Hypsocephalus dahli is a junior synonym of Microneta pusilla ( Araneae , Linyphiidae )

Comparison of the detailed species-specific original drawings of Microneta pusilla Menge, 1869 with the holotype of Hypsocephalus dahli (Lessert, 1909) and the record of one female close to the type locality of Microneta pusilla in Gdańsk, Poland indicate that Hypsocephalus dahli is a junior synonym of Microneta pusilla. Hypsocephalus pusillus (Menge, 1869) is therefore proposed as the valid name for this species. Here we discuss the taxonomic status of both species and present a distribution map that accounts for records in Poland.

The status of the nominal taxa Microneta pusilla Menge, 1869 andHypsocephalus dahli (Lessert, 1909) have long been obscure. Both names were used before and after WUNDERLICH (1972) synonymised these species and also after MILLIDGE (1978) declared M. pusilla a nomen dubium. FRICK (2007) summarised all available data about the two nominal species. However, soon after this publication, the second author of the present article discovered a new record of one female close to the type locality of M. pusilla, which again raised questions about the nomenclatural status of H. dahli and M. pusilla.

Systematics
The recent record of one female close to the type locality of M. pusilla indicates that H. dahli is indeed a junior synonym of M. pusilla. A closer look at the original drawings of MENGE (1869) revealed that they are detailed enough to recognise this species. They show the tip of the embolus, which clearly differentiates it from other Hypsocephalus species. Comparison of these figures with the holotype of Hypsocephalus dahli (Lessert, 1909) showed that they are conspecific (see FRICK 2007 for disposition of types). Consequently, we suggest resurrecting M. pusilla and accordingly consider Hypsocephalus pusillus (Menge, 1869) to be the valid name for this species.
However, the following arguments should briefly be discussed: First, no type material of M. pusilla is available. We tried to find the material on which Menge based his descriptions of M. pusilla without success. Some of his material was given to other collections before World War II. Checking the collections of the Natural History Museum of Stockholm (SE) and the Museum of Comparative Zoology in Cambridge (USA) -which are known to harbour such material -revealed no specimens of this species. If the remaining material was still in Gdańsk at that time, it disappeared towards the end of World War II (Kraus in litt.). Absence of types is very common in zoological nomenclature and in our opinion it is not reason enough per se to declare a name a nomen dubium if detailed figures with distinct characters are available. This condition is met in the present case. Therefore, MILLIDGE'S (1978) declaration of M. pusillus as nomen dubium solely because of the absence of a name-bearing type is not followed here.
The designation of a neotype for M. pusillus could therefore be suggested. The International Code of Zoological Nomenclature proposes the following conditions, under which a neotype should be designated (article 75.1): "no name-bearing type specimen is believed to be extant" and "that a namebearing type is necessary to define the nominal taxon objectively" (INTERNATIONAL COMMISSION ON ZOOLOGICAL NOMENCLATURE 1999). While the first condition is most probably met, the second is not due to the presence of detailed species-  specific figures based on the original type series. Additionally, designating a female neotype for a species with distinct male copulatory organs but minor differences in the female copulatory organs seems suboptimal.
Second, one might argue that the junior synonym (H. dahli) has been used by many more scientists than the senior synonym M. pusilla (see FRICK 2007) and should therefore be retained for the sake of nomenclatural stability. Here, we find decisive regulations in the International Code of Zoological Nomenclature (INTERNATIONAL COMMISSION ON ZOOLOGICAL NOMENCLATURE 1999). Following article 23.9.1 of the code, the junior synonym has priority only if it is in prevailing usage, i.e. the following conditions are both met: the senior synonym "has not been used as a valid name after 1899" and that the junior synonym has been used "in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years". While the second condition holds the first is obviously not met, because H. pusillus was used by various authors until 1995 (FRICK 2007: table  1a). Consequently, the species epithet pusillus has priority.

Distribution in Poland
The distribution of H. pusillus has been summarised in FRICK (2007) including the records in Poland, of which only the regions (voivodship) were known. Since then, new information on the records in Poland are available and are presented here including a completed distribution map ( Fig. 1):