Development and metamorphosis of the digestive system of larval lobsters, Homarus americanus (Decapoda: Nephropidae)

This study provides a detailed account of the development of the digestive system of larval lobsters (Homarus americanus H. Milne Edwards, 1837) and the morphological changes that occur at metamorphosis. The most dramatic of these changes involves the gastric mill of the cardiac stomach. First‐and second‐stage lobsters lack the medial and lateral teeth characteristic of the grinding stomach of adult lobsters. Clearly recognizable, heavily cuticularized teeth first appear in the third stage, and accessory lateral teeth do not appear until the fourth stage. In place of the teeth of the gastric mill, first‐ and second‐stage stomachs have a series of pads and ridges which are the apparent rudiments of the teeth. The development of the gastric mill during the larval stages enables lobsters to deal successfully with the more substantial food they encounter in the benthic environment, and corresponds to the drastic change of habitat and diet which occurs at metamorphosis.