Phylogeny and evolutionary history of diplobathrid crinoids (Echinodermata)

Order Diplobathrida is a major clade of camerate crinoids spanning the Ordovician–Mississippian, yet phylogenetic relationships have only been inferred for Ordovician taxa. This has hampered efforts to construct a comprehensive tree of life for crinoids and develop a classification scheme that adequately reflects diplobathrid evolutionary history. Here, I apply maximum parsimony and Bayesian phylogenetic approaches to the fossil record of diplobathrids to infer the largest tree of fossil crinoids to date, with over 100 genera included. Recovered trees provide a framework for evaluating the current classification of diplobathrids. Notably, previous suborder divisions are not supported, and superfamily divisions will require significant modification. Although numerous revisions are required for families, most can be retained through reassignment of genera. In addition, recovered trees were used to produce phylogeny‐based estimates of diplobathrid lineage diversity. By accounting for ghost lineages, phylogeny‐based richness estimates offer greater insight into diversification and extinction dynamics than traditional taxonomy‐based approaches alone and provide a detailed summary of the ~150 million‐year evolutionary history of Diplobathrida. This study constitutes a major step toward producing a phylogeny of the Crinoidea and documenting crinoid diversity dynamics. In addition, it will serve as a framework for subsequent phylogeny‐based investigations of macroevolutionary questions.     

A re‐interpretation of the ambulacral system of Eumorphocystis (Blastozoa,Echinodermata) and its bearing on the evolution of early crinoids

Recent debates over the evolutionary relationships of early echinoderms have relied heavily on morphological evidence from the feeding ambulacral system. Eumorphocystis, a Late Ordovician diploporitan, has been a focus in these debates because it bears ambulacral features that show strong morphological similarity to early crinoid arms. Undescribed and well‐preserved specimens of Eumorphocystis from the Bromide Formation (Oklahoma, USA) provide new data illustrating that composite arms supported by a radial plate that bear a triserial arrangement of axial and extraxial components encasing a coelomic extension can also be found in blastozoans. Previous reports have considered these arm structures to be restricted to crinoids; these combined features have not been previously observed in blastozoan echinoderms. Phylogenetic analyses suggest that Eumorphocystis and crinoids are sister taxa and that shared derived features of these taxa are homologous. The evidence from the arms of Eumorphocystis suggests that crinoid arms were derived from a specialized blastozoan ambulacral system that lost feeding brachioles and strongly suggests that crinoids are nested within blastozoans.     

New crinoids from the Baltic region (Estonia): fossil tip‐dating phylogenetics constrains the origin and Ordovician–Silurian diversification of the Flexibilia (Echinodermata)

This study documents previously unknown taxonomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the Baltic region (Estonia) that provide insight into two major features of the geological history of crinoids: the early evolution of the flexible clade during the Great Ordovician Biodiversification Event (GOBE), and their diversification history surrounding the end‐Ordovician mass extinction. The unexpected occurrence of a highly derived sagenocrinid, Tintinnabulicrinus estoniensis gen. et. sp. nov., from Upper Ordovician (lower Katian) rocks of the Baltic palaeocontinent provides high‐resolution temporal, taxonomic and palaeobiogeographical constraints on the origin and early evolution of the Flexibilia. The Silurian (lower Rhuddanian, Llandovery) Paerticrinus arvosus gen. et sp. nov. is the oldest known Silurian crinoid from Baltica and thus provides the earliest Baltic record of crinoids following the aftermath of the end‐Ordovician mass extinction. A Bayesian ‘fossil tip‐dating’ analysis implementing the fossilized birth–death process and a relaxed morphological clock model suggests that flexibles evolved c. 3 million years prior to their oldest fossil record, potentially involving an ancestor–descendant relationship (via ‘budding’ cladogenesis or anagenesis) with the paraphyletic cladid Cupulocrinus. The sagenocrinid subclade rapidly diverged from ‘taxocrinid’ grade crinoids during the final stages of the GOBE, culminating in maximal diversity among Ordovician crinoid faunas on a global scale. Remarkably, diversification patterns indicate little taxonomic turnover among flexibles across the Late Ordovician mass extinction. However, the elimination of closely related clades may have helped pave the way for their subsequent Silurian diversification and increased ecological role in post‐Ordovician Palaeozoic marine communities. This study highlights the significance of studies reporting faunas from undersampled palaeogeographical regions for clade‐based phylogenetic studies and improving estimates of global biodiversity through geological time.     

