Hexaiberobathynella Camacho and Serban, 1998

Camacho, A. I., Serban, E. & Guil, N., 2000, Phylogenetical review and biogeographic remarks on the interstitial and subterranean freshwater iberobathynells (Crustacea, Syncarida, Parabathynellidae), Journal of Natural History 34 (4), pp. 563-585 : 574-583

Genus Hexaiberobathynella Camacho and Serban, 1998

Type species: Hexaiberobathynella hortezuelensis Camacho and Serban, 1998 . (®gures 3, 4)

Genus diagnosis

Lbr.: with eight main teeth. Th. 8 male: outer lobe with anterior part shorter than posterior part and with the distal part strongly inclined toward caudal part of the thoracopod; main axis with inclination postero-distal; dentate lobe with the anterior right part shorter than inner lobe; inner lobe without setules at the distal end; exopod very diminished in size and completely covered by the distal part of the outer lobe. Md.: pars incisiva with four to six teeth and pars molaris with seven to eight claws. Mx.I: distal endite with six teeth. Mx.II: three-segmented, without setae on the proximal endite. Th.1: with exopod one-segmented and three setae. Th.2±6: with exopod two-segmented and four setae. Urp.: symp. with 6±15 spines; endp. with two short setae of diOEerent length; exp. with three barbed setae. Frc.: with 5±11 spines. With pronounced anal operculum.

Hexaiberobathynell a hortezuelensis Camacho and Serban, 1998 (®gures 3, 4)

Description

Body: Total length of type male is 1.3 mm (variation n = 27: 1.25±1.55 mm) of females (n = 26) 1.3±1.9 mm. Body elongated, segments progressively widening towards posterior end of body. Head of similar length and width.

A.I (®gure 3A): with seven segments; no sexual dimorphism; length of ®rst four segments greater than that of last three, and the ®rst three segments of similar length; setation as in ®gure 3A (segment 5 with one aesthetasc, segments 6 and 7 with three, one longer than the other two). A.II (®gure 3B): three-segmented, last of which is longest, with two smooth and one plumose terminal seta and a small, shorter seta in the middle; ®rst two segments without setae. Lbr. (®gure 3C): with eight main teeth and two smaller marginal ones on each side, the second of each pair with two tips at the distal end. Md. (®gure 3D, E): pars incisiva with ®ve to six well-developed teeth; pars molaris with seven teeth, the last with a large number of ®ne setules; mandibular palp one-segmented, apical seta does not exceed pars incisiva in length. Mx.I (®gure 3F): proximal endite with four claws (with diOEerent sizes of spines); distal endite with six strong claws, two smooth apical claws and the other four with spines; three smooth setae on outer distal margin. Mx.II (®gure 3G): three-segmented, without seta on basal segment; segment 2 with two long setae and one shorter seta at distal end, one additional seta on inner border: segment 3 elongated with 15 setae, four of them with setules. Thoracopods (®gure 4A±F): six pairs of well-developed thoracopods, length gradually increasing from pairs 1±4, last three pairs similar in size. Th.1±6 with one seta at distal end of basipodite; welldeveloped epipodite on pairs 2±6, half length of basipodite; coxa of Th.1±6 with distinct conical projection at inner distal border. Th.1 (®gure 4A): short, exp. onesegmented with three setae; endp. four-segmented: ®rst with one smooth dorsal seta; second with one smooth and one plumose seta; third with two setae, one small and smooth and the other tiny; terminal segment with two claws of diOEerent length and one smooth seta. Th.2±6 (®gure 4B±F): exp. biarticulated; segment 1 with two terminal setae, one short and smooth and one long, barbed seta; segment 2 with two terminal setae, one barbed and the other plumose; ctenidia at base of setae. Endp. four-segmented: segment 1 short and without setae; segment 2 with two groups of lateral ctenidia and one plumose and one strong smooth seta; segment 3 with one tiny seta and segment 4 with one seta and two strong claws which are slightly diOEerent in length. Th. 8 male (®gure 3J±M): outer lobe with anterior part shorter than posterior part and with the distal part strongly inclined toward caudal part of the thoracopod; main axis with inclination postero-distal; dentate lobe with the anterior right part shorter than inner lobe; inner lobe without setules at the distal end; exopod very diminished in size and completely covered by the distal part of the outer lobe. Th. 8 female (®gure 3H, I): small, triangular with one strong terminal spine and another on the inner lateral side. Dorsal margin of pleotelson (®gure 3P): anal operculum pronounced; one barbed seta on lateral side. Urp. (®gure 3N): symp. almost twice the length of endp. and six times as long as it is wide; with 10±15 barbed spines, the most distal one-third the length of endp. and slightly larger than the others; endp. almost same length as exopod, drawn out distally in slightly curved spur, with two smooth short outer setae at beginning of spur; exp. with two terminal barbed setae, on subterminal barbed seta and one plumose basiventral seta. Frc. (®gure 3P): with 8±11 (usually 10) barbed spines, two terminal ones longer than others; two dorsal plumose setae, one long and the other short.

