Morpho‐anatomy of the otic region in carapid fishes: eco‐morphological study of their otoliths

Abstract

Carapid species are characterized by so-called otophysical structures (sonic muscles, broad first apophyses covering the anterior part of the swimbladder, etc.) The family includes pelagic (Pyramodon and Snyderidia) and benthic (Echiodon) species and ones that are either commensal with (Onuxodon, Carapus) or parasites of (Encheliophis) invertebrates (sea cucumbers, etc). The aim of the present work was to seek possible relationships between the structures of the inner ear (particularly the sagitta) on the one hand and otophysical structures and lifestyles within the Carapidae family. In the eight species studied, the otic cavity is wide, the saccular otosac and its sagitta are particularly developed. The sacculi touch each other on the median line. A comparison of the inner ear structures reveals notably that the species with the most developed sagitta and sacculus are those with the largest parapophyses and have a commensal or parasitic lifestyle. 2001 The Fisheries Society of the British Isles

Relationships between inner ear and sagitta growth during ontogenesis of three Carapini species, and consequences of life-history events on the otolith microstructure

“…This led to the sagitta rising, from an approximately antero-ventral to an antero-dorsal orientation, which in turn similarly affected the sphenotic and consequently the recessus utriculi. The pterotic elongation caused an anterior displacement of the arch of the horizontal semicircular canal and an elongation of the pars superior, which thus appeared shorter than in non-otophysi teleosts (Parmentier et al 2001b). However, if sagitta require space for growth, this suggests that the pressure exerted on the otic cavity could be due to the endolymph.…”

“…These characteristics resulted in a semi-ellipsoid shape. The mean increment number varied depending on the species: 48 (±6.5; n=16) increments for C. boraborensis, 82.7 (±4.7; n=23) for C. homei and 68.4 (±7; n=5) for E. gracilis (Parmentier et al 2001b). 2.…”

“…It appears unlikely that brain development could guide otic capsule elongation. Whereas the encephalon filled up most of the space in the tenuis otic cavity, the brain became elongated during ontogenesis and was concentrated forward, with only a thin myelencephalon at the inner ear level (Parmentier et al 2001b). Furthermore, it was noteworthy that both the inner ear and sagitta shapes in tenuis of these three species were similar to those of Onuxodon fowleri, a Carapidae the adults of which present the least elongation of the otic cavity (Parmentier et al 2001b).…”

“…This thickening is greater in the parasitic species (E. gracilis) than in the commensal ones (C. boraborensis and C. homei). The latter differences could be related to the life style of the fish species (Parmentier et al 2001b).…”

“…However, the otic area and the stato-acoustic organ exhibit several particularities described in adult fish (Parmentier et al 2001b). The two most noteworthy concern the location of the pars inferior otolithic end organ (the sacculus and lagena) and the morphology of the sagitta.…”