Tuesday 26 July 2022

Barkeriella museensis: A new species of Systellommatophoran Slug from the tropical Afromontane greenhouse of the Science Museum of Trento, northern Italy.

Botanical gardens, Plant nurseries, and similar facilities are well known reserves of xenodiversity (diversity based upon introduced, non-local species). Such environments have been a route through which a wide range of Invertebrates, Micro-organisms, Fungi, and Plants are known to have spread from such centres into new environments, leading many countries to have introduced tight legislation around the importing of Plants and soil. In recent years taxonomists have described a number of new species from botanical gardens, including Fungi, Wasps, Gastrotrichs (four of the 800 species described within this group, or 0.5% of their total diversity), Arachnids, Insects, and Molluscs.

In a paper published in the Zoological Journal of the Linnean Society on 26 July 2022, Giuseppe Manganelli of the Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente at the Università di Siena, Andrzej Lesicki of the Department of Cell Biology at the Adam Mickiewicz University in Poznan, Andrea Benocci of the Museo di Storia Naturale dell’Accademia dei Fisiocritici, Debora Barbato, also of the Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente at the Università di Siena, Dannio Miserocchi of Ravenna, Joanna Pieńkowska, aslo of the Department of Cell Biology at the Adam Mickiewicz University in Poznan, and Folco Giusti, again of the Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente at the Università di Siena, describe a new species of Slug from the tropical Afromontane greenhouse of the Science Museum of Trento, northern Italy.

The new species is described from a population found living in the greenhouse in January and May 2019, but which could not be refound in February 2022. During the intervening time the part of the greenhouse where the Slugs were found was restructured, and the entire greenhouse suffered an infestation with burrowing Suriname Cockroaches, Pycnoscelus surinamensis, and it is believed the population is now extinct. 

An initial examination of the Slugs quickly revealed that they had transverse ridges on the foot, indicating that they did not belong to the Order Stylommatophora, the most numerous and diverse group of Pulmonate Gastropods, but rather the less numerous Order Systellommatophora. Members of the Systellommatophora are all Slug-like forms lacking shells, and are exclusively hermaphroditic. They are considered to be a sister group to the Stylommatophora, with the two groups together forming the clade Geophila. 

The Order Systellommatophora comprises three families. The Onchidiidae are large, oval-to-round, predominantly semi-marine Slugs, with a single pair of tentacles, found throughout the coastal zones of the temperate, subtropical, and tropical oceans, but most diverse and abundant in the eastern Indian Ocean and tropical western Pacific. The Veronicellidae are medium-to-large sized, dorsoventrally flattened, elongate Slugs, with leathery backs and two pairs of tentacles, found throughout the tropics and subtropics, although favouring moist climates and most abundant and diverse in primary and secondary rainforests. The Rathouisiidae are small, slender, typically keeled, carnivorous Slugs, with two pairs of tentacles, found in Southeast Asia and Australasia. 

The new Slug is a small, slender species with four pairs of tentacles, which shares many features associated with the Rathouisiidae. However, the species also has a number of unique features which prevent it being placed into any currently described Rathouisiid genus, most notably the structure of the reproductive system, considered important in the classification of Gastropods, prompting Manganelli et al. to place it in a new genus.

The new species is named Barkeriella museensis, where 'Barkeriella' honours New Zealand Gary Barker for his work on  terrestrial Gastropods, and 'museensis' means 'coming from MUSE', where MUSE is an abbreviation commonly used for the Science Museum of Trento.

Live specimen of Barkeriella museensis from the tropical greenhouse of the Science Museum of Trento, Italy. Debora Barbato in Manganelli et al. (2022).

Barkeriella museensis is a small Slug, at most 20 mm in length and no more than 3 mm in width. It has a rounded body, whitish in colour with a grey band on each side, separated by a white line marking the trace of a keel. There are two pairs of tentacles, with the upper being longer and tending to have a pinkish hue. The foot is elongate.

The origin of Barkeriella museensis is unclear. The given the known range of the Rathouisiidae, it is unlikely that the species originates in the montane forests of Africa. However, the Afromontane greenhouse of the Science Museum of Trento is known to contain species of non-African origin, chosen for their close resemblance to African species which were not available, and the majority of Plants in the greenhouse were sourced from other collections or commercial dealers in Italy anyway.

There are currently four known genera of Rathouisiids (excluding Barkeriella), each with its own distribution. The genus Rathouisia, which gives its name to the group as a whole, is known from southeastern China, and possibly South Korea. The genus  Atopos is known from Southeast Asia, Indonesia, New Guinea, and northern Australia. The genus Granulilimax contains a single species from Japan, with another genus known, but never formally named or described, from the Ryukyu Islands.

Theoretically, if the relationship between Barkeriella and these other genera could be established, then it might be possible to estimate its point of origin. Unfortunately the GenBank database, an open access database of gene sequences containing data from more than 500 000 species of species of Animals and Plants, contains only a limited number of sequences from the genera Atopos and Granulilimax, and none from Rathouisia, despite this being the largest genus in the family. In order to remedy this Manganelli et al. uploaded sequences from key parts of the genomes of both Barkeriella museensis and Rathouisia sinensis. Unfortunately none of the sequences available were close enough to Barkeriella museensis to shed any light on its point of origin.

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