Gandalfus Mclay, 2007, gen. nov.
Creators: name: Mclay, Colin
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Bythograeidae
Gandalfus

description: Gandalfus gen. nov.
Diagnosis. Carapace wider than long, transversely elliptical, flat; front broad, lateral margins rounded. Orbits elongate transversely, incomplete; eyestalks fixed; suborbital plate trapezoidal, not visible dorsally. Interantennular septum reduced to small dorsal and ventral keel. Epistome not projecting, gently sinuous in frontal view. Merus of third maxilliped almost as long as entire medial margin of endopod. Walking legs (P2-P5) shorter than chelipeds. Proximal portion of lateral projection of third maxilliped coxa not visible ventrally. G2 equal to or greater than G1. Male and female abdominal segments freely articulating.
Type species. Gandalfus puia sp. nov., by present designation.
Other species. Austinograea yunohana Takeda, Hashimoto & Ohta, 2000.
Etymology. Gandalfus is derived from the name of the omnipotent “Gandalf”, a character in J. R. Tolkien’s “Lord of the Rings”, which was made into a film by Peter Jackson, in New Zealand, the home of the type species. Gender is masculine.
Discussion. The first bythograeid genus to be found and described was Bythograea Williams, 1980 for B. thermydron Williams, 1980 from the Galapagos Rift area. Then de Saint Laurent (1984) added a second genus for Cyanagraea praedator de Saint Laurent, 1984 collected from the East Pacific Rise. Later Austinograea williamsi Hessler & Martin, 1989 from the Mariana Basin was added, and in the same year Segonzacia Guinot, 1989 was introduced to receive Bythograea mesatlantica Williams, 1988 from the mid-Atlantic Ridge. This had the effect of restricting Bythograea to the Pacific Ocean. The last genus to be established was for Allograea tomentosa Guinot, Hurtado & Vrijenhoek, 2002 from the Southeast Pacific Rise. Since that time, new species have been added to one or other of these five genera (although 3 genera remain monotypic) so that we now recognise 12 previously described species (Table 1) from all the major oceans: Pacific, Indian and Atlantic. These crabs are restricted to areas of submarine volcanic activity.
Allograea Guinot, Hurtado & Vrijenhoek, 2002 (type species Allograea tomentosa Guinot, Hurtado & Vrijenhoek, 2002) * Allograea tomentosa Guinot, Hurtado & Vrijenhoek, 2002
Austinograea Hessler & Martin, 1989 (type species Austinograea williamsi Hessler & Martin, 1989 * Austinograea alayseae Guinot, 1990
* Austinograea rodriguezensis Tsuchida & Hashimoto, 2002 * Austinograea williamsi Hessler & Martin, 1989
Bythograea Williams, 1980 (type species Bythograea thermydron Williams, 1980) * Bythograea galapagensis Guinot & Hurtado, 2003
* Bythograea intermedia de Saint Laurent, 1988 (maybe the same as B. thermydron Williams, 1980)
* Bythograea laubieri Guinot & Segonzac, 1997
* Bythograea microps de Saint Laurent, 1984
* Bythograea thermydron Williams, 1980
* Bythograea vrijenhoeki Guinot & Hurtado, 2003
Cyanagraea de Saint Laurent, 1984 (type species Cyanagraea praedator Saint Laurent, 1984) * Cyanagraea praedator de Saint Laurent, 1984
Gandalfus gen. nov. (type species Gandalfus puia sp. nov.) * Gandalfus puia sp. nov.
* Gandalfus yunohana (Takeda, Hashimoto & Ohta, 2000)
Segonzacia Guinot, 1989 (type species Bythograea mesatlantica Williams, 1988). * Segonzacia mesatlantica (Williams, 1988)
The main characters that have been used as the basis of these genera include features of the carapace surface, tubercles and tomentum, development of the orbits, mobility and size of the eyestalks, recession of cephalic appendages under the front, ventral exposure of the third maxilliped coxa, and other aspects of the third maxilliped, and the gonopods.
Amongst the Brachyura the G1 is a conservative feature (Guinot & Hurtado 2003: 436) but the G2 size shows considerable variation. In bythograeids several features of the gonopods show variation (Table 2). The G 1 in this family is usually stoutly constructed, curved, not twisted and largely unornamented except in Austinograea where it is slender, curved and ornamented with a longitudinal row of spines. The G1 usually narrows to a pointed tip with a terminal aperture. The G2 consists of a peduncle that is separated mid-way from the apical flagella by a notch. The length of the G2 is normally much greater than the G1 so that it can protrude from the terminal aperture and presumably enter the female gonopore. Tsuchida & Fujikura (2000) suggested that the bythograeid G2 does not have a pumping role in sperm transfer, but is instead a sensory device guiding the G1 into the female gonopore. However, this hypothesis ignores the setose notch mid-way along the G2, which seems to act as a valve so that, with the pumping action of the G2, sperm is impelled into the narrowing bore of the G1, forcing it out of the G1 tip and into the female spermatheca. This mechanism is widespread in other brachyuran crabs. It is likely that the G2 has a role in sperm transfer in all bythograeids regardless of its size and in species with length of G2 >>G1, it may have a role in disrupting sperm from previous matings.
The genus Austinograea, however, shows remarkable variation in G2 length: in A. alayseae, A. rodriguezensis the G2 is about half the length of the G1 while in A. williamsi it is less than half the length of G1. In A. yunohana, the G1 and G2 are about equal. Takeda et al. (2000) pointed out that this feature of A. yunohana did not fit the generic definition given by Hessler & Martin (1989). Therefore, to accommodate their new species, Takeda et al. (2000) modified the generic definition of Austinograea from “second male pleopod distinctly shorter than the first” to “male second pleopod as long as or longer than half the length of the first”. Like A. yunohana the present new species from New Zealand also has a G2 that is as long as the G1. However, now that we have another species it seems preferable to group these two species in a new genus. This change returns Austinograea to its original definition, wherein the G2 is distinctly shorter than the G1, and restricted to A. williamsi Hessler & Martin, 1989 (type species), A. rodriguezensis Tsuchida & Hashimoto, 2002 and A. alayseae Guinot, 1990.
This rearrangement of bythograeid species (see Table 1) establishes a consistent pattern in the G1 vs G2 character: in Segonzacia, Cyanagraea, and Bythograea the G2 is longer than or equal to the length of G1, while in Austinograea the G2 is only about half the length of G1, and in the closely related Gandalfus the G2 is approximately equal to the G1. A plausible hypothesis would be that the G2> G1 is the ancestral condition for bythograeids. Evidence that Austinograea and Gandalfus are the most derived genera is also supported by regression of their eyes so that these species lack functional eyes and are effectively blind. A parallel trend seems to be a tendency towards reduction in body size (see Table 2).
description: Published as part of Mclay, Colin, 2007, New crabs from hydrothermal vents of the Kermadec Ridge submarine volcanoes, New Zealand: Gandalfus gen. nov. (Bythograeidae) and Xenograpsus (Varunidae) (Decapoda: Brachyura), pp. 1-22 in Zootaxa 1524 on pages 2-5, DOI: 10.5281/zenodo.177502