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Research Article
Terrestrial isopods (Crustacea, Isopoda, Oniscidea) from Mesovoid Shallow Substratum habitats of Portugal
expand article infoRita P. Eusébio‡, Stefano Taiti§, Ana Sofia P. S. Reboleira‡
‡ Universidade de Lisboa, Lisbon, Portugal
§ Istituto di Ricerca sugli Ecosistemi Terrestri, Sesto Fiorentino (Firenze), Italy

Corresponding author: Ana Sofia P. S. Reboleira ( asreboleira@fc.ul.pt )

Academic editor: Fabio Stoch
© 2025 Rita P. Eusébio, Stefano Taiti, Ana Sofia P. S. Reboleira.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Eusébio RP, Taiti S, Reboleira ASPS (2025) Terrestrial isopods (Crustacea, Isopoda, Oniscidea) from Mesovoid Shallow Substratum habitats of Portugal. Subterranean Biology 53: 129-153. https://doi.org/10.3897/subtbiol.53.163632
ZooBank: urn:lsid:zoobank.org:pub:98FAD49E-ED52-4C9E-82B5-120452E46F19
Open Access

Abstract

The Mesovoid Shallow Substratum (MSS) is a largely unknown subterranean habitat formed by the accumulation of rock fragments in steep slopes. In this study, we investigated the diversity, abundance and seasonal dynamics of terrestrial isopods in MSS habitats across Portugal. We identified 12 species belonging to five families, with Porcellionidae and Armadillidiidae being the most represented. The new species, Eluma cristata, endemic to the MSS of Alcobertas, is described. The terrestrial isopod communities included both surface-dwelling and subterranean-adapted species, pointing out the connectivity between these habitats and highlighting the adaptability of terrestrial isopods to diverse environments. Widespread species occurring in multiple locations, and species confined to single sites are present. Seasonality does not seem to affect the community composition. Our findings highlight the rich diversity of MSS habitats, thus their importance for conservation.

Keywords

Crustaceans, Iberian Peninsula, new species, shallow subterranean habitats, subterranean ecosystems

Introduction

Subterranean habitats are some of the least explored ecosystems in terms of biodiversity (Mammola et al. 2019, 2020). Among these, the Mesovoid Shallow Substratum (MSS), a network of voids formed by the accumulation of rock fragments in steep slopes, has received limited attention despite its ecological importance (Juberthie et al. 1980; Mammola et al. 2016).

While deep subterranean habitats such as caves have increasingly attracted scientific and public attention for their biodiversity and conservation value (Mammola et al. 2019), MSS habitats, despite their global distribution across varied geomorphological settings, remain poorly studied. Their faunal composition and ecological dynamics are still poorly understood (Eusébio et al. 2021).

MSS habitats are characterized by relatively stable microclimatic conditions, including reduced thermal fluctuations compared with surface habitats. These features provide both a refuge from surface climatic extremes and a permanent habitat for a diverse range of species (Nitzu et al. 2014; Mammola et al. 2016). These habitats support rich and specialized invertebrate communities, including both subterranean-adapted and surface-dwelling species (Culver and Pipan 2009, 2014; Mammola et al. 2016, 2017).

Terrestrial isopods frequently found in subterranean ecosystems have limited dispersal abilities and preference for high moisture (Hornung 2011; Dixie et al. 2015). Very few papers deal with terrestrial isopods from the MSS (e.g., Nitzu et al. 2010, 2011; Reboleira et al. 2015, 2022; Cifuentes et al. 2021). In Portugal, terrestrial isopod fauna of subterranean habitats has been documented in caves and sporadically in the MSS (Vandel 1946; Reboleira et al. 2015, 2022). However, comprehensive data on isopod diversity, distribution and seasonal dynamics in MSS habitats of Portugal are still lacking.

Subterranean habitats and their specialized fauna face increasing threats from land-use change, global warming, and pollution (Mammola et al. 2019; Reboleira and Eusébio 2021, 2023; Reboleira et al. 2022). While cave invertebrates have been increasingly included in conservation assessments such as the IUCN Red List (IUCN 2025) and the Portuguese Red Book of Invertebrates (ICNF 2023), species from shallow subterranean habitats remain overlooked, despite their vulnerability and ecological importance (Eusébio et al. 2021).

We studied the diversity, abundance, and seasonal dynamics of terrestrial isopods in MSS habitats in Portugal. We analysed new spatial-temporal distribution patterns and described a new species of the genus Eluma Budde-Lund, 1885. This information is crucial to underline the relevance of the conservation of these shallow subterranean ecosystems.

Material and methods

Terrestrial isopod sampling was conducted in five MSS areas across Portugal: Unhais da Serra, Serra da Estrela (40°17'23.7"N, 7°35'20.1"W) at 1.330 m a.s.l, Vale dos Poios, Sicó (39°58'49.3"N, 8°33'03.1"W) at 150 m, Alcobertas, Estremenho Karst Massif (39°25'46.8"N, 8°54'58.7"W) at 400 m, Cabanas de Torres, Montejunto (39°10'11.2"N, 9°04'14.1"W) at 420 m, and São Lourenço, Arrábida (38°28'59.3"N, 9°00'09.9"W) at 300 m (Fig. 1).

