Soluta

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

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.

5 comments:

  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?

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

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  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.

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  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...).

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  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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