One-spotted waterlouse Proasellus meridianus, copyright Keith Lugg.

Belongs within: Asellota.
Contains: Asellus (Asellus).

The Asellidae are a group of freshwater crustacean of the Holarctic region (Henry et al. 1986).

Proasellus: life under water
Published 16 December 2013
Proasellus slavus, photographed by K. Grabow.

The animal in the picture above is not quite the animal that I was planning on telling you about today, but I couldn’t find an image of my particular target species. As long-time readers of this page will know, once a week I pick some random taxon to look at, and for this week I picked out the freshwater isopod Proasellus vignai. Most of you will know isopods as the woodlice that you may find in your garden, but the woodlice are really only one small part of the broad range of mostly aquatic isopod diversity. Proasellus belongs to a group of isopods known as the Asellota; as you can see in the picture above, asellotes differ from woodlice in (amongst other things) having the dorsal shields of each segment less tightly pressed together.

Proasellus is a genus of freshwater asellotes found around the Mediterranean: Europe, western Asia, northern Africa. Proasellus vignai is one of a number of species of Proasellus that are found in subterranean habitats, like P. slavus shown above. Both P. slavus and P. vignai, like most other subterranean animals, have lost the pigment and eyes of their surface-dwelling relatives. However, not all subterranean habitats are equal, and not all subterranean animals live in ‘caves’ as you might usually imagine them. Some Proasellus species are indeed found living in caves, but P. vignai and P. slavus are inhabitants of the hyporheic zone, the ground around rivers and streams where the water from the river soaks into the surrounding groundwater. Cave-dwelling Proasellus species tend to be broader and have more elongate limbs, so that they can maximise their chances of finding food in the nutritionally sparse cave waters. Hyporheic species, on the other hand, are narrower and more elongate, making them better suited for squeezing through the gaps between sediment particles.

Proasellus vignai seems to be a little known species (hence the lack of an available illustration). It is only known from the hyporheic zone of the Melfa river, in the Appenine mountains of the Lazio region of Italy (Bodon & Argano 1982). The Melfa is not a long river, only about 40 km long, so P. vignai may be a very localised species. It is a close relative of P. slavus, which lives in the water catchment of the Danube River. Other related species include P. ligusticus in the Ligurian Alps, P. sketi in Greece and P. boui in Languedoc in southern France. The scattered nature of the species of the P. slavus group, all of them hyporheic, suggests a certain degree of relictualism. Like other habitats that represent the edge of things, the hyporheic environment can be an uncertain one, vulnerable to outside influences. Should something change the nature of the Melfa river, Proasellus vignai might be taken with it.

Systematics of Asellidae

Characters (from Henry et al. 1986): Antenna bearing a squama; maxillipedal oostegite reduced to a “Wasserstrudelapparat” (water swirling apparatus); pleonites 1 and 2 reduced both in length and width, forming a stalk between pereion and pleotelson; male copulatory organ (endopodite of pleopods 2) secondarily uniarticulate, but complex.

