Hexabathynella sevillaensis, Camacho, 2005

Camacho, Ana Isabel, 2005, Expanding the taxonomic conundrum: Three new species of groundwater crustacean (Syncarida, Bathynellacea, Parabathynellidae) endemic to the Iberian Peninsula, Journal of Natural History 39 (21), pp. 1819-1838 : 1830-1836

Hexabathynella sevillaensis n. sp.

( Figures 5 , 6 )

Material examined

Santiago El Grande cave ( Constantina, Sevilla Province, Spain), collected by Alberto Tinaut (27 August 2002) and Antonio G. Valdecasas and Jaime Rodriguez (17 October 2003) (two and 15 males and no and 20 females, respectively). Fourteen specimens were studied. The holotype is a male and the type series contains 13 specimens (six females and seven males) (paratypes) ( MNCN 20.04 /5913) .

Diagnosis

This species can be distinguished by the male antennal organ; the first four segments of the antennule are short and thick; the shape of the female thoracopod 8 is unique; the sympod has five spines of similar length, the exopod of the uropod has three setae, the endopod is twice longer than the exopod, and the setation on the endopod of the uropod (two short smooth setae of not very different length) is also unique.

Description

Body. Total length males 0.67–1.10 mm (holotype 1.04) and of females 1.00– 1.20 mm. Body elongated, almost cylindrical, segments progressively widening and lengthening towards posterior end of body. Head longer than wide.

Antennule ( Figure 5A ). With six thick, short segments; with sexual dimorphism in the second segment (antennal organ present in the male only); length of first three segments more than 1.5 times greater than the other three, segments 5 and 6 of similar length; segment 5 with three terminal aesthetascs and segment 6 with three subterminal aesthetascs; antennal organ in the male located on a protuberance on the inner distal angle, and in the apical zone it bears two long prolongations of equal length. The tip of these two prolongations widens and then narrows giving it a ‘‘teat-like’’ form.

Antenna ( Figure 5B ). Five segments, the distal two are the longest; segment 4 with two setae and last segment with two smooth setae and one plumose terminal seta; first three segments without setae.

Labrum ( Figure 5C ). With nine similar main teeth on ventral side, and one smaller lateral tooth at each end.

Mandible ( Figure 5D ). Pars incisiva with four strong teeth; pars molaris with six teeth, one strong and distal and the other five proximal, the two most proximal joined and with fine setae; mandibular palp not reaching beyond pars incisiva.

Maxillule ( Figure 5E ). Proximal endite with four claws (spines of different sizes); distal endite with four claws, two smooth and two with spines concentrated on distal end, and three smooth setae on outer distal margin.

Maxilla ( Figure 5F ). Three-segmented, with two setae on basal segment; segment 2 with three setae; segment 3 elongated with 13 setae.

Thoracopods. Thoracopods 1–6 ( Figures 5G , 6A–E ): length gradually increasing from pairs 1 to 4, last two pairs similar in size; well-developed epipodite on pairs 2–6, almost exceeding half length of basipod. Thoracopod 1 ( Figure 5G ): basipod with one lateral terminal seta; exopod one-segmented with one terminal barbed seta, and with one group of ctenidia at the distal margin of the exopod; endopod four-segmented: segment 1 with one smooth seta, 2 with one plumose seta, 3 with one small, smooth seta, terminal segment with two claws of slightly different length. Thoracopods 2–6 ( Figure 6A–E ): basipod without seta; exopod biarticulated, segment 1 with two terminal setae, one smooth, the other barbed, and segment 2 with a terminal barbed seta (ctenidia at the distal margin of the segments); endopod four-segmented, segment 1 short and without setae, 2 with two groups of lateral ctenidia, and one plumose seta, 3 with one tiny seta and with two groups of lateral ctenidia and segment 4 with one strong claw. Thoracopod 8 male ( Figures 5J–H , 6F ): compact, twice as long as wide; endopod long and thick with two smooth setae of different length; basal segment of the protopod massive and almost reaching end of basipod, free side with teeth; basipod almost square ending in a point, with one seta; small, rounded exopod. Thoracopod 8 female ( Figure 5K ): small, almost cylindrical with two small terminal teeth. First pleopod ( Figures 5L , 6F ) as a simple seta on the pleon.

