ISSN 00310301, Paleontological Journal, 2010, Vol. 44, No. 2, pp. 120–124. © Pleiades Publishing, Ltd., 2010 Original Russian Text © N.V. Novozhilova, 2010, published in Paleontologicheskii Zhurnal, 2010, No. 2, pp. 118–121.
New Data on the Morphology and Systematics of Hyolithelminthes (Cambrian Problematic Organisms) N. V. Novozhilova Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Division, Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090 Russia email:
[email protected] Received May 12, 2008
Abstract—Phosphatic structures are discovered in the tube interior of the hyolithelminth species Hyolithellus vitricus from the Lower Cambrian of the Siberian Platform. Anatomic interpretation of these structures sug gests that these smallsized shelly fossils represent the earliest wormshaped organisms probably closely related to modern Nemathelminthes. Key words: Hyolithelminthes, small shelly fossils, Lower Cambrian, Siberia. DOI: 10.1134/S0031030110020024
INTRODUCTION Hyolithelminthes are tubeshaped shelly Cam brian fossils with a phosphatic shell, circular, oval, or lensshaped in cross section, open on both ends. The ornamentation of the external wall surface is com posed of transverse folds or ribs, often with longitudi nal or oblique hatching between the ribs, or the surface is smooth. Many tubes show dents and bends suggest ing that they were flexible (Missarzhevsky, 1989; Pyle
et al., 2006). Mineralization of the tubes probably occurred after the development of the organic sub strate, which could be distorted by external force. The tubes of Early Cambrian individuals are at most 20–25 mm long. The tube of hyolithelminthes is composed of two layers (Hurst and Hewitt, 1977; Grigorieva and Zhegallo, 1979; Grigorieva, 1980; Bengtson et al., 1990; Esakova and Zhegallo, 1996). The simple morphology of hyolithelminthes and the absence of diagnostic characters found in modern
Uncertain taxonomic affinity Phylum Coelenterata
Class Conulata Class inserta sedis
Phylum Annelida
Class Polychaeta
not established Phylum Pogonophora Phylum Mollusca
Order Hyolithelmintida Fisher, 1962
Table 1. Various interpretations of the taxonomy of Hyolithelminthes
Class Hyolitha
Fisher, 1962 Meshkova, 1969 Missarzhevsky and Mambetov, 1981 Bengtson et al., 1990 Wrona, 2004 Barrande, 1867 Boucek, 1939 Missarzhevsky, 1989 Vinn, 2006 Walcott, 1911 Grigorieva, 1980 Meshkova, 1985 Vasilieva, 1998 Valkov, 1987 Poulsen, 1963 Sysoev, 1962
Explanation of Plate 1 Figs. 1–3. Hyolithellus vitricus Mambetov, 1981; Lower Cambrian, Tommotian Stage, Nochoroicyathus sunnaginicus Zone, Pes trotsvet Formation; Siberian Platform, Aldan River, Ulakhan–Sulugur section: (1) specimen TsSGM, no. 1100/1: (1a) general appearance in cross section, (1b) fragment of the intestine wall, and (1c) vessel (or other internal organ?); (2) specimen TsSGM, no. 1100/2; general appearance of the tube in a cross section; (3) specimen TsSGM, no. 1100/3: (3a) general appearance of the tube; (3b, 3c) lateral view, several smaller tubules are clearly seen inside the shell tube; and (3d) phosphatized tubule wall.
120
NEW DATA ON THE MORPHOLOGY AND SYSTEMATICS
121 Plate I
3 µm
1b 100 µm
1a 1a
2 2 100 µm 10 µm 1c
3b 3a
100 µm
20 µm
100 µm
3c
3d 10 µm
PALEONTOLOGICAL JOURNAL
Vol. 44
No. 2
2010
122
NOVOZHILOVA a
v
h
animals were the reason for an array of hypotheses on their systematic affinity (Table 1). Most workers con sidered these organisms as the order Hyolithelminthes Fisher, 1962 of uncertain systematic position, or assigned it to the phylum Annelida. Two families are recognized in this order based on the differences of the tube cross section and other morphological charac ters. These are Hyolithellidae Walcott, 1886 (circular cross section) and Torellellidae Holm, 1893 (lenticu lar cross section). MATERIAL The material studied comes from the Sunnagin Member of the Pestrotsvet Formation (Lower Cam brian, Tommotian Stage, N. sunnaginicus Zone) in the Ulakhan–Sulugur section on the left bank of the Aldan River in the southeast of the Siberian Platform (collected by I.V. Korovnikov, 2002).The fossils were extracted from the limestone by dissolving it in 5% acetic acid. The selection and preliminary sorting of the organic remains were performed using a light ste reomicroscope, and a SEM was used for further exam ination and photography. The collection studied (no. 1100) is housed in the Central Siberian Geological Museum (TsSGM) at Trofimuk Institute of Petroleum Geology and Geo physics of the Siberian Division of the Russian Acad emy of Sciences.
