Articulata

Reconstruction of Pentacrinites, by Nobu Tamura.

Belongs within: Dendrocrinida.
Contains: Ampelocrinidae, Corythocrinidae, Cyrtocrinidia, Holopodinidia, Isocrinidae, Hyocrinidae, Apiocrinitidae, Millericrinidae, Pentacrinitidae, Comatulidia, Roveacrinidae, Somphocrinidae.

The Articulata are a group of crinoids with a flexible tegmen known from the Lower Triassic to the present, including all living members of the crinoids (Wienberg Rasmussen 1978).

The Comatulida, feather stars, are a group of crinoids in the larval column has been reduced to a single cirriferous centrodorsal attached to the calyx (Wienberg Rasmussen 1978). They are the most prominent crinoid group in the modern fauna.

Crinoids of the open seas
Published 12 February 2010
Lateral view of calyx of Saccocoma tenella from Brodacki (2006) showing the emergence angle of the arms.

Living crinoids can be divided morphologically between the stalked sea lilies and the stemless feather stars but, as described in an earlier post, the feather stars are not really entirely stemless. Rather, the column has been reduced to a single plate that still functions as the point of attachment for the cirri, the small tentacle-like appendages that the feather star uses to hang onto the substrate or move about. There were two groups of Mesozoic crinoids that went a step further, completely losing both column and cirri.

The Uintacrinida (of the late Cretaceous) and the Roveacrinida (throughout the Mesozoic) were both subgroups of the Articulata, the clade that includes all living crinoids, but they are very distinct from each other and probably lost their stalks independently. Milsom et al. (1994) placed the Uintacrinida as a derived subgroup of the feather stars while the relationships of the Roveacrinida remain mysterious. Because of the lack of any means of attachment to the substrate, both have been regarded as pelagic; as I’ll explain below, this seems likely for the roveacrinidans but not for the uintacrinidans.

Ventral reconstruction of Saccocoma from Milsom (1994) showing the arrangement of lateral plates in the proximal part and long branches in the distal part of the arms.

The roveacrinidans were absolutely tiny animals with the central cup only a couple of millimetres across and the total armspan up to a few centimetres. In the best-known example, Saccocoma, broad wing-like plates were attached to either side of the proximal part of the slender multi-branched arms while the skeleton as a whole was very thin and light. In an influential interpretation of Saccocoma, Otto Jaekel referred to the lateral plates on the arms as “Schwimmplatten” and suggested that they were used to propel the animal through the water. However, Brodacki (2006) pointed out that the mobility of the proximal part of the arms would not have been sufficient for the plates to be used in swimming. Instead, the distal branched parts of the arms would have provided the swimming force while the Schwimmplatten would have provided extra friction to reduce the rate of sinking. Because roveacrinidans would have been heavier than the surrounding water even with their lightened plates, they must have been active (and fairly continuous) swimmers rather than passive floaters. Swimming was probably done by slowly coiling the distal part of the arms inwards then rapidly straightening them outwards so the animal flicked itself through the water. An alternative suggestion (Milsom 1994) that Saccocoma was benthic on soft mud with the “Schwimmplatten” protecting the animal from being buried is contradicted by the fact that the arms would have emerged from the top of the theca at an angle of 45° rather than being flat. Also, Saccocoma plates are commonly found in coprolites whose mode of deposition indicates that they were produced by pelagic animals (Hess 1999a).

Fossil assemblage of the very aptly named Uintacrinus socialis, from Hess 1999b.

In contrast to the minute, light roveacrinidans, the two uintacrinidan genera Uintacrinus and Marsupites were very large crinoids with sack-like, flexible thecas up to 75 mm in diameter and arms up to a metre or more in length. Unlike roveacrinidans, uintacrinidan plates are not reduced but remain robust and heavy. The proximal parts of the arms were integrated into the theca which would have limited their ability to spread outwards as in Saccocoma. Orientation of preserved specimens (and Uintacrinus can sometimes be preserved in extraordinarily dense concentrations) indicates that the habitual life position of uintacrinidans was with the mouth upwards, contradicting suggestions that the theca could have contained some sort of buoyancy organ. Despite the lack of any means of attachment, without any clear adaptations for increasing buoyancy it seems that uintacrinidans would have been benthic rather than pelagic. They would have lived in soft mud with the theca buried (hence the lack of attachment structures) and the arms extending upwards from the substrate to collect food particles. Hess (1999b) compares the possible life appearance of Uintacrinus assemblages to “dense patches of tall eel grass”.

Paracomatula: feather star, or feather star wannabe?
Published 6 January 2014
Fossilised accumulation of Paracomatula helvetica, from here.

