A previously unknown feeding mode in millipedes and the convergence of fluid feeding across arthropods

Abstract

We report fluid feeding with a sucking pump in the arthropod class Diplopoda, using a combination of synchrotron tomography, histology, electron microscopy, and three-dimensional reconstructions. Within the head of nine species of the enigmatic Colobognatha, we found a pumping chamber, which acts as positive displacement pump and is notably similar to that of insects, showing even fine structural convergences. The sucking pump of these millipedes works together with protractible mouthparts and externally secreted saliva for the acquisition of liquid food. Fluid feeding is one of the great evolutionary innovations of terrestrial arthropods, and our study suggests that it evolved with similar biomechanical solutions convergent across all major arthropod taxa. While fluid-feeding insects are megadiverse today, it remains unclear why other lineages, such as Colobognatha, are comparably species poor.

Cellulose fermentation by the gut microbiota is likely not essential for the nutrition of millipedes

“…Additionally, millipedes produce endogenous GHs in their salivary glands and midgut for digesting non-structural plant material (23, 34, 55). Fluid feeding, described in Colobognatha millipedes, enables feeding on fresh plant material (66). These findings don’t exclude other roles of the millipede gut microbiota, such as detoxification of plant toxins (67), essential compound production (23), protection against pathogens (33), and even acquiring new genes through horizontal transfer (68).…”

Appearance of a transparent protrusion containing two pairs of legs on the apodous ring preceding the anamorphic molt in a millipede, Niponia nodulosa

“…To histologically observe the inner structures of the tail ends, paraffin sections were made according to the method described in previous studies [ 47 ]. Juveniles in the late preparatory period and the rigidation period were fixed in Bouin’s solution (saturated aqueous picric acid solution/formalin/acetic acid = 15:5:1) [ 48 ] for longer than 24 h and preserved in 70% EtOH until use. The specimens were dehydrated in increasing concentrations of ethanol, then transferred into xylene, and finally embedded into paraffin.…”

A new species of Illacme from southern California (Siphonophorida, Siphonorhinidae)

“…The identification and terminology of antennal sensilla followed that of Nguyen Duy-Jacquemin (1974) and Chung and Moon (2006) , summarized and reviewed by Sombke and Ernst (2014) . The terminology of mouthparts is from Silvestri (1903) , Koch (2015) , and Moritz et al (2022) .…”