Hexamerocerata
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''Millotauropus'' is a
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 pauropods in the
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 ...
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 ...
Millotauropodidae in the monotypic
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
Hexamerocerata. The order Hexamerocerata includes only eight species and was created in 1950 to contain the newly discovered genus ''Millotauropus'', which was found to have so many distinctive features as to warrant placement in a separate order. Before the discovery of ''Millotauropus'', for example, pauropods were thought to have no more than ten leg pairs, but adults in the order Hexamerocerata have eleven pairs of legs.


Description

Pauropods in the order Hexamerocerata are characterized by telescopic antennae with six stalk segments, unlike all other pauropods (those in the larger order
Tetramerocerata Tetramerocerata is an order of pauropods containing 11 families and more than 900 species. This order was created in 1950 to distinguish these pauropods from those in the newly discovered genus '' Millotauropus'', which was found to have such di ...
), which have antennae that are not telescopic and have only four stalk segments as adults. Two antennal branches emerge from the distal end of the fourth segment in Tetramerocerata, one dorsal and one ventral; in Hexamerocerata, however, the dorsal branch emerges from the distal end of the fifth segment, and the ventral branch emerges from the distal end of the sixth segment. In Hexamerocerata, the sixth segment also features a sense organ shaped like a candelabra. In Hexamerocerata, each antennal branch features a long flagellum; in all other pauropods, however, the ventral branch features two flagella, whereas the dorsal branch features only one. The lateral sides of the head feature two large eye-like organs, and in Hexamerocerata, these temporal organs are shaped like cups or umbrellas attached to a shallow depression in the head; in all other pauropods, these organs are flat or somewhat convex. Adults in the order Hexamerocerata feature a trunk with twelve entire tergites, whereas other adult pauropods have trunks with no more than six (entire or divided) tergites. The ventral surface of the first trunk segment, the collum, is smooth in Hexamerocerata; in all other pauropods, this surface features two appendages with a plate protruding in between. In Hexamerocerata, the
tergum A ''tergum'' (Latin for "the back"; : ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton wi ...
of the last trunk segment, the
pygidium The pygidium (: pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compos ...
, features five to eight pairs of
setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...
; this tergum in all other pauropods features only four pairs of setae. Adults in the order Hexamerocerata have eleven pairs of legs, whereas other adult pauropods have eight to ten leg pairs. Pauropods in the order Hexamerocerata have tracheae, a feature absent in all other pauropods. These tracheae take the form of two thin tubes on each side running from the base of the first pair of legs and reaching into the posterior part of the head. The bases of the other legs in Hexamerocerata feature short rudiments of tracheae.


Feeding

The
mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...
in the order Hexamerocerata are strong enough to allow these pauropods to consume solid food. The midgut of these pauropods can contain fungus, spores, and plant tissue. The mouthparts in the order Tetramerocerata are weaker, with mandibles that are used to puncture cell walls so that the pauropod can suck out fluids. No solid food has been found in the midgut in Tetramerocerata.


Development

Pauropods in the order Hexamerocerata go through a process of post-embryonic development that differs from that of most pauropods. Like most pauropods, those in this order go through five stages from the first
instar An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
to the adult. Juveniles in this order, however, begin with six pairs of legs and eight tergites and then become adults with eleven leg pairs and twelve tergites. Species in this order have six pairs of legs in the first stage, then eight pairs in the second, nine pairs in the third, ten pairs in the fourth, and finally eleven pairs in the fifth (adult) stage. Most other juvenile pauropods instead begin with three pairs of legs and three tergites, then become adults with nine leg pairs and six tergites, going through stages with three, five, six, eight, and nine pairs of legs.


Distribution

The order Hexamerocerata has a mainly tropical distribution, with species found in Brazil, tropical continental Africa, Madagascar, and
Seychelles Seychelles (, ; ), officially the Republic of Seychelles (; Seychellois Creole: ), is an island country and archipelagic state consisting of 155 islands (as per the Constitution) in the Indian Ocean. Its capital and largest city, Victoria, ...
, but this order has also been found in Japan.


Species

The order Hexamerocerata includes the following species: * '' Millotauropus acostae'' Scheller, 1997 * '' Millotauropus angustiramosus'' Remy, 1955 * '' Millotauropus frustatorius'' Remy, 1959 * '' Millotauropus hebetisetosus'' Remy, 1953 * '' Millotauropus latiramosus'' Remy, 1953 * '' Millotauropus machadoi'' Remy, 1953 * '' Millotauropus silvestrii'' Remy, 1953 * '' Millotauropus temporalis'' (Hüther, 1968)


References


External links

* {{Taxonbar, from=Q10585466 Myriapod genera Pauropoda Taxa described in 1950