<p>The family Eulimidae represents a diverse group of marine gastropods that form symbiotic relationships with echinoderms, exhibiting a wide range of morphological adaptations to parasitism. <i>Thyca crystallina</i>, an obligate ectosymbiont of the sea star <i>Linckia laevigata</i>, possesses a highly specialized anterior digestive system and attachment structures adapted for a parasitic lifestyle. This study presents a detailed histological examination of the anterior digestive system of <i>T. crystallina</i>, with a focus on its proboscis, salivary glands, and attachment disc. The results reveal that the proboscis, housed within the attachment disc, is asymmetrically retracted, featuring a muscular wall composed of multiple layers of smooth muscle cells. A narrow, slit-like mouth leads into a muscular pharynx with a triangular lumen, connected to a thin oesophagus passing through a massive pair of acinous salivary glands. The glandular epithelium, characterized by basophilic granulocytes and mucocytes, suggests a secretory function related to feeding. The attachment disc exhibits specialized depressions lined with epithelial cells and supported by dense muscle fibers, likely functioning as suction structures for firm adhesion to the host. Additionally, glandular pockets in the cephalic and pedal lobes contain secretory cells that may facilitate attachment, penetration, or host interaction. These findings provide new insights into the structural adaptations of <i>T. crystallina</i>, highlighting the evolutionary modifications that enable its symbiotic lifestyle. The combination of muscular and glandular specializations in the proboscis and attachment disc underscores the intricate host-parasite interactions within Eulimidae, contributing to a broader understanding of gastropod evolution and parasitism in marine ecosystems.</p>