Isotomidae

Gao, Yan, Potapov, Mikhail & Bu, Yun, 2022, A new blind genus of Anurophorinae (Collembola: Isotomidae) with seven anal spines from Northwest China, Zootaxa 5104 (1), pp. 80-88 : 86-87

Value of anal spines in taxonomy of Isotomidae

The modern generic system of Isotomidae is not finalized in spite of recent progress in understanding the value of several characters, such as development of furca, secondary sexual dimorphism and anal spines. Furca as a generic character has been criticised by Fjellberg (1993), Potapov (1997b), Potapov & Stebaeva (2002), Potapov et al. (2006) and others. Strong and weak sexual dimorphism of Isotomidae was reviewed by Palacios-Vargas & Castaňo-Meneses (2009) and Chimitova & Potapov (2011). This phenomenon was found within “non-dimorphic” genera, such as Vertagopus Börner, 1906 , Isotopenola Potapov et al., 2009 , Agrenia Börner, 1906 , and Scutisotoma Bagnall, 1948 . A few dimorphic species of these genera diminished the value of this character in generic taxonomy and compromised the status of Guthriella Börner, 1906 , Jestella Najt, 1977 , and Rhodanella Salmon, 1945 which were erected after spectacular sexual dimorphism.

Anal spines (spines at the end of abdomen) of isotomid genera were discussed previously ( Deharveng 1978, Greenslade 2015, Potapov et al. 2006, 2010, 2017). The use of this character is somewhat complicated by ecomorphosis since the ecomorphic specimens having spines sometimes led to the description of “false genera” ( Tetracanthura Martynova, 1971 , Spinisotoma Stach, 1926 , Cliforga Wray, 1952 ) in the past. Typical “unspined” genera, however, can also include species with spine-like setae, thin spines or protuberances at the end of abdomen, for example, Cryptopygus Willem, 1902 ( C. terranova Wise, 1967 ), Weberacantha Christiansen, 1951 ( W. octa Christiansen, 1951 ), Scutisotoma ( S. fjellbergi Dunger, 1982 ), Anurophorus Nicolet, 1842 ( A. rarus Yosii, 1939 ) ( Greenslade 2015, Potapov et al. 2006). In these cases the conventional “anal spines” often vary depending on specimen, they are rather thin and never have papilla. The similar ambiguity of anal spines occurs in other taxa of Collembola. The number of spines in large genus Friesea Dalla Torre, 1895 (Poduromorpha) varies from 0 to 16 depending on species or from 8 to 13 in the single species F. tilbrooki Wise, 1967 , while the number of spines in Tullbergiidae (also belonging to Poduromorpha ) is more conservative and is reliably used in generic taxonomy. Anal spines have been shown to be constant in the course of postembryonic ontogenesis ( Deharveng 1978) with rare exclusions ( Dimorphacanthella ). In spite of cases noted above, the number and the position of anal spines remains a key generic character among so-called “spined” genera of Isotomidae ( Deharveng 1978, Potapov et al. 2017). In this paper we take the most widely accepted position regarding the pair of true anal spines as an apomorphy of a particular genus.