Sclerite of Priscocaudina crucensis, from Boczarowski (2001). Scale bar = 200 µm.

Belongs within: Cucumariidae.
Contains: Eocaudina.

The Calclamnidae are a form taxon for thin, perforated plate-shaped sclerites known from the Devonian onwards. They may represent the ancestral lineage of the living holothuroid family Phyllophoridae (Boczarowski 2001). Members of this latter family are characterised by the possession of more than ten tentacles, together with a posteriorly prolonged calcareous ring with ossicles in a mosaic-like arrangement.

Bits of cucumber in the fossil record
Published 17 October 2023
Aggregation of Eocaudina septaforminalis sclerites from Boczarowski (2001). Scale bar = 200 µm.

Echinoderms are a dream group of animals for invertebrate palaeontologists (that’s palaeontologists who study invertebrates, not palaeontologists who are invertebrates). Their calcified skeletons mean that their fossil record is extensive and detailed. When most of the body is covered in plates, looking at the fossil can give you an instant idea of what the animal looked like when alive. But as with all things in biology, there are notable exceptions. The sea cucumbers are one group of echinoderms that has significantly reduced the original skeleton, sacrificing a hard outer skeleton for increased flexibility. Instead of solid plates, the sea cucumber skeleton is made up of many minute sclerites embedded in the skin. And while this may be all well and good for the sea cucumber, it is not so convenient for the palaeontologists. In the fossil record, these minute sclerites become separated, and one separated sclerite does not tell you much about the appearance of the sea cucumber as a whole.

As a result, palaeontologists looking at sea cucumber remains have found themselves presented with a conundrum. The classification of modern sea cucumbers is largely based on features of the soft body that are usually not preserved in the fossil record, making comparison of living and fossil cucumbers difficult. Also, the skeleton of a single sea cucumber may include different forms of sclerite, performing different roles. If two different types of sclerite are found close together in the fossil record, did they come from a single sea cucumber or from two different sea cucumbers that died close together? To bypass these barriers, palaeontologists have often used what are referred to as ‘parataxa’. A single type of sclerite is treated as a single ‘parataxon’, with the recognition that there may not be a perfect correlation between the parataxon and the theoretical taxon that it originally came from.

The Calclamnidae has been recognised as one such ‘parafamily’ of sea cucumber sclerites. As defined by Frizzell & Exline (1966), the Calclamnidae grouped together rounded or polygonal sclerites that are perforated with holes like a sieve, and that don’t have any sort of stalk or other ventral protrusion. This is a very common sort of sclerite for echinoderms: ‘calclamnid’ sclerites have been identified as far back as the Ordovician (Boczarowski 2001), and sclerites of this sort are still found in sea cucumbers today (just to confuse matters, the skeletons of some brittle stars also include very similar sclerites, raising the spectre of misidentification). Boczarowski (2001) recognised two subfamilies of Calclamnidae: in one, the Eocaudininae, the perforations of the sclerite are all more or less even in size, while in the other, Calclamninae, the pores towards the centre of the plate are larger and arranged in a cross-shape. The eocaudinines include the earliest calclamnid plates, with the calclamnines appearing during the Devonian.

Recognition of parataxa is a convenient tool for keeping records of things like biostratigraphy without getting bogged down, but what sort of sea cucumber did calclamnids actually come from? The calclamnids resemble sclerites found in the group of modern sea cucumbers called the Dendrochirotacea, so they have often been classified with this group. However, a number of features of the dendrochirotaceans, including perforated calclamnid-like sclerites, have been suggested to be primitive for sea cucumbers, so similarities between calclamnids and dendrochirotaceans may represent shared ancestral features rather than true affinities. Haude (1992) commented on a number of cases of sclerites found preserved in assemblages that he believed represented original life associations, including some containing calclamnids. One of these contained sclerites that Haude identified as similar to Calclamna germanica, the type species of the family, in association with large hook-shaped sclerites. Hooks are not characteristic of dendrochirotaceans, but of Apodacea, a different group of sea cucumbers characterised by the loss of tube feet (with the hooks working to provide mobility in their place). Haude suggested the possibility that Calclamna might represent a stem-group apodacean that retained some primitive sclerite features. In other fossil groups such as conodonts, the identification of preserved assemblages has allowed palaeontologists to progress beyond the use of parataxa and integrate more recognition of evolutionary relationships. Hopefully we get the same opportunity with sea cucumbers.

Systematics of Calclamnidae

Characters (from Frizzell & Exline 1966): Perforate plates, usually thin, rarely multilayered, flat or concavo-convex, shape variable, outline commonly indefinite; perforations not denticulate; lacking socket, strap or spire.