Filtration models, guilds, and biofacies: Crinoid paleoecology of the Stanton Formation (Upper Pennsylvanian), midcontinent, North America

Filtration models make several predictions concerning the distribution of crinoids among benthic habitats: (1) generally, higher energy shoreward settings should contain crinoid assemblages dominated by taxa with dense mesh filtration fans; (2) generally, lower energy offshore settings should be dominated by crinoids with open mesh filtration fans; (3) diversity should be highest in nearshore settings, which generally contain low energy microhabitats within high energy settings where both dense fan and open fan forms can co-occur, whereas offshore assemblages should be dominated by open fan taxa; thus, open fan forms should be more eurytopic than dense fan forms. Also, previous empirical models for crinoid distribution patterns note that nearshore assemblages are dominated by large forms whereas offshore assemblages are dominated by small forms. Filtration fan morphology and body size interact significantly to determine how and where crinoids feed and thus are used here as criteria for distinguishing late Paleozoic crinoid guilds. The distribution patterns of crinoid taxa and guilds among the benthic paleoenvironments of the Upper Pennsylvanian (Missourian) Stanton Formation were used to test the predictions of the filtration models.

The results of quantitative analyses show that large, dense fan crinoids are significantly more abundant in shoreward assemblages than smaller, open fan crinoids, which are more abundant in offshore assemblages; these results are consistent with the aforementioned models. However, diversity patterns are not consistent with the filtration models, indicating that mid-depth and aerobic offshore assemblages are more taxonomically and trophically diverse than nearshore and dysaerobic offshore assemblages, ostensibly due to the overlapping ranges of characteristically nearshore and offshore taxa. Analysis of guild distribution patterns also indicates some contradictions to predicted patterns of stenotopy and eurytopy, indicating additional complexities to late Paleozoic crinoid paleoecology.

Five recurrent crinoid assemblages, or biofacies, have been identified from the Stanton Formation of midcontinent North America. The guild structure and diversity of these biofacies are characterized here as: (1) a moderate diversity nearshore biofacies dominated by large calyx, dense fan guilds; (2) a high diversity midshelf biofacies characterized by equitable contributions of many taxa and guilds; (3) a moderate diversity offshore biofacies dominated by non-pinnulate and small calyx, open fan pinnulate guilds; (4) a low diversity offshore dysaerobic biofacies dominated by small calyx pinnulate guilds; (5) a depauperate offshore biofacies dominated by a unique stalkless species, Paragassizocrinus tarri. Except for Biofacies 5, the number of guilds appears to increase offshore; however, the equitability of taxa among and within the guilds generally decreases offshore. This pattern indicates that the heterogeneity of resources, or the recognition by taxa of different classes of resources, as reflected by the variety of functional types, increased from nearshore to offshore, but that the abundance or accessibility of these resources, and/or the relaxation of competition within guilds, increased from offshore to nearshore.     

Homology of posterior interray plates in crinoids: a review and new perspectives from phylogenetics,the fossil record and development

Despite their importance for understanding phylogeny, character evolution and classification, well-constrained homology relationships for posterior plating in crinoids have only recently been attempted. Here, we re-evaluate posterior plate homologies in all major crinoid lineages using development, fossil ontogenies and phylogenetic evidence. Based on these lines of evidence, we change terminology for some posterior plates to correct misnomers and make recommendations for updated terminology of others to better reflect homology. Among pentacrinoids (disparids, hybocrinids, eucladids, flexibles and articulates) the relative position of posterior interray plates, not their topology, reflects homology. From proximal to distal, pentacrinoid posterior plates are the radianal, anal X and right sac plate, regardless of the total number of plates in the adult calyx. Camerate posterior plating contrasts with pentacrinoids, but insufficient data are available to resolve homology relationships between these two clades. More examples of early post-larval ontogeny are needed in camerates and other Palaeozoic crinoids.     

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.     