    |--Gallasellus Henry & Magniez 1977HLM86
    |    `--G. heilyi (Legrand 1956)HLM86
    |--Stygasellus Chappuis 1943HLM86
    |    `--S. phreaticus (Chappuis 1943) [=Stygonectes phreaticus]HLM86
    |--Uenasellus Matsumoto 1962HLM86
    |    `--U. iyoensis (Matsumoto 1960)HLM86
    |--Salmasellus Bowman 1975HLM86
    |    `--S. steganothrix Bowman 1975HLM86
    |--Psammasellus Braga 1968HLM86
    |    `--P. capitatus Braga 1968HLM86
    |--Calasellus Bowman 1981HLM86
    |    |--C. californicus (Miller 1933)HLM86
    |    `--C. longus Bowman 1981HLM86
    |--Lirceolus Bowman & Longley 1976HLM86
    |    |--L. pilus (Steeves 1968)HLM86
    |    `--L. smithii (Ulrich 1902)HLM86
    |--Lirceus Rafinesque 1820HLM86
    |    |--L. culveri Holsinger & Bowman 1973HLM86
    |    |--L. fontinalisHLM86
    |    `--L. usdagalum Estes & Holsinger 1976HLM86
    |--Nipponasellus Matsumoto 1962HLM86
    |    |--N. aioii (Chappuis 1955)HLM86
    |    |--N. hubrichti (Matsumoto 1956)HLM86
    |    |--N. kagaensis (Msatsumoto 1958)HLM86
    |    |--N. takefuensis (Matsumoto 1961)HLM86
    |    `--N. tonensis (Matsumoto 1961)HLM86
    |--Bragasellus Henry & Magniez 1968HLM86
    |    |--B. aireyi Henry & Magniez 1980HLM86
    |    |--B. boui Henry & Magniez 1974HLM86
    |    |--B. comasi Henry & Magniez 1976HLM86
    |    |--B. comasioides Magniez & Brehier 2004F05
    |    |--B. conimbricensis (Braga 1946)HLM86
    |    |--B. escolai Henry & Magniez 1978HLM86
    |    |--B. frontellum (Braga 1964)HLM86
    |    |--B. incurvatus Afonso 1984HLM86
    |    |--B. lagari Henry & Magniez 1973HLM86
    |    |--B. pauloae (Braga 1958)HLM86
    |    `--B. seabrai (Braga 1943)HLM86
    |--Synasellus Braga 1944HLM86
    |    |--S. albicastrensis Braga 1960HLM86
    |    |--S. barcelensis Noodt & Galhano 1969HLM86
    |    |--S. brigantinus Braga 1959HLM86
    |    |--S. exiguus Braga 1944HLM86
    |    |--S. fragilis Braga 1946HLM86
    |    |--S. insignis Afonso 1984HLM86
    |    |--S. lafonensis Braga 1959HLM86
    |    |--S. longicauda Braga 1959HLM86
    |    |--S. mariae (Braga 1942)HLM86
    |    |    |--S. m. mariaeHLM86
    |    |    `--S. m. favaiensis Eiras 1974HLM86
    |    |--S. mateusi Braga 1954HLM86
    |    |--S. meirelesi Braga 1959HLM86
    |    |--S. minutus Braga 1967HLM86
    |    |--S. nobrei Braga 1967HLM86
    |    |--S. pireslimai Braga 1959HLM86
    |    |--S. serranus Braga 1967HLM86
    |    `--S. transmontanus Braga 1959HLM86
    |--Asellus Geoffroy 1762HLM86
    |    |  i. s.: A. cavaticusT30
    |    |         A. meridianusN29
    |    |         A. nipponensis Nicholls 1929N29
    |    |         A. variegatus Risso 1826R26
    |    |         A. vulgarisG20
    |    |--A. (Asellus)HLM86
    |    |--A. (Baikaloasellus Stammer 1932)B50
    |    |    |--A. (B.) angarensisB50
    |    |    |--A. (B.) baikalensisB50
    |    |    |--A. (B.) korotnewiiB50
    |    |    `--A. (B.) minutusB50
    |    |--A. (Conasellus) communisH47
    |    |--A. (Mesoasellus Birstein 1939)HLM86
    |    |    |--A. (M.) dentifer Birstein & Levanidov 1952HLM86
    |    |    |--A. (M.) dybowskiiB50
    |    |    `--A. (M.) strinatii Chappuis 1955HLM86
    |    `--A. (Phreatosellus Matsumoto 1962)HLM86
    |         |--A. (P.) akiyoshiensis (Ueno 1927)HLM86
    |         |--A. (P.) higoensis Matsumoto 1960HLM86
    |         |--A. (P.) iriei Matsumoto 1978HLM86
    |         |--A. (P.) kawamurai (Tattersall 1921)HLM86
    |         |--A. (P.) minatoi Matsumoto 1978HLM86
    |         |--A. (P.) miurai Chappuis 1955HLM86
    |         |--A. (P.) uenoi Matsumoto 1978HLM86
    |         `--A. (P.) yoshinoensis Matsumoto 1960HLM86
    |--Caecidotea Packard 1871HLM86
    |    |--C. acuticarpa Mackin & Hubricht 1940HLM86
    |    |--C. adenta Mackin & Hubricht 1940HLM86
    |    |--C. alabamensis Stafford 1911HLM86
    |    |--C. ancyla (Fleming 1972)HLM86
    |    |--C. antricola (Creaser 1931)HLM86
    |    |--C. barri (Steeves 1965)HLM86
    |    |--C. beattyi Lewis & Bowman 1981HLM86
    |    |--C. bicrenata (Steeves 1963)HLM86
    |    |    |--C. b. bicrenataHLM86
    |    |    `--C. b. whitei Lewis & Bowman 1981HLM86
    |    |--C. bisetus (Steeves 1968)HLM86
