Fossilised Patellispongia encrustations, from Carrera (2000).

Belongs within: Metazoa.
Contains: Archaeocyatha, Permosphincta, Homoscleromorpha, Calcispongia, Hexactinellida, Demospongiae.

Is it a sponge, or is it a plant?
Published 28 September 2007
Receptaculites, from Wikimedia.

The fossil order Receptaculitida occurs from the Ordovician to the Carboniferous, possibly to the Permian (Nitecki et al. 2004). They are quite spectacular fossils with a striking geometric arrangement of plates on a globose body. Complete fossils are rare but we have a reasonably good idea of overall structure.

One end of the fossil (shown above in an image from Gould & Katz 1975) provided the centre that the plates radiated from (the nucleus), and is the most often preserved section. The other end (the lacuna) appears to have been open at the tip (Nitecki et al. 1999). The plates radiated off a central axis to which they were attached by lateral branches known as meroms.

The relationships of receptaculitids have been debated ever since they were discovered. Various authors have regarded them as giant foraminifera, sponges or algae. Part of the problem is that, as with Stylophora, receptaculitids are a group of fossil taxa different enough from anything still living that authors have disagreed on which end was up and which down. Those who would see the receptaculitids as algae have argued for an orientation with the closed nucleus upwards, while an uncalcified stalk would have attached the organism to the substrate through the lacuna. On the contrary, if receptaculitids are to be sponges, the orientation is reversed—the nucleus becomes the lower, while the open lacuna corresponds to the osculum of other sponges, the ejection point of filtered water. Also, like a palaeontological version of the famous two faces vs. vase optical effect, some authors have seen the meroms as solid branches supporting the plates, while others would see them as hollow canals. Authors have also disagreed about whether the nucleus or the lacuna represented the growing end of the receptaculitid, but the existence of specimens with secondarily fused plates at the nucleus, in contrast with the less calcified plates at the lacunar end, strongly implies that the lacuna is the growing end.

Acetabularia, a representative of Dasycladales, from here.

A word of caution at this point—the term “alga” is often a difficult one in palaeontology. It is well-known that the various groups of living algae (green, red, brown, etc.) are a polyphyletic group, with multicellularity arising multiple times from unicellular ancestors. Unfortunately, the characters distinguishing the various groups are usually fine scale features, often at the cellular level. At the macroscopic level, the simple organisation of many algae means that members of different groups may be superficially quite similar in appearance, and may be indistinguishable as fossils. As a result, referring to fossils of completely extinct groups as “algae” often implies a certain degree of agnosticism about their actual relationships. At worst, the term “fossil alga” sometimes seems to be a shorthand for “sessile organism that we haven’t a clue where else to put it”. In the case of receptaculitids, fortunately, an actual modern algal analogue has been suggested in the form of the Dasycladales, an order of calcified green algae that also possess a radial arrangement of side-branches around a central stem. However, there are problems in attributing receptaculitids directly to Dasycladales as that would effectively require the nucleus to be the growing end.

Nevertheless, an algal interpretation (whatever that might mean) of Receptaculitida does seem more likely than a sponge. The solid outer casing of receptaculitids doesn’t compare that well to the more porous structure of sponges. The question of the life-orientation of receptaculitids is even harder to comment on—while an open lacuna-upward position does seem more appealing if the lacuna is the growing tip, an attached lacuna-downwards position is still not impossible though receptaculitids would then be perhaps the only group other than grasses to have evolved a basal meristem.

In 1972, Zhuravleva and Myagkova assigned receptaculitids to an association with other Palaeozoic sessile problematica such as Archaeocyatha in a new extinct kingdom Archaeata unrelated to both plants and animals (Rowland 2001). Archaeocyaths were cup-shaped Cambrian organisms that are now almost universally agreed to be sponges of some form. The concept of Archaeata never gained much recognition outside Russia, though it must be admitted that at least part of this may have been due to the inaccessibility of Russian publications in the West.

Cyclocrinites, from Dry Dredgers.

The Cyclocrinales are another group of Palaeozoic “algae” found from the Middle Cambrian to the Lower Devonian (Nitecki et al. 2004). Cyclocrinales are superficially similar to receptaculitids, with a similar basic body plan. They differ in having a less organised nucleus, generally lacking a lacuna, and branching laterals that come off the axis in certain areas rather than over the entire length as in receptaculitids. Cyclocrinales are more easily accepted as related to Dasycladales, and most authors appear to have done just that.

Systematics of Porifera
<==Porifera [Spongita]CV16
    |  `--CalcispongiaCV16
    `--Silicispongea [Hyalospongiae, Silicea, Silicispongia]BB05
Porifera incertae sedis:
  Rhabdocnemis Pomel 1872Z93
  Phormosella ovata Hinde 1888B04
  Dictyophyton danbyi (M’Coy 1852)B04
  Plectoderma scitulum Hinde 1883B04
  Asconema Schmidt 1880S00
    `--A. setubalensePP64
  Rodiella tissieriPP64
  Vaccipraticola reticulata (Ulrich 1878) [=Anomaloides reticulatus; incl. V. ypsilon Nilsson & Bengtson 1982]D94
  Receptaculitida [Receptaculitales]NW04
    |  i. s.: LepidolitesNW04
    |         LeptopoterionNW04
    |    |--IschaditesNW04
    |    |--SelenoidesNW04
    |    `--Tetragonis murchisoni Eichwald 1840NW04, D94
    |    |--FisheritesNW04
    |    `--Receptaculites Defrance 1827W77
    |         |--R. australisF71
    |         `--R. clarkeiM87
         |--Calathella Rauff 1894NW04, EB93
         `--Calathium Billings 1865NW04, EB93
              `--C. pannosumNW04
  ‘Olynthus’ Haeckel 1869 non Hübner 1819K18
  Grantia compressaM01
  Spinosella pliciferaSBM11
  Tuphia lacustrisG20
  Trichostemma hemisphericumN79
  Wyvillethomsonia wallichiiN79
  Meyerina Gray 1872N79
  Meyerella Gray 1872N79
    |--H. cyclostomaC00
    |--H. irregularisC00
    `--H. porosaC00
    |--P. argentinaC00
    |--P. occulataC00
    `--P. robustaC00
  Hexadella Topsent 1896SU21
  Ausia fenestrateEL11
  Rugoconites Glaessner & Wade 1966EL11, G79
    |--*R. enigmaticus Glaessner & Wade 1966G79
    `--R. tenuirugosusEL11
  Thectardis avalonensisEL11
Inorganic: Calathium paradoxicum Billings 1865 [=Nipterella paradoxica]H75

