We use a morphological approach to describe a new species of isopod in the genus Baeticoniscus, found so far only in an underground gallery system created during the Roman period, approximately two thousand years ago, located beneath the modern town of Carmona (Seville, Spain). Specimens have been observed inhabiting rotten wood in the aphotic zone. The new species, Baeticoniscus carmonaensis sp. nov. differs from related species in the presence of the eyes as well as the number and arrangement of the tubercles and ribs on the cephalon and pereion. The description of this new species of Baeticoniscus represents one of the few cases worldwide in which the description of a new taxon has been described in a subterranean archaeological site.

Crustacea, Iberian Peninsula, Isopoda, taxonomy, Trichoniscidae, urban ecology

Nineteen families of terrestrial isopods and 269 species have been recorded in the Ibero-Balearic region, 52 of which were described in the last seven years (unpublished data). Most of these species fit into three families: Armadillidiidae Brandt, 1833, with 41 species; Porcellionidae Brandt & Ratzeburg, 1831, with 76 species; and Trichoniscidae Sars, 1899, with 89 species. Among the trichoniscids, the subfamily Trichoniscinae G.O. Sars, 1899 includes the largest number of species, while the subfamily Haplophthalminae Verhoeff, 1908, is only represented by fourteen species belonging to the following genera: Baeticoniscus Garcia, 2020, Balearonethes Dalens, 1977, Graeconiscus Strouhal, 1940, Haplophthalmus Schöbl, 1860, Iberoniscus Vandel, 1952 and Moserius Strouhal, 1940.

To date, underground ecosystems remain overlooked in conservation policies, and our knowledge of subterranean life is far from complete (Mammola et al. 2019; Nanni et al. 2023). Within these ecosystems, those created by human activities are even less studied, and many of such places often remain unknown. The role that fauna can play in utilizing human-made infrastructures, whether abandoned or still in use, is only now beginning to be properly understood. For example, some amphibians have been detected in abandoned railway tunnels (Herrero and Hinckley 2014), and drainage galleries (Rosa and Penado 2013), and Italian speleologists discovered a new subspecies of beetle, Boldoria ghidinii ghidinii, exclusively found in the subterranean dungeons of a castle in Brescia (Giachino and Vailati 2010). In this article, we describe a new terrestrial isopod species based on morphological characters of specimens collected from the only known location for this species, a subterranean gallery system built during the Roman period in Carmona (Seville, Spain). The conservation status of the new species remains unknown, but all specimens were detected at a single point within the artificial gallery system.

The subfamily Haplophthalminae Verhoeff, 1908, within the family Trichoniscidae G.O. Sars, 1899, includes genera whose species exhibit an integument characterized by prominent tubercles. The differences in the ornamentation patterns of many of these species are minimal, which is why Schmalfuss et al. (2004) recommended a review of this subfamily. Additionally, the differences in the secondary sexual characters, mainly in the first two pairs of pleopods of the males, are also usually small, complicating the identification of specimens.

Until now, fourteen species belonging to six genera of this subfamily are known in the Iberian Peninsula:

Balearonethes Dalens, 1977 with B. sesrodesanus Dalens, 1977 from the Balearic Islands (Dalens, 1977; Cruz, 1991a).

Graeconiscus Strouhal, 1940 with G. gevi Garcia, Miralles-Núñez & Pérez-Fernández, 2020 from Málaga (Garcia et al. 2020).

Haplophthalmus Schöbl, 1860, the most important in terms of the number of species, with H. alicantinus Cruz & Dalens, 1989 from Alicante (Cruz and Dalens 1989; González Silvestre 2015); H. asturicus Vandel, 1952 from Asturias (Vandel 1952; Cifuentes et al. 2021); H. chisterai Cruz & Dalens, 1989 from Alicante and the Balearic Islands (Cruz and Dalens 1989; Cruz 1991a; Cifuentes 2021b); H. danicus Budde-Lund, 1880 with a wide distribution area, as it has been reported from Bizkaia, Cantabria, Barcelona, the Balearic Islands, Orense, Pontevedra, Seville, Tarragona and Teruel (Arcangeli 1924; Schmölzer 1955, 1971; Cruz 1991a; Garcia and Cruz 1996; Barrientos 2005; Garcia 2009; Gregory et al. 2012; Cifuentes 2019, 2021a; Cifuentes and Tinaut 2019; Cifuentes et al. 2021); H. gibbus Legrand & Vandel, 1950 from the Balearic Islands (Vandel 1960); H. mengii (Zaddach, 1844) from Barcelona, Bizkaia, Cantabria, Gipuzkoa Girona and Navarra (Arcangeli 1924; Cifuentes et al. 2021); H. siculus Dollfus, 1896 from Girona and Tarragona in Spain, Faro and Setúbal in Portugal (Vandel 1946; Cruz 1991a); H. transiens Legrand & Vandel, 1950 from Castellón and Málaga (Vandel 1952, 1960; Cifuentes 2021b) and H. valenciae Cruz & Dalens, 1989 only known from Valencia (Cruz and Dalens 1989; González Silvestre 2015).

Iberoniscus Vandel, 1952 with I. breuili Vandel, 1952 from Cádiz and Málaga (citation that we consider doubtful as stated below) in Spain, and from Gibraltar (Vandel 1952).

Moserius Strouhal, 1940 with M. inexpectatus Reboleira & Taiti, 2015 from Santarém in Portugal (Reboleira et al. 2015).