i
100 µm b dv
i
p vv
c h hc i
Fig. 1. Major internal structures of several wormlike organ isms: (a) cross section of Hyolithellus vitricus Mambetov; (b) schematic representation of the annelid segment (after Westheide and Rieger, 2008, simplified); and (c) a general ized body plan of Ecdysozoa (after Malakhov, 2009), a group that includes Nematoda. Designations: (dv) dorsal vessel, (h) heart, (hc) hemocoel, (i) intestine, (p) parapo dium, (sw) shell wall, (v) vessel, and (vv) ventral vessel.
RESULTS AND DISCUSSION The material studied contained the hyolithelminth species Hyolithellus vitricus Mambetov, 1981 with pre viously unknown internal structures. The external sur face of the specimens studied was smooth, the cross section was circular, the tube fragments were on aver age 12–15 mm long and 0.3–0.5 mm in diameter. Sev eral specimens (Pl. 1, figs. 2, 3) contained smaller tubes (from 2 to 5) of unknown affinity. It is possible that these are fragments of various organisms found together with hyolithelminthes in the same small shell fossil assemblage (SSF) in the lower part of the Pes trotsvet Formation (Guidebook …., 1973, Repina and Rozanov, 1992). Due to the highenergy depositional settings of the Sunnagin Member (Stage Stratification …, 1984), the buried tubes of hyolithelminthes are filled with debris, including fragments of skeletons (Pl. 1, figs. 3b, 3d). However, it is also possible that the tubes represent fossilized inner organs of hyolithelminthes. This is supported by two other specimens of H. vitricus (Pl. 1, figs. 1, 2). The specimen represented by a fragment of a tube about 1.5 mm long and 0.5 mm in diameter (Pl. 1, fig. 1a) is better preserved. The interior of this specimen contains a longitudinally orientated tube with a circular cross section and about 0.3 mm in diameter. The wall is twolayered with small, vertically orientated, diagonally arranged laminae (Pl. 1, PALEONTOLOGICAL JOURNAL
Vol. 44
No. 2
2010
NEW DATA ON THE MORPHOLOGY AND SYSTEMATICS
fig. 1b). One wall of the tube shows a groove with a small narrow tubule in the center. This tubule is circu lar in cross section and 40 µm in diameter, its wall is doublelayered, with a denser inner layer. In places the outer layer is curved in a zigzag manner. Thus, the wall structure of the shell tube (Grigorieva, 1980) is different from that of the tubules located inside the specimen under discussion. Judging from the anatomy of some modern inverte brates (e.g., roundworms), it is possible to suggest that the tube contained phosphatized remains of the diges tive system (Fig. 1): the intestine is a longitudinal tubule 0.3 mm in diameter and an adjacent vessel (or other internal organ?) represented by a longitudinal tubule 40 µm in diameter. With regard to the taxonomic position of the order Hyolithelminthes, they are certainly not coelenterates (such as solitary coral polyps). The body of a polyp consists of three major sections: the attachment (foot) disk, cylindrical body (stalk), and distal oral field with a central orifice and grabbing tentacles at the periph ery (Westheide and Rieger, 2008). In addition, the pharynx in polyps has one or two pharyngeal grooves, and the gastral cavity in some taxa is subdivided by septa. Although hyolithelluses have a cylindrical tube and are occasionally found in association with ring shaped laminae with a hole in the center, which sup posedly served to fix firmly the tube in the substrate (Missarzhevsky, 1989), the inner structure of their tubes does not corroborate the presence of septa. Many scientists considered hyolithelminthes to be closely related to Annelida (Table 1). Higher annelids have the following distinguishing characters: clear subdivision into the head, segmented body, and poste rior body part; each body segment usually possesses one pair of parapodia with setae; a straight digestive tract as a tube; epithelium covered by cuticle, which