Entoprocta

Barentsia discreta, copyright Crispin Middleton.

Belongs within: Eumetazoa.
Contains: Loxosoma.

Tiny flowers of the sea
Published 19 March 2008
Entoprocts, from here.

The greatest feeling in biology is undoubtedly that which comes with seeing a particular organism for the first time. You can read on it, study specimens of it, think you know it inside out—and then you actually see one, and suddenly you realise that it’s so much more than you ever imagined. This is the feeling that drives bird enthusiasts to spend their life’s savings on trips to some malaria-infested corner of the third world to try and catch a brief glimpse of the Lesser Spotted Turntwick or some such. This is the feeling that inspires deep-sea biologists spending whole days lying on the bottom of the ocean in miniature submarines in which they can’t move more than a few centimetres in any direction, just so that they can watch a tube-worm wave its tentacles at them. It can only be described as a mystical experience, this moment in time that really brings it home to you that this is why you study biology.

I had a brief such moment when I encountered representatives of an animal phylum that I’d never seen before. I was tutoring a lab for which some live specimens of encrusting bryozoans had been brought in. Unfortunately, the bryozoans were being very unco-operative and refusing to emerge from their protective skeleton. While scanning the colony under a microscope to try and find some emerging zooids, I saw some soft white structures overgrowing the colony. A quick change of focus brought them into view, and I was presented with my first ever view of an entoproct.

Selected little-known inverterbrate: (left to right) an entoproct colony, a gnathostomulid, and a myxosporidian. From here.

It seems to be quite impossible to find an image available online that does these animals justice. Entoprocts are minute colonial animals with a body shaped like a wine-glass, topped by a ring of feeding tentacles. The relationships of entoprocts are rather uncertain at the present point in time. In the past they were included in the Bryozoa, but it is now widely agreed that the apparent similarities to Bryozoa in the stricter sense are only superficial, and the two groups are probably not closely related. It is accepted that entoprocts belong somewhere within the Spiralia, the large group of animals that includes, among others, molluscs, annelids and flatworms (and probably bryozoans), but exactly where in this group they sit is very much an open question. The specimens I saw each arose from the substrate on their own individual stalks, which according to the guide book on Australian marine life that was lying in the lab meant that they belonged to the family Loxosomatidae, as opposed to the Pedicellinidae which have multiple zooids budding from a single stalk.

Personally, though, I was stunned by just how beautiful these little animals were. They looked like minute, frilly tulips, balanced ethereally on their long slender stalks. If I looked closely, I could see a line of fine white filigree connecting each individual to its neighbours in the colony, forming delicate tracings over the substrate. I was enthralled, and the thought crossed my mind—”This is why I study biology”.

