Corresponding author: Ilaria Mazzini (
Academic editor: Hans Jurgen Hahn
Groundwater ecosystems host a rich and unique, but still largely unexplored and undescribed, biodiversity. Several lineages of ostracod crustaceans have subterranean representatives or are exclusively living in groundwaters. The stygobitic genus
Rossetti G, Stoch F, Mazzini I (2022) A reassessment of the origin and distribution of the subterranean genus
Although groundwater ecosystems form the largest freshwater biome (
It is well documented that stygobionts (i.e., taxa occurring exclusively in groundwater during their entire life cycle) can have a double origin (
The class
The ostracod family
In this paper, after a comprehensive literature review and the description of two new living species from springs in the Northern Apennines, Italy, we critically revise the previously proposed scenarios in the light of the new available data and offer a morphological analysis of all living and fossil
Ostracod specimens described in this paper were sampled from the Cirone rheocrene spring and the Poiano spring system (Emilia Romagna region) (Suppl. material
Ostracods were preserved in ethanol 75%. Dissections were done under a stereomicroscope (Zeiss 47 50 22). Valves were examined by Scanning Electron Microscopy (
Chaetotaxy of the limbs in descriptions follows
The outlines of valves obtained both from
Rheocrene spring Cirone, road from Bosco di Corniglio to Cirone pass, municipality of Corniglio, province of Parma, Emilia-Romagna region, coordinates
One adult female designated as holotype, with valves stored dry in a micropaleontological slide (used for
From the Latin adjective abditus-a-um, meaning hidden, concealed, but also mysterious, due to the fact that only one individual of this species was collected despite repeated samplings in the type locality and in other springs of the same region.
Valves (Figs
Appendages (Fig.
Valve length 308 μm, height 173 μm (n = 1).
The species is known from its type locality only.
both valve and soft features are described, allowing us to clearly distinguish the new species from its congenerics;
so far only two other living species are known for the genus
the habitat from which the species was collected strikingly differs from those of other living congeners (see below);
further samplings performed in the type locality and surrounding spring areas did not yield additional specimens.
We are thus confident that
Poiano springs, Upper Secchia Valley, municipality of Villa Minozzo, province of Reggio nell’Emilia, Emilia-Romagna region, coordinates
More than 30 specimens from the type locality and sample of the holotype, and additional specimens from nearby localities (see below). Previously reported as
GR804, adult ♂, soft parts dissected in glycerine in a sealed slide, valves used for
This species is dedicated to GR’s daughter, Sofia Rossetti Tekleab. Furthermore, among the different meanings of the ancient Greek noun ”σοφία” there are also “knowledge” and “wisdom”. Our hope is that the description of this new species will shed more light on morphological characteristics and evolutionary relationships of the genus
Valves (Figs
Appendages (Fig.
Valve length 303–331 µm (n = 9).
In addition to individuals drifted from the Poiano spring, rare specimens of
Hemipenis of Recent species of
Valve outlines of Recent and fossil species of
The distal segment of walking legs in
Frasassi cave complex (Marche, Italy), inner lakes of the Grotta del Fiume (cadastre number 8 Ma), in the remains of the subfossil eels at Lago delle Anguille; outside the cave, sulfidic springs on the bank of Sentino River (Fig.
Slightly brackish groundwater habitats in Apulia, Italy, were cited as ‘type localities’ by
Superimposition of valve outlines of Recent and fossil species of
Interstitial of a temporary stream, beach in front of La Baillaury (site Ba-2), Bay of Banyuls, France (Fig.
Cave Skuljica, Krk Island, Croatia (Fig.
Paleogeographic map of the Mediterranean basin and Western Paratethys during Midde Miocene (13 Ma, after Ron Blakey, Colorado Plateau Geosystems, Arizona, USA,
A well fed by freshwater, 19 m from the seashore on the northwestern coast of Euboea (Evvia) Island, village Aghios Georghios, Greece (Fig.
Inner shelf of the northeastern coast of Black Sea, approximately 2.4 km from the town of Gelendzhik, and living in the freshwater underflow of the small Jeane River, 16 km upstream off the town of Gelendzhik (Fig.
Black Sea, Tsemes Bay (town of Novorossiysk) at a depth of 2 m. The attribution of the figured specimens to the genus
Vodeni Rat anchialine cave, 13 m above sea level, and about 30 m inland from the rocky coast, Sveti Klement Island, Pakleni Archipelago, southeastern of the island of Hvar (Croatia) (Fig.
The described species of the genus
There are several differences in the morphology of the hinge among
Miocene (Badenian) of the Vienna Basin, Hainburg, Lower Austria (Fig.
According to
The authors report seven specimens form the late Pliocene Saïss basin, Douar section, Northern Marocco. Possibly the same as
Late Pleistocene, Saïss plain, Douar section, in an old quarry of Douar El Mechmach on the road from Fès to Aïn Chkef Morocco. One left valve, length ~230 μm, either small-sized species or A-1 stage.
Cores drilled in the harbour of Salerno, Tyrrhenian Sea, Italy. Considered as an allochthonous species. It was found in sample GS1 7.50, Holocene fine sands and rare gravels of the unit US5 (in some levels of the unit US5 ceramic fragments of Roman age occur, and in the lower part is present a level dated at 7553–7411cal BP), and in sample GS1 16.50, Pleistocene, older than the Campanian Ignimbrite super-eruption (∼40 ka), possibly the substage MIS 5e (
The left valves of
Speciation in subterranean habitats is commonly explained as the result of divergent selection in geographically isolated populations (
Differences between extant
The evolutionary origins of subterranean Recent ostracods are best understood as due to an interplay of vicariance and dispersal.
As reported by
Moreover,
Recently, different biogeographical models have been explored to explain the distribution in the groundwaters of the Apennine and Balkanic peninsula, separated each other by the Adriatic Sea, of three different clades of stygobitic amphipods of the genus
The occurrence of repeated and independent colonizations and local speciation events seems to be further supported by the finding of
Furthermore, it is worth noting that most
Osmoregulatory mechanisms that make it possible to cross the salinity boundary (
Negative rheotaxis has been observed in different meiofaunal taxa, demonstrating movements directed upstream in the hyporheic zone (
Our analyses have been directed toward reassessing existing theories on evolution and biogeographic patterns of subterranean non-marine ostracods, based on the known distribution and new findings of species belonging to the genus
Limited accessibility to hypogean habitats determines a still fragmented knowledge of groundwater ostracod biodiversity. In addition, poor taxonomic resolution often hinders the possibility to identify patterns and scenarios at suitable space and time scales. Extensive research in hypogean environments will significantly increase our poor knowledge on ostracod diversity in groundwater and will contribute to a better understanding of their evolutionary and systematic relationships. Up to now, the rarity and difficulty to collect
This article is dedicated to Dan L. Danielopol and Koen Martens, two giants on whose shoulders it is always exciting to be guided in the fascinating world of ostracods. We are grateful to Valentina Pieri and Elisa Bottazzi for their valuable help in preliminary studies on
Figures S1–S5
Occurrences and images
Additional information on the sampled localities and the geographycal distribution of the genus