# The Morphology of the Rare Beetle Silphopsyllus desmanae (Leiodidae), a Commensal of the Semiaquatic Russian Desman

## TL;DR

This paper studies the beetle Silphopsyllus desmanae, which lives in the fur of the Russian desman, and compares its physical features to related beetles to understand its evolution and adaptations.

## Contribution

The paper provides a detailed morphological analysis of Silphopsyllus desmanae using modern methods and clarifies its phylogenetic relationships within the Leiodidae family.

## Key findings

- Silphopsyllus desmanae is less adapted to a semiaquatic host compared to the beaver beetle Platypsyllus.
- Leptinillus is identified as the sister group to the rest of the Platypsyllinae.
- Platypsyllinae is the sister group to Coloninae + Cholevinae based on morphological data.

## Abstract

Silphopsyllus desmanae, a species of the small subfamily Platypsyllinae of Leiodidae, lives in the fur of the semiaquatic Russian desman, and is apparently adapted to this highly specialized life style. Even though the morphology of adults of the species was described almost 70 years ago, we re‐examined it with modern methods and documented its external and internal features in detail, and discuss them with respect to phylogeny and function. Our analyses of morphological data place Leptinillus as the sister group of the remaining genera of Platypsyllinae, and Leptinus as the sister group of Silphopsyllus + Platypsyllus. Platypsyllinae are supported by many putative autapomorphies: supraantennal ridges directed mesad but not extending beyond the antennal insertions and not forming a transverse ridge; tentorium without connected laminatentoria anterior to the tentorial bridge; submentum subrectangular; labrum about as wide as the maxillary‐labial complex; elongate and posteriorly projecting lateral lobes of the mentum; antennomeres lacking periarticular gutters (and Hamann's organs); cervical sclerites absent; precoxal prosternal region distinctly longer than the coxal rests; mesocoxal cavities situated closer to the body midline than to the lateral mesothoracic margins; metanepisterna fused with the metaventrite; metascutum laterally overlapping the meso‐ and metapleural regions; procoxae subglobose or only slightly elongate; mesocoxae subglobose. Platypsyllinae are most likely the sister group of Coloninae + Cholevinae. Eight unique apomorphies differentiating Platypsyllus from all the remaining Platypsyllinae are mainly adaptations for living in the fur of beavers. Silphopsyllus is much less adapted to life on a semiaquatic host than Platypsyllus.

We document in detail the morphology of Silphopsyllus desmanae (Leiodidae), a commensal of the endangered semiaquatic Russian desman, and discuss it with respect to phylogeny and function. Silphopsyllus is much less adapted to life on a semiaquatic host than the closely related beaver beetle Platypsyllus. Our analyses of morphological characters place Leptinillus as sister to the remaining Platypsyllinae, and Platypsyllinae as sister to (Coloninae + Cholevinae).