Arkhangelsk Oblast eventually spread well beyond the Arkhangelsk Region. The Mezen horses, bred in the Mezen River valley, are rather small but suitable for difficult work and easily survive cold winters. The area of current Arkhangelsk Oblast has always been located on the trading routes connecting central Russia to the White Sea, and, in fact, in the 17th century the White Sea was the main sea export route for Russia. The whole course of the Northern Dvina is navigable, as well as the lower course of some of its tributaries, most notably the Vychegda, the Vaga, and the Pinega. The Mezen is
Onega stepanovi by an undivided zone. The surface of the undivided region of "Onega" is covered with small tubercles. "Onega" was originally described by Mikhail Fedonkin as a problematic organism, being grouped together with "Vendia", "Praecambridium" and "Vendomia" as possible stem-group arthropods due to a vague similarity with primitive Cambrian trilobites and arthropods. In 1985 Mikhail Fedonkin erected Phylum Proarticulata, in which he placed: "Onega", "Dickinsonia", "Palaeoplatoda", "Vendia", "Vendomia", "Praecambridium" and "Pseudovendia sp.", although he did not exclude the possibility that "Onega" may still be related to various lower Cambrian arthropods, such as "Skania". Andrey Yu. Ivantsov has proposed that "Onega" be