DERMAPTERA

Herhold, Hollister W, Davis, Steven R, Degrey, Samuel P & Grimaldi, David A, 2023, COMPARATIVE ANATOMY OF THE INSECT TRACHEAL SYSTEM PART 1: INTRODUCTION, APTERYGOTES, PALEOPTERA, POLYNEOPTERA, Bulletin of the American Museum of Natural History 459 (1), pp. 1-184 : 1-184

ORDER DERMAPTERA

Dermaptera have been the subject of recent micro-CT studies, including the discovery of active tracheal compression via synchrotron imaging ( Westneat et al., 2003) as well as a detailed analysis of the head of Forficula auricularia ( Neubert et al., 2017) . Dermaptera phylogeny is considered to be generally unresolved, with distinctions between lower Dermaptera and higher Dermaptera considered somewhat arbitrary ( Haas, 2018). Recent transcriptomic and morphological studies have refined relationships within Dermaptera ( Wipfler et al., 2020) ; however, these analyses omit the fossil record (Tihelka et al., in prep). The taxa here consist of one “lower” dermapteran ( Anisolabis maritima , Anisolabidae , female) and one “higher” ( Forficula auricularia , Forficulidae , male), and although Anisolabis lacks wings, they are alike in tracheal architecture. Sex was determined for both species based on sexual dimorphism of the cerci. While the specimens were scanned at similar resolutions, 11.6 mm 3 /voxel for Anisolabis and 13.5 mm 3 /voxel for Forficula (see table 3 for all scan parameters), substantially more visceral tracheae are visible in the Anisolabis scan. This may be the result of slightly higher resolution, but also possibly due to different scanning parameters or preservation artifacts (fluid filling of small tracheae postmortem). Regardless, sufficient detail is present in both specimens to assess tracheal homology.

The two dermapteran specimens are similar in their overall tracheal layout, with most differences in the heads. Wing base tracheae T2,3-Wbr are well-developed in Anisolabis , even though apterous; however, wing tracheae T2,3-W-c-r and T2,3-Wcu-a are absent. A1-S is positioned dorsally in both specimens, unlike the remaining abdominal spiracles, possibly a modification for the ability of earwigs to raise the abdomen dorsally and forward to use the forceps for predation and defense. Additionally, the A n -VLT-Vi in Anisolabis all proceed anteriorly, whereas in Forficula , there appears to be a “split” where A n -VLT proceeds anteriorly for A2..5-VLT-Vi..5, but posteriorly for A6..7-VLT-Vi.

DESCRIPTION: HEAD: Majority of tracheal structures similar between Anisolabis and Forficula , differences described here for comparative clarity. H-DCT and H-VCT of similar diameter; H-DCTs curve inward slightly such that left and right tracheae nearly touch before turning laterally outward on entry to head capsule; H-VCT proceeds straight into head. H-DCT with several branches just anterior of cervix: H-DCC, H-DCT-DVi, H-Oc, and H-Ant. H-DCC present. H-DCT-Dvi running laterally and dorsad. H-Oc arcing laterally, with several small tracheae extending into eye, then continuing anteriorly and ventrad via H-Oc-Md to link with ventral H-Md; H-Oc-Ant branches off H-Oc in Anisolabis into antenna. H-Ant extends anteriorly through head into antenna; left side of Forficula as H-Ant-Ft with H-Ft branching off H-Ant near base of antenna. H-Ant with multiple tracheae in Anisolabis ; likely present in Forficula but not visible in this scan. H-VCT likewise with several branches just anterior of cervix: H-VCT-Vi, H-Ft-Lbr (absent in Forficula ), H-VC (off H-Ft-Lbr in Anisolabis ), and H-Mx-Md. H-VCT-Vi runs laterally and ventrad, like dorsal trachea. In Anisolabis , H-Ft-Lbr runs anteriad, with H-VC extending medially to link left and right sides; H-Ft branching laterally and anteriad with H-Lbr directly anteriad. In Forficula , H-VC branching directly from H-VCT. Both H-VC with H-VC-Dvi running directly anteriad, extending as far as frontal area in Forficula . H-Ft-Lbr (absent in Forficula ) running anteriad, with small H-Ft splitting laterally and anteriad, remaining H-Lbr anteriad. H-Mx-Md runs anteriad and slightly laterally, with several branches: H-Lbm running ventrad, with short H-LbmPlp; H-Mx ventrad, with short H-MxPlp. Remaining H-Md branch runs anteriad, with H-Oc-Md connection from H-DCT; H-Md-Ant branching dorsally (absent in Forficula left side) to join H-Ant from H-DCT.

