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 Timema cf. californicum “ California timema (walkingstick)” Figures 79 , 80 (lateral, anterior, posterior); 81 , 82 (dorsal, anterior, posterior); 83 , 84 (ventral, anterior, posterior) Plates 49 (lateral), 50 (dorsal), 51 (ventral) The tracheal morphology of Timema is nota- ble for the proliferation of comparatively thin tracheae that form networks throughout the body. These networks make assessment of homology difficult especially in the thorax, where differentiating similarly networked tracheae from other taxa is unclear. Identifiable homologous tracheae are labeled here, and incorporation of data from some of the 20 or so other Timema species could help to resolve ambiguous structures. Notably, T 2,3- DLT are absent in Timema , with the additional absence of the corresponding T 2,3-DB; however, the networked nature of tracheae elsewhere likely compensates for the lack of dorsal longitudinal connections. Although distantly related, the Timema thorax is rather reminiscent of termites, with (possibly) dual ventral commissures, which may be convergent. DESCRIPTION: HEAD : Head tracheae with several networked interconnections dorsoventrally; due to three-dimensional nature of head tracheal architecture, readers are encouraged to refer to models in supplementary digital data. Prominent H-DCT-VCT-Loop at anterior margin of prothorax, with smaller H-DCT and H-VCT branching from dorsal and ventral portions of loop. H-DCT extending anteriad and slightly dorsad, splitting into dorsal branch to H-DX intersection near vertex; and anteriad H-DCT-Ant branch, joining with ventral H-VCT-Ant branch and extending into H-Ant. H-DX with anteriad branches extending laterally and ventrad, reconnecting with H-VCT-Ant as H-DX-VCT-Loop. H-VCT runs anteriad, with H-VCT-Ant branching anterodorsally to join with H-DCT-Ant. H-VCT continues anteriad with H-Mx branching ven- trad; H-Mx with H-VC before branching to H-MxPlp. H-VCT with continued anterodorsal curve, with H-Md branching anteriad; H-VCT joining with H-DCT via H-VCT-Ft-Loop; H-FtLbr branching ventrad near anterior apex of H-VCT-Ft-Loop. THORAX: T 2- S with three branches: H-DCT, H-VCT, and T 2- AWL . H-DCT runs directly anteriad toward head; small T 1-Cx ventrad in middle of prothorax. H-VCT likewise running anteriad, with T 1- AL ventrad at posterior margin of prothorax; T 1- PL not present. T 1- AL with medial branch to T 1-VX. T 1-VX branching into three anteriad tracheae, extending toward head as H-VLT, with right side H-VLT fusing with H-VLT-Med anteriad of cervix. T 2- AWL runs ventrad and mediad before turning dorsally and posteriad in an S-shaped curve; small T 2-DB and T 2-VB branching dorsad and ventrally (respectively) from T 2- AWL . T 2-DB linking with apparent T 1- DLT anteriad; T 2- DLT not visible. T 2-VB runs ventrad at bottom of T 2- AWL S-curve, bifurcating into anterior and posterior branches, both leading to network of tracheae forming numerous ventral commissures. Remainder of T 2- AWL bifurcating into T 2-Wbr and T 2- AL ; T 2-Wbr directly posteriad, linking with T 3- S via T 2- PWL ; T 2- AL posteriad and ventrad, linking with T 2- PL and extending into midleg. T 3 with three branches: T 2- PWL , T 3- AWL , and T 3-VB. T 2- PWL runs anteriad, splitting into T 2-Wbr dorsally and T 2- PL ventrad; T 2- PL joining with T 2- AL and extending into midleg. T 3- AWL runs dorsad, curving posteriorly and splitting into T 3-Wbr posteriad and T 3- AL ventrad; T 3- AL joining with T 3- PL and extending into hind leg. T 3-VB splitting into four tracheae close to T 3- S ; at least two of these extending into network of ventral commissures; several X-shaped commissure intersections present. FIGURE 77. Oligotoma ( Embioptera : Oligotomidae ) in A . lateral and B. ventral views, showing extent of air-filled alimentary canal and effect of distention on position of tracheae. Tracheae in orange, alimentary canal in grey. FIGURE 78. Volume rendering of Oligotoma ( Embioptera : Oligotomidae ) venter. Volume rendering as a visualization technique can reveal small details with subtle intensity differences that are difficult to hand-segment; note apparent presence of A3..7-VC, displaced against body wall by air-filled alimentary canal. FIGURE 79. Timema cf. californicum ( Phasmatodea : Timematidae ) anterolateral view. FIGURE 80. Timema cf. californicum ( Phasmatodea : Timematidae ) posterolateral view. FIGURE 81. Timema cf. californicum ( Phasmatodea : Timematidae ) anterodorsal view. FIGURE 82. Timema cf. californicum ( Phasmatodea : Timematidae ) posterodorsal view. FIGURE 83. Timema cf. californicum ( Phasmatodea : Timematidae ) anteroventral view. FIGURE 84. Timema cf. californicum ( Phasmatodea : Timematidae ) posteroventral view. ABDOMEN: A 1..8- S present, short A n -SB spiracular branch present on all A 1..8- S . A 1- S branching pattern slightly modified from remaining A 2..8- S , with T 3- PWL running anteriad, splitting into T 3-Wbr anteriad and T 3- PL ventrad, with T 3- PL joining with T 3- AL and extending into T 3- L . A 1..8-MLT present, with A 1..5-DB branching dorsad from A n -MLT; A 6..8-DB branching directly from A 6..8-SB. All A 1..6-DB linking with thin, sinuous A 1..6- DLT along dorsum; A n -DC not present. A 7,8- DLT substantially larger, with fanlike morphology expanding into highly tracheated hind- and midgut “appendices” ( Shelomi et al., 2015 ). A 1..8-VB present, extending to link with sinuous A n - VLT along venter; A 2,3,6,7,8-VC present; given distribution, other A n -VC likely present but not visible. Numerous visceral tracheae, most notably forming asymmetric connectives A 4- A 5-Vi-AsymC and A 5- A 6-Vi-AsymC; A 7-Vi-VC also present.