Mosquoceratidae Ruzhencev & Shimansky 1954

Family Mosquoceratidae Ruzhencev & Shimansky, 1954 Fig. 26 Diagnosis Family of the superfamily Pleuronautiloidea with a large, rapidly growing first whorl. Whorl profile weakly depressed, subhexagonal to trapezoidal. Venter broad, weakly convex; ventrolateral shoulder angular, flanks convex and strongly divergent; umbilical margin, if present, very weakly developed. Sculpture with ventrolateral, longitudinally elongated nodes. Suture line with a wide external, a narrower lateral and a narrow internal lobe; without annular process (after Ruzhencev & Shimansky 1954). Included genera Mosquoceras Ruzhencev & Shimansky, 1954 (Moscovian to Kungurian; 9 species). Articheilus Ruzhencev & Shimansky, 1954 (Artinskian; 1 species). Leonardocheilus Ruzhencev & Shimansky, 1954 (Kungurian; 1 species). Remarks According to Ruzhencev & Shimansky (1954: 85), the family Mosquoceratidae is closest to Tainoceratidae (which they interpret more broadly than it is currently done). The family Mosquoceratidae differs greatly from most of the other families of the Pleuronautiloidea in the morphology of the first volution, which is large, stout and rapidly growing in the Mosquoceratidae, whereas it is smaller and, above all, much slenderer in the other families. The similarity between these families is evident in both the shape of the conch and the suture lines. There are also sculptural differences. In the Mosquoceratidae, the tubercles are longitudinally elongated and coincide exactly with the ventrolateral shoulder; in the other families, the tubercles are usually rounded conical. The species of the family Aktubonautilidae also possess a large first whorl, but differ in the shape of the whorl profile, which is semicircular or reniform with broadly rounded venter.