Nesticus citrinus, Taczanowski, 1874,
treatment provided by
Taxon classification Animalia Araneae Nesticidae
Theridium citrinum : Taczanowski 1874: 57 (♀).
Theridium citrinum : Keyserling 1884: 86, pl. 4, f. 54 (♀).
Nesticus citrinus : Levi 1963: 490 (transfer of species without argumentations).
7♀ "Uassa-Guyane français, leg. K.Yeliki, det. H.T. Taczanowski" from Zoological Museum, Polish Academy of Sciences. Lectotype ♀ designated here, paralectotypes 3♀ and 3 juv. Most likely one syntype was taken by Keyserling (1884) who mentioned 8 specimens. Specimens were dried out and original colouration in alcohol can not be described.
Uassa was not located on current and old maps of the region.
Female. Total length 3.45. Carapace length 1.6, width 1.13. According to Keyserling (1884) prosoma and appendages yellow. Tarsi of leg I‒II with dark tips (Fig. 1). Abdomen covered with white guanine spots lacking only in front of spinnerets (Figs 1-2). Palpal tarsi with large almost straight pectinate claws (Fig. 3).
Epigyne as in Figs 4-8, large, extending epigastral fold, strongly swollen, wider than long, width subequal to 1/2 of abdomen width. Epigynal plate surrounded with long transparent hairs, its anterior edge more sclerotized than another parts. Epigynal plate with pair of round weakly sclerotized copulatory openings (Co), and two round pits (Rp) on lateral sides of the plate. Diameter of round pits more than 2 times larger than those of the copulatory openings. Copulatory openings lead to relatively short (about half of plate’s width) insemination ducts (Id). Receptacles (Re) very large, egg-shaped.
All syntype females have one or two tips of embolus left (Be) in the epigyne (Figs 4-8). Shape and size of broken tip of emboli are the same in all observed specimens, which indicates that the embolus has a certain break-off point. The embolus penetrates not only into the insemination duct but also into the receptacle (Figs 7-8). The embolus tip (Ct), is quite complex and it is wider than rest of the broken part of the embolus.
Conformation of both the epigyne and tip of the embolus is unknown in other Nesticidae . This may indicate that " Nesticus " citrinus does not belong in Nesticus and most probably does not belong in the family Nesticidae as well.
Broken-off tip of embolus is known to occur in several families and superfamilies of spiders included in Araneoidea : Theridiidae and Linyphiidae ( Wiehle 1967). " Nesticus " citrinus can not be placed in Linyphiidae due to lack of a median plate of the epigyne, and in having distinct copulatory ducts, lacking in Linyphiidae . It can neither be placed in any known Theridiidae genera, due to straight palpal claw. Bent palpal claw is known to occur in Hadrotarsinae , but it is rather short and not straight. In addition Hadrotarsinae have modified prosoma with very high clypeus, and habitually are very different from " Nesticus " citrinus .
Even though placement in Nesticus is somewhat doubtful, we believed it is better that it remains in Nesticus for now, until new specimens or a male is discovered, that could shed some light on a very mysterious spider.
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