Figure 1. 

Distribution map. Sampling locations marked in coloured triangles: blue – Serra da Estrela, purple – Sicó, pink – Alcobertas, orange – Montejunto, yellow – Arrábida. The green zones represent the protected areas of Portugal.

Specimens were collected using pitfall traps modified to sample MSS habitats following the method of Eusébio et al. (2021), with only one collecting pitfall cup at a 50 cm depth. In each location five traps were installed, 10 m away from each other and 1 m away from the shrub edge, using pork liver as bait and propylene glycol as a preserving liquid. Samples were collected every three months for one year (March 2022 – March 2023).

Terrestrial isopod specimens were identified to species level based on morphological characters and the pertinent literature, under Wild M5 and M20 microscopes. Specimens were dissected and mounted in micro preparations using Hoyer’s liquid.

Specimens were drawn using a camera lucida, and photographed using a Leica DMC4500 camera, with a Leica Z6 APO microscope, and stacked with the Leica LAS X software. Background of specimens’ images was cleaned using Adobe Photoshop (Version 24.2.0).

Data analysis was done in R software version 4.4.2 (R Core Team 2024). Species abundance was visualized using the ggplot function (Wickham 2016). Non-metric multidimensional scaling (NMDS) was used to visualize the spatial and seasonal community patterns, using the Bray-Curtis dissimilarity in the vegan package (Oksanen et al. 2025), only considering stress values below 0.2, which indicate a good data representation of the two-dimensional ordination space (Clarke 1993).

Specimens are deposited in the National Museum of Natural History and Science (MNHNC), in the crustacean collection (MB11), University of Lisbon, Portugal, and in the Museo di Storia Naturale “La Specola” (MZUF), Florence, Italy.

Results

Taxonomy

Class Malacostraca Latreille, 1802

Order Isopoda Latreille, 1817

Suborder Oniscidea Latreille, 1802

Family Trichoniscidae Sars, 1899

Genus Trichoniscoides Sars, 1899

Trichoniscoides machadoi Vandel, 1946

Fig. 6A

Trichoniscoides machadoi Vandel, 1946: 168, figs 8–12; Vandel 1947: 270; Vandel 1948: 129, fig. 14;Vandel 1952: 262, figs 2, 9; Schmölzer 1965: 37, figs 79–82; Schmölzer 1971: 4, 75, 139, map 4; Schmalfuss 2003: 303; Reboleira et al. 2015: 6, fig. 2; Cifuentes 2019: 48; Cifuentes and Da Silva 2023: 7.

Material examined.

Portugal – Sicó • 2 ♂♂, 3 ♀♀; 39°58'51.8"N, 8°33'13.1"W; 19.XII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001283, 001285, 001287 • 1 ♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001379. – Arrábida • 1 ♂, 2 ♀♀; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001141 • 3 ♂♂; 22.III.2023; same data as for preceding; MNHNC:MB11:001313, 001323.

Distribution.

Endemic to Portugal. This species is widely distributed throughout the country.

Ecological notes.

This species can be found in caves, MSS, and endogean habitats.

Seasonal patterns in Portuguese MSS habitats.

This species was found in two locations, Sicó and Arrábida. In Sicó it was captured during fall and winter, with a higher abundance in fall (Fig. 7A). In Arrábida it was captured during spring and fall in equal abundances (Fig. 7A).

Family Philosciidae Kinahan, 1857

Genus Ctenoscia Verhoeff, 1928

Ctenoscia minima (Dollfus, 1892)

Fig. 6B

Philoscia minima Dollfus, 1892: 187, fig. 3.

Philoscia (Benthana) minima Jackson, 1926: 196, pl. VIII figs 152–165.

Ctenoscia minima Vandel, 1946: 196, figs 42–49; Schmölzer 1965: 141, fig. 605; Schmölzer 1971: 20; Schmalfuss 2003: 87; Reboleira et al. 2015: 40; Cifuentes and Da Silva 2023: 36.

Ctenoscia dorsalis; Gregory et al. 2012: 17.

Material examined.

Portugal – Sicó • 19 ♀♀; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001130, 001133, 001144, 001149, 001165 • 1 ♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001256. – Alcobertas • 1 ♂, 3 ♀♀; 39°25'46.5"N, 8°54'59.0"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001185, 001187, 001202 • 6 ♀♀; 20.IX.2022; same data as for preceding; MNHNC:MB11:001205, 001212, 001218 • 3 ♀♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001294, 001298 • 1 ♂, 2 ♀♀; 01.IV.2023; same data as for preceding; MNHNC:MB11:001357, 001360. – Montejunto • 2 ♂♂, 13 ♀♀; 39°10'11.4"N, 9°04'14.8"W; 22.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001181, 001192 • 2 ♂♂, 3 ♀♀; 21.IX.2022; same data as for preceding; MNHNC:MB11:001223, 001231 • 2 ♂♂; 21.XII.2022; same data as for preceding; MNHNC:MB11:001340 • 2 ♀♀; 21.III.2023; same data as for preceding; MNHNC:MB11:001385. – Arrábida • 17 ♀♀, 1 juv.; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001137, 001151, 001154, 001172, 001176 • 4 ♂♂, 10 ♀♀, 2 juvs; 20.IX.2022; same data as for preceding; MNHNC:MB11:001233, 001237, 001245 • 2 ♂♂, 11 ♀♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001306, 001314, 001324.

