Rhagidia (Deharvengiella) serpentiforma Zacharda, 2011

Zacharda, Miloslav, Grafitti, Giuseppe & Piva, Erminio, 2011, New taxa of Rhagidia and Foveacheles (Acari: Prostigmata: Rhagidiidae) from Italian and French caves, with keys to adults of subgenera Deharvengiella and Mediostella, Journal of Natural History 45 (11 - 12), pp. 667-683 : 672-675

Rhagidia (Deharvengiella) serpentiforma Zacharda , sp. nov.

( Figure 3 )

Material examined

Holotype. Adult female, Italy, Sardinia, Cagliari, Iglesias , Miniera di San Giovanni mine, Grotta di Santa Barbara Cave , coll. S. Papinuto, 13 February 2004; deposited in the Museum of Biological Diversity , Ohio State University, Type No. OSAL007451

Diagnosis

Rhagidial organ I comprises four strikingly long, parallel, serpentine rhagidial solenidia lying in separate depressions; stellate famulus (ε) between first and second rhagidial solenidia; rhagidial organ II with three long, slender, rhagidial solenidia lying in slightly oblique, separate depressions; spiniform famulus (ε) subtends proximal rhagidial solenidion. Dorsodistal lanceolate solenidion on tibia II small, recessed in deep insertion pit with broadly open surface pore. Coxae I, II, III, IV with 3-1-6-3 finely pubescent setae, respectively. Adoral setae on subcapitulum short, internal pair not overlapping apex of subcapitulum, external pair overlapping apex of subcapitulum only slightly.

Description

Adult female (one examined). Length of idiosoma 590 µm. Ratio of leg I length to idiosomal length 1.40.

Gnathosoma . Subcapitulum broadly oval ( Figure 3G ), subtriangular; ratio of length to breadth 1.07; distal hypostomal lips with spiniform internal and serrate external malar processes; adoral setae nude, short, internal pair not overlapping apex of subcapitulum, external pair overlapping apex of subcapitulum only slightly; proximal subcapitular setae pubescent, external pair sharply pointed, internal pair blunt and shorter than external pair. Dorsal surface of chelicera with saddle-shaped depression at level of bases of digits; cheliceral digits slender; fixed digit smooth along masticatory surface ( Figure 3A ) and with lateral fissure at level of insertion of proximal cheliceral seta; movable digit smooth along masticatory surface. Chelicera with two setae, proximal seta inserted above articulation of movable digit; tip of proximal seta

A,B,C,D,E,G F

not reaching insertion of distal seta; tip of distal seta slightly overlaps apex of fixed digit. Length of chelicera 160 µm, dorsoventral width 53 µm, length of movable digit 53 µm, length of proximal and distal cheliceral setae 13 and 29 µm, respectively, distance between their insertions 26 µm. Ratios: cheliceral length to dorsoventral width 3.05; length of movable digit to length of chelicera 0.33; length of movable digit to dorsoventral width of chelicera 1.00. Palpal tarsus about same length as femorogenu ( Figure 3F ), ratio of length to width of tarsus 1.87. Length of palpal trochanter, femorogenu, tibia and tarsus 29, 59, 23 and 49 µm, respectively. Number of setae on palpal trochanter, femorogenu, tibia and tarsus 0-2-3-10, respectively; tarsal solenidion indiscernible.

Prodorsum. Naso well developed, with pair of internal vertical setae v 1. Bothridial setae sc 1 filiform, finely pubescent. Length of setae: v 1 30, v 2 33, sc 1 82 µm, sc 2 torn off.

Opisthosomal dorsum. All setae on opisthosomal dorsum torn off.

Podosoma. Coxae I, II, III, IV with 3-1-6-3 finely pubescent setae, respectively.

Genital region. Genital valves each with five finely pubescent setae of similar length, about 20 µm, arranged evenly along medial edge of valve. Five pairs of aggenital setae of similar length, about 26–29 µm. Length of genital valves 79 µm.

