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112 PAOLO RUSSO
VENICE LAGOON (Figs. 29–31) It is interesting to observe that the morphotype
from the coast of Portugal is by far morphologically
Small sized the closest to that from the Northern Adriatic (Figs.
Shell rather thick and almost always eroded 32-33). This may not be surprising when one con-
Siphonal canal short siders that the Northern Adriatic lagoon environ-
Teleoconch consisting of 5–6 whorls ments show, for concomitant geographical, climatic
From dark brown to almost black in colour and environmental factors, sub-Atlantic rather than
Axial ribs not very raised and often eroded Mediterranean characteristics (Sacks, 1977, 1983;
Spirals cords thin and of little raised White, 1983; Mizzan, 1999). Among the Northern
Always acarinate Adriatic malacofauna we can include at least two
In some areas of the Venice Lagoon, during the other "cold" guests as Littorina saxatilis (Olivi,
1792) and Calliostoma virescens (Coen, 1933).
low tide, it lives in absence of water
Protoconch diameter 664 µm, nucleus 385 µm A feature common to all the described morpho-
types, is the presence of secondary cords, regularly
RESULTS AND DISCUSSION spaced between the primary ones. It is believed that
this element is a diagnostic character (Merle, 2001,
Each of these morpha shows such morphologi- 2005; Spreader et al., 2012; Russo, 2013) ( Fig. 9).
cal characteristics to be easily separated from the
others, therefore, despite being F. rostratus a poly- It can therefore be said that the alternation of
morphic species, it is stable within the analyzed (primary cords, secondary cords) is a valuable cha-
morpha. racter for the determination of F. rostratus, or rather,
the presence of this sequence, excludes other spe-
cies with the exception of F. buzzurroi Prkic et
Table 2. h/D ratio of the described morphotypes.
