Abstract
Although Cyprideis torosa is one of the most studied ostracods, its ecophenotypic variability has always impeded a clear definition of its carapace morphology. As a consequence, it is often difficult to identify this species in fossil material and very little is known about its phylogenetic origin. In this paper, we attempt to answer two main questions: when and from what species did C. torosa originate? To reach this goal we first analysed living and Recent populations of C. torosa collected from different salinity environments to define its variability. We found that the valve outline, the size of rounded normal sieve pores and the percentage width of the anterior inner lamella seem to vary independently of salinity. Secondly, to look for possible ancestors we analysed several Neogene species and found that Cyprideis sp. from the mid-Serravallian of Spain could possibly be the common ancestor of the Late Miocene Mediterranean and Lake Pannon lineages and that C. torosa is strictly linked to the Mediterranean stock, particularly to the phyletic lineage C. ruggierii – C. crotonensis . In this framework Cyprideis gr. torosa originated in the late Tortonian and C. torosa s.s. is thought to have been differentiated from C. crotonensis at the beginning of the Calabrian. Supplementary material: biometric tables and the list of the examined material is available at https://dx.doi.org/10.6084/m9.figshare.c.3636170.v1
Highlights
The genus Cyprideis Jones, 1857 was established, as a possible subgenus of Candona Baird, on Recent specimens of Candona torosa Jones, 1850 on the basis of its oblong carapace, marginal edges thickened, presence of selvage, left valve hinge with anterior and posterior sockets and central small teeth, surface of the valve punctated, upper antennae not plumous as well as the low pair (Jones 1857, p. 20)
To look for possible ancestors we analysed several Neogene species and found that Cyprideis sp. from the mid-Serravallian of specimens from the Ebro Basin (Spain) could possibly be the common ancestor of the Late Miocene Mediterranean and Lake Pannon lineages and that C. torosa is strictly linked to the Mediterranean stock, to the phyletic lineage C. ruggierii–C. crotonensis
To unravel the complex history of the origin of C. torosa we analysed in detail the morphology of C. pannonica, C. alberti, C. seminulum, C. sublittoralis, C. macrostigma, C. tuberculata, C. ruggierii, C. agrigentina, and C. crotonensis, comparing them with C. torosa
Summary
Hinge; the percentage of the denticulated postero-median element length of the LV hinge compared with the total posterior elements, the width of inner lamella on the anterior margin compared with the total length of the valve, using a stereomicroscope in transmitted light and a scanning electron microscope (Fig. 1). Some specimens fall out of this cloud (showing a greater morphometric distance) They were collected in the oligohaline Lake Trasimeno, the mesohaline Santa Pola and the hyperhaline Bella and Salinella samples in the case of females, and from the oligohaline Massaciuccoli marsh and the mesohaline Santa Pola locality in the case of males. 11 – 15 rectangular squared rectangular narrow rectangular rectangular narrow narrow ovoidal or rectangular narrow tiny or smooth Rim below the faint anterior element of the left valve hinge (Fig. 1) Number of teeth on 0 – 7 the posterior plate of the hinge occasionally rectangular to smooth square faint not present negligible to faint faint.
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