Reinterpretation of thecal plate homology and phylogeny in the Class Crinoidea

Since the Class Crinoidea was erected in 1821 there has been a consistent failure to resolve the phylogeny of this major group on even the coarsest scale. Reinterpretation of crinoid thecal plate homology, using the orientation of the stem rather than the position of the arms as a reference point for the theca, indicates that two-circlet (monocyclic) crinoids may be derived from three-circlet (dicyclic) taxa by the loss of any one of the three plate circlets in the theca rather than just the lowest circlet as has been assumed previously. Cladistic analysis utilizing this new homology, which is supported by evidence from ontogeny and from the position of other plates in the theca, suggests that Aethocrinus is sister group to all other crinoids and that the Cladida are primitive sister group to both the Disparida and Camerata. The Disparida, Hybocrinida and Perittocrinidae together represent a monophyletic clade. The Camerata also are monophyletic, but the orders Monobathrida and Diplobathrida can no longer be considered to represent natural taxa, with two-circlet camerates probably having evolved more than once. This reinterpretation of thecal plate homology sheds new light on the relationships between the major crinoid groups and the pattern of early crinoid evolution. □ Echinodermata, Crinoidea, homology, phylogeny.     

Phylogeny of Indo‐West Pacific pontoniine shrimps (Crustacea: Decapoda: Caridea) based on multilocus analysis

The phylogenetic relationships and evolutionary processes within the subfamily Pontoniinae, a speciose group of shrimps with diverse lifestyles (free living, semi‐symbiotic and symbiotic) inhabiting the coral reefs of tropical oceans, are an interesting and undeveloped subject of study. In this work, two mitochondrial ribosomal genes (12S rRNA and 16S rRNA) and two protein‐coding nuclear genes (Histone 3 and the sodium–potassium ATPase α‐subunit) were employed to reconstruct the phylogenetic relationships of 42 genera and 101 species within Pontoniinae. Compared to previous studies, ten additional genera were shown to be monophyletic groups, and the genera Dactylonia and Periclimenaeus were shown to be paraphyletic. The shallow‐water crinoid‐associated pontoniines were divided into several groups which were mostly consistent with the morphological analysis. The studied bivalve‐associated taxa exhibited ancestries that were traceable to different lineages, and two groups could be distinguished: Anchiopontonia + Conchodytes and Anchistus. The similar situation occurred in other echinoderm‐associated pontoniines. These results suggest that pontoniines sharing the same hosts may have different evolutionary origins resulting from multiple intrusions of their hosts by morphologically plastic ancestral groups.     

Unusual tabulate‐crinoid biocoenosis from the Lower Devonian of Morocco

The Early Devonian (Pragian: sulcatus to pireneae conodont zones) crinoid–coral biocoenosis from Hamar Laghdad, Morocco contains fragments of crinoid stalks of various taxa encrusted by spherical and ellipsoidal coralla of the tabulate coral Hamarilopora minima. These corals were encrusting host crinoids syn vivo, and this is evidenced by pluricolumnals exceeding 30 elements overgrown from all sides. Most known to date crinoid–epibiont associations display various types of reaction to the epibiont, such as swellings and deformations. In the case discussed here, no clear interaction is visible; therefore, this association can be classified as paroecia. It can be inferred, however, that due to a change in mechanical properties of the crinoid stalk (losing flexibility), the epizoan influence on the host was negative, while the coral was profiting from the elevated position over the seafloor and nutrient‐bearing water currents. It can be supposed that this interaction was close to parasitism. No strict species‐specific relationship between the epizoan and the host was observed.     