Finally, the genus Baeticoniscus Garcia, 2020, was monospecific until this study, with B. bullonorum Garcia, 2020, as its only representative. Garcia (2020) described B. bullonorum from 31 specimens, 10 males and 21 females, from Cueva de la Pileta, located in Benaoján, province of Málaga (Spain) (Garcia et al. 2020). Baeticoniscus bullonorum is characterized by the presence of prominent tubercles on the cephalon, 4 ridges (2+2) on pereonites 1 to 6, and 2 ridges (1+1) on pereonite 7, a smooth pleon, and striations on the tip of the endopod of the male’s first pleopod. All these characteristics are present in Baeticoniscus carmonaensis sp. nov., which justifies its classification within this genus.

From the same Cueva de la Pileta, Vandel (1952) studied five specimens, two males and three females, which along with other specimens from the Cueva de las Motillas in Jerez de la Frontera (Cádiz) and from the Old St Michel’s Cave in Gibraltar, were used for the description of Iberoniscus breuili Vandel, 1952. A comparison between the descriptions of both species, I. breuili and B. bullonorum, reveals important differences between them in the ornamentation of the integument. I. breuili presents five pairs of ribs on the pereion (Fig. 1A) and a tubercle in the pleonite 3, whereas B. bullonorum has two pairs of ribs on the pereion and lacks a pleon tubercle (Fig. 2B, C). Note also the presence of a developed carpal lobe on the pereopod 7 of the male in I. breuili, which is absent in B. bullonorum. However, the drawings of the cephalon tubercles provided by both authors for their respective species are very similar (see Vandel 1952 p. 350 and Garcia 2020 p. 261).

We studied 12 specimens (six males and six females) of B. bullonorum from the Cueva de la Pileta, consistent with the description of this species by Garcia (2020). These specimens exhibit the same arrangement of tubercles on the cephalon (Fig. 2C) as I. breuili described by Vandel, but without the accessory ribs on the pereion and the large tubercle on pleonite 3 characteristic of that species. In the Vandel collection deposited at the Muséum national d’Histoire naturelle (MNHN) in Paris, under reference MNHN-IU-2013-19986, there is a single tube containing several poorly preserved specimens of I. breuili from two of the localities mentioned by Vandel (1952). Of one of these specimens, which lacks the cephalon, have been photographed (Fig. 2A) and the accuracy of Vandel’s description can be confirmed in relation to the ribs of the pereion and the tuberculation of the pleon, but as it lacks the cephalon, the tubercles cannot be observed. As noted earlier, since the only preserved specimens belong to the two localities are mixed, it is not possible to determine which cave the specimen in the photograph originates from. We consider it unlikely that two species from different genera, in which the integument ornamentation is a crucial character, would exhibit the same arrangement of tubercles on the cephalon. Since all 43 specimens studied from the Cueva de la Pileta by both Garcia (2020) and us undoubtedly correspond to B. bullonorum, it is highly probably that I. breuili is not present in the Cueva de la Pileta as Vandel (1952) said. It is likely that the specimens Vandel studied from this locality actually belong to B. bullonorum. Thus, until the Cueva de las Motillas in Jerez de la Frontera (Cádiz) and the Old St. Michael’s Cave in Gibraltar can be revisited, I. breuili would only be known from these caves, not from the Cueva de La Pileta in Málaga.

Baeticoniscus carmonaensis sp. nov. is differentiated from B. sesrodesanus, as the latter species has spiny tubercles arranged in several rows, not forming ribs. In G. gevi and I. breuili there is a large tubercle on the third pleonite, and in M. inexpectatus there are two, neither of which are found in B. carmonaensis sp. nov. In Haplophthalmus species, the tubercles are much weaker than those found in B. carmonaensis sp. nov. Finally, B. carmonaensis sp. nov. (Figs 2D, E, 3A) differs from other species in the genus Baeticoniscus due to the presence of the ocular apparatus, the absence of lateral roughness and the cephalon tubercle, as it only has two elongated median tubercles and four posterior ones, compared to the bilobed frontal tubercles of B. bullonorum (Fig. 2B, C).

The description of this new species is significant for different reasons. Beyond enhancing our understanding of underground biodiversity and European terrestrial isopods, this discovery represents one of the few descriptions of a new species in an urbanized area. Considering the growing effort for a greater recognition of subterranean ecology, the discovery of a new species in an urban underground environment- alongside other species as Platyarthrus caudatus- can help draw attention to these often overlooked ecosystems, particularly in cities with archaeological sites, canals, and tunnels. Regarding the unknown conservation status of the species, increasing research is demonstrating how cities can play a role in nature conservation, sometimes being the main habitat for species (Luna and Rausell-Moreno 2024). For Baeticoniscus carmonaensis sp. nov. future surveys in other underground environments in southern Spain could confirm its presence in new cave systems, both artificial and natural, which would help inform conservation measures with more comprehensive knowledge. In any case, the species is currently only known from a single population, found in decaying wood, consisting of several hundred specimens.

We would like to express our gratitude to MR. J.T. Bullón for his generosity in providing specimens, facilitating access and accompanying us during the sampling at the Cueva del Cerro de la Pileta, in Benaoján (Málaga). We also express our gratitude to Paula Rodriguez Moreno, Collection Manager at the Muséum national d’Histoire naturelle de Paris (MNHN) for providing us with the photograph of the Vandel specimen mentioned in the text. Finally, we thank the members of the AAES (Asociación Andaluza de Exploraciones Subterráneas), for their contribution to the broader understanding of the underground system studied in this project. In particular, we wish to express our heartfelt thanks to José Millán for his unwavering dedication to the speleological exploration of the region. Sadly, he passed away during the course of this work.