formed an elastic cover around the body. Some anne lids have a shell tube of calcium carbonate with a dou blelayered or triplelayered wall (Serpullidae, Spiror bidae, Sabellidae) (Ippolitov and Rzhavsky, 2008; Vinn et al., 2008). Among Polychaeta, there are also species with completely reduced parapodia with a few setae, or with no setae. These are mainly small forms, with larval features, Archiannelida (Westheide and Rieger, 2008). Hyolithelminthes show no segmenta tion, nor do they have parapodia, setae, or remains of the head division. The specimen examined demon strates a less complex organization (presence of intes tines and perhaps of the blood vessel). Thus, it is pos sible that Hyolithelminthes from the family Hyolithellidae were representatives of Archiannelida. In their level of organization, Hyolithelminthes are most similar to other modern organisms, i.e., round worms Nemathelminthes (Nematoda), which have an unsegmented cylindrical or fusiform body. The cuticle is multilayered and represents an external skeleton (Dogel, 1981). In marine forms, it can be smooth, annulate, ornamented by scutellae, crests, and other PALEONTOLOGICAL JOURNAL
Vol. 44
No. 2
2010
123
elements. Modern nematodes are extremely abundant and constitute about 70% of the meiofauna (Chesunov, 2001). Anatomically, marine nematodes are more primitive than freshwater nematodes, soil nematodes, and, particularly, parasitic nematodes (Malakhov, 1986). The intestine is a straight tube extending throughout the body. The Nemathelm inthes affinity of Hyolithellidae is primarily supported by their nonsegmented cylindrical body and, secondly, by the presence of the layered tube wall in many spe cies and intestines in the shape of a longitudinal tube. It should also be noted that they are found in abun dance in the assemblages of the Early Cambrian SSF. The study of Early Cambrian hyolithelminthes and their comparison with modern organisms have shown that the family Hyolithellidae should be assigned to the roundworms Nemathelminthes (Nematoda?), although their affinity to Archiannelida cannot be excluded. It is likely that the diverse faunas of the Early Cambrian tubular problematics currently assigned to the order Hyolithelminthes contain representatives of different phyla. Further studies require a more detailed examination and reconsideration of the sys tematics of all problematic organisms. ACKNOWLEDGMENTS I am grateful to I.V. Korovnikov for the donated material from the UlakhanSulugur section and P.Yu. Parkhaev for valuable consultations and comments. REFERENCES 1. J. Barrande, Système Silurien du centre de la Bohême: 1ère Partie: Recherches paléontologiques, Vol. 3: Classe des Mollusques, Ordre des Pteropodes (Prague, 1867), pp. 60–75. 2. S. Bengtson, S. Conway Morris, B. Cooper, et al., Early Cambrian Fossils from South Australia (Assoc. Australas. Paleontol., Brisbane, 1990). 3. B. Boucek, “Conularida,” Handb. Paleozool. 2, 42–50 (1939). 4. V. A. Dogel, Invertebrate Zoology (Vyssh. Shkola, Mos cow, 1981) [in Russian]. 5. N. V. Esakova and E. A. Zhegallo, “Biostratigraphy and Fauna of the Lower Cambrian of Mongolia,” Tr. Sovm. Ross.–Mongol. Paleontol. Exped. 46, 1–216 (1996). 6. D. W. Fisher, “Small conoidal shells of uncertain affin ities,” in Treatise of Invertebrate Paleontology, Part W (Univ. Kansas Press, Lawrence, 1962), pp. 130–143. 7. N. V. Grigorieva, “To the Question of the Study of the Microstructure of Hyolithelminthes,” in Reports of Soviet Geologists on the XXVI Session of the International Geological Committee: Paleontology and Stratigraphy (Nauka, Moscow, 1980), pp. 49–55 [in Russian]. 8. N. V. Grigorieva and E. A. Zhegallo, “On the Study of Microstructures of Some Tommotian Fossils,” Paleon tol. Zh., No. 2, 142–144 (1979). 9. Guidebook of the Excursion to the Aldan and Lena Rivers: International Excursion on the Problem of the Cam
124
10. 11. 12. 13. 14.
15.
16.
17.
18.
