Selachochernes, Mahnert & Ch-, 2011

Mahnert, Volker, 2011, New records of pseudoscorpions from the Juan Fernandez Islands (Chile), with the description of a new genus and three new species of Chernetidae (Arachnida: Pseudoscorpiones)., Revue suisse de Zoologie 118 (1), pp. 17-29 : 20

Selachochernes gen. n.

DIAGNOSIS: Member of Chernetidae , Chernetinae.Tegument normally sclerotized, vestitural setae of cephalothorax, tergites and pedipalps short and strongly clavate. Cephalothorax with two eyespots, two indistinct transverse furrows, the subbasal one much nearer to posterior margin than to median furrow; most tergites divided, XI without tactile setae. Chelicera with 5 simple setae on hand; galea short, with 4 apical/subapical branchlets, rallum with 4 setae, the distal one dentate on anterior margin. Pedipalps heavily granulate, the strongly clavate setae of femur and patella inserted on coarser granula, distal setae on hand less clavate, fixed finger at base and on dorsal face with two long and stout setae; fixed chelal finger in distal half with acute, spaced teeth followed by lower, retrorse, cusped teeth, accessory teeth present on antiaxial face: the spaced marginal teeth and the accessory teeth forming two rows of teeth (like shark teeth); movable finger distally with slightly spaced teeth; long venom duct present in movable finger only. Trichobothria: 8 on fixed finger, est-ib-isb in middle of finger (near strong seta), ist forming a group with it-et; movable finger: 3 trichobothria (probably sb lacking). Leg IV: tarsus without tactile seta, arolia undivided, claws smooth.

TYPE SPECIES: Selachochernes allodentatus sp. n.

DISTRIBUTION: Chile, Juan Fernandez Islands (Masatierra).

ETYMOLOGY: From the Greek noun „selachos“ (cartilaginous fish, shark, ray), referring to the unusual, shark-like arrangement of teeth on the fixed chelal finger.

AFFINITIES: Within the Chernetinae with a rallum of four setae, Selachochernes gen. n. is quite isolated and characterized at once by the particular trichobothrial pattern on the fixed finger (ib and isb distinctly distal of eb-esb opposite est) and the reduced number of trichobothria on the movable finger. By the presence of strongly clavate and a few long, stout setae on the chela it resembles Pseudopilanus Beier (type species fernandezianus Beier ), but that genus differs in having a rallum of 3 setae, trichobothria ib-isb basal near eb-esb, and the chelal teeth numerous and closely set (27 on fixed, 30 on movable finger). For further evaluation of importance of some taxonomic characters see the following remarks. Since spermathecae of Pseudopilanus species from Chile are unrecorded, at least that of P. kuscheli from mainland Chile is shown (Fig. 22) as first step to a better knowledge of this genus.

REMARKS: The presence of two superficially similar and not related genera in the Juan Fernandez archipelago might seem to be improbable, but the differences between P. fernandezianus and S. allodentatus sp. n. cannot be explained by possible ontogenetic changes or variability of the one or the other taxonomic character (e.g. number of setae of rallum). Within a chernetid genus the number of setae of the rallum is relatively stable, variability is very unfrequent, the setae being frequently difficult to observe (particularly in case of a rallum with 4 setae, observation errors might therefore occur more frequently than natural variability); during ontogeny numbers of these setae are not changing from tritonymphs to adults, in Chernetidae at least. In the following species currently placed in Pseudopilanus , the rallum is composed of 3 setae (personal observations): fernandezianus (holotype), kuscheli (paratype), chilensis (syntype), crassifemoratum (holotype, paratype). Tooth morphology and arrangement on chelal finger are very similar (small, densely set, retrorse, cusped teeth) in fernandezianus , chilensis (syntypes: 39-41 teeth on fixed finger, 46 on movable finger), kuscheli (syntypes; 34-37 on fixed finger, 37-42 on movable finger), crassifemoratum (31 teeth on fixed, 32-33 teeth on movable finger). Tooth morphology is identical in tritonymph and adults (female, male) of crassifemoratum, an ontogenetic modification of tooth morphology from tritonymphal to adult stages in Chernetidae is unknown to me. Even in (slightly) sexual dimorphic species like Pseudopilanus chilensis (chelal finger of male in middle curved and therefore gaping when closed; those of female straigth and not gaping) no difference in tooth morphology or arrangement is observable. This is also the case in strongly dimorphic species like Parachernes melanopygus Beier or Parachernes setiger Mahnert ( Chernetidae , both from Amazonia). Ontogenic changes cannot explain the fundamental difference in trichobothrial pattern found in allodentatus (ist in distal third of fixed finger and close to it, ib-isb-est grouped together in middle of finger, eb-esb isolated near finger base) and fernandezianus (ib-isb grouped with eb-esb near finger base, est in middle of finger), since the position of the trichobothria ib-isb compared to that of eb-esb and of est does not change much from tritonymph to adult stage, as far as documented in the literature. This latter pattern (ist indistinctly distal of est in middle of finger, ib-isb near finger base and distinctly basal of est-ist) is found in P. chilensis , and also in kuscheli and crassifemoratum (where ist-est are more basally placed), and it anticipates probably the pattern of adult fernandezianus . The presence of only three trichobothria in S. allodentatus might be variable and of importance on specific and not on generic level (e.g. in Americhernes incertus Mahnert from Amazonia). Furthermore, distribution of paraxial trichobothria on the fixed finger is considered of generic importance in Chernetidae (e.g. difference between the groups Parachernes / Anaperochernes and Asterochernes / Parazaona ) ( Beier, 1964a).