Distribution.

Portugal, Spain, Italy, France (Corsica), Malta, Tunisia, and Morocco.

Ecological notes.

This epigean species can also be found in caves and MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in four locations, Sicó, Alcobertas, Montejunto and Arrábida. In Sicó it was captured during spring and summer, with a higher abundance in spring (Fig. 7B). In Alcobertas it was captured during all seasons, with abundance increasing towards summer and then decreasing till winter (Fig. 7B). In Montejunto this species was also captured during all seasons, with abundance decreasing steadily towards fall and then staying the same in winter (Fig. 7B). In Arrábida it was captured during spring, summer, and fall, with a steady decrease in abundance from spring to fall (Fig. 7B).

Family Porcellionidae Brandt, 1831

Genus Porcellionides Miers, 1877

Porcellionides cingendus (Kinahan, 1857)

Fig. 6C

Porcellio cingendus Kinahan, 1857: 279, figs. 1, 2, 4, 6, 8, 9.

Porcellio (Porcellionides) lusitanorum Arcangeli, 1935a: 21, figs 13–18.

Metoponorthus (Lusitoniscus) cingendus Vandel, 1946: 274, figs 91–97; Schmölzer 1965: 195, figs 698–699; Schmölzer 1971: 33.

Porcellionides cingendus Schmalfuss, 2003: 240; Gregory et al. 2012: 18; Reboleira et al. 2015; Cifuentes and Da Silva 2024: 4, figs 1, 2A, 3A, 4A–D, 5, tab. 1.

Material examined.

Portugal – Sicó • 54 ♂♂, 58 ♀♀, 2 juvs; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001123, 001127, 001128, 001129, 001134, 001143, 001147, 001166 • 18 ♂♂, 38 ♀♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001255, 001257, 001258, 001259, 001262, 001263 • 32 ♂♂, 31 ♀♀; 19.XII.2022; same data as for preceding; MNHNC:MB11:001275, 001278, 001282, 001284, 001288 • 30 ♂♂, 6 ♀♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001372, 001374, 001376, 001381, 001383. – Alcobertas • 6 ♂♂, 21 ♀♀; 39°25'46.5"N, 8°54'59.0"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001188, 001197, 001199, 001201 • 13 ♂♂, 58 ♀♀; 20.IX.2022; same data as for precedings; MNHNC:MB11:001204, 001211, 001215, 001217 • 34 ♂♂, 46 ♀♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001293, 001297, 001299, 001303 • 56 ♂♂, 23 ♀♀; 01.IV.2023; same data as for preceding; MNHNC:MB11:001350, 001352, 001353, 001358. – Montejunto • 32 ♂♂, 44 ♀♀; 39°10'11.4"N, 9°04'14.8"W; 23.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001161, 001178, 001180, 001190 • 3 ♂♂, 33 ♀♀; 21.IX.2022; same data as for preceding; MNHNC:MB11:001220, 001222, 001226, 001230 • 55 ♂♂, 57 ♀♀, 2 juvs; 21.XII.2022; same data as for preceding; MNHNC:MB11:001329, 001338, 001339, 001346 • over 500 specimens (♂ and ♀); 21.III.2023; same data as for preceding; MNHNC:MB11:001387, 001393, 001397, 001400, 001403. – Arrábida • 11 ♂♂, 17 ♀♀, 3 juvs; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001136, 001142, 001155, 001171, 001175 • 18 ♂♂, 64 ♀♀, 46 juvs; 20.IX.2022; same data as for preceding; MNHNC:MB11:001234, 001236, 001242, 001246 • over 200 specimens (♂ and ♀); 20.XII.2022; same data as for preceding; MNHNC:MB11:001307, 001315, 001320, 001325, 001332 • 2 ♂♂, 2 ♀♀, 1 juv.; 22.III.2023; same data as for preceding; MNHNC:MB11:001363, 001368.

Distribution.

United Kingdom, France and Iberian Peninsula.

Ecological notes.

This epigean species can also occur in caves and MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in four locations, Sicó, Alcobertas, Montejunto and Arrábida. Specimens were found during all seasons in the four locations. In Sicó there was a steady decrease in abundance from spring to winter, in Alcobertas there was an increase from spring to winter, in Montejunto abundance decreased from spring to summer and then increased until winter (Fig. 7C). In Arrábida abundance increased steadily until fall and then decreased to exceptionally low numbers in winter (Fig. 7C).

Genus Porcellio Latreille, 1804

Porcellio scaber Latreille, 1804

Fig. 6D

Porcellio scaber Latreille, 1804: 45; Dollfus 1897: 206; Vandel 1946: 297; Gregory et al. 2012: 20, fig. 6.

Porcellio (Porcellio) scaber Arcangeli, 1935a: 9.

Porcellio (Euporcellio) scaber var. scabrior Verhoeff, 1907: 266.

Porcellio scaber scaber Schmölzer, 1971: 39.

