Perlodes mortoni Klapálek 1906

Zwick, Peter, 2011, Polymorphism And Taxonomic Problems In The Perlodes Microcephalus Group (Plecoptera: Perlodidae); Perlodes Mortoni Removed From Synonymy, Illiesia 7 (26), pp. 291-296 : 293-295

Perlodes mortoni Klapálek 1906 , species propria

Material examined. Syntypes. The complete original material sent by K. J. Morton seems to be in Klap {lek's collection in the Natural History Museum at Praha Kunratice. Most specimens are from "Uddington, 13.iv.1902, K.J. Morton " or very similar collecting dates, plus several specimens from Carluke, Scotland, K.J. Morton (several dates; one ♀ with " Dictyopteryx microcephala Pict. " in Morton's hand). There are also 1♂, 1♀ from "3.v.80 Gotha Dr. Müller " mentioned in Klap{lek (1906). Several Scottish specimens are labelled "Cotype", only 2♀ from "Uddington, 13.iv.1902, K. J. Morton " are labelled "Type". For lack of time, biometry was not performed and only one of the latter two females was studied for eggs. Its abdomen is detached and on a card pinned with the fore body, several eggs are in Euparal on a plastic slide pinned with the specimen, plus a few eggs on a glass slide presently in my collection .

Additional material. Scotland: R. Tweed at Innerleithen , 1.v.2010, D. Pryce, under stones, 25♂, 15♀ ; Perthshire , Dunkeld , R. Tay , late April 1990, Andreas Zwick, 1♂, 1♀ ; Wales: R. Dee at Pen-y-Lan, Clwyd / Shropshire border, iii.2004, Malaise trap, D. Pryce, 4♂, 3♀ ;

Brachypterism. Very similar to P. dispar , male wings between 1.4 and 1.8 times as long as head width, peaking at a RWL of 1.6 ( Fig. 4 ).

Egg structure ( Fig. 5 ). Sclerites on the anchor disc margin differ extremely between specimens taken together, ranging from relatively large plates longer than wide and in one case also with a clockwise twist (mo-3) to irregularly shaped sclerites placed at distances from each other along the disc periphery, to a single row of short, transverse sclerites (mo-5), and ultimately, numerous small sclerites which on their medial edge may not be clearly separate from very small sclerotized patches (mo-6, mo-7).

The spectrum of observed character expressions was similar between British rivers, there were more specimens with relatively small than with large sclerites. There are no clear differences from the presumed aberrant population of P. microcephalus from Medingen, N. Germany.

Unlike in P. dispar , brown pigmentation and sclerotization of structures along the anchor disc margin were always expressed.

Notes. Illies (1955) formally synonymized P. mortoni with P. microcephalus . Evidence for this decision was not mentioned. Historical specimen labels reveal that K. J. Morton had felt the same. Other students also agreed that the single British - Irish Perlodes is indeed P. microcephalus (for example, Hynes 1967, 1977, Costello 1988a, Elliott 1992, Ashe, O'Connor & Murray 1998). Short-wingedness of the Irish Plecoptera received special attention but no male P. mortoni was available ( Costello 1988b).

I abstain from the originally intended lectotype designation because: 1, not all of the evident syntypes could be adequately studied; 2, fresh material shows that egg anchor sclerites vary too much for any single specimen to represent a reference specimen characteristic of the species.

Figures

Fig 5. Perlodes spp., sclerite platelets on periphery of anchor disc of German P. microcephalus (River Fulda at Ried), P. dispar (River Fulda nr Schlitz), and Scottish P. mortoni. mo-1 to mo-7 show individual ♀♀, most from River Tweed, mo-2 from River Dee. There are 5 ♀♀ similar to mo-3 (including one from River Tay), 4 ♀♀ are similar to mo-6, 5 ♀♀ (rivers Tweed and Dee) are similar to mo-7. Orientation (centre of anchor disc is towards right hand side) and scale same for all.

Figs. 1-4. Perlodes spp., frequency (% of sample) of particular relative wing-lengths (RWL = WL/HCW) in males and females. 1. P. microcephalus. 2. P. microcephalus (?) from Medingen, N. Germany. 3. P. dispar. 4. P. mortoni. Figures in legends are the numbers of specimens measured; compare text for origin of samples.