Anatomical and Histological Descriptions of the Digestive and Excretory Systems in Aulonogyrus concinnus (Klug, 1834) (Coleoptera: Gyrinidae) Based on Light and Scanning Electron Microscopies

Morphological information on the digestive and excretory systems of aquatic coleopterans remains extremely limited, despite their importance for understanding morphology and systematic studies. As a predatory aquatic beetle, Aulonogyrus concinnus contributes to natural regulation of pest populations in freshwater ecosystems. This study provides a morphological description of the digestive and excretory systems of A. concinnus using light and scanning electron microscopies. The digestive system consists of a foregut (~2.50 mm), midgut (~1.30 mm), and hindgut (~2.20 mm), with the midgut being the shortest region. The foregut includes the oesophagus, crop, and proventriculus, all lined with a single layer of epithelium, muscle layer and chitinous intima. The oesophagus and crop bear characteristic cuticular spines, while the proventriculus contains four star‐shaped plates with brush‐like spines. The midgut surface displays 60 finger‐shaped gastric caeca, each lined with monolayered epithelial cells with well‐developed apical microvilli. Two pairs of Malpighian tubules are found at the junction of the midgut and hindgut and show distinct proximal and distal regions with a single‐layered cuboidal epithelium containing secretory granules. The hindgut comprises ileum and rectum, both surrounded by a single layer of epithelium, muscle layer and chitinous intima. These findings fill a significant gap in the literature and provide a morphological basis for future studies on aquatic beetles.