Material examined.

Portugal – Serra de Estrela • 1 ♂, 1 ♀; 40°17'22.9"N, 7°35'19.7"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001167 • 1 ♂, 9 ♀♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001240, 001248, 001249 • 1 ♂, 1 ♀; 19.XII.2022; same data as for preceding; MNHNC:MB11:001269, 001273.

Distribution.

Widespread in Europe and introduced into many parts of the world.

Ecological notes.

This epigean species can also be found in MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in one location, Serra da Estrela, during spring, summer, and fall, and with abundance peaking in summer (Fig. 7D).

Porcellio dilatatus Brandt, 1831

Fig. 6E

Porcellio dilatatus Brandt in Brandt and Ratzeburg 1831: 78, Pl. 12, fig. 6c, d; Vandel 1946: 316, fig. 135; Schmölzer 1971: 44.

Porcellio (Porcellio) dilatatus Arcangeli, 1935a: 12.

Porcellio dilatatus dilatatus; Reboleira et al. 2015: 46.

Material examined.

Portugal – Sicó • 1 ♀; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001122 • 1 ♂; 19.XII.2022; same data as for preceding; MNHNC:MB11:001274 • 1 ♂, 3 ♀♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001371, 001382. – Montejunto • 1 ♂; 39°10'11.4"N, 9°04'14.8"W; 21.III.2023; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001389. – Arrábida • 22 ♂♂, 41 ♀♀, 182 juvs; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001135, 001138, 001140, 001150, 001152, 001158, 001169, 001170, 001173, 001174 • 2 ♂♂, 12 ♀♀, 20 juvs; 20.IX.2022; same data as for preceding; MNHNC:MB11:001235, 001238, 001243, 001247 • 28 ♂♂, 23 ♀♀, 32 juvs; 20.XII.2022; same data as for preceding; MNHNC:MB11:001304, 001308, 001310, 001316, 001317, 001319, 001322, 001326, 001330, 001333 • 16 ♂♂, 13 ♀♀; 22.III.2023; same data as for preceding; MNHNC:MB11:001361, 001364, 001365, 001366.

Distribution.

Common across Europe and introduced into many parts of the world.

Ecological notes.

This species is mainly found in caves and MSS habitats but does not show any adaptation to subterranean habitats.

Seasonal patterns in Portuguese MSS habitats.

This species was found in three locations, Sicó, Montejunto and Arrábida. In Sicó and Montejunto it was found in very low numbers (Fig. 7E). In Arrábida it was captured during all seasons, with abundance decreasing from spring to summer, then increasing slightly in fall and decreasing again in winter (Fig. 7E).

Porcellio dispar Verhoeff, 1901

Fig. 6F

Porcellio dispar Verhoeff, 1901: 407; Vandel 1946: 289, figs 110–111; Schmölzer 1965: 228; Schmölzer 1971: 36; Schmalfuss, 2003: 222; Cifuentes and Da Silva 2023: 36.

Porcellio (Euporcellio) dispar Verhoeff, 1907: 269.

Porcellionides dimorphus Jackson, 1926: 186, pl. I figs 1–22.

Porcellio (Porcellio) dispar Arcangeli, 1935a: 10, figs 3–7.

Material examined.

Portugal – Sicó • 6 ♀♀; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001131, 001145, 001164 • 1 ♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001264 • 2 ♀♀; 19.XII.2022; same data as for preceding; MNHNC:MB11:001277 • 3 ♀♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001373. – Montejunto • 2 ♂♂, 4 ♀♀; 39°10'11.4"N, 9°04'14.8"W; 23.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001160, 001179 • 1 ♀; 21.XII.2022; same data as for preceding; MNHNC:MB11:001343 • 3 ♂♂, 23 ♀♀; 21.III.2023; same data as for preceding; MNHNC:MB11:001386, 001394.

Distribution.

Portugal, NW Spain, and France.

Ecological notes.

This epigean species can also be found in caves and MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in two locations, Sicó and Montejunto. In Sicó it was captured in all seasons, with abundance decreasing from spring to summer, then increasing slightly until winter (Fig. 7F). In Montejunto it was captured during spring, fall and winter, with abundance decreasing from spring to fall and increasing to its highest in winter (Fig. 7F).

Porcellio novus Arcangeli, 1935

Fig. 6G

Porcellio (Porcellio) novus Arcangeli, 1935b: 40, figs 1–6.

Porcellio novus Vandel, 1946: 322; Schmölzer 1955: 314; Schmölzer 1965: 230, fig. 835; Schmölzer 1971: 38; Schmalfuss, 2003: 231.

Material examined.

Portugal – Alcobertas • 2 ♂♂, 3 ♀♀; 39°25'46.5"N, 8°54'59.0"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001196 • 6 ♂♂, 10 ♀♀, 1juv.; 20.IX.2022; same data as for preceding; MNHNC:MB11:001208, 001210, 001214, 001219 • 1 ♂, 3 ♀♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001290, 001292 • 2 ♀♀; 1.IV.2023; same data as for preceding; MNHNC:MB11:001355.

Distribution.

Portugal and western Spain.

Ecological notes.

