Descriptions of four nearctic Procladius skuse pupal exuviae

Associated Procladius Skuse (Holotanypus Roback) material from the Sublette collection was found to have specimens with undescribed immature stages. Pupal exuviae of two species are described for the first time: P. barbatulus Sublette and P. clavus Roback. Adult and larval features are included for P. barbatulus. In addition, specimens of Nearctic P. denticulatus Sublette are compared to Palearctic P. signatus (Zetterstedt) to determine if exuviae features can separate these species or suggest that P. signatus is a senior synonym. Finally, associated pupal and larval traits of P. prolongatus Roback are compared to the original description, corroborating the theory that features are unique enough to warrant subgeneric status.


Introduction
Within Procladius Skuse, Holotanypus Roback is a diverse subgenus in the Nearctic region with 18 described species (Ashe and O'Connor 2009), of which six have not previously been described in the pupal stage.While comparing recently collected material to the Sublette collection at the University of Minnesota, a number of associated specimens were noted within Procladius, including two species (P.barbatulus Sublette and P. clavus Roback) with undescribed pupal exuviae.Along with these, we also compare an associated specimen of the Nearctic P. denticulatus Sublette to the morphologically similar Palearctic P. signatus (Zetterstedt) to determine if the pupal stage can be used to better distinguish these species.Finally, we used eight associated rearings from Alaska to reevaluate if P. prolongatus Roback is unique enough to have a separate subgenus designation (Roback 1980(Roback , 1982)).

Materials and Methods
All specimens in the University of Minnesota, St. Paul (UMSP) collection were originally identified by J. E. Sublette and adult features were reconfirmed for this study using Roback (1971).P. prolongatus reared associations were provided by Malcom Butler and will be added to the UMSP collection.Measurements and terminology follow Saether (1980).Additional specimens of P. denticulatus were identified by W. P. Coffman and D. Oliver, while additional specimens of P. signatus were identified by P. H. Langton.
Remarks.As only the second specimen reported, after the holotype, adult and larval traits were included for comparison to Sublette (1964) and Roback (1971).In Roback (1980) this specimen keys to couplet 18 for P. freemani, and in Saether (2010) to couplet 9 and P. freemani.With only a single specimen, it is not certain that any feature can be used to distinguish P. barbatulus from P. freemani in the pupal stage.Features span all three of Roback's variants (with var. 2 the best fit) and are also similar to specimens described by Saether.The larva keys to couplet 14 in Roback and appears indistinguishable from other species in this couplet.
Remarks.All specimens were pharate, making adult features difficult to observe so only hypopygium measurements were included.In Roback (1980) these specimens key to couplet 13, in Saether (2010) to couplet 6, and are similar to P. culiciformis.Saether's measurements of P. culiciformis were generally similar to Sublette's Riske Creek specimens, but it is possible that P. clavus can be distinguished by the wider apical constric- 4 5 tion of the horn chamber, which also leads to a smaller ratio for width of plastron plate/width of constriction.Remarks.Roback (1980) described features that suggested subgeneric status for P. prolongatus, and he formally implemented this distinction among Holotanypus groups in Roback (1982).
From associated Prudhoe Bay material, we can  The anal lobes from Roback's Barrow, Alaska, specimens were described as "unusually shaped" with a "projecting outer curve".The Prudhoe Bay specimens usually do have a rounded lateral shape, but none are as expansive as in Roback's description and some also have lateral edges that are straight.Based on descriptions in Roback (1980) and material from Isle Royale, Michigan, P. dentus also has a large anal lobe that can be rounded laterally.P. dentus and prolongatus can both have a fold near the respiratory organ neck, but in both species this feature is not always observed.Therefore, these two features are not diagnostic and without a series of specimens may create confusion when using the key in Roback (1980).These species may be reliably separated by tergite IV and VIII shagreen, which is elongate (4-7 µm) in P. prolongatus and short (1-4 µm) in P. dentus.In addition, the number of spines on the anal lobe will distinguish these species, with 30-48 in P. prolongatus and 56-63 (from Isle Royale) and 68 (from the single specimen reported by Roback) in P. dentus.
Larvae have one proleg that is apparently diagnostic in Procladius, with a wide, triangular base and a tight apical hook (see figure 244, Roback 1980).Prudhoe Bay tundra pond specimens have this feature.Larvae of P. dentus, though undescribed, should presumably have simple proleg claws, similar to all other known larvae in Holotanypus (Roback 1982).
Known range is Nunavut, Canada, and Alaska, USA.
Abdomen.Tergites with color pattern 3, minimal  Remarks.Separating this species from P. signatus, which has been suggested as a possible senior synonym (Roback 1971), is difficult since the two species are exceedingly alike.Including an additional three specimens (collected by W. P. Coffman and D. Oliver) to the one described here, we observe that on the whole P. denticulatus is smaller (ThL 400-430 µm), whereas P. signatus is larger (ThL 480-624 µm, mean = 546, n = 13).Roback (1980) gives the range for P. denticulatus ThL as 370-540 µm (mean = 468) and Saether (2010) a ThL range of 393-577 µm (mean = 469), so there is overlap.However, the means are well separated so ThL should be a useful feature unless a specimen falls into the intermediate range and geographic provenance is unknown.Size may be useful for total exuviae length as well, with a range of 5.7-8.5 mm (mean = 6.6) for P. signatus (Langton 1991).
In addition, points on tergite IV are smaller on P. denticulatus (1-2 µm), which are smaller than on tergite VIII (3-4 µm), whereas points on the two tergites for P. signatus are of similar size (4 µm, Langton 1991).This feature is independent of exuviae size.A final structural difference that may hold for P. signatus is that the strong points of the thoracic horn wall continue over the 'shoulder', where the horn constricts apically, and onto the 'hood', the apical region containing the plastron plate (Fig. 15).In contrast, P. denticulatus points on the hood are reduced in size and density.
Procladius denticulatus is widespread in the northern Nearctic.

Discussion
For the two newly described pupal exuviae, P. barbatulus does not appear to be distinguishable morphologically from P. freemani, but P. clavus does have a distinct set of features and appears to be most similar to P. culiciformis.In P. prolongatus there are distinct features in immature life stages that will separate it from similar species.
Whether P. denticulatus and P. signatus are at two ends of a cline from the Eastern Palearctic to the Nearctic, or if they are two distinct species that are only slightly diverged from a common ancestor, cannot be fully answered here.But our results do suggest that most specimens can be separated using the thoracic horn length and tergite IV sha- 12 13 14 green.As Roback (1980) points out, some intermediate specimens will complicate identification, particularly when a comparing a "larger series from a broad geographical range." Two exuvial features may be worth consideration for future Procladius revisions.First, variability in the pattern of tergite shagreen shows this is not necessarily a stable feature in some Procladius species, yet spinule size and comparison between T IV and T VIII appear useful.Finally, variation in size and distribution of points on the 'shoulder' and 'hood' of the thoracic horn should be investigated in this genus.
the immature traits used to support the subgenus.
Total length approximately 3.7 mm.
Known range for P. barbatulus is California, USA, in Fresno and Mono Counties.