Among millipedes, adult males of the Helmintomorpha possess gonopods on the VII body ring. These specialized appendages differentiate in a very advanced phase of postembryonic development, changing from legs, to squamiform appendages, to gonopods. This transformation involves variable numbers of moults in the different species and is limited to one or very few nonterminal serially homologous elements in an otherwise morphologically homogeneous series of trunk rings. Here, we describe the changes affecting this area through three subsequent developmental stages. Our study, based on Nopoiulus kochii (Gervais, 1847), included observations on external morphology and internal anatomy as well. By this double approach, we discovered a dramatic remodeling of the endoskeletal, muscular, and nervous system. Most evident is the considerable reduction of the ring lumen caused by gonopod growth. This affects the course of the ventral nerve cord that is displaced dorsally comparing with immature stages. The complexity of the gonopod endoskeletal component is studied using confocal laser scanning microscopy. This technique permits us to describe their fine morphology in situ, avoiding the problems of accidental damages deriving from the dissection. Thus, we could note two gonopod apodemes that surround the digestive tract ventrally and laterally and offer insertion to two muscles, which are present only in the adults. This data can be the starting point from which the morphogenetic processes involved in the formation of the gonopods can be investigated.

Nonsystemic Metamorphosis in the Development of Millipede Gonopods

DRAGO, LEANDRO;FUSCO, GIUSEPPE;MINELLI, ALESSANDRO
2008

Abstract

Among millipedes, adult males of the Helmintomorpha possess gonopods on the VII body ring. These specialized appendages differentiate in a very advanced phase of postembryonic development, changing from legs, to squamiform appendages, to gonopods. This transformation involves variable numbers of moults in the different species and is limited to one or very few nonterminal serially homologous elements in an otherwise morphologically homogeneous series of trunk rings. Here, we describe the changes affecting this area through three subsequent developmental stages. Our study, based on Nopoiulus kochii (Gervais, 1847), included observations on external morphology and internal anatomy as well. By this double approach, we discovered a dramatic remodeling of the endoskeletal, muscular, and nervous system. Most evident is the considerable reduction of the ring lumen caused by gonopod growth. This affects the course of the ventral nerve cord that is displaced dorsally comparing with immature stages. The complexity of the gonopod endoskeletal component is studied using confocal laser scanning microscopy. This technique permits us to describe their fine morphology in situ, avoiding the problems of accidental damages deriving from the dissection. Thus, we could note two gonopod apodemes that surround the digestive tract ventrally and laterally and offer insertion to two muscles, which are present only in the adults. This data can be the starting point from which the morphogenetic processes involved in the formation of the gonopods can be investigated.
2008
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2447063
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