This epigean species can also be found in MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in one location, Alcobertas, during all seasons, with abundance increasing from spring to summer, then decreasing steadily towards winter (Fig. 7G).

Family Armadillidiidae Brandt, 1833

Genus Eluma Budde-Lund, 1885

Eluma caelata (Miers, 1877)

Fig. 6H

Armadillidium caelatum Miers, 1877: 665, pl. 7 fig. 3.

Rhacodes inscriptus Eaton, 1882: 360 (not Rhacodes inscriptus C.L. Koch in Rosenhauer 1856: 422).

Eluma purpurascens Budde-Lund, 1885: 48, 294; Preudhomme de Borre 1886: 112; Dollfus 1889a: 126; Dollfus 1889b: 306; Dollfus 1896a: 357; Norman 1899: 69; Verhoeff 1908: 370; Vandel 1946: 357, fig. 158.

Eluma caelatum Arcangeli, 1935a: 3; Arcangeli 1948: 242; Schmölzer 1965: 303, fig. 1213; Schmölzer 1971: 58; Schmalfuss 2003: 107.

Eluma caelata Gregory et al., 2012: 21, tab. 2, 3; Reboleira et al. 2015: 47; Recuero et al. 2022: 1315, tab. 1; Cifuentes and Da Silva 2023: 29, figs 1A, 2A-C, 4G.

Material examined.

Portugal – Serra de Estrela • 1 ♀; 40°17'22.9"N, 7°35'19.7"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001121 • 1 ♂, 1 ♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001250 • 5 ♂♂, 7 ♀♀; 19.XII.2022; same data as for preceding; MNHNC:MB11:001268, 001270, 001271, 001272 • 4 ♂♂, 5 ♀♀; 19.XII.2022; same data as for preceding; MZUF 10034 • 1 ♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001347. – Sicó • 3 ♀♀; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001126, 001148, 001163 • 2 ♂♂, 3 ♀♀; 19.IX.2022; same data as for preceding; MNHNC:MB11:001251, 001254, 001265, 001267 • 1 ♀; 19.XII.2022; same data as for preceding; MNHNC:MB11:001280 • 3 ♀♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001369, 001380. – Alcobertas • 34 ♂♂, 27 ♀♀; 39°25'46.5"N, 8°54'59.0"W; 1.IV.2023; leg. R.P. EusébioEusébio, R.P. leg; MSS pitfall trap; MNHNC:MB11:001349, 001359. – Montejunto • 14 ♂♂, 9 ♀♀; 39°10'11.4"N, 9°04'14.8"W; 23.VII.2022; ; MSS pitfall trap; MNHNC:MB11:001159, 001182, 001183, 001193 • 1 ♂, 11 ♀♀; 21.IX.2022; same data as for preceding; MNHNC:MB11:001221, 001224, 001228 • 11 ♂♂, 4 ♀♀; 21.XII.2022; same data as for preceding; MNHNC:MB11:001327, 001336, 001342, 001345 • 38 ♂♂, 26 ♀♀, 1 juv.; 21.III.2023; same data as for preceding; MNHNC:MB11:001388, 001391, 001395, 001398, 001401. – Arrábida • 8 ♂♂, 9 ♀♀; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001157 • 1 ♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001311 • 1 ♂, 2 ♀♀; 22.III.2023; same data as for preceding; MNHNC:MB11:001367.

Distribution.

United Kingdom, France, Iberian Peninsula, The Netherlands, Belgium, Morocco, and Western Sahara. It was introduced to Australia (Tasmania) and French Guiana.

Ecological notes.

This epigean species can also be found in caves and MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was found in all locations. In Serra da Estrela, Sicó and Montejunto it was captured during all seasons. In Serra da Estrela abundance increases towards fall then decreases in winter (Fig. 7H). In Sicó abundance increases toward summer, decreases in fall and increases again in winter (Fig. 7H). In Montejunto abundance decreases in summer then increases steadily towards winter (Fig. 7H). In Alcobertas it was captured only in winter (Fig. 7H). In Arrábida it was captured during spring, fall and winter, with abundance decreasing from its peak in spring towards fall, then increasing slightly in winter (Fig. 7H).

Eluma tuberculata Cruz, 1991

Fig. 6I

Eluma tuberculata Cruz, 1991: 73, fig. 1a–f; Schmalfuss 2003:107; Reboleira et al. 2015: 49, figs 30, 31 (nec specimens from MSS near Gruta de Alcobertas, Estremenho Massif); Cifuentes and Da Silva 2023: 33, figs 1C, 2D-F, 4H.

Material examined.

Portugal – Sicó • 68 ♂♂, 114 ♀♀; 39°58'51.8"N, 8°33'13.1"W; 20.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001124, 001125, 001132, 001146, 001162 • 5 ♂♂, 5 ♀♀; 20.VII.2022; same data as for preceding; MZUF 10035 • 39 ♂♂, 93 ♀♀, 13 juvs; 19.IX.2022; same data as for preceding; MNHNC:MB11:001252, 001253, 001260, 001261, 001266 • 10 ♂♂, 10 ♀♀; 19.IX.2022; same data as for preceding; MZUF 10036 • 27 ♂♂, 78 ♀♀, 14 juvs; 19.XII.2022; same data as for preceding; MNHNC:MB11:001276, 001279, 001281, 001286, 001289 • 23 ♂♂, 35 ♀♀; 20.III.2023; same data as for preceding; MNHNC:MB11:001370, 001375, 001377, 001378, 001384.

