Hyolithellida

Life reconstruction of Hyolithellus micans, from Fisher (1962).

Belongs within: Cnidaria.

The Hyolithellida are a group of small, tubular fossils known from the Cambrian and Ordovician periods. Their affinities are uncertain; though often classified with the hyoliths (and here placed with them for convenience), their shells are phosphatic rather than calcitic, making such a relationship unlikely. Hyolithellidans may be divided between the Hyolithellidae, whose tubes have a circular cross-section and were sealed with an operculum bearing paired muscle scars, and the Torellellidae with elliptical or biconvex tubes for which an operculum is unknown (Fisher 1962).

Characters (from Fisher 1962, as Hyolithelminthes): Small (length usually 5–15 mm), almost cylindrical, brownish-black narrow, conical tubes (growth angle in adult region one to four degrees); curved and irregular near closed apex, straightening toward aperture. Cross section circular to elliptical. Exterior surface sometimes covered by small transverse ridgelets and striae; shell laminated, usually thick, with smooth interior surface. Body cavity elongate, devoid of septa or any other structure. Circular to subcircular operculum composed of many laminae, with eccentrically situated apex surrounded by closely spaced concentric growth lines; adult opercula thicker than translucent juvenile ones; underside of operculum with paired muscle scars originating form point opposite apex, showing bilateral symmetry. Tube and operculum composed of calcium orthophosphate.

<==Hyolithellida [Hyolithelminthes]
    |  i. s.: Byronia Matthew 1899WS93, H62 [incl. Phosphannulus Müller, Nogami & Lenz 1974MW04; Byroniida]
    |           |--*B. annulata Matthew 1899H62
    |           |--B. naumovi Kozłowski 1967WS93
    |           `--B. universalis (Müller, Nogami & Lenz 1974)MW04
    |--HyolithellidaeF62
    |    |--Barella Hedström 1930F62
    |    |--Mobergella Hedström 1923H75
    |    |    |--*M. holsti (Moberg 1892) [=Discinella holsti]H75
    |    |    |--M. radiolata Bengtson 1968WS93
    |    |    `--M. turgida Bengtson 1968WS93
    |    `--Hyolithellus Billings 1871F62 [incl. Discinella Hall 1872F62, H75]
    |         |--*H. micans (Billings 1871) [=Hyolithes micans]F62
    |         |--H. cuyanus Rusconi 1951WS93
    |         |--H. fistula (Holl 1865) [=Hyolithus (Orthotheca) fistula]MB-M99
    |         |--H. mendozanus Rusconi 1951WS93
    |         |--H. tenuis Missarzhevsky 1966D94
    |         `--H. vladimirovae Missarzhevsky 1966D94
    `--TorellellidaeF62
         |--Rushtonia Cobbold & Pocock 1934F62
         |    `--*R. lata Cobbold & Pocock 1934F62
         |--Pseudorthotheca Cobbold 1935F62
         |    |--*P. acuticincta Cobbold 1935F62
         |    |--P. danicaMB-M99
         |    `--P. rotundicincta Cobbold 1935MB-M99
         `--Torellella Holm 1893F62
              |--*T. laevigata (Linnarsson 1871) [=Hyolithes laevigatus]F62
              |--T. bisulcata Li 2004L04
              |--T. curva Missarzhevsky 1966L04
              |--T. ensifosmis (Jiang 1982)L04
              |--T. lentiformis (Syssoiev 1960)L04
              |--T. sulcata Missarzhevsky 1982V06
              `--T. toolsensis Popov & Khazanovich 1989V06

*Type species of generic name indicated

References

[D94] Dzik, J. 1994. Evolution of ‘small shelly fossils’ assemblages of the early Paleozoic. Acta Palaeontologica Polonica 39 (3): 247–313.

[F62] Fisher, D. W. 1962. Small conoidal shells of uncertain affinities. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W98–W143. Geological Society of America, and University of Kansas Press.

[H75] Häntzschel, W. 1975. Treatise on Invertebrate Paleontology pt W. Miscellanea Suppl. 1. Trace Fossils and Problematica 2nd ed. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[H62] Howell, B. F. 1962. Worms. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W144–W177. Geological Society of America, and University of Kansas Press.

[L04] Li G.-X. 2004. Early Cambrian hyolithelminths—Torellella bisulcata sp. nov. from Zhenba, southern Shaanxi. Acta Palaeontologica Sinica 43 (4): 571–578.

[MB-M99] Malinky, J. M., & V. Berg-Madsen. 1999. A revision of Holm’s Early and early Mid Cambrian hyoliths of Sweden. Palaeontology 42: 25–65.

[MW04] Malinky, J. M., M. A. Wilson, L. E. Holmer & H. Lardeux. 2004. Tube-shaped incertae sedis. In: Webby, B. D., F. Paris, M. L. Droser & I. G. Percival (eds) The Great Ordovician Biodiversification Event pp. 214–222. Columbia University Press.

[V06] Vinn, O. 2006. Possible cnidarian affinities of Torellella (Hyolithelminthes, Upper Cambrian, Estonia). Paläontologische Zeitschrift 80 (4): 384–389.

[WS93] Wills, M. A., & J. J. Sepkoski Jr. 1993. Problematica. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 543–554. Chapman & Hall: London.

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