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Name derivation:
"Knee-mouth" or "Bent-mouth". From the Greek gony, knee, and stoma, mouth
Classification:
Gonyostomum K.Diesing 1866; all 5 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013). Class Raphidophycea; Order Chattonellales
Morphology:
Motile cells with two flagella approximately as long as the cell itself. Cells have a convex dorsal surface and a flattened ventral surface. Gonyostomum is in the "green line" of raphids.
Reproduction:
Reproduction is both sexual and asexual, at least in G. semen (Figueroa and Renegefors 2006.
Similar genera:
Effects on Human Health:
Large concentrations or blooms of Gonyostomum semen are connected with skin itching allergic reactions (Cronberg, Lindmark and Björk 1988). Similarly, the organism has been increasingly a problem in Finland since 1978, causing an ‘unpleasant slimy coating’ on the skin after swimming (Lepistö, Antikainen and Kivinen 1994). The irritation is caused by ejections of slime threads up to 200 µm long (Johansson et al. 2013) from ejectosomes (less accurately called ‘trichocysts’, because they are organelles, not cells) lining the Gonyostomum cells.
Predators:
Because the cell length of Gonyostemum semen is 36 – 92 µm only the largest zooplankton will consume it. Both Eudiaptomus gracilis and Holopedium gibberum are potential regulators of G. semen populations, consuming 1.5 and up to 2 cells per minute respectively, while Daphnia cristata and Ceriodaphnia spp. and Diaphanosoma brachyurum do not graze on them (Johansson et al. 2013).
Habitat:
Gonyostomum spp. occur mainly in low pH humic freshwaters, swamps, and acid bogs. G. semen has been reported to be increasing in Sweden since the 1960s, both in small humic lakes and spreading to non-humic lakes as well (Ibid.). A similar increase is also reported in Estonia since the 1980s (Laugaste and Noges 2002). More recently it has been reported to be invasive and a nuisance in Norway (Hagman et al. 2015) Anthropological contribution to lake acidification is often cited as a reason for invasion of G. semen into more lakes. Abundance of G. semen has been positively correlated with both phosphorus and DOC (dissolved organic carbon) in Lake 979, Experimental Lakes Area, Ontario Canada (Findlay et al. 2005).
References:
Cronberg, G., G. Lindmark and S. Björk 1988. Mass development of the flagellate Gonyostomum semen (Raphidophyta) in Swedish forest lakes – an effect of acidification? Hydrobiologia 161:217-236. Figueroa, R.I., and K. Rengefors  2006.  Life cycle and sexuality of the freshwater raphidophyte Gonyostomum semen (Raphidophyceae).  Journal of Phycology 42:859-871. Findlay, D.L., M.J. Paterson, L.L. Hendzel and H.J. Kling 2005. Factors influencing Gonyostomum semen blooms in a small boreal reservoir lake. Hydrobiologia 533:243-252. Graham, L. and L. Wilcox 2000. Algae. Prentice-Hall . Guiry, M.D. and G.M. Guiry 2013. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 10 September 2013. Hagman, C.H.C., a. Billot, D.Ø. Hjermann, B. Skjelbred, P. Brettum and R. Ptacnik 2015. The occurrence and spread of Gonyostomum semen (Her.) Diesing (Raphidophyceae) in Norwegian lakes. Hydrobiologia 744:1-14. Johansson, K.S.L., T. Vrede, K. Lebret and R.K. Johnson 2013. Zooplankton feeding on the nuisance flagellate Gonyostomum semen. PLOS one 8(5): e62557. doi:10.1371/journal.pone.0062557 (online) Laugette, R., and P. Noges 2002. LAKE2002. Symposium on conservartion, restoration and management of aquatic ecosystems. Speaker 3. (online) Lepistö, L, S. Antikainen and J. Kivinen 1994. The occurrence of Gonyostomum semen (Her.) Diesing in finnish lakes. Hydrobiologia 273:1-8.