Acta Musei Nationalis Pragae, Series B, Natural History, 59 (3–4): 151–162 issued December 2003 Sborník Národního muzea, Serie B, Přírodní vědy, 59 (3–4): 151–162 PLASIACYSTIS MOBILIS, GEN. ET SP. N., A STRANGE “CARPOID” (ECHINODERMATA, ?HOMOIOSTELEA: SOLUTA) IN THE BOHEMIAN ORDOVICIAN (CZECH REPUBLIC) RUDOLF J. PROKOP Department of Palaeontology, Museum of Natural History, National Museum, Václavské nám. 68, 115 79 Pra- ha 1, Czech Republic; e-mail: [email protected] VÁCLAV PETR Zoological Library, Faculty of Science, Charles University, Viničná 7, 128 44 Praha 2, Czech Republic; e-mail: [email protected] Prokop, R. J. and Petr, V. (2004): Plasiacystis mobilis, gen. et sp. n., a strange “carpoid” (Echinodermata, ?Homoiostelea: So- luta) in the Bohemian Ordovician (Czech Republic). – Acta Mus. Nat. Pragae, Ser. B, Hist. Nat., 60 (2004) (3–4): 151–162. Praha. ISSN 0036-5343 Abstract. This is a first report on the occurrence of a new, very unusual “carpoid” echinoderm, described here as Plasiacystis mobilis gen. et sp. n., that is relatively common in the Middle Ordovician of Bohemia (Czech Republic) and Spain. Plasia- cystis has a large, armless, sac-like theca, composed of numerous polygonal, poreless plates and the flexible cylindrical prox- istele followed with rigid dististele which is transformed into a flat, elongated paddle, composed of two columns of transverse plates. Plasiacystis gen. n., is placed here provisionally within the echinoderm Class Homoiostelea GILL et CASTER, 1960, Order Soluta JAEKEL, 1901 and Family Plasiacystidae fam. n. (here stated). A note on the concept of Calcichordata is added. I Echinodermata, “Carpoidea”, “Calcichordate Theory”, Homoiostelea, Soluta, Plasiacystis gen. n., Plasiacystidae fam. n., Lower Palaeozoic, Ordovician, Barrandian. Received October 24, 2003 Introduction Plasiacystis gen. n., has a very low, almost cystoid-like anal pyramid. The stele is remarkably shaped. The flexible prox- Fragments of the unique carpoid genus Plasiacystis gen. istele is cylindrical and resembles structurally a very high n. described here and coming from the Šárka and Dobrotivá turret or “Theka-Turm” of pyrgocystid and rhenopyrgid Formations (Middle Ordovician, Barrandian area) had been edrioasteroids, composed of distinctly imbricating scale- already known to some former palaeontologists as Joachim like plates arranged in numerous horizontal rings. The rigid Barrande, Otto Jaekel, and Ferdinand Prantl. The animal dististele or “tail” is transformed into a rather flat, elongat- has been described for the first time by Barrande (1887) ed paddle, with dimerous plan, composed of two columns of who supposed that the Plasiacystis’s many-plated theca transverse plates, rather unevenly paired; this distal paddle with pore-less plates belonged to a cystoid, particularly to a bears one distinct, hollow thorn. Plasiacystis gen. n. is rather problematical specimen of Echinosphaerites infaus- placed here provisionally within Homoiostelea GILL et tus BARRANDE 1887. Jaekel (1918), on the other hand, CASTER, 1960: Soluta JAEKEL, 1901 and Family Plasia- described Plasiacystis’s rigid paddle-like dististele as a cystidae fam. n. (designated herein). “root” (“Wurzel”) of the mitrate “carpoid” Mitrocystella We are convinced that the whole bauplan of Plasiacystis barrandei JAEKEL 1918. Ferdinand Prantl collected frag- gen. n. creates one of arguments against the so-called “Cal- ments of Plasiacystis’s proxisteles and designated them as cichordate Theory” of R.P.S. Jefferies. Jefferies (1990) has Lepidocoleus bohemicus sp. n. (Machaeridia) but did not extended his Calcichordate Theory to embrace also the so- publish any paper on them. lutan “carpoids”, however, many authors (see e.g. Parsley Certainly, Plasiacystis gen. n. is almost as strange as 1997) disagree with such an extension, and, in fact, many ophiocistioid echinoderms, bearing characteristics of differ- specialists disagree with the whole concept of Calcichorda- ent groups of animals. It has a large, polyplated and proba- ta and Dexiothetica (e.g. Philip 1979; Ubaghs 1981; Kolata bly sac-like theca. All thecal plates are clearly and Jollie 1982; Lefebvre, Racheboeuf and David 1998; Le- echinoderm-like and without pores. In some specimens febvre and Vizcaino 1999; and even Ruta 1999; see also the there seem to be present also slender marginal plates (re- short note on the Calcichordate Theory below). Morpholog- sembling partly mitrates) but they are clearly pseudo- ical characteristics of the new solutan species rather support marginals resulting from post-mortem collapse of theca. the old echinoderm concept (e.g. Ubaghs 1967). 