Contributions to Zoology, 85 (2) – 2016Fabio Scarpa; Piero Cossu; Tiziana Lai; Daria Sanna; Marco Curini-Galletti; Marco Casu: Meiofaunal cryptic species challenge species delimitation: the case of the Monocelis lineata (Platyhelminthes: Proseriata) species complex

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A conservation issue?

A shared trait of the new species is their apparent restricted distribution; both are known from only one station. Monocelis algicola nov. sp. is the only Mediterranean Monocelis species occurring on algae. Since the habitat has not been thoroughly sampled elsewhere for Proseriata, the species may be more widespread than presently known.

Monocelis exquisita nov. sp. may prove to be a different case. It is only known from a shallow brackish water habitat in Northern Sardinia (Porto Puddu). Specimens were first sampled in 2002 (Casu and Curini-Galletti, 2004), and at that time, the species was present throughout the inlet and in an adjacent creek mouth. Afterwards, the area underwent massive modifications due to the construction of a pier and a marina (S12) and a real estate development. Extensive sampling performed in June 2014 revealed that the species had possibly disappeared from most of the stations where it was common in 2002, and its presence was only confirmed in the unaffected creek (S12). Closely related species of the genus Pseudomonocelis Meixner, 1943 have strict sediment preference, and populations have disappeared after natural or human mediated sedimentary imbalance (Cognetti and Curini-Galletti, 1993; Casu and Curini-Galletti, 2006). The apparent disappearance of the inlet population of M. exquisita nov. sp. may thus be linked to the observed silting of the sediments of the area, presumably caused by reduced exchange with the sea following the construction of the pier.

Brackish water habitats, and especially brackish microhabitats, are numerous throughout Sardinia, and it would be pretentious to assume that we managed to sample all of the habitats suitable for the species. However, over the years, extensive sampling along most of the Sardinian coast (our own unpubl. data) failed to detect the species. Instead, we consistently found one or the other of OTUs A and B. Brackish areas were not as thoroughly investigated for Proseriata outside of Sardinia, but we have conducted numerous sampling campaigns in many parts of the northern and central Mediterranean (mostly unpubl. data). In most of the brackish areas of the Mediterranean, one or the other of OTUs A and B were abundantly found, but in none of them were specimens of M. exquisita present. The demise of the species in its only known station is thus particularly worrying.

The species meets the IUCN criteria of Critically Endangered (CR), as the species is: “... known to exist at only a single location.” (point V, B2.a), and the area, extant and quality of habitat is in “continuing decline, observed, inferred or projected ...” (point V, B2.b iii) (IUCN Red List Categories and Criteria. Version 3.1, 2001).