Legs. Leg I 832 µm long, about 1.40 as long as idiosoma. Empodia of all legs setulose, slightly longer than claws; claws each with small basal tubercle ventrobasally. Tarsus I slender, its tip slightly tapered in lateral view, ratio length to width 5.80, with four strikingly long serpentine rhagidial solenidia lying in separate depressions dorsodistally ( Figure 3B,C ); stellate famulus (ε) subtending second rhagidial solenidion; tarsus II with three long rhagidial solenidia lying in separate oblique depressions; spiniform famulus (ε) subtending proximal rhagidial solenidion ( Figure 3 D ). Dorsodistal rhagidial solenidion on tibia I small, recessed in deep depression. Dorsodistal lanceolate solenidion on tibia II small, recessed in deep depression with broadly open surface pore ( Figure 3E ). Spiniform solenidia on all tibiae and genua were not discernible in the studied specimen.

Affinities

Rhagidia (D.) serpentiforma sp. nov. differs from the other known representatives of the genus by the extremely elongated serpentine rhagidial solenidia in the rhagidial organ I. These are thought to be morphological adaptations to life in the cave environment.

Etymology

The epithet serpentiforma reflects the serpentine shape of the extremely long rhagidial solenidia on the tarsi I. Feminine gender.

Remarks

The cave of Santa Barbara was discovered in 1952 while digging a gallery near the mine of San Giovanni, not far from Iglesias, in southwestern Sardinia. Today it is considered one of the oldest in Europe, being around 500 million years old ( Forti et al. 2005a,b). Because it was isolated from the outside world, it was preserved in pristine condition until its discovery. Evidence that this cave has been flooded from the surface some thousand years before present comes from studies of clay–silt sediments ( Bini et al. 1988).

In addition to R. serpentiforma sp. nov., Collembola have been documented in this cave system ( Negri et al. 2004; Grafitti 2005; Grafitti and Merella 2008), which appears to be interconnected with the surrounding landscape, provided with an input of energy, and colonized by small litter- and soil-dwelling invertebrates.

The curious extremely elongated serpentine rhagidial solenidia in the rhagidial organ I indicate a troglobitic species morphologically adapted to life in the cave. The enlarged rhagidial solenidia may extend the range at which prey are percieved in the extremely resource-limited subterranean environment. If, as has been suggested by Culver and Pipan (2009), the degree of troglomorpy functions as a morphological clock, then the extreme troglomorphy observed in R. (D.) serpentiforma sp. nov. would suggest that its lineage has evolved relatively longer in the subterranean environment than other species in the subgenus.

Key to adults of Rhagidia (Deharvengiella)

1. Rhagidial solenidia in rhagidial organ I in oblique depressions. Coxae I, II, III, IV with 3-1-4-3 pubescent setae, respectively. Opisthosomal setae f 1 absent. In Grotte de la Buhadére cave, Haute-Garonne, Couledoux, the French Pyrenees......................................................

.................................... R. (D.) troglomorphica Zacharda, 1987

Rhagidial solenidia in rhagidial organ I in serpentine or parallel depressions. Coxae I, II, III, IV with 3-1-5-3 or 3-1-6-3 pubescent setae, respectively. Opisthosomal setae f 1 present........................................... 2

2. Rhagidial solenidia in rhagidial organ I in serpentine depressions; coxae I, II, III, IV with 3-1-6-3 pubescent setae, respectively. In Grotta di Santa Barbara cave, Miniera di San Giovanni mine, Iglesias, Cagliari, Sardinia ............

............................................. R. (D.) serpentiforma sp. nov.

Rhagidial solenidia in rhagidial organ I in parallel depressions; coxae I, II, III, IV with 3-1-5-3 pubescent setae, respectively. In Gouffre de l´Oule cave, Lot and Dordogne, France...............................................

.............................................. R. (D.) paralleloseta sp. nov.

Figures

Figure 3. Rhagidia (D.) serpentiforma sp. nov., adult female: (A) chelicera, lateral aspect; (B) rhagidial organ I, left lateral aspect; (C) rhagidial organ I, right lateral aspect; (D) rhagidial organ II, dorsal aspect; (E) dorsodistal lanceolate solenidion (Φ) on tibia II, lateral aspect; (F) palpus, lateral aspect; (G) subcapitulum, ventral aspect.