151 Text-fig. 1: Schematic sketch of dististele (paddle) of Plasiacystis mobilis gen. et sp. n. drawn by Jaekel (1918) (his figure 110 H, J, K, L on page 121), erroneously associated with Mitrocystella Barrandei JAEKEL. Systematic part Remarks: A distant relative (?) of Plasiacystis gen. n. seems to be the homoiostelean genus Castericystis Phylum Echinodermata UBAGHS et ROBISON, 1985 from the Middle Cambrian ? Class Homoiostelea GILL et CASTER, 1960 of Utah, USA. Both genera have sac-like thecae composed ? Order Soluta JAEKEL, 1901 of irregular polygonal plates and have almost identical mor- phology of proxistele. Of course, Castericystis differs clear- Family Plasiacystidae fam. n. ly from Plasiacystis gen. n. in presence of relatively long arm and by the different shape and structure of the anal Diagnosis: Solutans (?) with the skeleton distinctly pyramide. The flat dististele of Castericystis also consists of composed of the large sac-like theca without rigid arms and the transversaly arranged plates but differs markedly from the relatively long, flexible cylindrical proxistele composed the dististele of Plasiacystis: it is relatively long, slender of imbricating scale-like platelets arranged in numerous and terminated by a whip-like tip (see Text-fig. 4) horizontal rings. Proxistele is followed with flat, elipsoidal “paddle” composed of two columns of transverse plates Plasiacystis mobilis sp. n. (dististele). Text-figs 1–4; Pls 1–4 Genus assigned: Plasiacystis gen. n. 1887 Echinosphaerites infaustus BARRANDE; Barrande, Pl. 25, fig. 15 (specimen with anterior-posteriorly strongly com- Plasiacystis gen. n. pressed theca, and also with a proxistele preserved); Pl. 39, fig. 29. (Fig. 30 shows a specimen that represents probably Type species: Plasiacystis mobilis gen. et sp. n.; true “Echinosphaerites” with theca composed of large plates Middle Ordovician, Barrandian area, Bohemia, Czech bearing both tubercules as well as short transverse channels Republic. on their borders) Diagnosis:The same as for the family. 1918 Mitrocystella Barrandei JAEKEL; Jaekel, p. 121, fig. 110 H, Stratigraphic and palaeogeographic dis- J, K, L (rigid paddle-like dististele belonging probably to tribution: Šárka and Dobrotivá Formations, Middle Or- two specimens or even more) dovician, Barrandian area (Bohemia, Czech Republic); 1947 Lepidocoleus bohemicus sp. n., PRANTL MS (proxistele) Middle Ordovician of Spain. Holotype: specimen inv. n. NM L 13216 coming 152 Text-fig. 2: Schematic sketch of idealized specimen of Plasiacystis mobilis gen. et sp. n. showing theca, proxistele and dististele (paddle with a thorn). from the Šárka Formation, Osek near Rokycany, with theca, Dobrotivá Formation: 2 parts of thecae, preserved in the proxistele and dististele, herein photographed on Pl. 1, nodules from the locality Praha-Šárka. figs 1, 2. Middle Ordovician (Llanvirnian?): 18 pieces of proxis- Locus typicus: Osek near Rokycany, Barrandian tele preserved in the nodules (very similar to the Bohemian area, Czech Republic. ones), coming from Casalla de la Sierrra near Sevilla, Spain Stratum typicum: Šárka Formation, Llanvirnian, (given by our friend, Dr. Juan-Carlos Gutiérez Marco). Middle Ordovician. Derivatio nominis: after Vladimír Plas (* 18. 4. Material: Šárka Formation: 31 thecae or fragments of 1905, † 10. 3. 1980), the famous collector of fossils and cus- thecae, 17 proxisteles and 3 isolated dististeles preserved in todian of the geological and palaeontological collections of the siliceous (originaly calcareous) nodules (called conven- the former Central Geological Survey (now the Czech Geo- tionally “Šárka” or “Rokycany” balls). Localities: Osek logical Survey), Prague. near Rokycany, Mýto, Praha-Šárka and Praha-Libuš. Description: A carpoid echinoderm with body built 153 flattened rigid paddle, with dimerous plan, composed of two columns of transverse plates, rather unevenly paired. One column of transverse plates of the paddle bears asym- metrically one very distinct, extremity resembling a “thorn” with rounded apex. This “thorn” seems to be hollow and we are completely uncertain about its purpose – it may have probably served for some kind of steering or may have been a kind of anchorage of the animal or it may have served for digging or it had been some specific kind of sexual dimor- phism? Dimensions (in mm): Text-fig. 3: Schematic sketch of idealized specimen of Plasia- Specimen L 13216 (holotype) cystis mobilis gen. et sp. n. showing enlarged, flat anal pyra- approx. dimensions width length mid. Theca 300 400 proxistele 50 300 dististele 100 200 up of two distinct skeletal parts: theca and stele, the latter approx. whole 900 being composed of equally distinct proxistele and dististele. Specimen L 29120 Even in the best-preserved specimen with both theca and approx. dimensions width length stele, there is no arm retained. If there was any arm or arm-