Muscular system of euconodont animals and their systematic position (Euconodontophylea)

A.P. Kasatkina & G.I. Buryi

Abstract. The muscular system of euconodont animals was studied in detail on the basis of the photographs of imprints from the Lower Carboniferous Shrimp Bed of Granton (Scotland), Upper Ordovician Soom Shale (South Africa), and Silurian Waukesha biota (North America). Superficial body structures are for the first time recognized for euconodont animals: external rings (annulation) (Panderodus imprint) and their traces (specimens 2 and 3 from Granton). This makes them looking like many invertebrates, such as annelids, priapulids, or pentastomids, and different from primitive chordates. In all other imprints of euconodont animals, a deep frontal break reaching their central part uncovers the inner transversal structures of the body, muscular fibers. As in invertebrates, they have different orientation. The medial apices of the fibers can be directed obliquely towards either the head (specimens 1, 2, 4, 5, 7 from Granton, and Promissum pulchrum Kovacs-Endrődy imprints) or the tail (specimens 2 and 6 from Granton) or to be perpendicular to the body axis (specimens 3-5 from Granton). Discontinuity of the transversal structures (specimens 1 and 6) appears to occur in the euconodont animals. This suggests that the transversal obliquely-oriented structures visible on the euconodont imprints, are not myomers typical of chordate animals. Differently directed position of medial apices of the obliquely-oriented muscular fibers depends, probably, on physical state (direction of movement) of the animal. The longitudinal median structure, in our opinion, cannot be considered a chord, but is rather a gut extending from pharynx to anus. Apparently, in spite of visual similarity, the euconodont animals under study cannot be classified as chordates, or chaetognaths, or pentastomids. Their muscular system differs from that of all known groups of animals and shows its own unique structure: its inner transversal structures are muscular fibers, which externally look like rings (annulation). This supports our earlier conclusion (Kasatkina & Buryi, 1997) that euconodonts constitute a separate phylum, Euconodontophylea Kasatkina & Buryi, 1997.

Zoosystematica Rossica, 2006, 15(2): 229–235  ▪  Published in print 2 March 2007


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References

Aldridge, R.J., Briggs, D.E.G., Clarkson, E.N.K. & Smith, M.P. 1986. The affinities of conodonts – new evidence from the Carboniferous of Edinburgh, Scotland. Lethaia, 19(4): 279-291. https://doi.org/10.1111/j.1502-3931.1986.tb00741.x

Aldridge, R.J., Briggs, D.E.G., Smith, M.P., Clarkson, E.N.K. & Clark, N.D.L. 1993. The anatomy of conodonts. Philos. Trans. R. Soc. London, Ser. 5, B 340: 405-421. https://doi.org/10.1098/rstb.1993.0082

Aldridge, R.J. & Theron, J.N. 1993. Conodonts with preserved soft tissue from a new Ordovician Konservat-Lagerstätte. J. Micropaleontol., 12: 113-117. https://doi.org/10.1144/jm.12.1.113

Bone, Q. & Duvert, M. 1991. Locomotion and buoyancy. In: Bone, Q. (Ed.). The Biology of Chaetognaths: 32-44. OxfordUniversity Press.

Briggs, D.E.G., Clarkson, E.N.K. & Aldridge, R.J. 1983. The conodont animal. Lethaia, 26(1): 1-14. https://doi.org/10.1111/j.1502-3931.1983.tb01139.x

Briggs, D.E.G. & Kear, A.J. 1994. Decay of Branchiostoma: implications for soft-tissue preservation in conodont and other primitive chordates. Lethaia, 26: 275-287. https://doi.org/10.1111/j.1502-3931.1993.tb01532.x

Buryi, G.I. & Kasatkina, A.P. 2004. Rounded phosphatic structures (H elements) of euconodonts and their function (Euconodontophylea). Zoosyst. Ross., 12(2): 157-161. https://doi.org/10.1016/j.tim.2004.02.002

Carroll, R.L. 1988. Vertebrate paleontology and evolution. NY: W.H. Freeman and Co. 698 p.

Casanovà, J.-P. & Duvert, M. 2002. Comparative studies and evolution of muscles in chaetognaths. Mar. Biol., 141: 925-938. https://doi.org/10.1007/s00227-002-0889-3

Donoghue, P.G.J., Forey, P.L. & Aldridge, R.J. 2000. Conodont affinity and chordate phylogeny. Biol. Rev., 75: 191-251. https://doi.org/10.1017/S0006323199005472

Gabbot, S.E., Aldridge, R.J. & Theron, J.N. 1995. A giant conodont with preserved muscle tissue from the Upper Ordovician of South Africa. Nature, 374: 800-803. https://doi.org/10.1038/374800a0

Kasatkina, A.P. & Buryi, G.I. 1997. Chaetodonta – a new superphylum of animals and its position in the classification of animal realm. Dokl. Ross. Akad. Nauk, 356(6): 843-845. (In Russian).

Kasatkina, A.P. & Buryi, G.I. 1999. The position of the phyla Chaetognatha and Euconodontophylea in the classification of Metazoa. Zoosyst. Ross., 8(1): 21-26.

Mikulic, D.G., Briggs, D.E.G. & Kluessendorf, J. 1985. A Silurian soft-bodied biota. Science (Wash.), 228(4700): 715-717. https://doi.org/10.1126/science.228.4700.715

Morris, S.C. 1989. Conodont palaeobiology: recent progress and unsolved problems. Terra Nova, 1: 135-150. https://doi.org/10.1111/j.1365-3121.1989.tb00345.x

Schram, F.R. 1973. Pseudocoelomates and a nemertina from the Illinois Pennsylvanian, J. Paleontol., 47(5): 985-989.

Zenkevich, L.A. (Ed.). 1951. Invertebrates (pentastomids, tardigrades, pantopods, protracheans, myriapods, chaetognaths). Rukovodstvo po zoologii (Manual of zoology), 3(2): 1-608. Moscow. (In Russian).

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