Belongs within: Echinodermata.
The Soluta are an Upper Cambrian to Lower Devonian group of echinoderms with a flattened asymmetrical theca with a biserial arm and elongate stalk-like 'tail'. They were mostly free-living, lying on the sea floor and using the biserial arm for feeding. The degree of asymmetry exhibited by the theca varied between taxa: Iowacystis sagittaria, for instance, had a superficially near-symmetrical triangular theca (albeit with an asymmetrical plate arrangement), while Dendrocystoides scoticus had a strongly asymmetrical lobate theca.
Characters (from Caster 1967): Eleutherozoic, asymmetrical echinoderms without obvious radial symmetry elements; usually depressed, and tending toward bisymmetry; theca of fixed form, multiplated; plates usually both facially and regionally differentiated (adsteleal, abbrachial, adanal); some regional provision for visceral expansion and contraction usual in thecal plating; single biserial, usually distal-lateral, arm bearing biserial cover plates; mouth subthecal; anus posterolateral in most forms; heterostele ("tail") posterior, long and composed of axially differentiated plates: proxistele flexible and fundamentally tetramerous; mesistele transitional from four-part to two-part plate symmetry: dististele usually biserial proximally and dimerous distally; adbrachial plate bearing hydropore and gonopore, where known.
<==Soluta [Astylophora, Dendrocystidae, Dendrocystitidae, Heterostelea, Homoiostelea]
| i. s.: Dehmicystis Caster 1967 C67
| `--*D. globulus (Dehm 1934) [=Dendrocystites (Dendrocystoides) globulus] C67
|--Coleicarpus Daley 1996 P97
| `--C. sprinklei (Ubaghs & Robison 1988) [=Castericystis sprinklei] J97
`--+--Castericystis vali Ubaghs & Robison 1985 P97, J97
`--+--Minervaecystis Ubaghs & Caster in Caster 1967 P97, C67 [Minervaecystidae]
| `--*M. vidali (Thoral 1935) [=Dendrocystis vidali] C67
`--+--+--Girvanicystis Caster 1967 P97, C67 [Girvanicystidae]
| | `--*G. batheri Caster 1967 C67
| `--+--Maennilia estonica Rozhnov & Jefferies 1996 P97, P99
| `--Heckericystis Gill & Caster 1960 P97, C67
| `--*H. kuckersiana (Gekker 1940) [=Dendrocystites kuckersiana] C67
`--+--Dendrocystites Barrande 1887 P97, C67 [=Dendrocystis Bather 1889 C67]
| |--*D. sedgwicki (Barrande 1867) [=Cystidea sedgwicki, *Dendrocystis sedgwicki] C67
| `--D. barrandei C67
`--+--Dendrocystoides Jaekel 1918 P97, C67
| `--*D. scoticus (Bather 1913) [=Dendrocystis scotica] C67
`--+--Rutroclypeus Wither 1933 P97, C67 [Rutroclypeidae]
| |--*R. junori Wither 1933 C67
| `--R. withersi C67
`--+--+--Scalenocystites P97
| `--Iowacystis Thomas & Ladd 1926 P97, C67 [Iowacystidae]
| `--*I. sagittaria Thomas & Ladd 1926 C67
`--+--Syringocrinus Billings 1859 P97, C67 [Syringocrinidae]
| |--*S. paradoxicus Billings 1859 C67
| `--S. sinclairi C67
`--+--Myeinocystites Strimple 1953 P97, C67
`--Belemnocystites Miller & Gurley 1894 P97, C67 (see below for synonymy)
`--*B. wetherbyi Miller & Gurley 1894 [=*Belemnocystis wetherbyi] C67
Belemnocystites Miller & Gurley 1894 P97, C67 [=Belemnocystis Bather 1900 C67; Belemnocystitidae]
*Type species of generic name indicated
REFERENCES
[C67] Caster, K. E. 1967. Homoiostelea. In Treatise on Invertebrate Paleontology pt. S. Echinodermata 1. General characters. Homalozoa-Crinozoa (except Crinoidea) (R. C. Moore, ed.) vol. 2 pp. S581-S627. The Geological Society of America, Inc., and The University of Kansas: Lawrence (Kansas).
[J97] Jefferies, R. P. S. 1997. How chordates and echinoderms separated from each other and the problem of dorso-ventral inversion. Paleontological Society Papers 3: 249-266.
[P97] Parsley, R. L. 1997. The echinoderm classes Stylophora and Homoiostelea: Non Calcichordata. Paleontological Society Papers 3: 225-248.
[P99] Parsley, R. L. 1999. The Cincta (Homostelea) as blastozoans. In Echinoderm Research 1998 (M. D. Candia Carnevali & F. Bonasoro, eds) pp. 369-375. A. A. Balkema: Rotterdam.