Pushing the Limits: New Data on the Morphology of Geophilus impressus C. L. Koch, 1847 (Geophilomorpha: Geophilidae)

Ecologica Montenegrina, 53, 2022, 38-44 Pushing the Limits: New Data on the Morphology of Geophilus impressus C. L. Koch, 1847 (Geophilomorpha: Geophilidae) GEORGE POPOVICI1, 2 1“Grigore Antipa” National Museum of Natural History, Pavel Dimitrievici Kiseleff St. 1, 011341, Bucharest, Romania. 2British School of Bucharest, Erou Iancu Nicolae St. 42, 077190 Voluntari, Ilfov County, Romania. E-mail: georgepop[email protected] Received 3 April 2022 │ Accepted by V. Pešić: 23 April 2022 │ Published online 27 April 2022. Abstract Three Geophilus impressus C. L. Koch, 1847 specimens collected in Băneasa Forest, Southern Romania are described and illustrated. The sampled population represents a new lower limit for the leg-bearing segment number of this species and morphological differences to previous descriptions that cast doubt on the reliability of using sizeand agedependent features of the maxillae and last-leg bearing segment when separating it from other closely related Geophilus. A discussion on postulated correlations between number of leg-bearing segments and latitude is presented for G. impressus, as well as on the importance of the carpophagus structures as diagnostic characters among its relatives in Geophilus. Key words: centipedes, taxonomy, geographic variation. Introduction The diverse Holarctic genus Geophilus is known to comprise several species complexes (Bonato & Minelli 2014). Geophilus alpinus Meinert, 1870 was the preferred name for 12 previously described species distributed across Europe (Bonato & Minelli 2014, Bonato et al. 2016) until recent nomenclatural revision, which decided that Geophilus impressus C. L. Koch, 1847 is to be accepted as the senior synonym for Geophilus alpinus and the many species synonymised under the latter (ICZN 2020). Its character variability makes it difficult to distinguish from closely related congeners, an issue further complicated by the significant intraspecific distances recorded within this species (Wesener et al. 2015). One of the most puzzling complexes comprises Geophilus impressus, Geophilus oligopus Attems, 1895 and Geophilus persephones Foddai & Minelli, 1999; all of these species having a characteristically shaped second maxillary pretarsus. Several past revisions (Barber 1999, Christian 1996) have attempted to clarify the morphological limits and taxonomic relations among them, however with limited examined material and a restricted number of populations within their Palearctic ranges. It is difficult to establish the reliability of several important diagnostic characters for the Geophilidae due to their variation in regard to age, population variability and environmental factors (Dányi 2007, 2008; Ecologica Montenegrina 53: 38-44 (2022) This journal is available online at: www.biotaxa.org/em https://dx.doi.org/10.37828/em.2022.53.5 POPOVICI Ecologica Montenegrina, 53, 2022, 38-44 39 Zarei & Seifali 2020). This is the case with many other Geophilidae, where sometimes distinct geographic varieties assigned to the same species can be found (Barber et al. 2020). Presently, new data on the morphology of the species Geophilus impressus is provided from specimens collected in a Romanian periurban forest (Pădurea Băneasa), in relation to G. oligopus, the only other representative of the complex present in Romania (which closely resembles the collected specimens), and an analysis of the significance of some morphological characters is carried out, establishing their reliability within Geophilus. Material and methods Specimens were hand collected from leaf litter and stored in 70% ethanol in the author’s personal collection. Examination was carried out by clearing according to the methods outlined by Pereira (2000), with an Olympus CX21 light microscope. Figures were made using a drawing tube. External anatomical features were described and named according to conventions proposed by Bonato et al. (2010) and Crabill (1954). Examined specimens. 