Late Ordovician extinction of North American and British crinoids

After reaching a diversity peak in the Caradocian, North American Ordovician crinoids underwent a gradual decline to a nadir in the early Ashgillian (Maysvillian). This interval, recording extinction of the Cleiocrinidae, Merocrinidae, Ottawacrinidae, Hybocystitidae, and several lineages of camerate crinoids, was apparently caused by major environmental shifts in seas of eastern North America resulting from a westward-prograding wedge of terrigenous clastics derived from the Taconic Highlands, possibly coupled with a marine transgression in the Maysvillian that allowed colder water slope biofacies to invade the craton. Crinoids suffered a major episode of extinction in the late Ashgillian (late Richmondian/Rawtheyan). This event, preceding the end of the Ordovician by at least one stage or 2 to 4 million years, resulted in extinction of 12 families of crinoids including the Xenocrinidae, Tanaocrinidae, Reteocrinidae, Archaeocrinidae, Anthracocrinidae, Cincinnaticrinidae, Iocrinidae, Anomalocrinidae, Carabocrinidae, Cupulocrinidae, Porocrinidae, and Hybocrinidae. Glacio-eustatic lowering of sea level may have triggered this crisis by partially draining the North American craton, resulting in changes in oceanic circulation, salinity, and temperature. Latest Ordovician (Hirnantian) carbonates of the North American mid-continent region contain pelmatozoan assemblages from which Silurian crinoids radiated. These taxa were largely unaffected by a minor extinction event at the Ordovician/Silurian boundary.     

Disarticulation patterns in Ordovician crinoids: Implications for the evolutionary history of connective tissue in the Crinoidea

Taphonomic information is examined to evaluate the early history of connective tissues in the Crinoidea. The pattern of stalk segmentation of Middle and Late Ordovician crinoids is consistent with the two-ligament (intercolumnal and through-going ligaments) pattern present in living isocrinid crinoids and interpreted for fossil isocrinids, holocrinids, and Lower Mississippian crinoids. A single rhombiferan was also examined; its taphonomic pattern is also indicative of this style of tissue organization. Furthermore, the taphonomy of all Middle and Late Ordovician crinoids may reflect that they lacked discretely organized muscles between arm brachials, which is consistent with the hypothesis that muscles evolved as a connective tissue between plates only once within the Crinoidea, during the Early Devonian. These data indicate that the two-ligament organization of the stalk is a primitive feature among the Crinoidea and perhaps even among stalked echinoderms. Therefore, the autotomy function of this column-tissue organization among living crinoids is an exaptation. On the other hand, discretely organized muscles as connective tissue in crinoid arms is a derived trait that first appeared during the middle Paleozoic; this adaptation proved very successful for the advanced cladid crinoids.     

Escalating predation on crinoids in the Devonian: negative community-level evidence

Previous morphological studies suggest that predation on stalked crinoids increased in the Devonian. However, there was no concomitant decline in the occurrence of dense, shallow-water stalked crinoid assemblages in North America from the Ordovician and Silurian to the Mississippian. The evolution of crinoid defensive adaptations may have kept pace with rising durophagy, forestalling the expected decline of crinoid communities. It is also possible that the demise of reefs after the Frasnian-Famennian mass extinction indirectly decreased predation pressure on crinoids by removing shelter for predatory fish. A third possibility is that stalked crinoid abundance was affected neither by new predators nor by the decline of reefs. □ Crinoidea, dense crinoid assemblages, Echinodermata, North America, Paleozoic, predation.     

Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate,Germany

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.     

Phylogenetic implications of the Protocrinoida: Blastozoans are not ancestral to crinoids

A traditional, widely cited hypothesis for over a century posits the origin of the crinoids from blastozoans. The blastozoan hypothesis is contradicted by the discovery of a new crinoid order, the Protocrinoida. Protocrinoids exhibit many traits that are consistent with a basal crinoid phylogenetic position, but inconsistent with a blastozoan ancestry. Protocrinoids are among the oldest crinoids and are therefore stratigraphically correctly placed. The blastozoan hypothesis in contrast, relies on putative homologies between blastozoans and crinoids taken from taxonomically and stratigraphically disparate representatives of both groups; these disparities indicate homoplasy rather than propinquity of descent. Data supporting these ideas are reviewed here. These findings reinforce insightful observations made by Georges Ubaghs decades ago with less data.     

