''Paxodillidium schawalleri'' is a

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species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

woodlouse A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood. ...

endemic to

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...

. It is currently the only known member of the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

''Paxodillidium''. Its true affinities within the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Armadillidiidae are not known.

Taxonomy

''Paxodillidium schawalleri'' was described as the only member of the genus ''Paxodillidium'' by Helmut Schmalfuss, in 1985, based on specimens collected from the island of Paxos. Its true affinities within the family Armadillidiidae are yet unknown, but two hypotheses have been made: *The first one states that ''Paxodillidium'' is related to '' Cyphodillidium'' and '' Echinarmadillidium'', two genera that also show a distinct ornamentation on the tergites. From these two, ''Paxodillidium'' is believed to be more closely related to ''Cyphodillidium'', with which it shares the development of a frontal edge on the head. On the other hand, it differs from it by the presence of more flattened epimera and individualized tubercles on the tergites. *The second one states that the genus could be more closely related to '' Trichodillidium'', as both of them have an oblique ridge on the uropod-protopodites.

Description

''Paxodillidium schawalleri'' is a small-sized species, reaching maximum dimensions of about 6 x 3 mm. Its tergites are decorated with a number of conspicuously large tubercles: 4 on the posterior part of the head and on each pereion-tergite and 2 on each pleon-tergite and on the

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

, along the mid-line. The tubercles of the pleon and telson are much smaller than those of the head and the pereion. The species is totally pigmenless, except for the eyes, which are black, or with some slightly pigmented areas on the head and pereion-tergites, the distribution and extent of which varies. The head bears a developed frontal triangle, with sharp-edged sides and a slightly indented surface. It also has a frontal ridge, which runs all the way towards the eyes and is formed by the continuation of the upper edge of the frontal triangle (''" Eluma''-type"). The secondary antennae have visible lobes at their bases, are slender and the second article of the

flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

is three times longer than the first. All of the epimera are kind-of flattened and protrude outwards and those of the first pair of pereion-tergites lack a ventral schisma/groove (a character present in ''Cyphodillidium'', but absent in ''Echinarmadillidium''). The telson is visibly wider than long and has a broadly truncated tip. Concerning the sexual characters of the male, the ischium of the seventh pereiopod is slightly indented ventrally and has a hair field at its apical part. The posterior lobe of the exopodite of the first

pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

is short and triangular and the apex of the endopodite is straight .

Distribution

''Paxodillidium schawalleri'' is endemic to various Ionian islands lying offshore western Greece. Particularly, until now, the species has been found in the islands of

Corfu Corfu (, ) or Kerkyra ( el, Κέρκυρα, Kérkyra, , ; ; la, Corcyra.) is a Greek island in the Ionian Sea, of the Ionian Islands, and, including its small satellite islands, forms the margin of the northwestern frontier of Greece. The isl ...

, Paxos,

Antipaxos Antipaxos ( el, Αντίπαξος, ) is a small island (5 km²) in Greece, about to the south of Paxos. It is administratively part of the municipality of Paxoi in Corfu regional unit in western Greece. , the resident population of the ...

Ithaki Ithaca, Ithaki or Ithaka (; Greek: Ιθάκη, ''Ithaki'' ; Ancient Greek: Ἰθάκη, ''Ithakē'' ) is a Greek island located in the Ionian Sea, off the northeast coast of Kefalonia and to the west of continental Greece. Ithaca's main islan ...

Kefalonia Kefalonia or Cephalonia ( el, Κεφαλονιά), formerly also known as Kefallinia or Kephallenia (), is the largest of the Ionian Islands in western Greece and the 6th largest island in Greece after Crete, Euboea, Lesbos, Rhodes and Chios. It ...

, Zakynthos and Strofades.

Ecology

''Paxodillidium schawalleri'' has been found in three types of habitat:

Olive The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ...

groves, phrygana and ''

Quercus ilex ''Quercus ilex'', the evergreen oak, holly oak or holm oak is a large evergreen oak native to the Mediterranean region. It is a member of the ''Ilex'' section of the genus, with acorns that mature in a single summer. Description An evergreen tr ...

'' forests. The function of its most remarkable character, the presence of "gigantic" (compared to its general body size) tubercles on the body, isn't known for sure, but is believed to be an anti-predator adaptation. The tubercles seem to increase the diameter of the rolled-up animal considerably, and, as such, put it outside of the prey-size spectrum of various predators, like lacertid lizards and geckos. Additionally, the tubercles may also cause injuries in the mouth cavity and the esophagus of these vertebrate predators.

References

{{reflist Woodlice Woodlice of Europe Crustaceans described in 1985 Monotypic crustacean genera