Troglohyphantes gracilis

Like all the members of the genus, Troglohyphantes gracilis is a relatively small spider.^[6] The female has a body length between 2.98 and 3.2 mm (0.117 and 0.126 in) and a cephalothorax 1.34 and 1.44 mm (0.053 and 0.057 in) long and between 1.06 and 1.2 mm (0.042 and 0.047 in) wide.^[7] It is very similar in shape to Troglohyphantes similis.^[8] The spider is reddish-orange, similar to Troglohyphantes spinipes, but it is lighter. The pattern on the top, which consists of five light arrow-shaped lines on the spider's abdomen, is also lighter.^[9] The spider's epigyne, the external and most visible of its copulatory organs, is similar to Troglohyphantes spinipes, but it is not as wide.^[10]

The male is similar to the female, typically 3.12 mm (0.123 in) in length. Its cephalothorax is generally smaller, typically 1.34 mm long and 1.2 mm (0.047 in) wide.^[7] It has multiple spines on its legs, incljuding five on the tibia.^[11] Its palpal bulb is similar to the related Troglohyphantes spinipes but the species differ in the existence of a shorter and straighter projection, or apophysis, that projects from the palpal bulb and differences in the shape of the lamella.^[12]

Most Troglohyphantes species live in the mountain ranges of Europe including the Pyrenees, Alps, Dinarides and Carpathians, usually in subterranean environments or caves.^[4] Troglohyphantes gracilis lives in three caves in the Kočevje mountains of Lower Carniola, Slovenia.^[13] Troglohyphantes similis, Troglohyphantes spinipes and this species are very closely related with ranges that are contiguous.^[12] The three species are all referred to as the Kočevje subterranean spider.^[14] The species is at risk of climate change reducing its habitat.^[15]

• Fage, Louis (1919). "Biospelogica XL. Etudes sur les araignées cavernicoles. III. Sur le genre Troglohyphantes" [Biospelogica XL. Studies on cave spiders. III. On the genus Troglohyphantes]. Archives de Zoologie Expérimentale et Générale (in French). 58: 55–148.
• Deeleman-Reinhold, Christina L. (1978). "Revision of the cave-dwelling and related spiders of the genus Troglohyphantes Joseph (Linyphiidae), with special reference to the Yugoslav species". Slovenska Akademija Znanosti in Umetnosti, Razred za Prirodoslovne Vede, Classis IV, Historia Naturalis (Prirod. Vede). 23 (6): 1–220.
• Koomen, Peter; Van Helsdingen, Peter Johan (1996). Listing of biotopes in Europe according to their significance for invertebrates. Vol. 77. Strasbourg: Council of Europe. ISBN 978-9-28713-002-0.
• Milano, Filippo; Borio, Luca; Komposch, Christian; Mammola, Stefano; Pantini, Paolo; Pavlek, Martina; Isaia, Marco (2022). "Species conservation profiles of the endemic spiders Troglohyphantes (Araneae, Linyphiidae) from the Alps and the north-western Dinarides". Biodiversity Data Journal: 19;10:e87261. doi:10.3897/BDJ.10.e87261. PMC 9848466. PMID 36761670.