Aletopauropus

''Aletopauropus'' is a genus of pauropods in the family Brachypauropodidae. This genus includes only two species: the type species, '' A. lentus'', which is found in California, and a second species, '' A. tanakai'', which is found in Japan. This genus is notable as one of only four genera of pauropods in which adults have only eight pairs of legs rather than the nine leg pairs usually found in adults in the order Tetramerocerata. Before the discovery of ''Aletopauropus'', adult pauropods were described as having only nine or (rarely) ten pairs of legs.

Discovery and distribution

The genus ''Aletopauropus'' and its type species ''A. lentus'' were first described in 1948 by the zoologists John W. MacSwain and Urless N. Lanham of the University of California at Berkeley. MacSwain and Lanham based their descriptions on twelve specimens that MacSwain collected in 1947. These specimens include a male holotype, a female allotype, seven paratypes (one male and six females), and three juveniles representing two earlier stages of post-embryonic development, all found in Berkeley in Alameda county in California.

In 1989, the biologist Yasunori Hagino of Ibaraki University described the second species in this genus, ''A. tanakai''. He based the original description of this species on one female holotype and three female partypes, all collected in Japan. The holotype and two paratypes were collected in 1985 in Ehime Prefecture on the island of Shikoku, whereas the other paratype was collected in 1984 in Ibaraki Prefecture on the island of Honshu. Since the original description of this species, several more specimens including four juveniles and at least one male have been recorded on the island of Honshu, found in Tochigi Prefecture, Saitama Prefecture, Chiba Prefecture, and Yamanashi Prefecture.

Description

Both species in this genus are small: The species ''A. lentus'' ranges from 0.56 mm to 0.60 mm in length. The species ''A. tanakai'' is larger, ranging from 0.66 mm to 0.76 mm in length. The head in this genus features three transverse rows of setae. Two to four tube-like extensions protrude from the temporal organ on each side of the head.

Adults in this genus have only eight pairs of legs, and each leg has five segments. These pauropods go through the first four stages of post-embryonic development typical of species in the order Tetramerocerata, with three leg pairs in the first stage, five pairs in the second, six pairs in the third, and eight pairs in the fourth, but reach sexual maturity in the fourth stage rather than in a fifth stage and do not add the ninth pair of legs that usually appear in a fifth stage for other species in this order. Thus, adults of this species also have only eleven trunk segments and five tergites and do not acquire the twelfth trunk segment and sixth tergite that other species in this order usually add in a fifth stage.

The first tergite is entire, with a single sclerite, whereas the second, third, and fourth tergites are each divided into at least four sclerites. The fifth tergite features an entire median sclerite. The setae on the tergites are shaped like bristles or spears. The sternum of the pygidium features two pairs of setae, one anterior and one posterior.

MacSwain and Lanham also described two other new genera in the family Brachypauropodidae, ''Zygopauropus'' and '' Deltopauropus'', along with ''Aletopauropus'', finding no more than eight pairs of legs in all three genera. Since then, the genus ''Deltopauropus'' has been found to include adults with the usual nine leg pairs, but no adults with more than eight leg pairs have been found in the genera ''Aletopauropus'' and ''Zygopauropus''. Since the descriptions of ''Aletopauropus'' and ''Zygopauropus'' by MacSwain and Lanham, adults in only two other genera of pauropods, '' Amphipauropus'' and '' Cauvetauropus'', have been found to have no more than eight leg pairs.

Pauropods in the genus ''Aletopauropus'' share several traits with other pauropods in the family Brachypauropodidae. These traits include not only an entire first tergite followed by second and third tergites that are each divided into at least four parts but also a pygidial sternum with at least two pairs of setae. The genus ''Aletopauropus'' shares an especially extensive set of traits with the genus ''Zygopauropus'', the only other genus in the family Brachypauropodidae in which adults have only eight leg pairs. For example, both of these genera have temporal organs with tube-like extensions and only two pairs of setae on the pygidial sternum.

Pauropods in the genus ''Aletopauropus'' can be distinguished from those in the genus ''Zygopauropus'' based on other traits. For example, the fifth tergite in ''Zygopauropus'' is divided down the middle longitudinally into two sclerites, whereas this tergite in ''Aletopauropus'' features an entire sclerite in the middle. Furthermore, the head features three rows of setae in ''Aletopauropus'' but four rows of setae in ''Zygopauropus''.

The two species of ''Aletopauropus'' can be distinguished from one another based on another set of traits. For example, all the sclerites of the tergites are reticulated in ''A. tanakai'' but not in ''A. lentus''. Furthermore, the middle of the posterior margin of the pygidial sternum features a distinct rounded bulge in ''A. tanakai'' but not in ''A. lentus''. Moreover, the styli (fourth pair of posterior setae) on the posterior margin of the pygidial tergum are nearly cylindrical rods in ''A. lentus'' but tapering in ''A. tanakai''.

References.

{{taxonbar, from=Q16527599

Pauropoda
Animals described in 1948