Cleidogona Cook & Collins, 1895

Genus Cleidogona Cook & Collins, 1895 View in CoL

Diagnosis. Cleidogonidae with undivided gonopod angiocoxites, unlike Psuedotremia Cope, 1869 and Solaenogona Hoffman, 1950b . Cleidogona lacks sternal projections anterior to the angiocoxites found in Dybasia Loomis, 1964 . Distinct from Tianella in lacking groups of flagelliform strips on the angiocoxites. Male ninth legs are only slightly reduced in size, consist of 4–6 articles, and femora are enlarged and triangular, unlike Cabraca Shear, 1982 , which has a single article, Tiganogona Chamberlin, 1928 which has 2–3 articles, and Lineagona Shear, 2024 which lacks enlarged, triangular prefemora.

Remarks. Males of Cleidogona , in addition to the gonopods (as described above for the family), have secondary sexual modifications of some of the legs. Legpairs 3–7 are much enlarged, with mesally curved prefemora and femora. These have been observed to clasp the head and anterior segments of the female during mating (pers. obs., WAS). The seventh legpair usually has prominent posterior knobs. These help perhaps in stabilizing the gonopods when retracted. The ninth legpair is variously reduced, but in North American species retains five or six podomeres; the prefemur and coxa are frequently fused. This has led to misinterpretations in some past studies, where the femora are referred to as prefemora. The ninth leg coxae usually have median knobs or processes which interlock with the gonopod colpocoxites at rest, holding the gonopods in the retracted position, and may also carry vestigial basal gland pores. The femora are elongate and distally enlarged, giving the impression of a triangular podomere. Coxae of the tenth and eleventh legpair are elongate and apically bear the openings of coxal glands; frequently the margins of these glands show modifications such as knobs or shelves. A prominent process extends anteriorly from the midline of sternum of the twelfth legs ( Shear 1972).

The gonopods consist of four elements, a sternum, two coxae and paired angiocoxites and colpocoxites. The sternum is broad anteriorly, with a distinct median depression and lateral lobes; posteriorly the sternum is narrow and in some species may be incomplete. The coxae are pyramidal in shape and well separated. They bear from 3 to 12 or more setae and there may or may not be a triangular process extending posteriorly. The angiocoxites are generally the most complex and distinctive of the elements. They extend dorsally to separate the coxae and in most species appear to be bilaterally fused. Distally there are anterior and posterior elements, the anterior being relatively complex and the posterior with a vertical groove containing many fine cuticular fimbriae. The colpocoxites are almost always smaller and less complex than the angiocoxites, but like them are basally fused. They are evenly curved, with the anterior part of the arc usually visible between the angiocoxites. The posterior part is always longer and distally divided into short, blunt, finger-like processes that at rest clasp the tips of the colpocoxites. The coxal knobs of the ninth legs interlock with the basal, posterior part of the posterior arc. The colpocoxites are freely movable through the agency of muscles internal to the gonopods and concealed by the sternum; their attachment to the gonopod complex is membranous.

Unlike most higher taxa of choredumatidans, the female genitalia of many species of Cleidogona have characters that permit species identification. The anterior receptacle is usually reduced to a simple, rounded lobe. The lateral and medial vulval valves may be entirely separate, or anteriorly fused (as is the case with the four species described herein). The valves frequently bear paired processes which may have distinctive shapes. The vulvae are subtended posteriorly by a postgenital plate that also may be distinctive. The postgenital plate appears to be a development of the second sternum.