*Type species of generic name indicated


[B04] Botting, J. P. 2004. An exceptional Caradoc sponge fauna from the Llanfawr Quarries, central Wales and phylogenetic implications. Journal of Systematic Palaeontology 2 (1): 31–63.

[BB05] Botting, J. P., & N. J. Butterfield. 2005. Reconstructing early sponge relationships by using the Burgess Shale fossil Eiffelia globosa, Walcott. Proceedings of the National Academy of Sciences of the USA 102: 1554–1559.

[CV16] Cannon, J. T., B. C. Vellutini, J. Smith, III, F. Ronquist, U. Jondelius & A. Hejnol. 2016. Xenacoelomorpha is the sister group to Nephrozoa. Nature 530: 89–93.

[C00] Carrera, M. G. 2000. Epizoan-sponge interactions in the Early Ordovician of the Argentine Precordillera. Palaios 15: 261–272.

[D94] Dzik, J. 1994. Evolution of ‘small shelly fossils’ assemblages of the early Paleozoic. Acta Palaeontologica Polonica 39 (3): 247–313.

[EL11] Erwin, D. H., M. Laflamme, S. M. Tweedt, E. A. Sperling, D. Pisani & K. J. Peterson. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334: 1091–1097.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[G79] Glaessner, M. F. 1979. Precambrian. In: Robison, R. A., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt A. Introduction. Fossilisation (Taphonomy), Biogeography and Biostratigraphy pp. A79–A118. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

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

Gould, S. J., & M. Katz. 1975. Disruption of ideal geometry in the growth of receptaculitids: a natural experiment in theoretical morphology. Paleobiology 1: 1–20.

[H75] Häntzschel, W. 1975. Treatise on Invertebrate Paleontology pt W. Miscellanea Suppl. 1. Trace Fossils and Problematica 2nd ed. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[JB12] Johnson, M. E., & B. G. Baarli. 2012. Development of intertidal biotas through Phanerozoic time. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 63–128. Springer.

[K18] Kury, A. B. 2018. Familial nomina in harvestmen (Arachnida, Opiliones). Bionomina 13: 1–27.

[M01] M’Intosh, W. C. 1901. The coloration of marine animals. Annals and Magazine of Natural History, series 7, 7: 221–240.

[M87] Mitchell, J. 1887. Notes on the geology of Bowning, N.S.W. Proceedings of the Linnean Society of New South Wales, series 2, 1 (4): 1193–1204.

Nitecki, M. H., H. Mutvei & D. V. Nitecki. 1999. Receptaculitids: A phylogenetic debate on a problematic fossil taxon. Springer.

[NW04] Nitecki, M. H., B. D. Webby, N. Spjeldnaes & Zhen Y.-Y. 2004. Receptaculitids and algae. In: Webby, B. D., F. Paris, M. L. Droser & I. G. Percival (eds) The Great Ordovician Biodiversification Event pp. 336–347. Columbia University Press.

[N79] Norman, A. M. 1879. The Mollusca of the fiords near Bergen, Norway. Journal of Conchology 2: 8–77.

[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.

[RB93] Rigby, J. K., G. E. Budd, R. A. Wood & F. Debrenne. 1993. Porifera. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 71–99. Chapman & Hall: London.

Rowland, S. M. 2001. Archaeocyaths—a history of phylogenetic interpretation. Journal of Paleontology 75 (6): 1065–1078.

[SU21] Santín, A., M.-J. Uriz, J. Cristobo, J. R. Xavier & P. Ríos. 2021. Unique spicules may confound species differentiation: taxonomy and biogeography of Melonanchora Carter, 1874 and two new related genera (Myxillidae: Poecilosclerida) from the Okhotsk Sea. PeerJ 9: e12515.

[S00] Siddiqi, M. R. 2000. Tylenchida: Parasites of plants and insects 2nd ed. CABI Publishing: Wallingford (UK).

[SBM11] Solomon, E. P., L. R. Berg & D. W. Martin (eds) 2011. Biology 9th ed. Brooks/Cole Cengage Learning.

[W77] White, C. A. 1877. Report upon the invertebrate fossils collected in portions of Nevada, Utah, Colorado, New Mexico, and Arizona, by parties of the expeditions of 1871, 1872, 1873, and 1874. U.S. Geographical Surveys West of the One Hundredth Meridian 4 (1): 1–219, pls 1–21.

[Z93] Zimmerman, E. C. 1993. Australian Weevils (Coleoptera: Curculionoidea) vol. 3. Nanophyidae, Rhynchophoridae, Erirhinidae, Curculionidae: Amycterinae, literature consulted. CSIRO Australia.

Leave a comment

Your email address will not be published. Required fields are marked *