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 Oligotoma negra “Black webspinner” Figures 75 (lateral), 76 (dorsal, ventral) Plates 47 (lateral), 48 (dorsal, ventral) The respiratory system of Embioptera remains rather understudied, with the most recent detailed analysis of tracheal anatomy by Lacombe (1958 , 1971 ). The specimen of Oligotoma shown here is a male and is notable because of the air-filled alimentary canal ( fig. 77 ). Male webspinners do not feed, and like Ephemeroptera ( fig. 21 ), the alimentary canal is coopted as a large air space, spanning the length of the body. In this specimen, the distention of the alimentary canal compressed tracheae against the inner body wall, making determination of morphology and assessment of homology challenging (particularly in the abdomen). Some notable differences were observed between Lacombe (1958) and the specimen here, particularly in the thorax, but her work was useful in mapping abdominal tracheae. FIGURE 75. Oligotoma negra ( Embioptera : Oligotomidae ) lateral view. FIGURE 76. Oligotoma negra ( Embioptera : Oligotomidae ) dorsal (left) and ventral (right) views. The meso- and metathoracic wing base T 2,3- Wbr are likely present but partial in this scan, likely due to fluid infilling of this specimen as it was frozen to -20° C rather than -80° C. Although a tympanal hearing organ in the femur (of pro- and mesoleg, and occasionally hind leg) of webspinners was described by Szumik et al. (2019) , there is no evidence of an air space in femur of any leg (as seen here in the foretibia of Gryllus , for example). DESCRIPTION: HEAD : H-DCT extending anteriad, curving laterally along head capsule; H-VCT slightly ventrad. H-DC present, slightly anterior of cervix. H-DCT with H-DCT-DVi running dorsad anterior of cervix, following head capsule. H-DCT runs directly anteriad, dividing into H-DVB ventrad and H-Ant. H-VCT with H-VCT-DVi extending dorsally, nearly in contact with H-DCTDVi and following head capsule laterally. H-VCT continues anteriorly, with dorsal H-DVB connection to H-DCT. After short extension, H-VCT divides into H-Lbm, and subsequently into H-MxPlp, H-Md, and H-Oc. H-Lbm branch connecting mediad as H-VC. Branch leading to H-Oc continues to H-Ft. THORAX: T 2- S with four branches: H-DCT, H-VCT, T 2-DB, and T 2-VB. T 2- CT absent. H-DCT runs directly anteriad, with T 1-DVi branching dorsad before continuing dorsally along prothoracic tergum. T 1-DC present, extending mediad near branching of T 1-DVi. H-VCT runs anteriad, with T 1- L branching ventrad just prior to a nearly 90° turn ventrad, subsequently turning anteriad along prothoracic sternite. T 1-VC present, branching off T 1- L . T 2-VB runs posteriad and slightly ventral briefly before curving dorsad; small T 2- AWL branching anteriad at apex of curve, dividing into T 2-AWba dorsad and T 2- AL continuing posteriorly toward midleg. T 2-DB continues, curving medially with several branches, likely for flight muscle, before extending posteriad as T 2-ADLT. Full DLT not visible but likely present, possibly fluid infilled; Lacombe (1958) indicates presence of dorsal connective. T 2-VB runs posteroventrad, with large T 2- FM branching dorsad and laterally. T 2-VB continues as T 2- VLT , connecting with T 3- S . T 2-VC present, branching mediad approximately halfway between T 2- S and T 3- S . T 3- S with four branches: T 3- AWL , T 2- PWL , T 3-DB, and T 3-VB. T 3- AWL running dorsad, curving posteroventrad where T 3-W-c-r splits dorsally and remaining branch continues as T 3- L . T 2- PWL connecting directly from anterior; T 2- PL branching ventrally, joining with T 2- AL after a short distance and continuing as T 2- L ; T 2-Wbr continues anteriad from T 2- PWL ; T 2-Wbr partial likely due to fluid infilling. T 3-DB runs mediad, dividing after a short distance into T 2-PDLT anteriorly and T 3- DLT posteriad. T 3-VB runs posteroventrad, with a connection to T 2- VLT very close to T 3- S ; T 3-VB continues posteriorly as T 3- VLT , linking up with A 1- S . T 2-VLT-Vi on right side, extending past T 3- S into abdomen; unclear if T 2-VLT-Vi links with an abdominal spiracle. T 3- S on right side slightly different from left, possibly due to displacement of tracheae by distended alimentary canal air space; T 3- S on right side with T 3- VLT positioned posteriad as with right side, but with short, curving spiracular branch dorsad and anteriad, with T 2- VLT connecting from anterior; branch continues dorsad to T 2- AWL , T 2-DB, T 2- PWL split as with left side. ABDOMEN: A 1..8- S present. A 1- S modified from subsequent abdominal segments; A 1- S with five branches: A 1-DB, T 3-PWBa, T 3- VLT , and T 3- PL . A 1-DB short and running mediad, connecting with T 3- DLT from anteriad and continuing as A 1- DLT posteriad. T 3-WBr (also partial, likely due to fluid infilling) runs anteriad, continuing with small T 3-W-cu-a into trailing edge of hind wing. T 3- VLT from directly ventrad. T 3- PL runs ventrad, lateral from T 3- VLT , joining with T 3- AL and extending into hind leg as T 3- L . Segments A 2..7 likely similar but morphology difficult to determine due to distention of air-filled alimentary canal. A 2..7- DLT present, arcing slightly dorsad and usually sinuous. A n - VLT present. A 6-VC visible; other A n -VC likely present but displaced against body wall, see figure 78 . Several visceral tracheae visible, but dif- ficult to determine morphology; A 3-Vi and A 4-Vi large and directly posteriad, spanning sev- eral segments. A-Cr visible at base of cerci.