Larval cases of caddisfly (Insecta: Trichoptera) affinity in Early Permian marine environments of Gondwana

Abstract

Caddisflies (Trichoptera) are small, cosmopolitan insects closely related to the Lepidoptera (moths and butterflies). Most caddisflies construct protective cases during their larval development. Although the earliest recognisable caddisflies date back to the early Mesozoic (Early and Middle Triassic), being particularly numerous and diverse during the Late Jurassic and Early Cretaceous, the first records of their larval case constructions are known exclusively from much younger, Early to Middle Jurassic non-marine deposits in the northern hemisphere. Here we present fossils from the Early Permian (Asselian-Sakmarian) marine deposits of Brazil which have strong morphological and compositional similarity to larval cases of caddisflies. If they are, which is very probable, these finds not only push back the fossil record of true caddisflies, but also indicate that their larvae constructed cases at the very beginning of their evolution in marine environments. Since modern caddisflies that construct larval cases in marine environments are only known from eastern Australia and New Zealand, we suggest that this marine ecology may have first evolved in western Gondwana during the Early Permian and later spread across southern Pangea.

Figure 1. Locality and lithology.

(a) Locality of the Campáleo outcrop in Brazil (arrowed). (b) Lithological section of the Lower Permian Lontras Shale (left) with the fossiliferous black shales containing the larval cases at the Campáleo site (right). The map was drawn using Corel Draw x5.

Figure 2. Early Permian fossils interpreted as caddisfly larval cases from Campáleo outcrop, Brazil.

(a,c,e) Close association of two larval cases surrounded by dispersed silk strips. (b,d,f) Single individuals, one with well-visible silk strips (b) and two (d,f) associated with hexactinellid sponge skeletons (arrowed). (a) CPE 5917, (b) CPI 454, (c) CPE 7812, (d) CPI 679, (e) CPE 7811, (f) CPI 680. Scale bars 5 mm.

Figure 3. Foreign particles gathered by the larvae and adhered to the silk cases.

(a–c) Plant fragments, CPE 3142. (d) insect fragment (arrowed), CPE 3142. (e) fish tooth, CPE 5917. (f) fish scales, CPE 3089. (g) sponge spicule (arrowed), CPE 5919. (h) scolecodont (arrowed), CPI 124. ESEM photomicrographs (a–d) and binocular microscope photomicrographs (e–h). Scale bars, 100 μm (a–b), 50 μm (c), 20 μm (d), 500 μm (e–g), 10 μm (h).

Figure 4. Structure and composition of the Early Permian larval cases.

(a,c,d) ESEM photomicrographs of thread-like structures of the silk building the larval cases. (b) EDS spectra showing the elemental composition of the case exterior and silk structure. White circles on (a) indicate the spots of EDS analyses. Scale bars 10 μm.