Earlier posts on this site have discussed examples of the feather stars, the most successful representatives in the modern environment of the crinoids. Originally a group whose members lived permanently attached to the substrate by a stalk, at some point crinoids diversified to a more mobile (or least shiftable) lifestyle, discovering the joys of travel. This was not, it should be noted, an entirely direct process. Many stalked crinoids are also mobile, able to detach themselves from their substrate and crawl to a new position. Other crinoids than the feather stars lost their stalks. And at least one group within the feather stars, the Mesozoic Thiolliericrinidae, reverted back to retaining as adults the larval stalk that most feather stars lose in the course of development.

Nevertheless, the feather stars had definitely made their appearance by the early Jurassic. One of the earliest taxa that has been assigned to the feather stars is Paracomatula, which is known from the very late Triassic to the middle Jurassic (Hess 2013). Paracomatula would have largely resembled a modern feather star in appearance, but had one significant difference. In modern feather stars, the base of the central cup is formed by a large conical plate known as the centrodorsal. In Paracomatula, however, the centrodorsal is replaced by a stack of five narrow plates. These correspond to much-shortened versions of the columnals that make up the stalked in other crinoids, and Wienberg Rasmussen (1978) and other authors suggested that Paracomatula‘s separate columnals became fused to form the centrodorsal of the feather stars proper.

However, not all authors have accepted this interpretation. Hess (2013) has argued that details of the development of modern feather stars from a stalked juvenile to a free-living adult indicate that the centrodorsal is derived from the enlargement of a single columnal rather than the fusion of a series. In the earliest definitive feather star, the Jurassic Palaeocomaster, the cirri (tentacle-like appendages) on the centrodorsal are arranged in a haphazard fashion consistent with their development on a single expanding plate, while Paracomatula has a more orderly array of one ring of cirri per columnal without the development of supernumerary cirri. Hess therefore argues that Paracomatula species were not the forebears of feather stars, but their rivals: a closely related group that was independently experimenting with a stalk-free way of life.

Systematics of Articulata

Characters (from Wienberg Rasmussen 1978): Cup dicyclic or cryptodicyclic, usually with five infrabasals, five basals and five radials. Infrabasals rarely distinct and exposed on surface of cup, more commonly small and concealed or missing, at least in adults. Basals generally small; may be strongly reduced or missing. No anal plates or compound radials and normally no plates separating radials or basals in the postlarval skeleton. Arms uniserial. Articulations between radial and arm and between some or all brachials muscular and with distinct fulcral ridge. Radials and brachials perforated by nerve canal, passing through fulcral ridge of muscular and synaxthrial articulations. Arms generally divided at primibrachs 2, commonly further divided, with nonmuscular articulation at primibrachs 1 to 2. Arms generally free, proximal brachials may be movably connected by interbrachial plates. Tegmen flexible, with calcareous spicules or grains or with irregular pattern of thin plates. Mouth and ambulacral grooves open to exterior. Pinnules present, articulated to all or most brachials, pinnules not axillary or with nonmuscular distal articulation. Column (if present) circular, elliptical or five-sided in section, with or without cirri on nodals. Columnal articulations synarthrial, symplectial, cryptosymplectial or synostosial. Central canal narrow. Attachment by distall cirri, radix, or terminal disc.