Distribution.

Endemic to Portugal.

Ecological notes.

This species can be found in caves and MSS habitats.

Seasonal patterns in Portuguese MSS habitats.

This species was only found in Sicó, during all seasons, and with a decrease in abundance from spring to winter (Fig. 7I).

Eluma matae Cifuentes and Da Silva, 2023

Fig. 6J

Eluma matae Cifuentes & Da Silva, 2023: 33, figs 1B, 3, 4A-F, I, K-Q.

Material examined.

Portugal – Montejunto • 6 ♂♂, 10 ♀♀; 39°10'11.4"N, 9°04'14.8"W; 22.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001177, 001184, 001194) • 10 ♀♀, 6 juvs; 21.IX.2022; same data as for preceding; MNHNC:MB11:001225, 001227, 001229 • 9 ♂♂, 13 ♀♀; 21.XII.2022; same data as for preceding; MNHNC:MB11:001328, 001335, 001337, 001344 • 5 ♂♂, 5 ♀♀; 21.XII.2022; same data as for preceding; MZUF 10037 • 30 ♂♂, 44 ♀♀, 1 juv.; 21.III.2023; same data as for preceding; MNHNC:MB11:001390, 001392, 001396, 001399, 001402.

Distribution.

Endemic to Portugal.

Ecological notes.

This epigean species can also be found in MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was only found in Montejunto, during all seasons, and with an increase in abundance from spring to winter (Fig. 7J).

Eluma cristata sp. nov.

https://zoobank.org/A53CD3DA-349D-4F64-BA23-DA0FD35C00D3
Figs 2, 3, 4, 5, 6K

Eluma tuberculata Reboleira et al., 2015: 49 (partim: specimens from MSS near Gruta de Alcobertas, Estremenho Karst Massif).

Type material.

Holotype. Portugal • ♂; Alcobertas; 39°25'46.5"N, 8°54'59.0"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001198. Paratypes: Portugal • 137 ♂♂, 138 ♀♀; same data as holotype; MNHNC:MB11:001186, 001189, 001195, 001198, 001200 • 115 ♂♂, 121 ♀♀; 20.IX.2022; same data as for preceding; MNHNC:MB11:001203, 001207, 001209, 001213, 001216 • 5 ♂♂, 10 ♀♀; same data as for preceding; MZUF 10038 • 280 ♂♂, 240 ♀♀; 20.XII.2022; same data as for preceding; MNHNC:MB11:001291, 001295, 001296, 001301, 001302 • 10 ♂♂, 10 ♀♀; same data as for preceding; MZUF 10039 • 68 ♂♂, 103 ♀♀; 1.IV.2023; same data as for preceding; MNHNC:MB11:001348, 001351, 001354, 001356.

Description.

Maximum length: ♂ 7.5 mm; ♀ 9.5 mm. Body strongly convex, able to roll up into perfect ball, euspheric type. Colour light brown, as in E. matae and E. tuberculata. Dorsal surface with ornamentation consisting of protruding crests on posterior margins of cephalon, pereonites 1–7 tergites and median part of pleonites 1–5, each crest ending in lobes of irregular shape and number; telson with two small paramedian tubercles (Figs 2A–E, 3A, G, H, 6K). Dorsum with scattered pointed scale-setae (Fig. 3B) and one line of noduli laterales per side located near top of crests on pereonites 1–7 far from lateral margins (Fig. 3G). Cephalon (Figs 2A–D, 3A, 6K) with triangular scutellum distinctly separated from and not bent over vertex; distinct frontal line and no postscutellar line; oblique antennary lobes, quadrangular and directed frontwards. Eye consisting of single large ocellus as in Fig. 2A,C. Pereonite 1 (Figs 2A, C, 3C, D, 6K) with deep dorsal groove on lateral margin, schisma on posterior corners with rounded inner lobe distinctly shorter than outer lobe; posterior margin slightly concave at sides. Pereonites 2 and 3 (Fig. 3E, F) epimera quadrangular with small and rounded lobe on ventral side. Pereonites 4–7 with quadrangular epimera and straight posterior margins. Pleonites 3–5 (Fig. 3G) with rectangular epimera, slightly divergent. Telson (Fig. 3G, H) triangular, wider than long, with slightly concave sides and rounded apex. Antennula (Fig. 3I) of three articles, second article much shorter than first and third, third article with tuft of superimposed aesthetascs subapically. Antenna (Fig. 4A) with flagellum slightly shorter than fifth article of peduncle, second flagellar article more than twice as long as first, bearing two aesthetascs on middle part. Mandibles (Fig. 4B, C) with dichotomized molar penicil and three or four free penicils; right mandible with one penicil and left mandible with two penicils on hairy lobe. Maxillula (Fig. 4D) outer lobe with 4 +6 (5 cleft) teeth; inner lobe with two thick subapical penicils and small triangular distal point. Maxilla (Fig. 4E) apically setose with outer lobe rounded, much wider than inner lobe. Maxilliped (Fig. 4F) with quadrangular endite bearing two triangular spines on distal margin and large subapical seta; basal article of palp with two large setae. Uropod (Fig. 4G) flattened; exopod about twice as wide as long with slightly concave distal margin; endopod slightly protruding backwards compared with exopod.

