindi Summers2, Kristian Taylor1 and Greg Rouse2 1. Nova Southeastern University Oceanographic Center, Dania Beach FL 2. Scripps Institution of Oceanography, University of California San Diego, La Jolla CA ABSTRACT: Extant crinoids—sea lilies and feather stars—number ~640 species, the fewest of the five extant echinoderm classes, in 184 accepted genus- and 45 family-level taxa. Despite their relatively low richness and exclusively suspension-feeding lifestyle, they are morphologically diverse and often abundant in many marine habitats, from shallow reefs to depths >9,000 m, and reach densities >100 m-2. Much contemporary IsocrinidaIsocrinida Hyocrinida Cyrtocrinida taxonomy dates from 1907-1909, when A.H. Clark described 75 genera and 17 family- level taxa derived from both new material (e.g., Albatross) and previous collections (e.g., Blake, Challenger). Taxonomic work has since revised numerous taxa and revealed new morphological features. However, although recent molecular phylogenies have supported some morphologically-based taxa at generic through ordinal levels, they have rendered others paraphyletic and polyphyletic. Similarly, whereas species-level th taxonomy established by mid-20 century suffered from poor understanding of Comasteridae ecophenotypic and ontogenetic variability and resulted in vast over-splitting, sequence data has revealed cryptic species so far unsupported by morphological distinctions. We are currently undertaking revisions at all categorical levels and searching for Caledonicrinus Comatulidina phylogenetically robust morphological features that will also apply to fossil taxa. Figure 1. Three major groups previously treated as orders returned as monophyletic: Isocrinida, Hyocrinida, and Cyrtocrinida, with weak support for grouping the latter two. Two groups that retain the stalk as adults and were formerly treated as separate suborders, Guillecrinina and Bourgueticrinina, nest within the former Comatulidina (now including all three as Comatulida), the “Tropiometroidea” other members of which shed the postlarval stalk and become mobile feather stars. Placement of Guillecrinina monotypic Caledonicrinus vaubani varied among analyses, but it never returned with other Bourseau et al. (1991) Guillecrinus bourgueticrinines, with which it was formerly classified. However, only 18S and 16S data (from Cohen et al. [2004]) were available for this taxon. Monachocrinus was represented by a museum Atelecrinidae Bourgueticrinina specimen and requires additional sequences to confirm its position. Hemery et al. (2013) returned Monachocrinus Figure 2. Representatives of 3 genera of Atelecrinidae feather stars form a the feather star family Atelecrinidae (bottom center—not included in Rouse et al. [2013]) within “Antedonoidea” the Bathycrinus/Democrinus/Porphyrocrinus “bourgueticrinine” clade (Figure 2). monophyletic clade nested among stalked “bourgueticrinines.” Maximum likelihood tree (lnL 52786.972333) inferred from the concatenated 5‐gene complete dataset (COI , 16S, CytB, 18S, 28S; 9 partitions). Branch lengths to Eleutherozoa terminals and to the ingroup shortened (//) for clarity. Symbols above or adjacent to nodes Porphyrocrinidae is also monophyletic. refer to posterior probability (PP), Bootstrap Scores (BS) and Parsimony Jackknife (JK) majority rule consensus tree values ,given in that Maximum likelihood tree inferred from combined 4‐gene order. Values <50% for BS or JK or <0.70 for PP are indicated by a space. Hyphen (‐) indicates node not found in MP analysis. * indicates >90 dataset (COI, 16S, 28S, 18S). Numbers =bootstrap values for BS or JK and >0.95 for PP for the node. Tree from Rouse et al. (2013). Bourgueticrinina >80%. Tree from Hemery (2013). Democrinus G. Rouse Recent phylogenetic reconstructions based on sequence data point to the need to re‐evaluate many morphological Colored blocks and squares in figure captions below refer to corresponding groups characters traditionally used in crinoid classifications (Rouse et al. 2013; Hemery et al. 2013; Roux et al. 2013). in Fig. 1 above. Holocrinida (Triassic) Isocrinida (Extant) Pentacrinoid postlarva Holocrinus dubius Cenocrinus asterius “bourgueticrinine” Porphyrocrinus n. sp. H‐J Streichan in Hagdorn (1993) NOAA Biolum 2009 G. Rouse Carpenter (1888) Figure 3. MORPHOLOGY—Oral pinnule combs (arrows) Figure 4. MORPHOLOGY—Combs tapering to a point Figure 5. MORPHOLOGY—Heteromorphic stalk with Figure 6. MORPHOLOGY—Stalk ossicles (columnals) articulated chiefly Figure 7. MOLECULES—link feather star families distinguish Comasteridae, the dominant extant feather star with teeth arising from center of pinnular rather than cirri arising at intervals from nodal ossicles diagnoses via synarthry; stalk lost