Articulata [Astylida, Canaliculata, Libera, Liberidae, Neocrinoidea, Pinnata, Stomatocrinoidea]
    |  i. s.: Dolichocrinus de Loriol 1891 [=Tetanocrinus Jaekel 1891]WR78
    |           `--*D. aberrans (de Loriol 1882) [=Eugeniacrinus aberrans, *Tetanocrinus aberrans]WR78
    |         Acariaeocrinus Biese 1935 [=Microcrinus Terquem & Piette 1865 non Emmons 1858]WR78
    |           `--*A. liasinus (Terquem & Piette 1865) [=*Microcrinus liasinus]WR78
    |--AmpelocrinidaWM03
    |    |--AmpelocrinidaeWM03
    |    `--CorythocrinidaeWM03
    |--Dadocrinus von Meyer 1847WR78 (see below for synonymy)
    |    |--*D. gracilis (von Buch 1845) [=Encrinus gracilis; incl. *Calathocrinus digitatus von Meyer 1847]WR78
    |    |--D. kunischi Wachsmuth & Springer 1887WR78
    |    `--‘Apiocrinus’ recubariensis Crema 1896 (see below for synonymy)WR78
    |--Cyrtocrinida [Coadunata, Compacta, Cyrtocrinina]WA17
    |    |  i. s.: Gutticrinus [Gutticrinidae]SG93
    |    |           `--G. guttiformisSG93
    |    |--CyrtocrinidiaSG93
    |    `--HolopodinidiaWR78
    |--Holocrinidae [Holocrinida]WA17
    |    |--Moenocrinus Hildebrand 1926WR78
    |    |    `--*M. deeckei Hildebrand 1926WR78
    |    `--Holocrinus Wachsmuth & Springer 1886WR78
    |         |--*H. beyrichi (Picard 1883) [=Encrinus beyrichi]WR78
    |         |--H. lunatus (Kristen-Tollman 1975)SG93
    |         |--H. smithi (Clark 1915)SG93
    |         `--H. wagneri (Benecke 1887)WR78
    |--Isocrinina [Isocrinida, Pentacrinacea]SG93
    |    |  i. s.: LaevigatocrinusSG93
    |    |           |--L. laevigatus (Münster 1841)SG93
    |    |           `--L. venustus (Klipstein 1845)SG93
    |    |         Tyrolecrinus subcrenatus (Münster 1841)SG93
    |    |--IsocrinidaeWA17
    |    `--Proisocrinus Clark 1910 [Proisocrinidae]WR78
    |         `--*P. ruberrimus Clark 1910WR78
    |--Millericrinida [Apiocrinacea, Millericrinina]UL78
    |    |  i. s.: Entrochus Hofer 1760SG93, J78
    |    |           `--E. silesiacus Beyrich 1857SG93
    |    |         Cyclocrinus d’Orbigny 1850UL78, WR78 [incl. Acrochordocrinus Trautschold 1859WR78; Cyclocrinidae]
    |    |           |--*C. rugosus (d’Orbigny 1841) [=Bourgueticrinus rugosus]WR78
    |    |           `--‘*Acrochordocrinus’ insignis Trautschold 1859WR78
    |    |--HyocrinidaeWA17
    |    `--MillericrinidiaSG93
    |         |--ApiocrinitidaeSG93
    |         `--MillericrinidaeUL78
    |--Comatulidina [Comatuladae, Comatulida, Comatulidae, Macrophreata, Macrophreatina, Oligophreata]WA17
    |    |  i. s.: Pachyantedon Jaekel 1891 (n. d.)WR78
    |    |           |--*P. beyrichi Jaekel 1891WR78
    |    |           `--P. gracilis (Walther 1886) [=Solanocrinus gracilis, Antedon gracilis]C50
    |    |--PentacrinitidaeSG93
    |    |--ComatulidiaSG93
    |    `--ParacomatulaceaUL78
    |         |--Paracomatula Hess 1951 [Paracomatulidae]WR78
    |         |    `--*P. helvetica Hess 1951WR78
    |         `--Eocomatula [Eocomatulidae]SG93
    |             `--E. interbrachiatus (Blake 1876)SG93
    |--RoveacrinidaYL78
    |    |--RoveacrinidaeWR78
    |    |--SomphocrinidaeSG93
    |    `--SaccocomidaeWR78
    |         |--Pseudosaccocoma Remeš 1905 [Pseudosaccocomidae, Pseudosaccocominae]WR78
    |         |    `--*P. strambergense Remeš 1905WR78
    |         `--SaccocominaeWR78
    |              |--Applinocrinus Peck 1973WR78
    |              |    |--*A. cretacea (Bather 1924) [=Saccocoma cretacea]WR78
    |              |    `--A. texanusWR78
    |              `--Saccocoma Agassiz 1836 (see below for synonymy)WR78
    |                   |--‘Euryale’ bajeri Koenig 1825 (see below for synonymy)WR78
    |                   |--S. pectinata [incl. Ophiurites decafilatus, O. filiformis octofilatus]B89
    |                   `--S. tenellumWR78 [=*Saccoma tenellaJ18]
    `--Encrinidae [Encrinacea, Encrini, Encrinida, Encriniens, Encrinoidea]WA17
         |--Palermocrinus Jaekel 1918J18, J78
         |    `--*P. jaekeli Gislén 1924M78
         |--Traumatocrinus Wöhrmann 1889SG93, ML78
         |    `--T. caudex (Dittmar 1868)SG93
         `--Encrinus Lamarck 1801 (see below for synonymy)ML78
              |--*E. liliiformis Lamarck 1801ML78
              |--E. aculeatus [=*Jenaicrinus aculeatus]J18
              |--E. brahliJ18
              |--E. carnalli [=*Beyrichocrinus carnalli]ML78
              |--*Flabellocrinites’ cassianus Klipstein 1845ML78
              |--E. ‘cassianus’ Laube 1865 non Flabellocrinites cassianus Klipstein 1845 [=*Cassianocrinus cassianus]ML78
              |--E. pentacrinitesG20
              |--E. schlotheimiJ18
              `--E. terebratularum Schmid 1876SG93
Nomina nuda: Asteriatites pentagonatus von Schlotheim 1813WR78
             Asteriatites spinosus von Schlotheim 1813WR78