NOVOZHILOVA brian–Precambrian Boundary (Yakutsk VIEMS, Mos cow, 1973) [in Russian]. J. M. Hurst and R. A. Hewitt, “Tubular Problematica from the Type Caradoc (Ordovician) of England,” Neues Jahrb. Geol. Paläontol. 153, 147–169 (1977). A. P. Ippolitov and A. V. Rzhavsky, “On the Microstruc ture of Tubes of Living Spirorbids (Annelida, Polycha eta),” Dokl. Akad. Nauk 418 (1), 131–133 (2008). V. V. Malakhov, Nematodes: Structure, Development, System, and Phylogeny (Nauka, Moscow, 1986) [in Russian]. V. V. Malakhov, “Revolution in Zoology: New System of the Bilateria,” Nature, No. 3, 40–54 (2009). N. P. Meshkova, “To the Question of the Paleontologi cal Characteristics of Lower Cambrian Deposits of the Siberian Platform,” in Biostratigraphy and Paleontology of the Lower Cambrian of Siberia and the Far East (Nauka, Moscow, 1969), pp. 158–174 [in Russian]. N. P. Meshkova, “New Tubular Problematics of the Middle Cambrian of Siberia and Central Asia,” Tr. Inst. Geol. Geofiz. Sib. Otd. Akad. Nauk SSSR, No. 632 (Problematics of the Late Precambrian and Paleozoic), 127–133 (1985). V. V. Missarzhevsky, “Earliest Skeletal Fossila and Stratigraphy of the Precambrian and Cambrian Bound ary Beds,” Tr. Geol. Inst. Akad. Nauk SSSR 443, 1– 237 (1989). V. V. Missarzhevsky and A. M. Mambetov, “Stratigra phy and Fauna of the Cambrian and Precambrian Boundary Beds of the Lesser KaraTau,” Tr. Geol. Inst. Akad. Nauk SSSR 326, 1–90 (1981). V. Poulsen, “Notes on Hyolithellus Billings, 1971, Class Pogonophora Johannson, 1937,” Biol. Medd. Dan. Vid. Selsk. 23 (12), 1–15 (1963).
19. L. J. Pyle, G. M. Narbonne, G. S. Nowlan, et al., “Early Cambrian Metazoan Eggs, Embryos, and Phos phatic Microfossils from Northwestern Canada,” J. Paleontol. 80 (5), 811–825 (2006). 20. L. N. Repina and A. Yu. Rozanov (Eds.), Cambrian of Siberia (Nauka, Novosibirsk, 1992) [in Russian]. 21. Stage Stratification of the Lower Cambrian: Stratigraphy, Ed. by B. S. Sokolov and A. Yu. Rozanov (Nauka, Mos cow, 1984) [in Russian]. 22. V. A. Sysoev, Hyoliths from the Cambrian of the Northern Slope of the Aldan Shield (Akad. Nauk SSSR, Moscow, 1962) [in Russian]. 23. A. K. Valkov, Biostratigraphy of the Lower Cambrian of the Eastern Siberian Platform: Yudomo–Olenekian Region (Nauka, Moscow, 1987) [in Russian]. 24. N. I. Vasilieva, A Small Shelly Fauna and Biostratigra phy from the Lower Cambrian of the Siberian Platform (VNIGRI, St. Petersburg, 1998) [in Russian]. 25. O. Vinn, “Possible Cnidarian Affinities of Torellella (Hyolithelminthes, Upper Cambrian, Estonia),” Palä ontol. Zeits. 80 (4), 383–388 (2006). 26. O. Vinn, H. A. ten Hove, and H. Mutvei, “On the Tube Ultrastructure and Origin of Calcification in Sabellids (Annelida, Polychaeta),” Palaeontology 51 (2), 295– 301 (2008). 27. C. Walcott, “Cambrian Geology and Palaeontology: II. Middle Cambrian Annelids,” Smithson. Misc. Coll. 57 (5), 109–144 (1911). 28. W. Westheide and R. Rieger (Eds.), Invertebrate Zool ogy, Vol. 1: From Protists to Mollusks and Arthropods (KMK, Moscow, 2008) [in Russian]. 29. R. Wrona, “Cambrian Microfossils from Glacial Errat ics of King George Island, Antarctica,” Acta Palaeon tol. Polon. 49 (1), 13–56 (2004).
PALEONTOLOGICAL JOURNAL
Vol. 44
No. 2
2010