Figure 2. 

Eluma cristata sp. nov. Paratype ♂ from Alcobertas A adult specimen in lateral view B dorsal view C side view of the cephalon and pereonites 1–4 D frontal view of cephalon E dorsal view of posterior pereonites, pleon, telson and uropods.

Figure 3. 

Eluma cristata sp. nov. Paratype ♂ from Alcobertas A cephalon, frontal B dorsal scale-seta C epimeron of pereonite 1, dorsal D epimeron of pereonite 1, ventral E epimeron of pereonite 2, ventral F epimeron of pereonite 3, ventral G pereonite 7, pleon, telson and uropods. n.l. = nodulus lateralis H telson and uropods I Antennula.

Figure 4. 

Eluma cristata sp. nov. Paratype ♂ from Alcobertas A antenna B right mandible C left mandible D maxillula E maxilla F maxilliped G uropod.

Figure 5. 

Eluma cristata sp. nov. Paratype ♂ from Alcobertas A pereopod 1 B pereopod 7 C genital papilla and pleopod 1 D pleopod 2 E pleopod 3 exopod F pleopod 4 exopod G pleopod 5 exopod.

Figure 6. 

Specimen habitus A Trichoniscoides machadoi from Sicó B Ctenoscia minima from Montejunto C Porcellionides cingendus from Sicó D Porcellio scaber from Serra da Estrela E Porcellio dilatatus from Arrábida F Porcellio dispar from Sicó G Porcellio novus from Alcobertas H Eluma caelata from Montejunto I Eluma tuberculata from Sicó J Eluma matae from Montejunto K Eluma cristata sp. nov. from Alcobertas L Armadillo officinalis from Arrábida.

Male. Pereopod 1–3 (Fig. 5A) with line of pointed setae on sternal margins of carpus and, to lesser extent, merus. Pereopod 7 (Fig. 5B) ischium with sternal margin distinctly concave, distal margin with rounded lobe and four stout setae; merus with sternal margin slightly convex; merus and carpus with line of long setae on sternal margin. Genital papilla (Fig. 5C) fusiform. Pleopod 1 (Fig. 5C) exopod with large distal lobe bent outwards and apically rounded; endopod with distal part quadrangular and short apical lobe directed outwards. Pleopod 2 (Fig. 5D) exopod triangular with a line of about five short setae on outer margin; endopod slightly longer than exopod. Pleopods 3–5 exopods as in Fig. 5E–G.

Etymology.

From Latin cristatus = crested. The name refers to the high crests on the posterior margins of the body segments.

Remarks.

At present, the genus Eluma comprises only five species, i.e., the four species included here and E. praticola Taiti & Rossano, 2015 from northern Morocco (see Schmalfuss 2003; Taiti and Rossano 2015; Cifuentes and Da Silva 2023). Eluma cristata sp. nov. is readily distinct from all the other species by the protruding dorsal crests on the posterior margins of the cephalon, pereonites and, to a lesser extent, pleonites. Moreover, it differs from E. caelata in lacking the basal triangular lobe on the male pereopod 7 merus (see fig. 32F,G in Taiti and Rossano 2015); from this species and E. praticola also in the male pleopod 1 endopod with thickset distal part, not bent outwards; from E. matae also in the much shorter dorsal scale-setae of different shape (see fig. 4A–F in Cifuentes and Da Silva 2023).

Ecological notes.

This species was only found in this MSS habitat.

Seasonal patterns in Portuguese MSS habitats.

This species was only found in Alcobertas, during all seasons, and with a decrease in abundance from spring to summer, highest abundance during fall and a new decrease in winter (Fig. 7K).

Figure 7. 

Total abundance per season for each of the species. Each colour represents one sampling location: blue – Serra da Estrela, purple – Sicó, pink – Alcobertas, orange – Montejunto, yellow – Arrábida A Trichoniscoides machadoi B Ctenoscia minima C Porcellionides cingendus D Porcellio scaber E Porcellio dilatatus F Porcellio dispar G Porcellio novus H Eluma caelata I Eluma tuberculata J Eluma matae K Eluma cristata sp. nov. L Armadillo officinalis.

Family Armadillidae Brandt, 1831

Genus Armadillo Latreille, 1802

Armadillo officinalis Duméril, 1816

Fig. 6L

Armadillo officinalis Duméril, 1816: 117; Budde-Lund 1885: 16; Preudhomme de Borre 1886: 112; Dollfus 1896a: 357; Dollfus 1896b: 527; Arcangeli 1935a: 2; Vandel 1946: 371.

Cubaris globator; Eaton 1882: 361.

Cubaris officinalis; Jackson 1926: 184.

Material examined.