THORAX: Although the thoraces of Anisolabis and Forficula differ substantially in overall exterior morphology, as seen in figure 43 , the tracheal topology of the thorax is retained between the two taxa. T2-S with four tracheae: H-DCT, H-VCT, T2-AWL, T2-DB; T2-CT absent. H-DCT arcs mediad before proceeding anteriorly; T1-Dvi branching close to T2-S, extending anteriad with several smaller branches; T1-DC present. H-VCT similar to H-DCT, arcing medially then anteriad toward head. T1-AWL branching dorsoventrally; T1-VC present, separating from T1-AL while remainder of T1-AL continues into foreleg. T2-AWL extending posteriad and slightly dorsad, bifurcating into T2-AL and T2-Wbr; T2-AL continues ventrad and posteriorly into midleg; T2-Wbr running dorsad and laterally, connecting directly with T2-S. T2-DB extending medially, ventrad and slightly anteriad, with three branches: T1-PL, T2-DLT, T2-VT. T1-PL extending through coxae before joining with T1-AL and continuing into proleg; T1-Fm visible. T2-DLT proceeds anteriorly to connect directly with T3-S via T3-DB. T2-VLT ventrad and posteriad, following mesothoracic sternite before arcing anteriad to link with T3-S. T3-S with four branches: T2-Wbr, T3-AWL, T3-DB, T3-VB. T2-Wbr extends from T2-S linking directly to T3-S. T3-AWL extending slightly dorsad before turning ventrad and laterally, bifurcating into T3-AL and T3-Wbr; T3-AL continues posteriorly into hindleg; T3-Wbr extending posteriad to connect directly to T3-S. T3-DB running mediad, linking with T2-DLT from anterior and T3-DLT continuing posteriorly. T3-VB runs mediad and posteriorly, with T3-VLT branching posteriad; T3-VB subsequently bifurcates into T2-PL and T2-VLT connection from T2-S. T2-PL runs anteriad from T3-S, joining with T2-AL from T2-S, continuing into midleg; several T2-Fm present. T3-VLT with T3-VL into hindleg femur.

ABDOMEN: A1..8-S present. A1-S highly modified from subsequent segments, placed dorsally with four branches: T3-Wbr, A1-DB, A1-VB, T3-PL. T3-Wbr connecting directly from T3-S; small T3-Wbr-Vi extends dorsad and medially along metathoracic tergite. A1-DB mediad, linking with T3-DLT from anterior and A1-DLT continuing posteriad. A1-VB ventrad, with A1-VLT branching directly posteriad; A1-VB continues ventrally, bifurcating into T3-Fm, extending laterally into hind leg, and A1-VC; T3-VLT connects with A1-VC. T3-PL runs ventrad and posteriad, joining with T3-AL before extending into hindleg. Tracheae from A2..6-S similar, A4-S described here as example. A4-S with three branches: A3-VLT, A4-DB, and A4-VLT. A3-VLT runs anteriad, extending from A3-S. A4-VLT branches medially and dorsad before curving posteriad and laterally toward A5.S. At apex of this arc A4-VLT- Vi extends anteriorly, spanning several segments. A n -VLT-Vi variable, see taxon descriptions below. Midway between A4-S and A5-S, A4-VC branches ventrad at right angle, following abdominal sternite. A4-DB directly dorsad; A3-DLT connecting from anterior and A4-DLT from posterior to form Y-shaped junction. Visceral tracheae extend from either end of A4-DB: A4-DB-Mvi extends laterally and dorsad from start (ventral end) of A4-DB; A4-DB-Dvi from base of Y-shaped junction with A3-DLT and A4-DLT. A4-DLT-Dvi present but A4-DC absent. A n -DLT-Vi numerous and highly variable, see descriptions below. A7-S connections like previous segments but distance between A7-S and A8-S greatly shortened. A8-DB with three tracheae: A7-VLT, A8-DB, and A8-VLT, but with posterior branching varying between taxa, see descriptions below. Extensive tracheation in A7 and A 8 in both genera, no doubt for large muscles that control the forceps.

Figures

FIGURE 43. Dermaptera thoraces, dorsal view: A. Forficula, B. Anisolabis.