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A new fossil conoidean from the pliocene of Italy 13

Table 1 Shell morphological features of the adults in the three turrids analyzed.
Species

Shell parameters B. trinacria B. menkhorsti B. zenetouae
Protoconch diameter size (in m)
Protoconch number of whorls 600–700 530–540 580–600
Protoconch sculpture 2.7–2.8 2.0–2.2 1.2
2.3–2.4 apical smooth, 1.6–1.8 apical smooth, smooth
Teleoconch axial folds (last whorl) remaining reticulated remaining reticulated
Shell length/width ratio
mean (std.dev.) 7–8 8 9
Shell length range (in mm) 2.2–2.6 2–2.7 1.8–2.5
Shell color 2.35 (0.06) 2.39 (0.05) 2.65 (0.07)
7–9 7–10 7–8
withish yellowish-brown or yellowish-brown,
[brownish] reddish-brown, white reddish-brown,
band on the middle white band on the
of the last whorl middle of the last
whorl, albino

Etymology This species is named after the In fact, the transition from the Pliocene to the
ancient land name of Sicily (Trinacria), used as a Pleistocene, accompanied by the increasing effect
noun in apposition. of the glacial cycles onto the Mediterranean Sea,
Distribution It is known from several Pliocene is marked by a number of biological transitions
outcrops (in Piedmont, Tuscany, Latium and in larval development of marine prosobranchs,
Sicily). where speciation events were associated with
Remarks Variability of the paratypes – proto- (and possibly driven by) the loss of planktotrophy
conch: no. whorls 2.7–2.8; maximum diameter (Oliverio, 1995a, 1996). In several cases anagenetic
0.60–0.70 mm. Teleoconch: shell length 7.2–8.8 mm, transformations resulted in a Pleistocene-Recent
width 3.0–3.8 mm. Outer lip variced, according to species without a planktotrophic phase, with
the stage of growth, whether the lip coincides the disappearance of the Pliocene planktotrophic
with an axial rib or an interspace. Colour of most ancestor. A turrid example is found in the
shells whitish, one paratype pale brownish. genus Clathromangelia, with the Lower Pliocene
The new species is very similar to the Recent C. quadrillum (planktotrophic) which gave rise
B. menkhorsti. It is diagnosed by the larger size to the Pleistocene-Recent non-planktotrophic
of the protoconch (diameter 0.60–0.70 mm vs. C. granum (Oliverio, 1995b). In many other
0.53–54 mm; 2.7–2.8 whorls vs. 2.0–2.2 whorls). instances a planktotrophic ancestor split into
The teleoconch is also nearly indistinguishable two living descendants: one with planktotrophic
from that of B. zenetouae, from which it is clearly development, the other without a planktotrophic
diagnosed by the totally different protoconch phase. The B. menkhorsti complex belong to
(multispiral vs. paucispiral). Morphological fea- the latter type of events, and the evident
tures of the three species dealt with herein are sister-species relationship of B. menkhorsti and
summarised in Table 1. B. zenetouae makes the use of the genus Fehria
phylogenetically erroneous, as already pointed
dIscussIon out by Bouchet (1990).
Loss of planktotrophy has been a common phe-
nomenon in the evolution of the caenogastro- Furthermore, the smaller number of proto-
pods (Oliverio, 1997; Duda & Palumbi, 1999). conch whorls in the Recent planktotrophic
B. menkhorsti (2–2.1) compared to the Pliocene
B. trinacria (2.7–2.8), recalls a phenomenon
already known in other turrid lineages (e.g.:
the Comarmordia gracilis Montagu 1803 lineage:
B. Sabelli pers. comm.), which show a decrease