Portugal – Arrábida • 28 ♂♂, 63 ♀♀; 38°28'59.2"N, 9°00'09.9"W; 21.VII.2022; leg. R.P. Eusébio; MSS pitfall trap; MNHNC:MB11:001139, 001153, 001156, 001168 • over 1000 individuals (♂ and ♀); 20.IX.2022; same data as for preceding; MNHNC:MB11:001232, 001239, 001241, 001244 • 84 ♂♂, 140 ♀♀, 2 juvs; 20.XII.2022; same data as for preceding; MNHNC:MB11:001305, 001309, 001312, 001318, 001321, 001331, 001334 • 1 ♀; 22.III.2023; same data as for preceding; MNHNC:MB11:001362.

Distribution.

Widely distributed in the Mediterranean and Black Sea area.

Ecological notes.

This epigean species can also be found in MSS.

Seasonal patterns in Portuguese MSS habitats.

This species was only found in Arrábida, during all seasons, and abundance increasing from spring to summer where it reaches its peak, then decreasing in fall (Fig. 7L).

Ecological analysis

Terrestrial isopod communities differ across locations and seasons (Fig. 8). All species were found in either three or four of the sampled seasons (Fig. 7). The spatial distribution plot (Fig. 8A) shows that these communities are relatively different from each other among the five sampled locations. Serra da Estrela shows a distinctly different isopod community composition compared with other locations, largely driven by the strong influence of Porcellio scaber (Fig. 8A). Alcobertas also has a distinct community composition, characterized primarily by Eluma cristata and Porcellio novus (Fig. 8A). In contrast, the other three locations (Sicó, Arrábida, and Montejunto) show a greater overlap in species composition, suggesting more similar isopod communities (Fig. 8A).

Figure 8. 

NMDS (Non-metric multidimensional scaling) of terrestrial isopod communities A species found in each of the five locations, with each point representing a species and each arrow representing a location B–F location specific seasonal NMDS B Serra da Estrela C Sicó D Alcobertas E Montejunto F Arrábida. In these panels each point represents one invertebrate trap (five traps per season), ellipses group the points by season, and the arrows represent the species.

The seasonal site-specific plots reveal varying degrees of variation in isopod communities (Figs 8B–F). In Serra da Estrela (Fig. 8B), isopod communities are composed only by two species with no clear seasonal pattern. In Sicó (Fig. 8C), Alcobertas (Fig. 8D) and Montejunto (Fig. 8E) the seasonal ellipses overlap almost completely, indicating similar isopod communities throughout the year in each location. In Arrábida (Fig. 8F) there is some demarked seasonal variation, with Armadillo officinalis and Porcellionides cingendus influencing summer and fall, and the other four species influencing spring.

Discussion

We found 12 species of terrestrial isopods in Portuguese MSS habitats, belonging to five families, three more species and two more families than those recorded in a similar study done in Spain (Cifuentes et al. 2021). The most well represented family is Porcellionidae with five species, followed by Armadillidiidae with four, and the remaining families are only represented by one species each. This study revealed a new species, Eluma cristata sp. nov., found exclusively in the MSS of Alcobertas.

The diversity of terrestrial isopods found in MSS habitats of Portugal includes both surface-dwelling species, such as Ctenoscia minima, Porcellionides cingendus, Porcellio scaber, P. dispar, P. novus, Eluma caelata, E. matae, and Armadillo officinalis, and species more frequently found in the surface-cave ecotone, such as Trichoniscoides machadoi, Eluma tuberculata and Porcellio dilatatus (Vandel 1946; Reboleira et al. 2015). This emphasises the connectivity between surface and subterranean habitats and reflects the broad ecological tolerance of terrestrial isopods and their preference for cryptic and dark environments (Hornung 2011; Dixie et al. 2015). On the other hand, the discovery of Eluma cristata sp. nov., highlights the relevance of shallow subterranean habitats as habitats for short range distributed species and high conservation value.

The spatial and seasonal distribution of terrestrial isopod species found in Portuguese MSS habitats displayed distinct patterns in abundance throughout the year. Widespread species such as Ctenoscia minima and Porcellionides cingendus were found in multiple locations and throughout all seasons, while Eluma cristata sp. nov. and Porcellio novus were restricted to single MSS sites. The use of MSS habitats by terrestrial isopod species differs depending on the location and species. Despite several species showing strong seasonal abundance patterns, seasonality does not seem to influence community composition in the majority of the studied locations.

Given the observed high diversity and ecological specialization, conservation of MSS habitats and their isopod communities is critical, not only in Portugal but worldwide. Despite being legally protected (ICNB 2000) and facing increasing threats (Mammola et al. 2019; Reboleira et al. 2022), MSS habitats and their fauna remain largely overlooked in biodiversity assessments. Therefore, their study and protection are essential to safeguard the unique invertebrate diversity they harbour.

Acknowledgments

This work was supported by the Portuguese National Funds through “Fundação para a Ciência e a Tecnologia” within the CE3C Unit funding (ref. UIDB/00329/2025), CHANGE (ref. LA/P/0121/2020) (https://doi.org/10.54499/LA/P/0121/2020) and PhD grant (ref. 2021.04868.BD) (https://doi.org/10.54499/2021.04868.BD), and by the Chair in Sustainability of Subterranean Ecosystems – Loulé, at the Faculty of Sciences of the University of Lisbon.

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