Cleidogonidae Cook, 1896

Shear, William A., 2024, Lineagona, a new millipede genus (Diplopoda, Chordeumatida, Cleidogonidae) from Texas, USA, and Nuevo León, México, Zootaxa 5397 (2), pp. 283-290 : 284-285

Family Cleidogonidae Cook, 1896

Cleidogonidae Cook, 1896: 8 – Shear (1972: 156); Hoffman (1980: 130, 1999: 210) (list).

Mexiceumidae Verhoeff, 1926: 110 – Shear (1972: 156).

Entomobielziidae Verhoeff,1909: 370 (in part, not including Entomobielzia Verhoeff, 1899 ).

Pseudocleididae Attems, 1926: 170 (in part, not including Pseudoclis Attems, 1899 ).

Bactropidae Chamberlin & Hoffman, 1950: 71 (recte: Bactropodidae) – Shear (1972: 156).

Dybasiidae Loomis, 1964: 100 – Shear (1972: 156).

Bactropodellidae Jeekel, 1969: 88 (replacement name for Bactropidae , preoccupied) – Shear(1972: 156).

Cleidogonid gonopods and male male ninth legs: The gonopods of exemplar species of Cleidogona and Pseudotremia were described in detail by Shear (1972), but new interpretations of chordeumatidan gonopods require some changes in terminology.

The relatively simple gonopods, developed from the eighth pair of legs of males, consist of a sternum, paired separate coxae, and two pairs of coxites. The anterior pair of coxites, the angiocoxites (called colpocoxites in Shear [1972]) are often if not always fused at the base and may or may not each be divided into two distinct branches, one lateral or posterior and one medial or anterior, and the lateral branch, if present, may be further subdivided. In Pseudotremia , the lateral branch bears a clearly defined (presumable) gland channel. The posterior coxites (colpocoxites) were referred to as “telopodites” in Shear (1972). They are usually small, simple, and fused at the base. Between the two pairs of coxites there may be one or more median processes of uncertain origin and homology; these are especially prominent in Pseudotremia .

The ninth legpair of males, as with all chordeumatidans, is modified, with the telopodites reduced or even absent. Adaptations of the coxae for holding the gonopods in place when not in use are common, and telopodite remnants may serve a protective function. It should be mentioned that in the superfamily Heterochordeumatoidea there is a tendency for the male ninth legs to take over the function of spermatophore transfer and the gonopods sensu stricto to be reduced. But in most Cleidogonidae the modification of the male ninth legs is minimal.All of the telopodite podomeres may be present, with only the tibiae and tarsi reduced in size, as in Cleidogona species. This rather small change, so that the male ninth legs in Cleidogona are little differentiated from walking legs, supports the argument that the cleidogonids are the most basal of chordeumatidans. In other genera the degree of reduction of the telopodites of the male ninth legs may be greater, eventuating in the presence of only a single podomere (the prefemur, as in several species of Pseudotremia ) or the total loss of the telopodite, seen only in Cabraca unigon Shear, 1982 . The male ninth leg coxae may have one or two knobs which interlock with the colpocoxites to hold the gonopods in place, but in Tiganogona species, the coxae are much more elaborately lobed.

Each cleidogonid genus can be easily diagnosed by a combination of just a few characters of the gonopods or ninth legs of the males. In Cleidogona , the angiocoxites of the gonopods are undivided and the femora of the only slightly reduced ninth leg telopodites are enlarged and triangular. Cabraca has similar gonopods, but the male ninth legs consist of only a single article; likewise for Tiganogona gonopods but in those species the ninth leg coxae are complexly lobed and the telopodites reduced to two or three podomeres. Pseudotremia species show a range of degrees of reduction of the ninth leg telopodites, but have divided and sometimes elaborately branched gonopod angiocoxites as well as one, two or three median processes arising between the angiocoxites. In species of Solaenogona , the gonopods and male ninth legs resemble those of Pseudotremia species, but the lateral branches of the angiocoxites are massive and have moved to a posterior position, while the gland channel follows the anterior branch. Dybasia , confined to Panama, is diagnosed by having a pair of presumed sternal processes anterior to the angiocoxites.