Cartilaginous fish rely on an array of sensory modalities for feeding, breeding and predator avoidance. Electroreception and mechanoreception are two non-visual senses mainly used for orientation and feeding at close range. Such modalities may become more important for survival in deep-sea environments, where sunlight is absent and food sources are scarce. Yet, the ampullary and lateral line systems have been described in very few deep-sea species to date, hindering our understanding of their ecological and evolutionary adaptations compared to shallower counterparts. This study aims to describe the histo-morphological organisation of these two sensory modalities in five ‘deep-sea’ chondrichthyans (three sharks, two chimaeras).
Pore distribution and abundance were assessed via digital mapping of the two sensory pore types and their corresponding canals. DiceCT imaging was used to increase mapping accuracy for both systems, especially to confirm size and position of ampullary clusters and the extent and orientation of canals. Pore sizes were measured from a random subset of ampullary pores per cluster and mechanosensory pores using light microscopy. Ampullary canal length was estimated using the average distance between pores and the corresponding cluster’s centre on the resulting map. The anatomical and cellular organisation of peripheral sensory organs were determined using histology. Preliminary results indicate interesting differences from previous literature and could suggest a combination of both shark and ray histo-morphological traits for the pore, canal and cluster morphometrics observed in the chimaera study species.
This study is the first to characterise both the electro- and mechanosensory systems in several deep-sea chondrichthyans from two subclasses, using a range of techniques including bioimaging, macro- and micro-morphology, and histology. Such knowledge will increase our understanding of the sensory ecology of these lesser-known species, and has the potential to discover new morphological aspects for these sensory modalities, which may shed light on key evolutionary adaptations.