Ivantsov A.Yu.1, Zakrevskaya M.A.1, Nagovitsyn A.L.2 2019. Morphology of integuments of the Precambrian animals, Proarticulata // Invertebrate Zoology. Vol.16. No.1: 19–26 [in English].
1 Borissiak Paleontological Institute, Russian Academy of Sciences, Profsouznaya st. 123, Moscow, 117997, Russia. E-mail: firstname.lastname@example.org
2 Arkhangelsk Regional Museum, Nab. Severnoy Dviny, 85/86, Arkhangelsk, 163000, Russia. E-mail: email@example.com
ABSTRACT: Proarticulata, the largest mobile animals of the Late Precambrian, inhabited shallow marine basins of normal salinity in Baltica (eastern and northern Europe) and East Gondwana (Australia) in the Late Ediacaran. They represented a substantial part of benthic palaeocommunities of macroorganisms inhabiting microbial mats, and at least some of them fed on the upper lamina of such a mat, absorbing the nutrition by their ventral side. Moulds attributed to the Proarticulata were formed by sub-bilateral organisms, divided into two transverse rows of half-segments (isomers). It was established that these moulds did not represent the entire body, but only a part, that was relatively resistant to decomposition. This sack-like structure, divided into transverse elements, enveloped the dorsal and ventral sides of the body but did not spread to its inner parts. It was dense and probably served as a resilient support. On the dorsal side, this integument created a continuous shield that showed no signs of segmentation. The outer surface of the dorsal side of several genera of the Proarticulata was covered with numerous evenly distributed tubercles. In a single specimen, the tissue at the posterior end of the body formed a pair of long filamentous outgrowths. Based on the feeding traces, it was inferred that the ventral side of the body was segmented externally similar to the supporting structure. The cover tissue on the ventral side probably bore cilia and furrows of suggested ciliary sweeping were preserved on the traces. The integument and segmented structure are interpreted as an epidermal tissue and a basal matrix underlying it. A tissue organization in combination with the anteroposterior and dorsoventral polarity of the Proarticulata body allow us to assign them to the Eumetazoa and Bilateria.
KEY WORDS: Dickinsonia, Yorgia, Proarticulata, Bilateria, Eumetazoa, Late Precambrian, Ediacaran.