Meeting Abstract
Limnognathia maerski is the sole representative of the latest described phylum Micrognathozoa. The most conspicuous character of this microscopic animal is the complex set of jaws which resembles those of Gnathostomulida and Rotifera. Until recently, the musculature of Micrognathozoa was mostly unknown, leaving many gaps in the understanding of the jaw functioning. Here we present the detailed morphological assessment of the pharynx of Micrognathozoa, investigated by immunohistochemistry and confocal laser scanning microscopy. The musculature of the jaw apparatus are described and compared with other Gnathifera, illustrating some similarities between the jaw musculature of Micrognathozoa and Rorifera. Furthermore, this study reveals the prominence of the fibularium, the largest sclerite of the micrognathozoans jaw, and their central role in supporting the pharynx. The most conspicuous muscle of the pharynx is a ventral muscular plate, absent in other Gnathifera; presumably involved in moving the whole jaw apparatus, and lies ventral to the fibularium. Additionally, several muscles related to the fibularium are implicated in the opening of the main jaws. Moreover, the position of these muscles is more similar to those found in gnathostomulids. Inferences on the detailed movement sequence of the jaws, indicating how the jaw system functions are discussed relative to previous behavioural observations of this animal which includes both food grasping, and the so-called “vomit behaviour”. These combined results and observations illustrate the necessity of detailed morphological descriptions to better understand how jaw systems function in such small and intricate organisms.