1 ♂ ,11.04.2021; 1 ♀, 25.04.2021; 1 ♀, 03.05.2021; Pădurea Băneasa forest (44.522085 N, 26.091379 E), alt. 102 m., leg. George Popovici. Results Summary description of examined specimens Head and antennae (Fig. 1 A). Cephalic plate without frontal sulcus, subquadrate, 1.15–1.17 times wider than long. Basal plate absent. Posterior margin straight, overlapping forcipular tergite. Antennae 3.6–4 times longer than cephalic plate. Articles III-XIII with single or paired sensilla brachyconica dorso-basally; sensilla trichoidea abundant, evidently longer on the dorsal side of each antennal article. Terminal article 1.76 times longer than wide; two medial fields of sensilla basiconica distributed in two grooves dorsolaterally, extending for 20% of its total length. Labrum and clypeus (Fig. 1 D). Clypeus uniformly reticulate, with three pairs of postantennal setae in regular arrangement. Labrum clearly divided into three pieces; with three denticles on its medial piece and 5+5 hyaline filaments on the lateral pieces. First maxillae (Fig. 1 B). Telopodites incompletely divided into two articles; with indistinct lappets; with distinct reticulation forming large cells. Second article with 1+1 large setae ventrally. Coxosternum without lappets and with incomplete medial division; uniform reticulation in the form of of large cells; 2+0 small setae ventrally. Coxosternal projections well-developed, shorter than the telopodites, with 3+3 small setae apically and 2+1 small setae basally. Second maxillae (Fig. 1 B). Coxosternum undivided, with 3+3 setae apically and 2+1 setae basally; uniform reticulation in the form of large cells. Telopodites divided into three clearly separated articles. First article with 1+1 small setae laterally, second article with 1+1 small setae laterally, and third article with 3+4 large setae apically, ending in a distinct tubercle. Forcipular segment (Figs. 1 C, 2 A). Forcipular tergite reduced. Forcipular coxosternite uniformly reticulated, with 45 setae and a straight, medially notched, anterior margin. 2+2 regularly spaced setae on anterior margin. Coxopleural sutures ending just before reaching the anterior margin. Chitin lines incomplete, vanishing before reaching the condyles. Tarsungulum with smooth, gently curved, internal margin and pronounced basal denticle; with 4+4 large setae basally. Calyx of venom gland short, approximately hemispheric in shape. Venom gland indistinct, located predominantly in the trochantheroprefemur. Trunk (Fig. 2 B). Male with 41 and both females with 43 leg-bearing segments. Carpophagus structures distinct, well-sclerotized, consolidated, present from sternite 2-4 to sternite 17, most developed on sternites 9–11. Anterior pore fields elliptical, spindle shaped, restricted to posterior half of metasternites 2– 17. Area of pore fields separated from metatergite by indistinct anterior transverse sulcus and posterior reticulation. Last leg-bearing segment (Fig. 2 C). Ultimate pleuropretergite complete. Metasternite trapezoidal, partly covering coxal organs. Each coxopleuron with 3+3 to 4+4 evident coxal organs opening ventrally and NEW DATA ON THE MORPHOLOGY OF GEOPHILUS IMPRESSUS 40 one separate, smaller, ventro-laterally positioned (inconspicuous in male specimen). Ultimate legs densely setose ventrally in both males and females, more swollen in males. Pretarsus simple, unguiform. Male gonopods biarticulate. Female gonopodal lamina indistinctly bilobed, devoid of setae. 1+1 anal organs. Figure 1. A – Cephalic capsule and antennae, dorsal view, B – Maxillae I and II, ventral view, C – Forcipular segment, ventral view, D – Clypeus and labrum, ventral view. Discussion Although all examined specimens were sexually mature, several important diagnostic features appeared inconspicuous upon initial examination. Among these, the presence of an isolated coxal organ described as a constant and distinguishing feature of G. impressus (Eason 1961) is more variable than initially considered, as this feature was absent in both the examined male specimen as well as in French populations described by Brolemann (1930) under Geophilus insculptus debilis Brolemann, 1930, which is now to be considered a synonym of G. impressus. Furthermore, its smaller size relative to the other coxal organs represents a new variation, as past literature almost invariably presented all coxal organs as being of uniform size (Eason 1964; Kaczmarek 1979; Barber 2009; Stojanović et al. 2019). As the number of coxal organs is correlated with specimen age in other Geophilid taxa (Horneland & Meidell 2009), care should be taken to prevent identifying immature specimens with closely related species with a shorter adult body length. The presence and distinctness of lappets on the first maxillae is similarly variable. In the examined specimens only POPOVICI Ecologica Montenegrina, 53, 2022, 38-44 41 telopodal lappets could be observed, although not as distinctly as illustrated in past literature (Christian 1996, Stojanović et al. 2019). Coxosternal lappets were absent, again in accordance with past descriptions (Christian 1996, Brolemann 1930, Eason 1964), although the reticulation of the first maxillae gives their lateral edges a “fringed” aspect which