    |    |--C. bowmani Lewis 1980HLM86
    |    |--C. brevicaudaHLM86
    |    |--C. cannula (Steeves 1963)HLM86
    |    |--C. carolinensis Lewis & Bowman 1977HLM86
    |    |--C. catachaetus (Fleming & Steeves 1972)HLM86
    |    |--C. chiapas Bowman 1975HLM86
    |    |--C. circulus (Steeves 1968)HLM86
    |    |--C. cyrtorhynchus (Fleming & Steeves 1972)HLM86
    |    |--C. dentadactylaHLM86
    |    |--C. dimorpha Mackin & Hubricht 1940HLM86
    |    |--C. extensolingualus (Fleming 1972)HLM86
    |    |--C. filicispeluncae Bowman & Hobbs 1983HLM86
    |    |--C. franzi Lewis 1981HLM86
    |    |--C. fustis Lewis 1981HLM86
    |    |--C. henroti (Bresson 1955)HLM86
    |    |--C. hobbsi Maloney 1939HLM86
    |    |--C. holsingeri (Steeves 1963)HLM86
    |    |--C. incurva (Steeves 1968)HLM86
    |    |--C. jordani (Eberly 1965)HLM86
    |    |--C. kendeighi (Steeves & Seidenbergh 1971)HLM86
    |    |--C. lesliei Lewis & Bowman 1981HLM86
    |    |--C. macropropoda Chase & Blair 1937 [incl. C. ozarkana Chase & Blair 1937]HLM86
    |    |--C. metcalfi (Fleming 1972)HLM86
    |    |--C. mitchelli Argano 1972HLM86
    |    |--C. nickajackensis Packard 1881HLM86
    |    |--C. nortoni (Steeves 1966)HLM86
    |    |--C. oculata Mackin & Hubricht 1940HLM86
    |    |--C. packardi Mackin & Hubricht 1940HLM86
    |    |--C. parva (Steeves 1964)HLM86
    |    |--C. pasquinii Argano 1972HLM86
    |    |--C. paurotrigonus (Fleming 1972)HLM86
    |    |--C. pricei Levi 1949HLM86
    |    |--C. recurvata (Steeves 1963)HLM86
    |    |--C. reddelli (Steeves 1968)HLM86
    |    |--C. richardsonae Hay 1901HLM86
    |    |--C. rotunda Bowman & Lewis 1984HLM86
    |    |--C. salemensis Lewis 1981HLM86
    |    |--C. scrupulosaHLM86
    |    |--C. scyphus (Steeves 1968)HLM86
    |    |--C. sequoiae Bowman 1975HLM86
    |    |--C. serrata (Fleming 1972)HLM86
    |    |--C. simonini (Bresson 1955)HLM86
    |    |--C. sinuncus (Steeves 1965)HLM86
    |    |--C. spatulata Mackin & Hubricht 1940HLM86
    |    |--C. steevesi (Fleming 1972)HLM86
    |    |--C. stiladactyla Mackin & Hubricht 1940HLM86
    |    |--C. stygia Packard 1871HLM86
    |    |--C. teresae Lewis 1982HLM86
    |    |--C. tridentata Hungerford 1922HLM86
    |    |--C. vandeli (Bresson 1955)HLM86
    |    |--C. vomeroi Argano 1972HLM86
    |    `--C. zullinii Argano 1972HLM86
    `--Proasellus Dudich 1925HLM86
         |--P. acutianus Argano & Henry 1972HLM86
         |--P. adriaticus Argano & Pesce 1979HLM86
         |--P. albigensis (Magniez 1965)HLM86
         |--P. ambracicus Pesce & Argano 1980HLM86
         |--P. amiterninus Argano & Pesce 1979HLM86
         |--P. anophtalmus (Karaman 1934)HLM86
         |    |--P. a. anophtalmusHLM86
         |    |--P. a. bosnicus (Sket 1965)HLM86
         |    |--P. a. dalmatinus (Karaman 1955)HLM86
         |    |--P. a. longisetus (Remy 1941)HLM86
         |    |--P. a. radikanus (Karaman 1955)HLM86
         |    |--P. a. rhausinus (Remy 1941)HLM86
         |    `--P. a. serbicus (Karaman 1955)HLM86
         |--P. aquaecalidae (Racovitza 1922)HLM86
         |--P. arnautoviciHLM86
         |    |--P. a. arnautoviciHLM86
         |    `--P. a. elongatus (Karaman 1953)HLM86
         |--P. arthrodilus (Braga 1945)HLM86
         |--P. bagradicus Henry & Magniez 1972HLM86
         |--P. bardaunii Alouf, Henry & Magniez 1982HLM86
         |--P. basnosanui (Codreanu & Codreanu 1962)HLM86
         |--P. bellesi Henry & Magniez 1982HLM86
         |--P. beroni Henry & Magniez 1968HLM86
         |--P. boui Henry & Magniez 1969HLM86
         |--P. burgundus Henry & Magniez 1969HLM86
         |--P. cantabricus Henry & Magniez 1968HLM86
         |--P. cavaticus (Leydig 1871)HLM86
         |--P. chappuisi Henry & Magniez 1968HLM86
         |--P. chauvini Henry & Magniez 1978HLM86
         |--P. coiffaiti Henry & Magniez 1972HLM86
         |--P. comasi Henry & Magniez 1982HLM86
         |--P. coxalis (Dollfus 1892)HLM86
         |    |--P. c. coxalisHLM86
         |    |--P. c. africanus (Monod 1924)HLM86
         |    |--P. c. banyulensis (Racovitza 1919)HLM86
         |    |--P. c. cephallenus (Strouhal 1942)HLM86
