Of the twelve books of his work Liber de natura rerum, the thirteenth-century encyclopaedist Thomas of Cantimpré devoted six to zoology. He intended not only to inform his readers about ordinary animals, but especially to amaze and entertain them by descriptions of various strange creatures. This is most clearly visible in books VI–VII where he described many unusual sea animals whose names are often hard to explain, both etymologically and semantically.

Among them, we find sea creatures that were given names of terrestrial animals on account of similarity (translatio nominis), e.g. a ‘sea hare’, a ‘sea calf’, a ‘sea fox’, a ‘sea swallow’ and a ‘sea spider’. The first part of the study discusses what illuminations in Thomas’s encyclopaedia may tell us: what animals medieval readers visualised under these names; how much their notions differed from the real appearance and behaviour of these animals; and to what extent were their impressions formed by the names of the sea creatures (vis nominis) and by their descriptions (vis textus). The next part deals with the reception of Thomas’s text in medieval Bohemia, especially by the fifteenth-century encyclopaedist Paulerinus who, according to the hypothesis presented here, supplemented the original descriptions by information about the animals’ looks based on illuminations in Bohemian manuscripts of Thomas’s encyclopaedia (vis imaginis).

At times, iconographic variations in illuminated copies of the work in fourteenth- and fifteenth-century Central European manuscripts testify to the imagination and creativity of their illustrators; yet, the artists also relied heavily on their models, especially on the iconographic plan of the oldest illuminated copy of the Liber de natura rerum which is kept in Valenciennes. The final part of the study points to possible ancient and early medieval literary and pictorial sources that might have influenced the way these sea animals were depicted between the thirteenth and fifteenth centuries.