A new genus of marine, interstitial schizorhynch (Platyhelminthes: Kalyptorhynchia) is described from sediment collected in Mosquito Lagoon and Indian River Lagoon, Florida, USA. Smithsoniarhynches is characterized by the presence of proboscis hooks constructed of ten individual spine-like teeth that emerge separately from a basal plate. Histology and confocal laser scanning microscopy are used to reveal additional details of the proboscis musculature and reproductive anatomy. The type species, Smithsoniarhynches sherryreedae sp. nov., is characterized by well-developed proboscis pads, four pairs of proboscis retractor muscles, and a pharynx in the midbody region. The male reproductive system consists of an anterior testis, muscular seminal vesicle, copulatory bulb lined with spiral and circular muscles, and a sclerotic stylet. The female system consists of an unpaired vitellarium, ovary, uterus and bursa. The bursa tissue surrounds a muscular bursa seminalis with distinct sphincter muscles. The new genus is compared with the known 11 genera within the Gnathorhynchidae to establish a tentative hypothesis of relationships.