Mississippian crinoid biodiversity,biogeography and macroevolution

Abstract: The biodiversity and biogeography of 217 genera of Mississippian crinoids from North America and the British Isles shed light on the macroevolutionary turnover between the Middle Palaeozoic and Late Palaeozoic Crinoid Evolutionary Faunas. This turnover resulted from steady differential extinction among clades during the middle Mississippian after crinoids reached their Phanerozoic peak of generic richness during the early Mississippian. This peak richness was primarily a function of Mississippian originations rather than Devonian–holdover taxa. North America had 100 per cent higher generic richness than the British Isles, but rarefaction analysis adjusts the difference to only 37 per cent higher. Rarefaction demonstrated that North America had increased biodiversity, compared to the British Isles, almost entirely among monobathrid camerates, disparids and primitive cladids. In contrast, diplobathrid camerates, advanced cladids and flexibles had the same generic biodiversity between regions, when compared using rarefaction. The early Mississippian radiation resulted from two primary causes: (1) the expansion of Tournaisian carbonate ramps following the Frasnian mass extinction of reef faunas and (2) the predatory release in the Tournaisian following the end‐Famennian Hangenberg extinction of durophagous fishes. A majority of crinoid genera from the British Isles are cosmopolitan. When combined with rarefaction analysis and evidence for more first occurrences in North America, this suggests higher origination rates in North America, especially when carbonate ramps were widespread. With the gradual reduction in the area of carbonate ramps from the early to late Mississippian, in conjunction with the radiation of new durophagous fishes, camerate crinoids in particular experienced continuous background extinction, without replacement, beginning during the earliest Viséan (late Osagean). By middle Viséan time (late Meramecian) advanced cladids were dominant in all settings. This resulted in the transition from the Middle Palaeozoic to the Late Palaeozoic Crinoid Macroevolutionary Fauna.     

Divergent sympatric lineages of the Atlantic and Indian Ocean crinoid Tropiometra carinata

The shallow water comatulid crinoid Tropiometra carinata is native to both the Atlantic and Indian Oceans, a distribution anomalous among shallow water crinoids and many other broadcast spawning species. Given this species' short pelagic larval duration, the findings of previous work that suggest that the Benguela upwelling is a significant barrier to gene flow in broadcast spawning species, and T. carinata's unexpected geographic distribution, we predicted that the crinoids presently recognized as T. carinata consisted of a species complex. To test this prediction, we sequenced a portion of the mitochondrial cytochrome oxidase 1 gene from 30 individuals of T. carinata collected from Brazil, the Mozambique Channel, Madagascar, and Reunion Island. We found that nucleotide divergence ranged 0.02–3.10% among haplotypes. Moreover, while a Bayesian phylogenetic tree indicated that there were two substantially divergent genetic lineages, there was no evidence to support that T. carinata is comprised of a species complex due to isolation‐by‐distance. Surprisingly, both lineages were found in sympatry in both the Atlantic and Indian Oceans. Likewise, a 95% parsimony haplotype network revealed that identical haplotypes are found in both oceans, suggesting that a species complex may indeed exist, just not one caused by geographic isolation. We discuss possible explanations for this unexpected genetic structure, such as natural dispersal or human‐mediated movement, and how the genetic structure found here is relevant to other marine organisms and to cryptic speciation.     

Fixed,free, and fixed: The fickle phylogeny of extant Crinoidea (Echinodermata) and their Permian–Triassic origin

Although the status of Crinoidea (sea lilies and featherstars) as sister group to all other living echinoderms is well-established, relationships among crinoids, particularly extant forms, are debated. All living species are currently placed in Articulata, which is generally accepted as the only crinoid group to survive the Permian–Triassic extinction event. Recent classifications have recognized five major extant taxa: Isocrinida, Hyocrinida, Bourgueticrinina, Comatulidina and Cyrtocrinida, plus several smaller groups with uncertain taxonomic status, e.g., Guillecrinus, Proisocrinus and Caledonicrinus. Here we infer the phylogeny of extant Crinoidea using three mitochondrial genes and two nuclear genes from 59 crinoid terminals that span the majority of extant crinoid diversity. Although there is poor support for some of the more basal nodes, and some tree topologies varied with the data used and mode of analysis, we obtain several robust results. Cyrtocrinida, Hyocrinida, Isocrinida are all recovered as clades, but two stalked crinoid groups, Bourgueticrinina and Guillecrinina, nest among the featherstars, lending support to an argument that they are paedomorphic forms. Hence, they are reduced to families within Comatulida. Proisocrinus is clearly shown to be part of Isocrinida, and Caledonicrinus may not be a bourgueticrinid. Among comatulids, tree topologies show little congruence with current taxonomy, indicating that much systematic revision is required. Relaxed molecular clock analyses with eight fossil calibration points recover Articulata with a median date to the most recent common ancestor at 231–252 mya in the Middle to Upper Triassic. These analyses tend to support the hypothesis that the group is a radiation from a small clade that passed through the Permian–Triassic extinction event rather than several lineages that survived. Our tree topologies show various scenarios for the evolution of stalks and cirri in Articulata, so it is clear that further data and taxon sampling are needed to recover a more robust phylogeny of the group.     