‘Apiocrinus’ recubariensis Crema 1896 [=*Cremacrinus recubariensis, *Recoarocrinus recubariensis; incl. Millericrinus recubariensis Bather 1897]WR78

Dadocrinus von Meyer 1847WR78 [incl. Calathocrinus von Meyer 1847WR78, Cremacrinus Jaekel 1918 non Ulrich 1886WR78, Recoarocrinus Gislén 1924WR78; DadocrinidaeSG93]

Encrinus Lamarck 1801 [=Encrina (l. c.); incl. Beyrichocrinus Jaekel 1918 non Waagen & Jahn 1899, Cassianocrinus Laube 1865, Chelocrinus von Meyer 1837 (n. d.), Chelocrinites Geinitz 1846 (n. d.), Flabellocrinites Klipstein 1845, Jenaicrinus Jaekel 1918, Porocrinus Dittmar 1866 non Billings 1857]ML78

‘Euryale’ bajeri Koenig 1825 [incl. Comatula pectinata filiformis Goldfuss 1831, Asteriatites filiformis, *Saccocoma pectinata filiformis, A. rosaceus]WR78

Saccocoma Agassiz 1836 [=Saccosoma (l.c.) non Motschulsky 1859; incl. Asteriatites von Schlotheim 1813 (n. d.), Saccoma Jaekel 1918]WR78

*Type species of generic name indicated

References

[B89] Boehm, G. 1889. Ein Beitrag zur Kenntniss fossiler Ophiuren. Berichte der Naturforschenden Gesellschaft zu Freiburg I. B. 4: 232–287, pls 4–5.

Brodacki, M. 2006. Functional anatomy and mode of life of the latest Jurassic crinoid Saccocoma. Acta Palaeontologica Polonica 51 (2): 261–270.

[C50] Clark, A. H. 1950. A monograph of the existing crinoids. Vol. 1. The comatulids. Part 4c. Superfamily Tropiometrida (the families Thalassometridae and Charitometridae). Bulletin of the United States National Museum 82 vol. 1 (4c): 1–383.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

Hess, H. 1999a. Upper Jurassic Solnhofen Plattenkalk of Bavaria, Germany. In: Hess, H., C. E. Brett, W. I. Ausich & M. J. Simms (eds) Fossil Crinoids pp. 216–224. Cambridge University Press.

Hess, H. 1999b. Uintacrinus beds of the Upper Cretaceous Niobrara Formation, Kansas, USA. In: Hess, H., C. E. Brett, W. I. Ausich & M. J. Simms (eds) Fossil Crinoids pp. 225–232. Cambridge University Press.

Hess, H. (in press, 2013) Origin and radiation of the comatulids (Crinoidea) in the Jurassic. Swiss Journal of Palaeontology.

[J18] Jaekel, O. 1918. Phylogenie und System der Pelmatozoen. Paläontologische Zeitschrift 3: 1–128.

[J78] Jeffords, R. M. 1978. Dissociated crinoid skeletal elements. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 3 pp. T928–T937. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

Milsom, C. V. 1994. Saccocoma: a benthic crinoid from the Jurassic Solnhofen Limestone, Germany. Palaeontology 37 (1): 121–129.

Milsom, C. V., M. J. Simms & A. S. Gale. 1994. Phylogeny and palaeobiology of Marsupites and Uintacrinus. Palaeontology 37 (3): 595–607.

[ML78] Moore, R. C., N. G. Lane, H. L. Strimple, J. Sprinkle & R. O. Fay. 1978. Inadunata. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 2 pp. T520–T759. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[SG93] Simms, M. J., A. S. Gale, P. Gilliland, E. P. F. Rose & G. D. Sevastopulo. 1993. Echinodermata. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 491–528. Chapman & Hall: London.

[UL78] Ubaghs, G., N. G. Lane, H. Wienberg Rasmussen & H. L. Strimple. 1978. Evolution. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 2 pp. T275–T316. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[WM03] Webster, G. D., C. G. Maples, R. Mawson & M. Dastanpour. 2003. A cladid-dominated Early Mississippian crinoid and conodont fauna from Kerman Province, Iran and revision of the glossocrinids and rhenocrinids. Journal of Paleontology 77 (Suppl. 3): 1–35.

[WR78] Wienberg Rasmussen, H. 1978. Articulata. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 3 pp. T813–T927. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[WA17] Wright, D. F., W. I. Ausich, S. R. Cole, M. E. Peter & E. C. Rhenberg. 2017. Phylogenetic taxonomy and classification of the Crinoidea (Echinodermata). Journal of Paleontology 91 (4): 829–846.

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