Brain and sense organ anatomy and histology of the Falkland Islands mullet, Eleginops maclovinus (Eleginopidae), the sister group of the Antarctic notothenioid fishes (Perciformes: Notothenioidei)

• Published in: Journal of Morphology
• Main Authors: Eastman, Joseph T., Lannoo, Michael J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Antarctic; The Antarctic; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1002/jmor.10571; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjmor.10571; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmor.10571

Abstract The perciform notothenioid fish Eleginops maclovinus , representing the monotypic family Eleginopidae, has a non‐Antarctic distribution in the Falkland Islands and southern South America. It is the sister group of the five families and 103 species of Antarctic notothenioids that dominate the cold shelf waters of Antarctica. Eleginops is the ideal subject for documenting the ancestral morphology of nervous and sensory systems that have not had historical exposure to the unusual Antarctic thermal and light regimes, and for comparing these systems with those of the phyletically derived Antarctic species. We present a detailed description of the brain and cranial nerves of Eleginops and ask how does the neural and sensory morphology of this non‐Antarctic notothenioid differ from that seen in the phyletically derived Antarctic notothenioids? The brain of Eleginops is similar to those of visually oriented temperate and tropical perciforms. The tectum is smaller but it has well‐developed olfactory and mechanoreceptive lateral line areas and a large, caudally projecting corpus cerebellum. Eye diameter is about twofold smaller in Eleginops than in many Antarctic species. Eleginops has a duplex (rod and cone) retina with single and occasional twin cones conspicuous centrally. Ocular vascular structures include a large choroid rete mirabile and a small lentiform body; a falciform process and hyaloid arteries are absent. The olfactory rosette is oval with 50–55 lamellae, a large number for notothenioids. The inconspicuous bony canals of the cephalic lateral line system are simple with membranous secondary branches that lack neuromasts. In Antarctic species, the corpus cerebellum is the most variable brain region, ranging in size from large and caudally projecting to small and round. “Stalked” brains showing reduction in the size of the telencephalon, tectum, and corpus cerebellum are present in the deep‐living artedidraconid Dolloidraco longedorsalis and in most of the deep‐living members of the Bathydraconini. Eye ...