Volume 35

The taxonomic identity of Iberus alonensis has traditionally been surrounded by great controversy because under this name a large number of similarly-shaped populations distributed over a vast geographical area and probably belonging to different species have been subsumed. The publication of the first phylogenetic study on the genus Iberus began to unravel the alonensis complex, defining other likely new lineages. One of them is I. alonensis-like 02, a provisional name assigned to the traditional populations of I. alonensis from Andalusia (southern Spain) but lacks sufficient biogeographic support to be formally defined as a new species. In this study, the potential distribution area of I. alonensis-like 02 is thoroughly explored through systematic sampling. The resulting geographical mapping together with a morphometric study and new molecular evidence allow us to confirm the historical name I. alonensis rhodopeplus as a valid taxonomic denomination which we divide into two cryptic subspecies named I. rhodopeplus rhodopeplus and I. rhodopeplus bastetanus ssp. nov. Besides, the subspecies I. alonensis labiatus has to be renamed. Our findings contribute to revealing the species complex involved under the classic name I. alonensis and to improving our knowledge on the cryptic nature of numerous taxa within the genus Iberus.

Several rostroconch specimens of the family Bransoniidae are discovered in the Pennsylvanian of the Russian Platform for the first time. All of them are assigned to the species Hoarepora parrishi (Worthen, 1890), which is the type species of Hoarepora Mapes in Mazaev, 2022. Until now, the distribution of this species has been restricted to the Morrowan – Missourian interval in the North American Midcontinent Basin. All studied specimens come from Moscovian and Gzhelian stages of two localities on the Russian Platform. Both shell morphology and taphonomy of this species are examined in detail. H. parrishi is redescribed, since the previous description lacks many specific characters. It is shown that Conocardium missouriensis Roundy in Girty, 1915 is a junior synonym of C. parrishi Worthen, 1890. The new occurrences significantly expands the geographical range of this species and supports the existence of biogeographical connections between the paleobasins of North America and the Russian Platform in the Pennsylvanian, and also increases the known geochronological range of H. parrishi by approximately two million years.

Buccinum osagawai is a valuable commercially exploited gastropod species inhabiting the northern Pacific. An accurate and reliable method for estimation the mollusk’s individual age is needed to understand the population dynamics and size-age structure of B. osagawai stock. The most commonly used method of estimation of the individual age of mollusks of the genus Buccinum is counting the increments on the operculum. However, this method has disadvantages, for example, since the operculum is an external recording structure, its readability is relatively low. To develop a more accurate method for determining individual age, the microstructure of statoliths of the gastropod B. osagawai and its features were studied and the possibility of using B. osagawai statoliths to determine the individual age of an animal by counting increments on thin sections of statoliths was tested. The relationship between the number of statolith increments and the number of marks on the operculum surface was studied. A comparative analysis of these two methods of age determination is provided.

This paper described the second species of the genus Calybium Morlet, 1892, Calybium plicatus sp. nov. was collected in Son Doong Cave, Phong Nha–Ke Bang National Park, Quang Binh Province, Central Vietnam. Calybium plicatus sp. nov. has a similar shell shape to Calybium massiei Morlet, 1892 but differs in having a smaller shell size, the parietal wall with six evenly spaced parietal lamellae. This discovery represents the first report of the genus Calybium in Vietnam.

A new shallow-water species Lepidochitona cubensis sp. nov. collected in the Caribbean Sea off Cuba in sea grass Thalassia testudinum is described. This chiton is closest to the species L. bullocki with which it forms a separate group within the genus, differing from other species of the genus by the presence of small square grooves on tegmentum of valves.