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 ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
millipede
Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...
in 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 ...
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
in this genus. This millipede is notable as one of only a few species in the orderChordeumatida with only 26 segments in adults (counting the collum as the first segment and the telson as the last), four fewer segments than typically found in adults this order. This species is found in
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
and
Luxembourg
Luxembourg, officially the Grand Duchy of Luxembourg, is a landlocked country in Western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France on the south. Its capital and most populous city, Luxembour ...
.
Discovery
The genus ''Chamaesoma'' and its only species were first described by the German
zoologist
Zoology ( , ) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one ...
Haute-Garonne
Haute-Garonne (; , ; ''Upper Garonne'') is a department in the southwestern French region of Occitanie. Named after the river Garonne, which flows through the department. Its prefecture and main city is Toulouse, the country's fourth-largest. ...
in the
Pyrenees
The Pyrenees are a mountain range straddling the border of France and Spain. They extend nearly from their union with the Cantabrian Mountains to Cap de Creus on the Mediterranean coast, reaching a maximum elevation of at the peak of Aneto. ...
Paris
Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...
.
Distribution and habitat
This species is present in Luxembourg as well as distributed across most of France, from the French Pyrenees and the Massif Central in the south to as far north as
Normandy
Normandy (; or ) is a geographical and cultural region in northwestern Europe, roughly coextensive with the historical Duchy of Normandy.
Normandy comprises Normandy (administrative region), mainland Normandy (a part of France) and insular N ...
and
Lorraine
Lorraine, also , ; ; Lorrain: ''Louréne''; Lorraine Franconian: ''Lottringe''; ; ; is a cultural and historical region in Eastern France, now located in the administrative region of Grand Est. Its name stems from the medieval kingdom of ...
. Since the discovery of this species in Haute-Garonne in France, this millipede has been recorded in other departments in the Pyrenees, including
Hautes-Pyrénées
Hautes-Pyrénées (; Gascon/ Occitan: ''Nauts Pirenèus / Hauts Pirenèus'' awts piɾeˈnɛʊs ; alts piɾiˈneʊs ) is a department in the region of Occitania, southwestern France. The department is bordered by Pyrénées-Atlantiques to t ...
Aude
Aude ( ; ) is a Departments of France, department in Southern France, located in the Occitania (administrative region), Occitanie Regions of France, region and named after the river Aude (river), Aude. The departmental council also calls it " ...
, and
Pyrénées-Orientales
Pyrénées-Orientales (; ; ; ), also known as Northern Catalonia, is a departments of France, department of the Regions of France, region of Occitania (administrative region), Occitania, Southern France, adjacent to the northern Spain, Spanish ...
Aveyron
Aveyron (; ) is a Departments of France, department in the Regions of France, region of Occitania (administrative region), Occitania, Southern France. It was named after the river Aveyron (river), Aveyron. Its inhabitants are known as ''Aveyro ...
,
Puy-de-Dôme
Puy-de-Dôme (; or ''lo Puèi Domat'') is a department in the Auvergne-Rhône-Alpes region in the centre of France. In 2021, it had a population of 662,285.Calvados,
Loiret
Loiret (; ) is a department in the Centre-Val de Loire region of north-central France. It takes its name from the river Loiret, which is contained wholly within the department. In 2019, Loiret had a population of 680,434.
,
Meuse
The Meuse or Maas is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea from the Rhine–Meuse–Scheldt delta. It has a total length of .
History
From 1301, the upper ...
oak
An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...
(''
Quercus petraea
''Quercus petraea'', commonly known as the sessile oak, Welsh oak, Cornish oak, Irish oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an un ...
hornbeam
Hornbeams are hardwood trees in the plant genus ''Carpinus'' in the family Betulaceae. Its species occur across much of the temperateness, temperate regions of the Northern Hemisphere.
