COMPARATIVE ANATOMY OF THE INSECT TRACHEAL SYSTEM PART 1: INTRODUCTION, APTERYGOTES, PALEOPTERA, POLYNEOPTERA Author Herhold, Hollister W Author Davis, Steven R Author Degrey, Samuel P Author Grimaldi, David A text Bulletin of the American Museum of Natural History 2023 2023-03-31 459 1 1 184 http://dx.doi.org/10.5531/sd.sp.55 journal article 10.5531/sd.sp.55 eb1717dc-9526-481c-a859-7ca8fd036425 0003-0090 7730159 Medauroidea extradentata “Vietnamese walking stick” Figures 91 , 92 (lateral, anterior, posterior); 93 , 94 (dorsal, anterior, posterior); 95 , 96 (ventral, anterior, posterior) Plates 55 (lateral), 56 (dorsal), 57 (ventral) Although Strauss (2021) conducted the most recent work on stick insect tracheae, he focused on the prothorax and prolegs, concentrating on hearing. He employed terminology from Ander (1939) , also incorporated here, although he left several branches unlabeled. In the Medauroidea scan here, T 1- AL and T 1- PL remain separate, at least as far as the distal end of the foretibia. Strauss indicates foreleg (and mid- and hind leg) adaptations for hearing; these cannot be verified from this scan. Medauroidea is a good example of assessing homology using secondary criteria (serial homology). The T 2-DB branching pattern posteriorly in Medauroidea is somewhat ambiguous, in particular the placement of T 2- AL and T 2-Wbr. T 2- AL and T 2-Wbr could be swapped; however, the decision that the dorsal one is T 2- AL is based on serial homology with T 3. Additionally, the shorter DB branches, such as T 3-DB and T 3-VB here in Medauroidea (but also applicable elsewhere), could be argued to be branching directly from the spiracle. The presence or absence of a spiracular “atrium” is not specific here; these structures are most prominent in groups such as Orthoptera , where a large “cavity” sits just inside the spiracle with multiple tracheae branching in various directions. In Medauroidea , it appears that a very short “stub” of DB or VB may have trachea branching from it. T 2- CT may be present, but this stub may also be a spiracular atrium, as the closest (phylogenetically) relative with T 2- CT is Plecoptera (rather distant). FIGURE 85. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) anterolateral view. FIGURE 86. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) posterolateral view. FIGURE 87. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) anterodorsal view. FIGURE 88. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) posterodorsal view. FIGURE 89. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) anteroventral view. FIGURE 90. Extatosoma tiaratum ( Phasmatodea : Phasmatidae ) posteroventral view. The tracheal branching in first abdominal segment is very unusual and assessing its homology calls for some explanation. A 1- DLT is quite clearly absent, as no tracheae arc posteriorly in the form of a DLT ; T 3- DLT connects directly to the dorsum of A 1- S with no continuation. A 1- VLT initially appears to be A 1-MLT, but the ventral branch of T 3-VL into the hind leg is indicative of it being a VLT , not MLT. Additionally, A 1-VC branches from T 3-VL, rather than A 1-VB, an unusual arrangement. This branch is not a section of A 1-VB, as A 1- VLT connects A 1- S and A 2- S . The remaining branches are typical. The second abdominal segment is also slightly modified from the remaining segments extending posteriad. A 2-DB and A 2-VB are basically absent—while A 2-DC and A 2-VC are present, they branch directly from A 2- DLT and A 2- VLT . The primary connection between A 2- S and A 1- S anteriad is A 1- VLT . A 2-DC extends a little anteriad of A 2- S ; A 2-DC could arguably be A 1-DC but the branching pattern is from A 2- DLT , so homologizing based on connectivity or branching pattern seems more reasonable. DESCRIPTION: HEAD : The head tracheal morphology of M. extradentata features a network of loops interconnecting both dorsoventrally and laterally. Exploration of the 3D models in the supplementary digital data is encouraged. Three sets of tracheae into head: H-DCT, H-VCT, and additional H-VLT. H-DCT dorsad, proceeding anteriorly and forming a prominent H-DCTVLT-Loop anteriad and ventrad, connecting directly with H-VLT. H-Lbm anteriad from ventral apex of H-DCT-VLT-Loop. H-VCT runs anteriad, dividing into H-Ant and two branches, one looping posteriad to connect with H-VCT, forming H-Ant-Loop; second branch looping ventrad and posteriad to join H-VLT. THORAX: T 2- S with four connections: possible T 2- CT , T 2-DB, T 2-VB, and T 1- PL . T 2- CT short and running directly anteriad, bifurcating into H-DCT and H-VCT near posterior margin of prothorax; as T 2- CT absent in other Phasmatodea , this T 2- CT is possibly a deeper spiracular atrium rather than T 2- CT . H-DCT runs anteriad, extending through prothorax into head. H-VCT anteriad, with T 1- AL splitting off into foreleg; short connection to T 1- VLT at this branching point. T 2-DB runs posteriad, curving slightly ventrad before splitting into two pairs: T 2- DLT / T 2- AL dorsal branch and T 2-Wbr/ T 2-lvl ventral branch; T 2- AWL notably absent. For dorsal T 2- DLT / T 2- AL pair, T 2- DLT as with other specimens, positioned along dorsum with connection posteriad to T 3-DB; T 2- AL extending posteriad, connecting with T 3- S via T 2-PWB. Ventral T 2-Wbr/ T 2-lvl pair with T 2- AL posteriad with shallow arc dorsad to connect with T 2- PWL ; T 2-lvl along venter, connecting with T 3- S via T 2- VLT connection just anteriad of T 3- S . T 2-VB short and directly ventrad, linking with T 2- VLT posteriad and T 1- VLT anteriorly. Both T 1-VC and T 2-VC present. T 1- PL runs anteriad, linking with T 1- VLT via short T 1-VL; T 1- PL extends into foreleg without joining T 1- AL . T 1- AL and T 1- PL do not join and remain separate at least until the distal end of the foretibia. Two small, visceral medial A 1-DVi-Med and A 1-VVi-Med extend through mesothorax, originating at A 1- S and extending into head. T 3- S with four branches: T 2- VLT , T 3-DB, T 3-VB, and T 2- PL . T 2- VLT from anterior, connecting T 2- S to T 3- S . T 3-DB short and mediad, quickly branching into T 3- AL posteriorly and remaining T 3-DB dorsad; T 3-DB joining with T 2- DLT anteriorly and T 3- DLT posteriorly in Y-shaped junction, linking to T 2- S and A 1- S . T 3- AL posteriad, joining with T 3- PL to form T 3- L , extending into hindleg. T 3-VB short, similar to T 3-DB, quickly splitting into T 3- VLT posteriad and remaining T 3-VB ventrad. T 3- VLT runs directly posteriad to A 1- S ; T 3-DC present toward posterior margin of metathorax. T 3-VB continues to T 3-PVC, which forms posteriad segment of hexagonal network comprised of T 3-VC anteriad and lateral sections connected to T 2- VLT . T 2- PL anteriad, joining T 2- AL and extending into mideg. T 2-VL branching from T 2- VLT , also extending into midleg; T 2-VL and T 2- L remain separate to distal end of midleg tibia. A 2-DVi-Med and A 2-VVi-Med extending through metathorax, with laterally asymmetric connections: A 2-DVi-Med to T 2- VLT on specimen’s left side, A 2-DVi-Med to T 2- VLT on specimen’s right side. ABDOMEN: A 1..8- S present. First abdominal segment approximately half as long as remaining abdominal segments. A 1- S and A 2- S branching patterns highly modified from remaining abdominal segments. A 1- S with four branches: T 3- DLT , A 1- VLT , T 3- VLT , and A 1- PL . A 1- S with additional A 2-VVi-Med connection on left side only, see description of A 2-VVi-Med below. T 3- DLT runs dorsad, connecting in anterior arc from T 3- S ; A 1- DLT notably absent. A 1- VLT runs directly posteriad to A 2- S ; T 3-VL directly ventrad from A 1- VLT ; A 1-PVC branching from T 3-VL. T 3- VLT from anterior, with two ventral commissures A 1-AVC1 and A 1-AVC2. T 3- PL ventrad, linking with T 3- AL before arcing posteriad to extend into hind leg. A 2- S with seven branches: A 1- VLT , A 2-DVi-Med, A 2-VVi-Med, A 2- DLT , A 2-DVi, A 2-VVi, and A 2- VLT . A 1- VLT runs directly anteriad from A 1- S . A 2-DVi-Med beginning as sinusoidal, looping branch, extending anteriorly and medially, each side combining in Y-shaped junction in metathorax and proceeding anteriorly along venter; A 2-DVi-Med asymmetric, with sinusoidal form on both sides but only right side leading to Y-shaped join, with left side coming from A 1- S . A 2-VVi-Med similar, arranged along venter. A 2- DLT runs dorsad and posteriad in arc connecting to A 3- S ; A 2-DC present off A 2- DLT . A 2-DVi and A 2-VVi ventrad, connecting with A 3- S . A 2- VLT likewise in ventral arc, also connecting with A 3- S ; four tracheae connect A 2- S with A 3- S . Remaining A 3.. A 8 segments similar, with varying degrees of A n -DB; A 3-DB short, A 4-DB not present, etc. A n - DLT and A n - VLT present on all, connecting segments longitudinally. A 3..8- S with anteriad visceral tracheae generally dorsad, posteriad visceral tracheae generally ventrad. A 4-Vi-VC present, formed from visceral tracheae and not from VLT as is typical.