can be confused with the distinct lappets seen in other Geophilidae. Figure 2. A – Apex of right forcipule, ventral view, B – Leg-bearing segment 9, ventral view, C – Last leg-bearing and postpedal segments of female, ventral view. NEW DATA ON THE MORPHOLOGY OF GEOPHILUS IMPRESSUS 42 Along with structures associated with the maxillae, these characters present significant intraspecific variability as well as being dependent on the developmental stage of the specimen examined (Stojanović et al. 2020). The distinction established by Christian (1996) regarding the reticulation pattern of the maxillary coxosternite and telopodites is found to have no taxonomic value in separating G. oligopus from the examined specimens of G. impressus. Contrastingly, the presence and development of the carpophagus pits were found to be highly consistent with the original and subsequent descriptions of both G. impressus (cited as G. alpinus) and G. oligopus (Dányi 2007, 2010) marking them as an important character state for the separation of these two taxa. Note on Leg-Bearing Segment Variation A noticeable trend among many European Geophilidae is the reduction of the number of leg-bearing segments with an increase in latitude. This phenomenon has been widely described in several geophilid taxa (Kettle & Arthur 2000; Simaiakis et al. 2013), and due to the pattern’s relative stability, has been named the “converse Bergmann’s Rule” (Hayden et al. 2012). Notable exceptions to this trend can be found in other Geophilomorpha where the opposite or no correlation exists with latitude (Bonato et al. 2003; Simaiakis et al. 2010), and its stability within Geophilus remains insufficiently studied. A notable feature of the examined specimens is the low number of leg-bearing segments for both male and females, 41 and 43 respectively, representing a new lower limit for both sexes in G. impressus. This character opposes trend for other Geophilidae (Hayden et al. 2012), where intraspecific variation in the number of leg-bearing segments relative to latitude shows a negative linear regression, however it agrees with the pattern observed in a congener, Geophilus proximus C. L. Koch, 1847 (Simaiakis et al. 2010). Previous records with similarly low numbers of leg-bearing segments have been recorded from Slovakia (Tuf pers. comm.) and other European localities (Bonato et al. 2016; Foddai et al. 1999; Stojanović et al. 2019), where males with 43 leg-bearing segments were occasionally found. Contrastingly, populations from the UK described by Eason (1964) show a lower limit of 45 leg-bearing segments for males while data collected by Lewis (2000) and Arthur & Blackburn (1999) from Yorkshire, Northumberland and Durham in Northern England places this limit higher, at 47 segments. Overall, these records suggest a possible positive correlation between latitude and number of leg-bearing segments for G. impressus across Europe. In the past this has been attributed to limiting environmental factors on embryonic and postembryonic development rates (Hayden et al. 2012), however this seems not to be the case for the population in Băneasa forest and its underlying cause remains unclear. The extent to which G. impressus populations differ in their number of leg-bearing segments across Romania and Europe remains insufficiently known until further sampling and morphological data is obtained. However, the present observation suggests that previous observation about the correlation between latitude and segment number requires additional revision via a regression analysis to establish the existence of any pattern among European G. impressus populations. Acknowledgements I am greatly indebted to the comments provided by Dr. Erhard Christian and Prof. Ivan Tuf on intraspecific variation in G. impressus. I would also like to thank Felix Vîjiac for digitization of the figures and Dr. Oana Paula Popa and Dr. Elena Iorgu for providing feedback on the initial draft manuscript. I am also grateful to the anonymous reviewers for their suggestions to improve the manuscript. References Arthur, W. & Blackburn, J. (1999) Limited variation in segment number in populations of Brachygeophilus truncorum and Geophilus insculptus in Northumberland and Durham. Bulletin of the British Myriapod Group, 15, 9–13. Barber, A. D. (1999) Geophilus insculptus or Geophilus oligopus?. Bulletin of the British Myriapod and Isopod Group, 15, 26–27. Barber, A.D. (2009) Centipedes. Synopses of the British Fauna (N. S.), 58, 1–228. POPOVICI Ecologica Montenegrina, 53, 2022, 38-44 43 Barber, A. D., Gregory, S. J. & Marquis, A. 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