Dorsal margin of the pleotelson ( Figure 6G, H ). Anal operculum very pronounced, almost as long as furca; one smooth seta on lateral side.

Uropod ( Figure 6H, I ). Sympod almost twice length of the endopod and almost four times as long as wide, with seven spines of equal length, which are located on the second half; endopod twice length of the exopod, with a rim of ctenidia and with two outer dorsal small, smooth setae (they do not reach tip of the endopod); exopod with three terminal barbed setae of different lengths (see Figure 6H, I ).

Furca ( Figure 6G, H ). With three similar smooth spines and two dorsal plumose setae, one long and one short.

Etymology

This species is named after the province in Sevilla where the genus Hexabathynella was found for the first time in a cave.

Remarks

The new species presents a series of unique characters within the genus (see Table IV). The antennal organ is unique; although the aspect of the two structures which form the antennal organ is comparable (except the tip) with H. nicoleiana Camacho, 1986 and H. otayana Cho, 2001 , the size of the protuberance is different, longer than in those two species. Besides, the tip of the prolongations is normally sharply pointed in almost all species and in the new species it is different to both (see Figure 5A ). In the new species the segments 5 and 6 are long, while in all other species of the genus all segments are short and wide, particularly 5. Hexabathynella sevillaensis n. sp. is the only species in the genus with 11 teeth on the labrum; the setal formula of the maxilla is unique: 2/3/13 setae on the three segments, respectively; the distal segment of the the maxillule has four claws like H. otayana (see Table IV), but in this species all are smooth and the new species has two denticulated and two smooth claws; the sympod of the uropod consists of six spines all similar in size. In all other species in this genus the distal spines are longest. The combination of setae on the exopod and endopod of the uropod (three barbed and two small and smooth setae, respectively) is similar to that of H. knoepffleri ( Coineau, 1965) .

The female thoracopod 8 is not significantly reduced in size, as occurs in many other species ( H. nicoleiana , H. minuta ( Noodt and Galhano, 1969) , H. valdecasasi Camacho, 2004 , H. knoepffleri , H. paranaensis ( Jakobi, 1972) , H. tenera ( Cvetkov, 1968) , H. longiappendiculata ( Cvetkov, 1970b) , H. otayana and H. muliebris Cho, 2001 ) (see Table IV). The mandible of the new species is similar to H. nestica ( Cvetkov, 1970a) and H. paranaensis .

The thoracopod 8 male is relatively large for the medium size of the species (as is also the case in H. nicoleiana ); the relative proportions of the lobes resemble only H. minuta (this is the species which is geographically closest to the new species), but H. minuta is a small species with a small and more square male thoracopod 8.

The presence of a single seta near the ventro-lateral base of the furcal rami of the pleotelson is shared with all European species, the three north American species ( H. otayana , H. muliebris and H. hessleri Cho, 2001 ), and H. pauliani ( Delamare Deboutteville, 1953) from Madagascar.

Hexabathynella sevillaensis n. sp. is a medium-sized species, as are the majority of the species in the genus except for H. hebrica ( Cvetkov and Petrova, 1964) which is the largest and H. minuta , H. pauliani and H. tenera which are small.

Some of the characters exhibited by the new species are present in other species in the genus (see Table IV), but the combination of all of them is unique to the new species.

Figures

Figure 5. Hexabathynella sevillaensis n. sp., male. (A) Antennule (dorsal view); (B) antenna (dorsal view); (C) labrum; (D) mandible (lateral view); (E) maxillule (lateral view); (F) maxilla (lateral view); (G) thoracopod 1; (H) thoracopod 8 male (latero-external view); (I) thoracopod 8 male (frontal view); (J) thoracopod 8 male (latero-internal view); (K) thoracopod 8 female (ventro-lateral view); (L) pleopod female (ventro-lateral view). Scale bars in mm.

Figure 6. Hexabathynella sevillaensis n. sp. male. (A) Thoracopod 2; (B) thoracopod 3; (C) thoracopod 4; (D) thoracopod 5; (E) thoracopod 6; (F) thoracopod 8 male and pleopod (dorsal view); (G) pleotelson and furca (dorsal view); (H) pleotelson and furca female (lateral view); (I) uropod (latero-internal view). Scale bars in mm.