Micro-computed tomography and histology to explore internal morphology in decapod larvae

Traditionally, the internal morphology of crustacean larvae has been studied using destructive techniques such as dissection and microscopy. The present study combines advances in microcomputed tomography (micro-CT) and histology to study the internal morphology of decapod larvae, using the common spider crab (Maja brachydactyla Balss, 1922) as a model and resolving the individual limitations of these techniques. The synergy of micro-CT and histology allows the organs to be easily identified, revealing simultaneously the gross morphology (shape, size, and location) and histological organization (tissue arrangement and cell identification). Micro-CT shows mainly the exoskeleton, musculature, digestive and nervous systems, and secondarily the circulatory and respiratory systems, while histology distinguishes several cell types and confirms the organ identity. Micro-CT resolves a discrepancy in the literature regarding the nervous system of crab larvae. The major changes occur in the metamorphosis to the megalopa stage, specifically the formation of the gastric mill, the shortening of the abdominal nerve cord, the curving of the abdomen beneath the cephalothorax, and the development of functional pereiopods, pleopods, and lamellate gills. The combination of micro-CT and histology provides better results than either one alone.Financial support was provided by the Spanish Ministry of Economy and Competitiveness through the INIA project (grant number RTA2011-00004-00-00) to G.G. and a pre-doctoral fellowship to D.C. (FPI-INIA)

The morphology of the foregut of larvae and postlarva of Sesarma curacaoense De Man, 1892: a species with facultative lecithotrophy during larval development A morfologia do estômago de larvas e pós-larvas de Sesarma curacaoense De Man, 1892: uma espécie com desenvolvimento larval lecitotrófico facultativo

Previous study on the resistance of larvae of Sesarma curacaoense submitted to starvation has revealed a facultative lecithotrophy during zoeal stages, but megalopa and first juvenile stages are exclusively feeding stages. In the present study, the gross morphology and fine structure of the foregut of S. curacaoense were investigated during larval, megalopa and first juvenile stages. The foregut of the zoea I show specific setae and a filter press apparently functional. The foregut undergoes changes in the zoea II (last larval stage) with increment of setae number, mainly on the cardiopyloric valve and complexity of the filter press. After metamorphosis to megalopa stage the foregut become rather complex, with a gastric mill supporting a medial and two lateral teeth well-developed. The foregut of the first juvenile is more specialized compared to the previous stage, showing similar characteristics of the decapod adults. These results provide further evidence of facultative lecithotrophic development in the larvae of S. curacaoense.<br>Estudo prévio sobre o efeito da inanição em larvas de Sesarma curacaoense propôs que estas larvas apresentam comportamento lecitotrófico facultativo. No presente trabalho a morfologia do estômago de S. curacaoense foi estudada durante os estágios larvais, megalopa e juvenil I. A estrutura do estômago da zoea I possui cerdas específicas e com filtro pilórico aparentemente funcional. Especialização no estômago do zoea II (último estágio larval) foi evidenciada pelo incremento do número de cerdas na válvula cárdio-pilórica e pela complexidade do filtro pilórico. Após a metamorfose para o estágio megalopa, o estômago ficou consideravelmente complexo, com o aparecimento de um moinho gástrico contendo um medial e dois laterais dentes bem desenvolvidos. O estômago do juvenil I mostrou-se ainda mais especializado que no estágio anterior, exibindo características morfológicas similares àquelas descritas para decápodes adultos. Estes resultados corroboram o proposto em trabalhos anteriores, nos quais é indicado que S. curacaoense possui um desenvolvimento larval lecitotrófico facultativo