    |    |--EocaudinaB01
    |    `--Elgerius Deflandre-Rigaud 1959B01
    |         |--*E. ostrea Deflandre-Rigaud 1959FE66
    |         `--E. innienensisFE66
       |    |--Priscocaudina Boczarowski 2001B01
       |    |    |--*P. crucensis Boczarowski 2001B01
       |    |    |--P. marginata (Lagenheim & Epis 1957)B01
       |    |    `--P. scotica (Frizzell & Exline 1955)B01
       |    `--Calclamna Frizzell & Exline 1955B01 [incl. Cibrum Frentzen 1964FE66]
       |         |  i. s.: *C. germanica Frizzell & Exline 1956FE66
       |         |         C. fusiformisFE66
       |         |--C. permotriassica Mostler & Rahimi-Yazd 1976B01
       |         `--+--C. noricaB01
       |            `--Fissobractites Kristan-Tollmann 1963B01
       |                 `--*F. subsymmetricus Kristan-Tollmann 1963FE66
            |--Ohshimella Heding & Panning 1954B01
            |    |--H. fastigata (Sluiter 1901)MG-H11
            |    `--H. versicolor (Semper 1868)SM15
            |--Neothyonidium inflatum (Sluiter 1901)MG-H11
            |--Semperiella [Semperiellinae]MG-H11
            |    |--S. buccalis (Stimpson 1855)SM15
            |    `--S. minutus (Clark 1938)SM15
            |--Propinquoohshimella Boczarowski 2001 [Propinquoohshimellinae]B01
            |    `--*P. remigia Boczarowski 2001B01
            |    |--P. brocki Ludwig 1888MG-H11
            |    |--P. magnusD49
            |    |--P. proteus Bell 1884SM15
            |    |--P. spiculata Chang 1935SM15
            |    `--P. urnaH04
            |--Hemithyone semperi (Bell 1884)SM15
            `--Thyone [Thyoninae]SM15
                 |--T. briareusBK77
                 |--T. fususBK77
                 |--T. gadeanaPP64
                 |--T. grisea Clark 1938SM15
                 |--T. impatiensG20
                 |--T. micra Clark 1938SM15
                 |--T. papuensis Théel 1886SM15
                 `--T. raphanusN64
Calclamnidae incertae sedis:
  Petropegia Summerson & Campbell 1958FE66
    |--*P. radiata Summerson & Campbell 1958FE66
    `--P. spinosaFE66
  Calclamnoidea Frizzell & Exline 1956 [incl. Palaeocucumaria Frentzen 1964 non Lehmann 1958]FE66
    |--*C. collaris (Deflandre-Rigaud 1946) [=Priscopedatus collaris]FE66
    |--C. angulataFE66
    |--C. canaliferaFE66
    |--C. goniaiaFE66
    |--C. inaequalisFE66
    |--C. irregularisFE66
    |--C. medioangustaFE66
    |--C. ocellataFE66
    |--C. perforataFE66
    |--C. proteusFE66
    `--C. spaniaFE66
  Mortensenites Deflandre-Rigaud 1952FE66
    |--*M. liasicus (Terquem 1866) [=Gromia liasica; incl. M. sievertsi]FE66
    |--M. circularisFE66
    |--M. cuneusFE66
    |--M. elongatusFE66
    |--M. hemisphaericusFE66
    |--M. insolitusFE66
    `--M. reticulatusFE66
  Costigerites Deflandre-Rigaud 1961FE66
    `--*C. piveteaui Deflandre-Rigaud 1961FE66
  Paracucumarites Deflandre-Rigaud 1961FE66
    |--*P. hamptoni Deflandre-Rigaud 1961FE66
    |--P. ancepsFE66
    `--P. porosaFE66
  Parvioctoidus Deflandre-Rigaud 1961FE66
    `--*P. spinosus Deflandre-Rigaud 1961FE66
  Pachopsites Kristan-Tollmann 1964FE66
    `--*P. annulatus Kirstan-Tollmann 1964FE66
Nomen nudum: Thyone floccosa Norman 1864N64

*Type species of generic name indicated


[BK77] Barel, C. D. N., & P. G. N. Kramers. 1977. A survey of the echinoderm associates of the north-east Atlantic area. Zoologische Verhandelingen 156: 1–159.

[B01] Boczarowski, A. 2001. Isolated sclerites of Devonian non-pelmatozoan echinoderms. Palaeontologia Polonica 59: 1–219.

[D49] Dawbin, W. H. 1949. Auto-evisceration and the regeneration of viscera in the holothurian Stichopus mollis Hutton. Transactions and Proceedings of the Royal Society of New Zealand 77 (4): 497–523.

[FE66] Frizzell, D. L., & H. Exline. 1966. Holothuroidea—fossil record. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt U. Echinodermata 3 vol. 2 pp. U646–U672. The Geological Society of America, Inc., and The University of Kansas Press.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

Haude, R. 1992. Fossil holothurians: sclerite aggregates as ‘good’ species. In: Scalera-Liaci, L., & C. Canicatti (eds) Echinoderm Research 1991 pp. 29–33. Balkema: Rotterdam.

[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.

[N64] Norman, A. M. 1864. On British Holothuriadae with reference to new species. Report of the British Association for the Advancement of Science 33 (Notices and Abstracts): 106.

[PP64] Peres, J. M., & J. Picard. 1964. Nouveau manuel de bionomie benthique de la mer Mediterranee. Recueil des Travaux de la Station Marine d’Endoume, Bulletin 31 (27): 5–137.

[SM15] Sampey, A., & L. M. Marsh. 2015. Kimberley marine biota. Historical data: echinoderms. Records of the Western Australian Museum Supplement 84: 207–246.

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