Publisher : Biodiversity Journal
Place of publication :
Publication year : 2015
Thematic : Species
Language : English
Note
Several species belonging to the genus Amphiope L.Agassiz, 1840 (EchinoideaAstriclypeidae)
from the Mediterranean Oligo-Miocene have been synonymised with A. bioculata (Des
Moulins, 1835), the type-species of the genus, based on the interpretation given by Philippe
(1998) as a taxon characterized by a large amount of morphological variability. A recent study
introduced the characters of the internal test structure and the plating patterns as taxonomic
tools in this genus. That paper indicated the occurrence of at least five different species in the
examined sample from the Oligo-Miocene of Sardinia, thus pointing to a previous overestimation
of the variability-range of the type-species and to the need of a review of the largely
unresolved taxonomy of Amphiope. According to a recent study, Amphiope is considered as a
shallow-water echinoid, inhabiting sandy bottoms with high hydrodynamic energy; so it
represents a coastline marker, useful for the study of the paleo-geographic changes occurred
in the Proto-Western-Mediterranean during the Miocene. The diffusion and speciation of
Amphiope were highly influenced by those changes. In particular, the speciation rate of this
genus was likely favored by the occurrence of isolated populations created when islands (e.g.:
Baleares, Calabria, Corse, Kabylies, Sardinia) separate from the mainland, above all in the western
part of that Basin, because of the opening of the Balearic Basin during the Late Oligocene-Early
Miocene and of the Tyrrhenian Sea during the Burdigalian-Tortonian (references
in this work). Two main morphotypes of Amphiope sensu Stara & Sanciu (2014), developed
in the Western Mediterranean from the late Oligocene to the late Miocene. They are herein
called the “bioculata†group, characterized by roundish to broad elliptical lunules with major
diameter/minor diameter ratio (SI) < 1.59, and the "nuragica" group, with more or less narrow
lunules and SI > 1.6. According to this authors, most Miocene forms with narrow elliptical
lunules would derive from A. nuragica (Comaschi Caria, 1955), late Oligocene-early Miocene
of Sardinia, the most archaic form so far known of this genus. The forms belonging to the
“bioculata†group likely derived from a different common ancestor bearing round to broad
ovoidal lunules. “A. bioculata†described by Cottreau (1914), from the Burdigalian (Philippe,
1998) of Saint Cristol (Nissan, Herault, France), is so far the most ancient known form belonging
to this group. This work proposes a possible speciation sequence of the “nuragica†group.
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Keywords : marine-protected-areas
Encoded by : Pauline Carmel Joy Eje
