A Cautionary Note on Linear Measurements and Their Ratios in Taxonomy

Abstract

Statisticians work with figures, whereas scientists work with estimated quantities. Every direct (physical) measurement has some degree of uncertainty. Single numbers pose no problems, and an implied range can always be specified. Difficulties arise when those numbers or sets of numbers are used to calculate derived figures. Statistical measures such as ratios can be skewed if uncertainty about the actual measurements used to derive those quantities is not taken into account. This lack of consideration may lead to incorrect figures being used and calls into question the criteria used to diagnose, identify or delimit new species. In this case study, I use data gathered from the literature on different species of the clade Hydrachnidia (Acari, Parasitengona) to show how range ratios of important characters differ when uncertainty is considered. I outline the successive steps taken during the measuring process—from microscope calibration to the calculation of several statistical values from the direct measurements—and suggest some corrections. I anticipate that the results and recommendations presented here will be applicable to other taxonomic groups for which linear measurements play a central role in the description and identification of species.

New records of the subgenus Soarella Koenike, 1907 from China (Acari, Hydrachnidia, Unionicolidae, Neumania), with the description of five new species

“…All holotypes and paratypes will be deposited in the Institute of Entomology, Guizhou University, Guiyang, P. R. China (GUGC) (Zhang 2018). The method and terms used follow Ding et al (2019), ratios are calculated follow Valdecasas (2022). The following abbreviations are used: asl= above sea level, A 1 = preantennal glandularia, A 2 = postantennal glandularia, ACG = anterior coxal group (Cx-I + Cx-II), Cx-I-IV = coxae I-IV, D 1 -D 4 = dorsoglandularia 1-4, C 1 -C 4 = coxoglandularia 1-4, H = altitude, I-L-1-6 = first-sixth segment of the first leg, L 1 -L 4 = lateroglandularia 1-4, L = length, LA= length between anterior end of Cx-I and posterior end of posterior apodeme of ACG, LP = length between anterior margin of Cx-III and posterior end of posterior apodeme of Cx-IV, O 1 = preocularia, O 2 = postocularia, P-1-P-5 = first-fifth plates in four groups, surface lightly reticulated, interspace between Cx-II and Cx-III narrow, suture line between Cx-III/IV complete, posterior apodemes of ACG extending to one-third of Cx-IV, posterior projection of Cx-IV somewhat hook-shaped (Figure 1B).…”

Looking Back on 2023—A Fruitful Year for Taxonomy

“…Thirtythree new species of bacteria, plants, and animals have been described in Taxonomy in 2023, documenting the need for reliable and serious journals devoted to taxonomy. Of course, papers on taxonomy and systematics-morphology-based [1][2][3] or with a focus on molecular data [4][5][6]-prevailed by far, but we also published papers with a focus on methodology [7,8].…”