following postlarval stage in Comatulidina, but Comasteridae and Thalassometridae taxon on modern coral reefs. MOLECULES—support edge is diagnostic of comasterid genus Oxycomanthus. Isocrinida (Fig. 1). MOLECULES—support monophyly, retained in adult Bourgueticrinina (Fig. 1). MOLECULES—nest most (Cosmiometra in Fig. 1) as sister groups (Rouse monophyly ; the combs are thus a valid synapomorphy (Fig. 1: MOLECULES—The genus is polyphyletic; species fall into but the character is probably plesiomorphic, e.g., it is bourgueticrinines within Comatulidina . Rouse et al. (2013) suggested et al. 2013; Hemery et al. 2013). red square). at least two separate groups (Fig. 1); this comb structure also in extinct and probably more basal (temporally using Comatulida for the entire clade, omitting Comatulidina as MORPHOLOGY—No synapomorphy yet appears to be homoplasious. earlier) Triassic Holocrinida. paraphyletic and redundant. The stalk is likely retained in diagnoses this clade. These families were “bourgueticrinine” taxa via paedomorphosis. previously placed in separate superfamilies. Guillecrinus Figure 11. New morphological characters that robustly link higher‐level (above family) taxa revealed by molecular data cc remain elusive (e.g., Fig. 7). Some may represent family‐level synapomorphies, e.g., probolus AdidasTM (pa) of Atelecrinidae (A) (Messing 2003), and centrodorsal pores in Atopocrinidae (B, arrows). Others may represent homoplasies developed as biomechanical responses to environmental conditions, e.g., the alternating projecting (pf) and recumbent (rf) muscular fossae in apparently unrelated Atelecrinidae (C) and Pentametrocrinidae (D). mf mf mf mf 50 50 LITERATURE CITED Améziane N, Roux M (2005) Environmental control versus phylogenic fingerprint Figure 8. MORPHOLOGY—Prismatic pinnules (left, center) with in ontogeny: the example of the development of the stalk in the genus ambulacral covering plates (arrows) characterize superfamily Guillecrinus (stalked crinoids, Echinodermata). Journal of Natural History 39:2815–2859. Tropiometroidea, vs. pinnules round in cross section without covering Hemery LG (2011) Diversite moleculaire, phylogeographie et phylogenie des plates in other feather star groups, e.g., Mariametroidea (right). CGM Crinoides (Echinodermes) dans un environnement extreme: l’ocean Austral. MOLECULES—recover individual tropiometroid families as PhD dissertation, Museum national d’Histoire naturelle, Paris. 381 pp. Hemery LG, Roux M, Améziane N, Eléaume M (2013). High‐resolution crinoid monophyletic (e.g., Thalassometridae, Charitometridae) but split Figure 9. MORPHOLOGY—Stalk articular facets are widely Figure 10. MORPHOLOGY—High thin muscular phyletic inter‐relationships derived from molecular data. Cahiers de Biologie superfamily as polyphyletic (Fig. 1: blue squares). Prismatic pinnules used as taxonomic characters. MOLECULES—may not link fossae on ray ossicles are characteristic of Marine 54:511‐523. are also found in stalked Isocrinida and Hyocrinida; they are thus Antedonoidea (mf in C & D), but most features are Messing CG (2003) Unique morphology in the living bathyal feather star, groups with similar morphologies (e.g., Guillecrinina and Atelecrinus Carpenter (Echinodermata: Crinoidea). Invertebrate Biology possibly plesiomorphic and repeatedly lost. Hyocrinida). Facets remodeled during growth exhibit also found in other groups (A. large centrodorsal 122(3):280‐292. cavity [cc]; B. embayed synarthries [arrows]) or do Rouse GW, Jermiin LS, Wilson NG, Eeckhaut I, Lanterbecq D, Oji T, Young CM, Data contributing to this research was acquired under grants different ontogenetic pathways, reflecting functional responses to different hydrodynamic regimes. New not occur throughout the group. MOLECULES— Browning T, Cisternas P, Helgen LE, Stuckey M, Messing CG (2013) Fixed, free, from NSF; NOAA; Nova Southeastern University; Muséum and fixed: the fickle phylogeny of extant Crinoidea (Echinodermata) and their columnals develop under the crown at the top of the stalk; return Antedonoidea as polyphyletic , e.g., Permian‐Triassic origin. Molecular Phylogenetics and Evolution 66(1):161‐81. national d’Histoire naturelle, Paris; South Australian Museum, columnal 50, recently developed with a flexible articulation antedonid Caryometra atlantidis (C) and Roux M, Eléaume M, Hemery LG, Améziane N, (2013). When morphology meets zenometrid Psathyrometra fragilis (D) return in molecular data in crinoid phylogeny: a challenge. Cahiers de Biologie Marine and Australian Research Council. Images © CG Messing unless in the juvenile, becomes modified as rigid in the adult. 54:541‐548. otherwise indicated. Based on Ameziane & Roux (2005). separate clades (Fig. 1: green squares)..