• journal_title：Geology
• Contributor：Artem Kouchinsky ; Stefan Bengtson ; Lisa-ann Gershwin
• Publisher：Geological Society of America
• Date：1999-
• Format：text/html
• Language：en
• Identifier：10.1130/0091-7613(1999)027<0609:CLEAWT>2.3.CO;2
• journal_abbrev：Geology
• issn：0091-7613
• volume：27
• issue：7
• firstpage：609

Phosphatized spheroids, ∼0.5 mm in diameter, in the Lower Cambrian Manykay Formation at the Bol'shaya Kuonamka River in northern Sakha (Yakutia) are interpreted as cnidarian embryos of late developmental stages. One of the poles has a double cross-like structure, consisting of two sets of four bands each. The bands of the upper set radiate at 90° from each other; those of the lower set also radiate at about right angles from each other, but the set is rotated 45° in respect to the upper set. Although there is a resemblance to the cross-like arrangements of cells in pregastrulation spiralian eggs, in particular those of annelids, the combined evidence favors an interpretation of the bands as incipient tentacles of a cnidarian actinula larva. The embryos occur with one of the first assemblages of shelly fossils in northern Siberia, that of the Angustiochrea lata zone. The co-occurring shelly fossils, anabaritids, probably also represent the phylum Cnidaria, but because their tubes have a consistent triradial symmetry, the connection with the tetraradially symmetrical embryos is problematic. The size of the embryos suggests that they are nonplanktotrophic, and the presence of actinula-like features suggests the lack of a free planula stage.