Population variation

The adult animals are very homogeneous, variation has been detected only in two characters: number of spines on the sympod of the uropod and number of spines on the furca.

We studied 42 adult specimens varying in size between 1.25 and 1.9 mm; number of spines on the sympod of uropod varied between nine and 15 and number of spines on the furca between eight and 11. There is no signi®cant positive correlation between the size of the specimens and the number of spines on the sympodite of the uropod (r =0.429), or the number of spines on the furca (r = 0.527). There is only a slight positive correlation between the greater number of spines on the furca and the greater number of spines on the sympod of the uropod (r = 0.673).

Discussion

The presence of six pairs of thoracopods in Hexaiberobathynella is a particular case in the Iberobathynellini that implies an important and original diversi®cation in the whole group. This process, however, does not involve modi®cation of the other features of the group but it de®nes structural limits which are more signi®cant than those of a genus, they de®ne a subtribe: Hexaiberobathynellina Camacho and Serban . Hexaiberobathynell a hortezuelensis shows the diagnostic features of the subtribe Hexaiberobathynellina : six pairs of thoracopods with the exopods of thoracopods two-segmented in almost all of them.

In the family Parabathynell a there is another genus with six pairs of thoracopods, Hexabathynella Schminke, 1972 . But in this case this feature is accompanied by the following modi®cation of the general structure: six-segmented antennules with sexual dimorphism; antenna ®ve-segmented; convex labrum; thoracopod 8 male with endopod well developed; with pleopods; etc.

The genus diagnosis is based on the morphology of the male thoracopod 8 in the type species, Hexaiberobathynell a hortezuelensis .

The original description of the other species of the genus, Hexaiberobathynella mateusi ( Galhano, 1967) is incomplete and there are a few mistakes in the interpretation of the structure of the male thoracopod 8: the endopod is confused with the exopod (in ®gure 4b, Galhano, 1967); the view showing the latero-external face presents some problems and it is obvious that the thoracopod has been too ¯attened by the cover glass on the slide. Later, the male thoracopod 8 was drawn again by Schminke (1973, p. 35, ®gure 7) and the mistake corrected, but, even so the structure is not clear.

Because we have found this species many times in Spain and Portugal the diOEerentiation of both species of the genus is now easy, in spite of the fact that the original description of Hexaiberobathynell a mateusi is incomplete. Hexaiberobathynell a hortezuelensis and H. mateusi (®gures 3±5), new combination, can be distinguished by features shown in table 5. There can therefore be no doubt that Hexaiberobathynell a hortezuelensis is a diOEerent species from H. mateusi , and that both species belong to the genus Hexaiberobathynella .

Population variation in Hexaiberobathynell a mateusi (®gures 4, 5)

We studied one population in Portugal (P1) and 12 in central and southern Spain (P2±P13) (table 2) and we also show the features of the type material of Hexaiberobathynell a mateusi from Duero River (P14) in Portugal (see Galhano, 1967). All specimens came from the Tajo and Duero basin or nearby localities .

The principal diOEerent characteristics are shown in table 6. In general, this is a medium-sized species for the iberobathynellids. The species type material (P14) shows the greatest size, both females and males, followed by the population from the Reguerillo Cave (P12). The Teruel population (Santos stream, P6), and the one population from the spring (P11), included the smallest specimens (less than the average for the species). For the populations studied, the diOEerences in the remaining characteristics are a very slight variation in the length of the setae of the endopodite of the uropod (®gure 5H±J); they are short in one of the populations of the small specimens (P6) and in another specimen larger than the average (P13). However, they are long in the other population of small specimens, and in some populations for which we lack data on the length of the specimens. The average length predominates (the setae do not reach the edge of the endopodite), this is the case in specimens from six populations. We have not been able to establish a correlation between this character and the basin where the populations are found, there appears to be no regularity.

The minor diOEerences can be seen in ®gures 4, 5: A.I (®gure 4G, H) diOEerent length of the segments and small number and size diOEerences in setae; Md. (®gure 4I, J) number and size of teeth and setation; Mx.I (®gure 5A, B) setation and size of teeth; Th. 8 female (®gure 5C, D) general aspect; Th. 8 male (®gure 5E±G)

aspect and size of the lobes; Th.4 (®gure 5L, M) relative size of the segments and setae.