Dorsal and ventral views of Syringocrinus sinclairi, from Caster (1967).

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


[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.


  1. I remember these bizarre creatures from undergraduate zoology, 20 years ago... back then, there was little agreement on how these animals lived, I remember reading a paper where it was argued that they were in fact sessile and the 'tail' was a stalk that would have anchored them in muddy substrates. I can't say it sounded convincing, but it wasn't any less strange than having a motile, armoured animal with a feeble propulsion surface and an inconvenient armoured tentacle up front. Any new light on the ecology of these beasties since then?

  2. PS what's the 'dotted line' around the body?

  3. I'm guessing that the dotted line is meant to indicate a missing circlet of plates, but the source doesn't explain. Ecology-wise, my understanding is that most solutes were free-living, and have generally been regarded as such. Jeffries (1997) did state that the basalmost Coleicarpus was attached by its 'tail', while the next-up Castericystis was attached as a juvenile but became free-living when mature. Whether that is specifically the case or not, most researchers seem to have regarded the 'tail' as a modified homologue of the stalk of other, sessile echinoderms. Solutes were probably suspension-feeders, with the arm as the food-gathering appendage.

  4. Thanks Christopher. The tail does look particularly ill-suited for propulsion but I guess these were pretty sluggish creatures at best, so maybe they didn't need much (besides, I suppose their movements were pretty random...).

  5. In that regard, I suspect they'd probably be like the modern 'free-living' crinoids, which generally only move to find a slightly better position to sit in one place and filter-feed.


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