Paxodillidium
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''Paxodillidium'' is a genus of
woodlice Woodlice are terrestrial isopods in the suborder Oniscidea. Their name is derived from being often found in old wood, and from louse, a parasitic insect, although woodlice are neither parasitic nor insects. Woodlice evolved from marine isopods ...
endemic to Greece. It is
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
, being represented by the single species ''Paxodillidium schawalleri''. Its true affinities within the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Armadillidiidae Armadillidiidae is a family (biology), family of woodlice, a terrestrial animal, terrestrial crustacean group in the order Isopoda. Unlike members of some other woodlice families, members of this family can roll into a ball, an ability they sha ...
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 Paxos () is a Greek island in the Ionian Sea, lying just south of Corfu. As a group with the nearby island of Antipaxos and adjoining islets, it is also called by the plural form Paxi or Paxoi (, pronounced in English and in Greek). The main t ...
. 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 A ''tergum'' (Latin for "the back"; : ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'margin'. ...
. 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 hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
, 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 An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
, 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 (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
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 anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...
is short and triangular and the apex of the endopodite is straight .


Distribution

''Paxodillidium schawalleri'' is endemic to various
Ionian islands The Ionian Islands (Modern Greek: , ; Ancient Greek, Katharevousa: , ) are a archipelago, group of islands in the Ionian Sea, west of mainland Greece. They are traditionally called the Heptanese ("Seven Islands"; , ''Heptanēsa'' or , ''Heptanē ...
lying offshore western Greece. Particularly, until now, the species has been found in the islands of
Corfu Corfu ( , ) or Kerkyra (, ) is a Greece, Greek island in the Ionian Sea, of the Ionian Islands; including its Greek islands, small satellite islands, it forms the margin of Greece's northwestern frontier. The island is part of the Corfu (regio ...
, Paxos,
Antipaxos Antipaxos (, ) is a small island (5 km2) in Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest ...
,
Ithaki Ithaca ( ), also Ithaki ( ) or Ithaka ( ''Ithákē'' ), 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 island has an area of and in 2021 had a population ...
,
Kefalonia Kefalonia or Cephalonia (), formerly also known as Kefallinia or Kephallonia (), 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 is also a separate regio ...
,
Zakynthos Zakynthos (also spelled Zakinthos; ; ) or Zante (, , ; ; from the Venetian language, Venetian form, traditionally Latinized as Zacynthus) is a Greece, Greek island in the Ionian Sea. It is the third largest of the Ionian Islands, with an are ...
and
Strofades Strofades (; also called Strofadia, , or Stromphides, ) is a group of two small Greek islands in the Ionian Islands. They lie about south-southeast of the island of Zakynthos. Administratively they are part of the Municipality of Zakynthos. The ...
.


Ecology

''Paxodillidium schawalleri'' has been found in three types of
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
:
Olive The olive, botanical name ''Olea europaea'' ("European olive"), is a species of Subtropics, subtropical evergreen tree in the Family (biology), family Oleaceae. Originating in Anatolia, Asia Minor, it is abundant throughout the Mediterranean ...
groves, phrygana and ''
Quercus ilex ''Quercus ilex'', the holly oak, also (ambiguously, as many oaks are evergreen) evergreen oak, is a large evergreen oak native to the Mediterranean region. It is a member of the section (botany), section ''List of Quercus species#Section Ilex, Il ...
'' 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 Anti-predator adaptations are mechanisms developed through evolution that assist Predation, prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, na ...
. 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 Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
, like lacertid lizards and
geckos Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates. They range from . Geckos are unique among lizards f ...
. Additionally, the tubercles may also cause injuries in the
mouth cavity A mouth also referred to as the oral is the body orifice through which many animals ingest food and vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also the first part of the alimentar ...
and the
esophagus The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...
of these
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
predators.


References

{{Taxonbar, from1=Q107272422, from2=Q15728865, from3=Q1946557 Woodlice Woodlice of Europe Crustaceans described in 1985 Monotypic isopod genera