Development of Cyathidium foresti (Echinodermata: Crinoidea, Cyrtocrinida) from early attached larvae to adult-like juveniles

To date, knowledge about ontogenetic development of crinoids has been exclusively based on comatulid species, since early stages of other crinoid taxa have not been available so far. The authors now present a scanning electron microscopical and light microscopical study on a developmental series of young sessile individuals of the cyrtocrinid Cyathidium foresti. This species displays a developmental type of its own. In some aspects, the early stages resemble the early attached larva of comatulids (e.g. vestibulum, enteric sac, somatocoelomic cavity) but differ clearly in other (e.g. far oral position of hydrocoelomic primordium, pattern of podia formation, early splitting of the roof, absence of chambered organ). Therefore a specific term is proposed for this new kind of larva: cyathidula. Older juveniles are quite similar to adults; the developmental course is direct. Consequently the group of holopodid crinoids to which Cyathidium and Holopus belong, can be concluded to originate phylogenetically from neotenic larvae.     

A test of Simpson's "rule of the survival of the relatively unspecialized" using fossil crinoids

Temporally long-ranging (=long-lived) taxa have been postulated to have unusual properties that aid their prolonged geologic survival. Past studies have examined dispersal capabilities, geographic ranges, and single-character morphological adaptations as factors that may contribute to geologic longevity. Here, I test whether long-lived fossil crinoid taxa are morphologically unusual using a whole suite of morphological characters. I define long-lived taxa in several explicit, comparative ways. I find that long-lived crinoid genera and families are often less distant from mean morphologies of their crinoid orders than their shorter-lived relatives; that is, they are relatively less specialized. I also compare the morphology of crinoid genera relative to basal members of their respective orders; mean morphological distances of long-lived genera from basal morphologies are seldom distinct from those of their shorter-lived relatives. I observe that long-lived crinoid genera are less distant from mean morphologies of their temporal cohorts compared with shorter-lived genera but not in a statistically significant manner. I conclude that long-lived crinoids are relatively unspecialized, in the sense that they are relatively closer to mean morphologies of their taxonomic groups.     

Assessment of hidden diversity of crinoids and their symbionts in the Bay of Nhatrang,Vietnam

Crinoid associates represent an abundant and diverse, but poorly explored, component of the hidden biodiversity of coral-reef ecosystems. We studied data from 5 years of collecting in the Bay of Nhatrang (BN), Vietnam, to assess the diversity of crinoids and their symbionts, to compare it with other areas of the Indo-West Pacific, and to elucidate the extent to which the observed diversity of crinoids and their symbionts corresponds to their true diversity. In total, about 2,287 specimens of symbionts belonging to 70 species were found on 203 specimens of crinoids belonging to 33 species. Among the crinoids, the most numerous species were Himerometra robustipinna (36 specimens) and Cenometra bella (29 specimens), among the symbionts the polychaete Paradyte crinoidicola (c. 850 specimens) and the galatheid crustacean Allogalathea elegans (180 specimens). Species accumulation curves suggest that we have sampled most of the crinoid diversity in the BN, whereas the diversity of their symbionts remained undersampled. Estimated species richness of crinoids was higher than previously observed richness, and varied from 39 (estimated by bootstrap) to 46 (jackknife 2). Estimated species richness of symbionts was higher than observed richness, and varied from 71 (bootstrap) to 93 (jackknife 2). We suggest a slight increase in the number of crinoid species to result from more detailed studies of nocturnal species, and an increase in the number of symbiotic species when studies of nocturnal crinoid associates and sibling species among decapods are included. Our study revealed a rather rich crinoid fauna in the bay compared to other areas of the Indo-West Pacific, and the highest species richness of crinoid associates known from anywhere in the World Ocean.