Common names
The common English name ''hornbeam'' derives ...
trees (''
Carpinus betulus
Hornbeams are hardwood trees in the plant genus ''Carpinus'' in the family Betulaceae. Its species occur across much of the temperateness, temperate regions of the Northern Hemisphere.
Common names
The common English name ''hornbeam'' derives ...
'').
Description
This millipede ranges from brown to gray. This species is notable for its small size: Adult males are only 3.25 mm long, and adult females only 4 mm long. This millipede is also one of only a few species in the order Chordeumatida with only 26 segments in adults, the minimum number recorded in this order. Accordingly, the adult female of this species has only 42 pairs of legs, and the adult male has only 40 pairs of walking legs, excluding the eighth and ninth leg pairs, which become gonopods.
Like other millipedes in the family Chamaesomatidae, ''Chamaesoma'' features small paranota. Like most other genera in this family, this genus also features anterior gonopods with well developed telepodites. In this genus, these telepodites are long, smooth, and curved. Unlike most other genera in the same family, however, this genus features body pigmentation.
This genus shares an especially extensive set of traits with ''
Xystrosoma
''Xystrosoma'' is a genus of millipede in the family Chamaesomatidae. The French zoologist Henri Ribaut first described this genus in 1927 to contain five species newly discovered in France, including the type species '' X. tectosagum''. This g ...
'', another genus in the same family. These shared traits place these two genera in the same subfamily (Chamaesomatinae). For example, the head and dorsal surface of the trunk in both genera are covered with small
lamellae
Lamella (: lamellae) means a small plate or flake in Latin, and in English may refer to:
Biology
* Lamella (mycology), a papery rib beneath a mushroom cap
* Lamella (botany)
* Lamella (surface anatomy), a plate-like structure in an animal
* Lame ...
arranged as vertical plates oriented longitudinally.
The males in these two genera also develop similar modifications to their legs. For example, the anterior gonopods in both genera feature angiocoxites in front that are separate rather than fused, a colpocoxite toward the rear that is undivided rather than divided in the middle, and no flagella. The posterior gonopods in both genera feature a coxa with a medial process and a telepodite with two segments, including a minute distal segment. Furthermore, the eleventh leg pair in males of both genera feature coxal hooks.
The millipedes in the genus ''Chamaesoma'' can be distinguished from the species in the genus ''Xystrosoma'', however, based on other traits. For example, the dorsal lamellae are pointed and shaped like triangles in ''Chamaesoma'', but these lamellae are rounded and shaped like semicircles in ''Xystrosoma''. Furthermore, the fifth segment of each antenna is as wide as long in ''Chamaesoma'', but this segment is longer than wide in ''Xystrosoma''.
Development
The species ''C. broelemanni'' arrives at a lower number of segments and legs through a process of post-embryonic development that deviates from the
anamorphosis
Anamorphosis is a distorted projection that requires the viewer to occupy a specific vantage point, use special devices, or both to view a recognizable image. It is used in painting, photography, sculpture and installation, toys, and film speci ...
usually observed in the order Chordeumatida. Like other species in this order, ''C. broelemanni'' is teloanamorphic, adding segments and legs through a series of molts until the adult stage, when the molting stops and the adult emerges with a final number of segments and legs. This species, however, reaches maturity and stops molting one stage earlier, in the eighth stage rather than in a ninth stage. Furthermore, ''C. broelemanni'' conforms to the pattern usually observed in most species of Chordeumatida only through the first five stages, then adds one fewer segment than usual upon entering the sixth and seventh stages. Thus, in this process, ''C. broelemanni'' goes through stages of development with 6, 8, 11, 15, 19, 22, and 24 segments, before emerging as an adult with 26 segments in the final stage.
This process is the same as that observed in the species '' Opisthocheiron canayerensis'', one of the other species in the order Chordeumatida with only 26 segments in adults, but with one difference. In ''C. broelemanni'', the transformation of legs into gonopods in the male begins in the sixth stage and continues until the eighth and final stage. In ''O. canayerensis'', however, this process does not begin until the seventh stage.