         |    |--P. c. cyrenaicus (Arcangeli 1942)HLM86
         |    |--P. c. gabriellae (Margalef 1950)HLM86
         |    |--P. c. leucadius (Strouhal 1942)HLM86
         |    |--P. c. lucifugus (Deeleman-Reinhold 1965)HLM86
         |    |--P. c. perarmatus (Remy 1936)HLM86
         |    `--P. c. peyerimhoffi (Racovitza 1919)HLM86
         |--P. cretensis Pesce & Argano 1980HLM86
         |--P. danubialis (Codreanu & Codreanu 1962)HLM86
         |--P. delhezi Henry & Magniez 1973HLM86
         |--P. deminutus (Sket 1959)HLM86
         |    |--P. d. deminutusHLM86
         |    |--P. d. intermedius (Sket 1965)HLM86
         |    `--P. d. vulgaris (Sket 1965)HLM86
         |--P. elegans (Codreanu & Codreanu 1962)HLM86
         |--P. escolai Henry & Magniez 1982HLM86
         |--P. espanoli Henry & Magniez 1982HLM86
         |--P. exiguus Afonso 1983HLM86
         |--P. franciscoloi (Chappuis 1955)HLM86
         |--P. gardinii (Arcangeli 1942)HLM86
         |--P. gauthieri (Monod 1924)HLM86
         |    |--P. g. gauthieriHLM86
         |    `--P. g. theodori (Birstein 1951) [incl. P. gauthieri numidicus Monod in Gauthier 1928 (n. n.)]HLM86
         |--P. gjorgjevici (Karaman 1933)HLM86
         |--P. gourbaultae Henry & Magniez 1981HLM86
         |--P. hercegovinensis (Karaman 1933)HLM86
         |--P. hermallensis (Arcangeli 1938)HLM86
         |--P. hussoni (Remy 1941)HLM86
         |    |--P. h. hussoniHLM86
         |    `--P. h. curvifrons (Remy 1941)HLM86
         |--P. hypogeus (Racovitza 1922)HLM86
         |--P. infirmus (Birstein 1936)HLM86
         |--P. istrianus (Stammer 1932)HLM86
         |--P. jaloniacus Henry & Magniez 1977HLM86
         |--P. karamani (Remy 1934)HLM86
         |--P. lagari Henry & Magniez 1982HLM86
         |--P. lescherae Henry & Magniez 1977HLM86
         |--P. linearis (Birstein 1967)HLM86
         |--P. ljovuschkini (Birstein 1967)HLM86
         |--P. lusitanicus (Frade 1938)HLM86
         |--P. lykaonicus Argano & Pesce 1978HLM86
         |--P. maleri Henry 1977HLM86
         |--P. margalefi Henry & Magniez 1982HLM86
         |--P. mateusorum Afonso 1982HLM86
         |--P. meridianus (Racovitza 1919)HLM86
         |    |--P. m. meridianusHLM86
         |    `--P. m. belgicus (Arcangeli 1935)HLM86
         |--P. minoicus Pesce & Argano 1980HLM86
         |--P. monodi (Strouhal 1942)HLM86
         |--P. monsferratus (Braga 1948)HLM86
         |--P. montenigrinus (Karaman 1934)HLM86
         |    |--P. m. montenigrinusHLM86
         |    `--P. m. macedonicus (Karaman 1955)HLM86
         |--P. nolli (Karaman 1952)HLM86
         |--P. notenboomi Henry & Magniez 1982HLM86
         |--P. parvulus (Sket 1960)HLM86
         |--P. patrizzi (Arcangeli 1952)HLM86
         |--P. pavani (Arcangeli 1942)HLM86
         |    |--P. p. pavaniHLM86
         |    `--P. p. orientalis (Sket 1965)HLM86
         |--P. racovitzai Henry & Magniez 1972HLM86
         |--P. rectangulatus Afonso 1982HLM86
         |--P. rectus Afonso 1982HLM86
         |--P. remyi [incl. P. remyi f. nudus (Karaman 1953)]HLM86
         |--P. rouchi Henry 1980HLM86
         |--P. similis (Birstein 1967)HLM86
         |--P. sketi Henry 1975HLM86
         |--P. slavus (Remy 1948)HLM86
         |    |--P. s. slavusHLM86
         |    |--P. s. histriae (Sket 1963)HLM86
         |    |--P. s. salisburgensis (Strouhal 1957)HLM86
         |    |--P. s. serbiae (Sket 1963)HLM86
         |    |--P. s. styriacus (Sket 1963)HLM86
         |    |--P. s. vindobonensis (Karaman 1955)HLM86
         |    `--P. s. zeii (Sket 1963)HLM86
         |--P. slovenicus (Sket 1957)HLM86
         |--P. solanasi Henry & Magniez 1972HLM86
         |--P. spelaeus (Racovitza 1922)HLM86
         |--P. spinipes Afonso 1979HLM86
         |--P. strouhali (Karaman 1955)HLM86
         |    |--P. s. strouhaliHLM86
         |    `--P. s. puteanus (Henry 1966)HLM86
         |--P. synaselloides Henry 1963HLM86
         |--P. thermonyctophilus (Monod 1924)HLM86
         |--P. valdensis (Chappuis 1948)HLM86
         |--P. vandeli Magniez & Henry 1969HLM86
         |--P. variegatus Afonso 1982HLM86
         |--P. vignai Argano & Pesce 1977HLM86
         `--P. walteri (Chappuis 1948)HLM86

