Bythograea thermydron (William 1980)

Background
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Family: Bythograeidae

Geography
Bythograea thermydron, or the hydrothermal vent crab, is a particularly abundant species of hydrothermal vent sites (Van Dover et al., 1987). It is found at sites along the East Pacific Rise and Galapagos Rift (Fig. 1) and between the latitudes of 21oN and 18oS (Dittel et al., 2005; Desbruyéres et al., 2006).

Adapted from Vrijenhoek (2010), this map highlights, in red, the tectonic boundaries of East Pacific Rise and Galapagos Rift. The hydrothermal vent crab, Bythograea thermydron, is found at sites distributed along these boundaries.
Figure 1: Adapted from Vrijenhoek (2010), this map highlights, in red, the tectonic boundaries of East Pacific Rise and Galapagos Rift. The hydrothermal vent crab, Bythograea thermydron, is found at sites distributed along these boundaries.

Within these sites, B. thermydron mostly lives in the vestimentiferan zone, amongst Riftia pachyptila (Fig. 2), as well as in the mussel beds of Bathymodiolus thermophiles (Desbruyéres et al., 2006). Due to their distribution amongst these species, B. thermydron is most abundant when temperatures range between 1.8-12oC (Grassle, 1985; Micheli et al., 2002).

Bythograea thermydron are found amongst Riftia pachyptila and in the vestimentiferan zone at hydrothermal vent sites.
Figure 2: Bythograea thermydron are found amongst Riftia pachyptila and in the vestimentiferan zone at hydrothermal vent sites.

Appearance and Identification
Like other hydrothermal vent species, B. thermydron is completely white in colour (Fig. 3); although in some species the cheliped – or ‘pincers’ – can sometimes be near black, especially on the fingers (Fig. 4). These cheliped are also unequal, with some displaying slight rugosity – meaning it isn’t smooth but instead has a ‘pebbled’ – texture (Williams, 1980; Dittel et al., 2008); however, all will have a fixed finger on which there are approximately 12 teeth.
Williams (1980) also describes the overall shape of the B. thermydron carapace as being broad but transversely elliptical (Fig. 3), with a slight arch from anterior to posterior. There are no teeth to the margin so that it is smooth. This species has walking legs that are long and flattened which finish with pointed dactyls (Fig. 3) (Dittel et al., 2008).

Figure 3: Bythograea thermydron, the hydrothermal vent crab, is white in colour with pointed dactyls at the end of its flattened walking legs.
Figure 3: Bythograea thermydron, the hydrothermal vent crab, is white in colour with pointed dactyls, the end leg segment of it flattened walking legs.

Feeding Strategy
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References
Desbruyéres, D., Segonzac, M. & Bright, M. (2006) Handbook of Deep-Sea Hydrothermal Vent Fauna. Austria, Landesmuseen.

Dittel, A.I., Epifanio, C.E. & Perovich, G. (2005) Food sources for the early life history stages of the hydrothermal vent crab Bythograea thermydron: A stable isotope approach. Hydrobiologia, 544, 339-346.

Dittel, A.I., Perovich, G. & Epifanio, C.E. (2008) Biology of the vent crab bythograea thermydron: A brief review. Journal of Shellfish Research, 27, 63-77.

Grassle, J. (1985) Hydrothermal vent animals – distribution and biology. Science, 229, 713-717.

Micheli, F., Peterson, C.H., Mullineaux, L.S., Fisher, C.R., Mills, S.W., Sancho, G., Johnson, G.A. & Lenihan, H.S. (2002) Predation structures communities at deep-sea hydrothermal vents. Ecological Monographs, 72, 365-382.

University of Delaware. (2014) Bythograea thermydron amongst Riftia pachyptila (Figure 2). Available: http://invertebrates.si.edu/Features/stories/vestimentifera.html [09/12/2014, 2014].

University of Delaware. (2009) Bythograea thermydron (figure 3). Available: http://deepseanews.com/2009/05/do-vent-crabs-do-it-under-the-gyre/ [09/12/2014, 2014].

Vandover, C.L., Franks, P.J.S. & Ballard, R.D. (1987) Prediction of hydrothermal vent locations from distributions of brachyuran crabs. Limnology and Oceanography, 32, 1006-1010.

Vrijenhoek, R.C. (2010) Bythograea thermydron distribution map, from: Genetic diversity and connectivity of deep-sea hydrothermal vent metapopulations. Molecular Ecology, 19, 4391-4411.

Williams, A.B. (1980) A new crab from the vicinity of submarine thermal vents on the Galapagos Rift crustacea decapoda brachyura. Proceedings of the Biological Society of Washington, 93, 443-472.

 

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