Abstract
Larval development and shape ontogeny of the kelpfish Myxodes viridis (Clinidae) are described for the first time. A total of 214 individuals ranging between 3.51 and 23.09 mm standard length collected off central Chile were assessed employing classic and geometric morphometrics, illustration with camera lucida and a double-staining technique for cartilaginous and bone structure observation. Based on characteristics such as yolk sac presence and fin formation, six stages of larval development were differentiated: yolk sac, preflexion, flexion, early postflexion, late postflexion and juvenile. Shape changes during development are subtle and occur smoothly, being more significant in the head and preanal length, and ontogenetic allometry accounts for almost 15%. Cartilage formation takes place first at the branchial arches and cranium; then hypural, haemal and neural arches are consecutively formed. Bony structure ossification occurs late in the development. Vertebral centra ossify directly, without cartilaginous matrix replacement.
Highlights
Fish larvae often go through very complex processes of metamorphosis during growth
The objective of this work is to describe the larval development and shape changes during the early ontogeny of the kelpfish Myxodes viridis using two complementary methodologies, in order to increase the taxonomic knowledge of this family in South America
Measurements used here are defined by Moser (1996), and correspond to standard length (SL), head length (HL), preanal length (PAL), snout length (SnL), eye diameter (ED), and body depth (BD) (Fig. 1)
Summary
Fish larvae often go through very complex processes of metamorphosis during growth. A wide variety of developmental patterns, characterized by differential growth of different regions of the body at different sizes, are described for marine species and justified via ecomorphological hypotheses about the allocation of energy during growth (Russo et al 2007). In fish species with pelagic and filiform larval stages and an elongate adult body form, the ontogenetic growth intensities are not distributed uniformly across the body but in a regular pattern, constituting a smooth, continuous gradient. The gradient is characterized by a period with terminal growth centres (high intensities), corresponding to head and tail, and a continuous, Ushaped gradient between them (Fuiman 1983). In these species, the completion of the head is crucial for feeding and respiratory functions, whereas the completion of the tail is pivotal for cruising and escape reactions (Russo et al 2009)
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