Seven syntypes of Halichondria isodictyalis, type species of Lissodendoryx, were rediscovered and studied. By choosing a lectotype and studying it along with the paralectotypes, we find that L. isodictyalis, subgenus Lissodendoryx, is a Caribbean sponge characterized by smooth megascleres, ectosomal tylotes and choanosomal styles, and one size-class of microscleres comprising arcuate isochelae and sigmas. Having determined these characteristics, we re-erect Lissodendoryx (Lissodendoryx) carolinensis (previously synonymized with L. isodictyalis), with the same smooth megascleres but two distinct size categories of microscleres, isochelae and sigmas; and we add a new western Atlantic species, Lissodendoryx (L.) spinosa sp. nov., with coarse spines on the megasclere terminals and with two size-classes of isochelae and sigmas. Other species in the region are Lissodendoryx (L.) colombiensis, with smooth tylotes and robust strongyles, and two categories of microscleres (isochelae and sigmas) accompanied by conspicuous raphids arranged in trichodragmas; Lissodendoryx (L.) strongylata, with smooth tylotes and slim strongyles, one size-class each of isochelae and sigmas, rare and very thin raphids. Lissodendoryx sigmata is here assigned to the subgenus Anomodoryx, with smooth tylotes exclusively as megascleres, two size-classes of isochelae, and one or two sizes of sigmas; it may represent a species complex far more diverse than previously thought. To this subgenus we add another species, Lissodendoryx (A.) amphispinulata sp. nov., characterized by fine spines ornamenting both tyles of part of the tylotes. A third subgenus, Ectyodoryx, is represented by Lissodendoryx (E.) acanthostylota sp. nov., with smooth tylotes and finely spined acanthostyles in two size-classes, as well as two size-classes each of isochelae and sigmas as microscleres. All species studied alive occur in shallow lagoon habitats with mangroves and sea grass (Thalassia) but museum specimen records show that some may reach a depth of 60 m.