Haliclona (Flagellia) Van Soest, 2017 is a recently erected subgenus characterized by the presence of flagellosigma microscleres which are often distinctive between species (Van Soest 2017). Members of the taxon also have normal sigmas within a confused skeleton formed by oxea megascleres. The subgenus has a global distribution and contains 10 species (Van Soest et al. 2019). A large and abundant new species collected throughout the southern Gulf of St. Lawrence is characterized by thick and abnormally shaped flagellosigmas, two sizes of oxea, and abundant normal sigmas. Lambe (1896) previously reported Haliclona (Flagellia) porosa (Fristedt, 1887) from the Gulf of St. Lawrence, and the species is known to occur in nearby Arctic waters (Fristedt 1887; Lundbeck 1902; Hentschel 1916; Koltun 1959, 1966; Van Soest 2017; Dinn Leys 2018). However, H. (F.) porosa is characterized by the presence of very few normal sigmas and no thick flagellosigmas. Type specimens were preserved in 95% ethanol and were deposited in the Atlantic Reference Centre (ARC) in St. Andrews, New Brunswick, Canada. The taxonomic identification was performed through spicule analysis using light and scanning electron microscopy, following methods described by Dinn et al. (2020).
Keywords: Porifera, Demospongiae, Heteroscleromorpha.