Oligotoma negra, Hagen, 1885

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

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.

The meso- and metathoracic wing base T2,3- 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: T2-S with four branches: H-DCT, H-VCT, T2-DB, and T2-VB. T2-CT absent. H-DCT runs directly anteriad, with T1-DVi branching dorsad before continuing dorsally along prothoracic tergum. T1-DC present, extending mediad near branching of T1-DVi. H-VCT runs anteriad, with T1-L branching ventrad just prior to a nearly 90° turn ventrad, subsequently turning anteriad along prothoracic sternite. T1-VC present, branching off T1-L. T2-VB runs posteriad and slightly ventral briefly before curving dorsad; small T2-AWL branching anteriad at apex of curve, dividing into T2-AWba dorsad and T2-AL continuing posteriorly toward midleg. T2-DB continues, curving medially with several branches, likely for flight muscle, before extending posteriad as T2-ADLT. Full DLT not visible but likely present, possibly fluid infilled; Lacombe (1958) indicates presence of dorsal connective. T2-VB runs posteroventrad, with large T2-FM branching dorsad and laterally. T2-VB continues as T2-VLT, connecting with T3-S. T2-VC present, branching mediad approximately halfway between T2-S and T3-S. T3-S with four branches: T3-AWL, T2-PWL, T3-DB, and T3-VB. T3-AWL running dorsad, curving posteroventrad where T3-W-c-r splits dorsally and remaining branch continues as T3-L. T2-PWL connecting directly from anterior; T2-PL branching ventrally, joining with T2-AL after a short distance and continuing as T2-L; T2-Wbr continues anteriad from T2-PWL; T2-Wbr partial likely due to fluid infilling. T3-DB runs mediad, dividing after a short distance into T2-PDLT anteriorly and T3-DLT posteriad. T3-VB runs posteroventrad, with a connection to T2-VLT very close to T3-S; T3-VB continues posteriorly as T3-VLT, linking up with A1-S. T2-VLT-Vi on right side, extending past T3-S into abdomen; unclear if T2-VLT-Vi links with an abdominal spiracle. T3-S on right side slightly different from left, possibly due to displacement of tracheae by distended alimentary canal air space; T3-S on right side with T3-VLT positioned posteriad as with right side, but with short, curving spiracular branch dorsad and anteriad, with T2-VLT connecting from anterior; branch continues dorsad to T2-AWL, T2-DB, T2-PWL split as with left side.

ABDOMEN: A1..8-S present. A1-S modified from subsequent abdominal segments; A1-S with five branches: A1-DB, T3-PWBa, T3-VLT, and T3-PL. A1-DB short and running mediad, connecting with T3-DLT from anteriad and continuing as A1-DLT posteriad. T3-WBr (also partial, likely due to fluid infilling) runs anteriad, continuing with small T3-W-cu-a into trailing edge of hind wing. T3-VLT from directly ventrad. T3-PL runs ventrad, lateral from T3-VLT, joining with T3-AL and extending into hind leg as T3-L. Segments A2..7 likely similar but morphology difficult to determine due to distention of air-filled alimentary canal. A2..7-DLT present, arcing slightly dorsad and usually sinuous. A n - VLT present. A6-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; A3-Vi and A4-Vi large and directly posteriad, spanning sev- eral segments. A-Cr visible at base of cerci.

Figures

FIGURE 21. Air sacs formed from alimentary canal in subimago and adult Ephemeroptera, shown in lateral views. A. Neocloeon triangulifer subimago; B. N. triangulifer adult; C. Ephemera sp. adult. Specimens not to same scale.

FIGURE 75. Oligotoma negra (Embioptera: Oligotomidae) lateral view.

FIGURE 76. Oligotoma negra (Embioptera: Oligotomidae) dorsal (left) and ventral (right) views.

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.