A new stem-chordate solute fromthe Middle Ordovician of Estonia

A probable case of heterochrony in the solutan Dendrocystites Barrande, 1887 (Echinodermata: Blastozoa) from the Upper Ordovician of the Prague Basin (Czech Republic) and a revision of the family Dendrocystitidae Bassler, 1938

“…In contrast, in more derived solutans (e.g., Dendrocystites, Girvanicystis, Iowacystis, Scalenocystites), the theca is generally flattened and differentiated into two opposite surfaces with distinct morphologies: one side is convex, whereas the other one is usually more depressed and plano-concave (Bather 1913, Thomas & Ladd 1926, Parsley & Caster 1965, Caster 1967, Kolata et al 1977, Daley 1992. Moreover, in derived solutans, the theca consists either in a high number of thin, tesselated platelets (e.g., Dendrocystites, Maennilia, Rutroclypeus; Bather 1913, Gill & Caster 1960, Caster 1967, Rozhnov & Jefferies 1996, Parsley et al 2012, or a reduced number of thick and large skeletal elements (e.g., Belemnocystites, Iowacystis, Scalenocystites; Thomas & Ladd 1926, Parsley & Caster 1965, Parsley 1972, Kolata 1973, Kolata et al 1977. In derived forms, thecal outlines can be either markedly asymmetrical and pear-shaped (e.g., Dendrocystoides, Girvanicystis, Maennilia, Scalenocystites; Bather 1913, Kolata 1973, Jefferies 1990, Daley 1992, Rozhnov & Jefferies 1996, Parsley et al 2012, or almost bilaterally symmetrical and sub-triangular (e.g., Iowacystis; Parsley & Caster 1965, Kolata et al 1977, rounded (e.g., Rutroclypeus; Gill & Caster 1960), or subelliptical (e.g., Belemnocystites, Syringocrinus; Parsley & Caster 1965, Parsley 1972).…”

“…Moreover, in derived solutans, the theca consists either in a high number of thin, tesselated platelets (e.g., Dendrocystites, Maennilia, Rutroclypeus; Bather 1913, Gill & Caster 1960, Caster 1967, Rozhnov & Jefferies 1996, Parsley et al 2012, or a reduced number of thick and large skeletal elements (e.g., Belemnocystites, Iowacystis, Scalenocystites; Thomas & Ladd 1926, Parsley & Caster 1965, Parsley 1972, Kolata 1973, Kolata et al 1977. In derived forms, thecal outlines can be either markedly asymmetrical and pear-shaped (e.g., Dendrocystoides, Girvanicystis, Maennilia, Scalenocystites; Bather 1913, Kolata 1973, Jefferies 1990, Daley 1992, Rozhnov & Jefferies 1996, Parsley et al 2012, or almost bilaterally symmetrical and sub-triangular (e.g., Iowacystis; Parsley & Caster 1965, Kolata et al 1977, rounded (e.g., Rutroclypeus; Gill & Caster 1960), or subelliptical (e.g., Belemnocystites, Syringocrinus; Parsley & Caster 1965, Parsley 1972). In some derived solutans (e.g., Belemnocystites, Girvanicystis, Iowacystis, Syringocrinus), thecal outlines are framed by enlarged, massive skeletal elements (or marginals), extending on both thecal sides (Parsley & Caster 1965, Parsley 1972, Kolata 1973, Kolata et al 1977, Daley 1992).…”

“…In some derived solutans (e.g., Belemnocystites, Girvanicystis, Iowacystis, Syringocrinus), thecal outlines are framed by enlarged, massive skeletal elements (or marginals), extending on both thecal sides (Parsley & Caster 1965, Parsley 1972, Kolata 1973, Kolata et al 1977, Daley 1992). In derived solutans, thecal plates can be either smooth (e.g., Dendrocystoides; Jefferies 1990), granular or pustulose (e.g., Belemnocystites, Iowacystis, Scalenocystites; Thomas & Ladd 1926, Parsley & Caster 1965, Caster 1967, Kolata et al 1977, or ornamented either with radial ribs (e.g., Maennilia; Rozhnov & Jefferies 1996, Parsley et al 2012 or small spines (e.g., Heckericystis, Rutroclypeus; Hecker 1940, Gill & Caster 1960. Strong ridges and protuberances are sometimes present on one (e.g., Girvanicystis; Caster 1967, Daley 1992 or both thecal surfaces (e.g., Dendrocystoides; Bather 1913, Jefferies 1990.…”

“…In some other solutans (e.g., Iowacystis, Scalenocystites), only one perforated tubercle is present, but it is then surrounded by several small pores (Parsley & Caster 1965, Kolata et al 1977. Finally, some other solutans (e.g., Maennilia) do not exhibit any perforated tubercle close to the insertion of the feeding appendage, but instead, numerous tiny orifices forming a sieve-like structure (Rozhnov & Jefferies 1996, Rozhnov 2002, Parsley et al 2012. Comparison with both modern and extinct echinoderms suggests that the two orifices located close to the insertion of the feeding appendage can be readily identified as the hydropore (single or multi-perforated, sieve-like opening) and the gonopore (single rounded hole; Thomas & Ladd 1926, Bather 1928, Caster 1967, Ubaghs 1970, Kolata et al 1977, Ubaghs & Robison 1985, Jefferies 1990, Daley 1996, David et al 2000, Smith 2005.…”

“…from the Šárka Formation described by Lefebvre et al (2012), this opening occurs as a tiny hole at the top of a low, almost flat, polyplated valvular structure, with circular outlines (see also Prokop & Petr 2003). In Dehmicystis, Dendrocystoides, Girvanicystis, Maennilia and Rutroclypeus, the main thecal opening corresponds to a small slit-like orifice located at the summit of a low, modified valvular pyramid, consisting of several elongate, radial platelets and two enlarged, cone-shaped elements ("sugar-loaf plates"; Bather 1913, Caster 1967, Jell & Holloway 1982, Jefferies 1990, Daley 1992, Rozhnov & Jefferies 1996, Parsley et al 2012, Rahman & Lintz 2012. In some other solutans (e.g., Belemnocystites, Iowacystis, Myeinocystites, Scalenocystites), radial platelets are lost, and the main body orifice consists in a narrow slit in between two particularly enlarged "marginal" plates forming a clam shell door-like structure (Caster 1967, Parsley 1972, Kolata 1973, Kolata et al 1977).…”