Systematics of Entoprocta
<==Entoprocta [Endoprocta, Kamptozoa]
    |--Loxosomatidae [Loxosomidae, Solitaria]Ha15
    |    |--LoxosomaHa15
    |    |--Loxosomella Mortensen 1911GO06, Ha15
    |    |    |--*L. crassicauda [=Loxosoma crassicauda]Ha15
    |    |    |--L. davenporthMS98
    |    |    |--L. murmanica (Nilus 1909)GO06, Ha15 [=Loxosoma murmanicumHa15]
    |    |    `--L. phascolosomataA99
    |    `--Loxocalyx Mortensen 1911Ha15
    |         |--*L. rajaHa15
    |         |--‘Loxosoma’ alatum Barrois 1877 [incl. L. pes Schmidt 1878]Ha15
    |         |--‘Loxosoma’ cochlear Schmidt 1876Ha15
    |         |--L. leptoclini (Harmer 1885) [=Loxosoma leptoclini]Ha15
    |         |--L. lineatus Harmer 1915Ha15
    |         |--‘Loxosoma’ neapolitanum Kowalevsky 1866Ha15
    |         `--‘Loxosoma’ tethyae Salensky 1877Ha15
    `--Pedicellinidae [Coloniales]Ha15
         |--Urnatella Leidy 1851Ha15, M68
         |    `--U. gracilisHa15
         |--Pedicellinopsis Hincks 1884Ha15
         |    `--P. fruticosaHa15
         |--Pedicellina Sars 1835Ha15
         |    |--*P. cernua (Pallas 1771) [=Brachionus cernuus]M68
         |    |--P. australis Ridley 1881Ha15
         |    |--P. brensingi Studer 1889Ha15
         |    `--P. compacta Harmer 1915Ha15
         `--Barentsia Hincks 1880 (see below for synonymy)Ha15
              |--*B. bulbosa Hincks 1880Ha15
              |--B. benedeni [=*Arthropodaria benedeni]Ha15
              |--B. capitata Calvet 1904Ha15
              |--B. discreta (Busk 1886) (see below for synonymy)Ha15
              |--‘Ascopodaria’ fruticosaHe15
              |--B. geniculata Harmer 1915Ha15
              |--B. gracilis (Sars 1835) (see below for synonymy)Ha15
              |--B. hildegardaeGD00
              |--B. laxa Kikpatrick 1890Ha15
              |--B. macropus Ehlers 1890Ha15
              |--B. major Hincks 1888 [incl. B. m. var. elongata Jullien & Calvet 1903]Ha15
              |--B. matsushimanaA99
              |--B. ramosa [=Gonypodaria ramosa]Ha15
              |--B. variabilis Calvet 1904Ha15
              `--B. variarticulataHa15

Barentsia Hincks 1880 [incl. Arthropodaria Ehlers 1890, Ascopodaria Busk 1886, Gonypodaria Ehlers 1890; Barentsiidae]Ha15

Barentsia discreta (Busk 1886) [=Ascopodaria discreta; incl. Pedicellina australis Jullien 1888 non Ridley 1881, A. misakiensis Oka 1890, Barentsia misakiensis, B. timida Verrill 1899-1900]Ha15

Barentsia gracilis (Sars 1835) [=Pedicellina gracilis, Ascopodaria gracilis; incl. B. belgica, Pedicellina gracilis var. nodosa Lomas 1886, Ascopodaria nodosa, Barentsia nodosa, Gonypodaria nodosa]Ha15

*Type species of generic name indicated

References

[A99] Ax, P. 1999. Das System der Metazoa II. Ein Lehrbuch der phylogenetischen Systematik. Gustav Fisher Verlag: Stuttgart (translated: 2000. Multicellular Animals: The phylogenetic system of the Metazoa vol. 2. Springer).

[GD00] Giribet, G., D. L. Distel, M. Polz, W. Sterrer & W. C. Wheeler. 2000. Triploblastic relationships with emphasis on the acoelomates and the position of Gnathostomulida, Cycliophora, Plathelminthes, and Chaetognatha: a combined approach of 18S rDNA sequences and morphology. Systematic Biology 49: 539–562.

[GO06] Giribet, G., A. Okusu, A. R. Lindgren, S. W. Huff, M. Schrödl & M. K. Nishiguchi. 2006. Evidence for a clade composed of molluscs with serially repeated structures: Monoplacophorans are related to chitons. Proceedings of the National Academy of Sciences of the USA 103 (20): 7723–7728.

[Ha15] Harmer, S. F. 1915. The Polyzoa of the Siboga ExpeditionPart I. Entoprocta, Ctenostomata and Cyclostomata. E. J. Brill: Leyden.

[He15] Hedley, C. 1915. Presidential address. Journal and Proceedings of the Royal Society of New South Wales 49 (1): 1–77, pls 1–7.

[MS98] Margulis, L., & K. V. Schwartz. 1998. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth 3rd ed. W. H. Freeman and Company: New York.

[M68] Mayr, E. 1968. Bryozoa versus Ectoprocta. Systematic Zoology 17 (2): 213–216.

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