# The lateral line and electrosensory systems of two holocephalans

## TL;DR

This study examines the sensory systems of two deep-sea chimaeras to understand how they detect prey in low-light environments.

## Contribution

The paper provides the first detailed morphological analysis of lateral line and electrosensory systems in two deepwater holocephalans.

## Key findings

- Harriotta avia uses its rostrum as a sensory probe for detecting prey.
- Hydrolagus bemisi relies less on electroreception compared to Harriotta avia.
- The sensory systems reflect similar feeding strategies for benthic prey detection.

## Abstract

The mechanosensory (lateral line) and electrosensory systems are two important non-visual sensory modalities, especially in low light environments. Despite their importance, these sensory systems have received little attention in deepwater chondrichthyans. Here, we describe the morphological organisation of the peripheral lateral line and electrosensory systems in two species of chimaeras; the pale ghost shark Hydrolagus bemisi (Chimaeridae) and the Australasia narrow-nosed spookfish Harriotta avia (Rhinochimaeridae), occupying depth ranges of 400–1,100 m and 260–1,278 m, respectively. Using topographic mapping, computed tomography, histology, and scanning electron microscopy, the distribution, abundance, size, and microstructure of lateral line grooves and organs (neuromasts), and ampullary organs (pores, canals, and bulbs) are described. The arrangement of the peripheral sense organs in both these systems may reflect comparable feeding strategies for detecting benthic prey. While the elongated rostrum of Harriotta avia is likely used as a sensory probe, providing spatially-resolved information about minute hydrodynamic disturbances and electric fields of potential prey beneath the animal, the arrangement of sense organs in Hydrolagus bemisi indicates that this species may rely less on electroreception. The study compares the morphology and provides information on the relative importance of two (non-visual) sensory modalities in two demersal holocephalans that remain vulnerable to anthropogenic disturbances.