Hexapodibius christenberryae, Pilato, Giovanni & Binda, Maria Grazia, 2003

Hexapodibius christenberryae View in CoL sp. n. (Figs 1,2)

Description of the holotype

Body length about 420 m ( Fig. 1 View FIGURE 1 ), colourless, eyes present, cuticle smooth. Hind legs reduced and without trace of claws. Buccal tube 43.6 m long and 5.5 m wide (pt = 12.6) ( Fig. 2 View FIGURE 2 A), rigid and asymmetrical with respect to the frontal plane by presence of the ventral lamina. Mouth anterio­ventral without peribuccal lamellae but with small peribuccal papulae. In caudal portion of the buccal cavity three short dorsal and three short and thin ventral transversal ridges are present ( Fig. 2 View FIGURE 2 A, arrow). The stylet supports are inserted on the buccal tube wall at 75% of its length (pt = 75.0). The pharyngeal bulb with apophyses and only two macroplacoids; microplacoid absent. First macroplacoid with central incision and 9.9 m long (pt = 22.7); second 5.2 m long (pt = 11.9); the entire placoid row 16.3 m long (pt = 37.4).

The claws, of Calohypsibius type ( Fig. 2 View FIGURE 2 B), with slender main branch with thin but well evident accessory points with upright terminal portion; the secondary branch short but not very reduced; external claws are clearly longer than internal claws. On second pair of legs external claws 8.3 m long (pt = 19) including accessory points, 8 m (pt = 18.3) accessory points excluded; internal claws 6.6 m long (pt = 15.1) accessory points included and 6.4 m (pt = 14.7) accessory points excluded; on third pair of legs claws slightly longer (0.2 m) and the values of the index pt are slightly higher (0.5). Lunules, and other cuticular thickenings on the legs are absent.

Eggs were not found.

Etymology

We named the new species christenberryae in honour of Deirdre Christenberry who collected and sent us the holotype.

Discussion

As above mentioned, Hexapodibius christenberryae differs from all the known species of the genus by having only two macroplacoids. The first macroplacoid has a central incision but it is not subdivided into two portions (so we are sure that the placoid has to be considered unique).

It also differs from Hexapodibius micronyx by having the stylet supports inserted on the buccal tube in a more cephalic position, narrower buccal tube, lower value of the pt index relative to the placoid row length ( Table 1 View TABLE 1 ), more slender claws with more evident accessory points, external and internal claws of each leg more different in length from one another ( Table 1 View TABLE 1 ).

The new species also differs from H. reginae by having markedly shorter claws ( Table 1 View TABLE 1 ). Vargha (1995) does not draw accessory points and gives no specification in the text about their presence or absence.

Hexapodibius christenberryae also differs from H. boothi by having a shorter buccal tube and shorter claws ( Table 1 View TABLE 1 ); as a consequence of the different buccal tube length ( Table 1 View TABLE 1 ), the values of the pt index relative to the claw length appear similar in the two species. The shape of the claws is different (those of H. christenberryae are more slender and with more developed accessory points).

The new species also differs from H. bindae by having clearly longer claws ( Table 1 View TABLE 1 ) with more evident accessory points.

It also differs from H. pseudomicronyx in the shape of the claws which have more developed secondary branches.

*) In table 1 the claws of H. christenberryae are measured excluding the accessory points that can be erected. This choice is necessary because in the other species the accessory points are not so long and so erect, and therefore they do not affect the claw length.

As a rule, we do not describe a new species when we have only one specimen, and when the locus typicus and the collecting date are not exactly known; but in this case we think that an exception is justified primarily because it is opportune to describe a species surely new to science and well describable also as refers to the quantitative characters, and secondarily because Christenberry in the letter of May 1978 wrote: “I still hope to find more specimens of the 2­placoid Hexapodibius ”; this means that it is not sure that other specimens have been found, and therefore the only possible alternative is not to describe a well recognizable species.