Ctenocheles Kishinouye, 1926

Hyžný, Matúš & Dulai, Alfréd, 2014, Deep-water fossorial shrimps from the Oligocene Kiscell Clay of Hungary: Taxonomy and palaeoecology, Acta Palaeontologica Polonica 59 (4), pp. 947-965 : 955-956

Genus Ctenocheles Kishinouye, 1926

Type species: Ctenocheles balssi Kishinouye, 1926 , by monotypy; Ohsu near Kashiwasaki, Niigata Prefecture, Japan .

Species included: See Table 2.

Emended diagnosis. ―Rostral carina and rostral spine present; dorsal surface of eye flattened; third maxilliped with or without exopod, distal margin of merus usually with spine; chelipeds unequal, and dissimilar; major cheliped carpus small, cup shaped; major cheliped merus with or without hook; palm of major cheliped bulbous, longer than high, narrowing distally; fingers elongate and pectinate; fixed finger straight or arcuate; occlusal surface of fixed finger with long, needle-like teeth, teeth of variable size, tips curving proximally. Palm of minor cheliped rectangular; fixed finger long, narrow, straight; uropodal exopod with lateral incision (emended from Manning and Felder 1991: 784).

Discussion.― Ctenocheles is a poorly known genus. Although six nominate species have been described from extant environments ( Table 2), virtually all of them are based on a handful of specimens ( Kishinouye 1926; Ward 1945; Powell 1949; Rodrigues 1978; Rabalais 1979; Matsuzawa and Hayashi 1997; Sakai 1999a). The best known taxon seems to be C. balssi (the type species), in which a statistically robust amount (40) of detached major chelipeds were also examined ( Matsuzawa and Hayashi 1997). Complete animals are rarely found whereas detached chelipeds usually are collect- ed ( Balss 1914; Holthuis 1967; Crosnier 1969). Similarly the fossil record of the genus consists almost exclusively of its chelae ( Schweitzer and Feldmann 2001). Ctenocheles secretanae Schweitzer and Feldmann, 2002 and C. rupeliensis ( Beurlen, 1939) , known from near-complete animals are notable exceptions.

The typical shape of the major propodus and dactylus,.e., bulbous palm with long pectinate fingers, usually allow specimens to be immediately assigned to the genus, and therefore the genus is easily recognizable; the minor chelipeds are less significant. Minor chelipeds may be misinterpreted, and this has happened previously in Ctenocheles rupeliensis , as documented below. No sexual dimorphism in major cheliped morphology of Ctenocheles is known ( Matsuzawa and Hayashi 1997).

Ctenocheloides Anker, 2010 has a similarly shaped major cheliped, but its fingers are distinctly shorter than in Ctenocheles . Moreover, Ctenocheloides has weakly unequal and asymmetrical chelipeds, whereas Ctenocheles is strongly heterochelous.

Tshudy and Sorhannus (2000) studied evolutionary trends in the occurrence of pectinate chelipeds in decapod crustaceans. They postulated convergence in four lineages. In the current classification ( De Grave et al. 2009) two of them are nephropid lobsters (Astacidea), one is a palaeopentachelid Polychelida) and the other is Ctenocheles (Axiidea) . Other examples of convergent development of pectinate chelae can be found in astacidean families Stenochiridae ( Stenochirus Oppel, 1861 ) (e.g., Schweigert et al. 2006) and Erymidae Lissocardia Von Meyer, 1851 ) (e.g., Garassino et al. 1999) and brachyuran families Leucosiidae Samouelle, 1819 and Iphiculidae Alcock, 1896 .

Discussion on the fossil record, palaeobiogeography and palaeoecology of Ctenocheles was provided by Förster and Mundlos (1982), Feldmann et al. (1995), Tshudy and Sorhannus (2000), and Schweitzer and Feldmann (2001, 2002).

Stratigraphic and geographic range. ―Cenomanian to Holocene. Two species are known from the Late Cretaceous, C. madagascariensis Secrétan, 1964 (recently re-examined by Charbonnier et al. 2012) and C. inaequidens ( Pelseneer, 1886) from Madagascar and the Netherlands, respectively. The genus has been widely reported from the Cenozoic from all over the world. Today, there are 6 named and a few unnamed species known worldwide except from the eastern Pacific ( Sakai 1999 a, b, 2005, 2011) ( Table 2). Burukovsky 2005) described Thaumastochelopsis plantei Burukovsky, 2005 on the basis of a single specimen from the continental shelf of Madagascar. However, the animal apparently does not represent a lobster, but an axiidean shrimp, most probably a member of Ctenocheles ( Chan 2010: 156) .