*Type species of generic name indicated


Bodon, M., & R. Argano. 1982. Un asellide delle acque sotterranee della Liguria orientale: Proasellus ligusticus n.sp. (Crustacea, Isopoda, Asellota). Fragm. Entomol. 16 (2): 117–123.

[B50] Brooks, J. L. 1950. Speciation in ancient lakes. Quarterly Review of Biology 25: 30–60.

[F05] Fernández, J. 2005. Noticia de nuevos táxones para la ciencia en el ámbito Íbero-Balear y Macaronésico. Nuevos táxones animales descritos en la península Ibérica y Macaronesia desde 1994 (IX). Graellsia 61 (2): 261–282.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[H47] Hatch, M. H. 1947. The Chelifera and Isopoda of Washington and adjacent regions. University of Washington Publications in Biology 10 (5): 155–274.

[HLM86] Henry, J.-P., J. J. Lewis & G. Magniez. 1986. Isopoda: Asellota: Aselloidea, Gnathostenetroidoidea, Stenetrioidea. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 434–464. E. J. Brill/Dr W. Backhuys: Leiden.

[N29] Nicholls, G. E. 1929. A new species of Asellus (A. nipponensis) from Japan. Archives de Zoologie Expérimentale et Générale 68 (1): 33–38.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

[T30] Tattersall, W. M. 1930. Asellus cavaticus, a blind isopod new to the British fauna, from a well in Hampshire. Proceedings of the Linnean Society of London 141: 7.

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