Calaxius Sakai & de Saint Laurent, 1989

Komai, Tomoyuki, 2016, Reappraisal of the two axiid genera Manaxius Kensley, 2003 and Calaxidium Sakai, 2014, and description of a new species of Calaxius Sakai & de Saint Laurent, 1989 from French Polynesia, Southwest Pacific (Crustacea: Decapoda: Axiidea), Zootaxa 4098 (3), pp. 498-510 : 499-501

Genus Calaxius Sakai & de Saint Laurent, 1989

Calaxius Sakai & de Saint Laurent, 1989: 84 ; Poore 1994: 97 (key); Sakai 1994: 192; Clark et al. 2007: 64. Manaxius Kensley, 2003: 367 ; Sakai 2011: 131.

Calaxidium Sakai, 2014: 887 .

Type species. Calaxius acutirostris Sakai & de Saint Laurent, 1989 , original designation.

Diagnosis. Emended from Poore & Collins (2009). Carapace smooth or tuberculate; cervical groove visible laterally over third distance to anterolateral margin. Rostrum acutely triangular, with 2 or 3 pairs of lateral spines, usually distinctly longer than eyestalks, not depressed below level of carapace, continuous with definite lateral carinae; supraocular spines prominent; lateral carina with at least 1 spine or denticle; submedian carina present, with 1 or more spines or denticles; median carina a weak ridge, with 1 or few spines or tubercles; postcervical carina absent or restricted to posterior part. First pleomere with acutely pointed pleuron; pleuron of second pleomere acute or rounded, pleura of third to fifth pleomeres acute, sometimes with anteroventral tooth, or rounded. Telson with lateral fixed spines and posterolateral spiniform setae; posterior margin rounded. Eyestalk cylindrical, articulating; cornea pigmented. Antenna with scaphocerite long, acute. Third maxilliped with exopod not clearly bent at base of flagellum. Pleurobranchs present above second to fourth pereopods; podobranchs and arthrobranchs well developed; epipods present on second maxilliped to fourth pereopod. First pereopods (chelipeds) nearly symmetrical to clearly asymmetrical, with propodus compressed laterally; dorsal margin of palm with moderate to strong spines (rarely obsolete), covered with tufts of long setae. Third and fourth pereopods each with transverse rows of spiniform setae on lateral surface of propodus; dactyli tapering, each with longitudinal rows of spiniform setae on lateral surface and flexor margin. Second to fifth pleopods each with appendix interna in both sexes. First pleopod of male absent. Second pleopod of male with rod-like appendix masculina clearly separated from appendix interna. Uropodal endopod with lateral and distolateral spines; exopod with transverse suture.

Remarks. The above generic diagnosis is slightly emended from that presented by Poore & Collins (2009), incorporating interspecific variation of some characters. For example, C. inaequalis and C. jenneri are unusual in having the rostrum just reaching to the distal corneal margins ( Rathbun 1901; Williams 1974). The development of the postcervical carina on the carapace varies according to species presently assigned to Calaxius . In C. acutirostris , C. manningi and C. tungi , the postcervical carina is distinct, running over the entire length of the postcervical carapace (Sakai and de Saint Laurent 1989; Zhong 2000; Kensley et al. 2000), whereas it is absent or present in the other species.

Sakai (2011) realized that Kensley’s (2003) Manaxius pitatucensis was not Axiopsis (Axiopsis) pitatucensis , a species which he then redescribed and illustrated from type material as Colemanaxius pitatucensis . Sakai (2011) invoked ICZN Article 70.3 ‘Misidentified type species’ to clarify the confusion. He chose as type species of Manaxius the one actually involved in the misidentification, which he named Manaxius aganaensis . However, he did not designate name bearing type from the three individuals from Guam, or the one from Okinawa Island, Japan, illustrated by Kensley (2003), as required under ICZN Article 72.3. As pointed out by Poore (2015b), the name Manaxius aganaensis Sakai, 2011 is not available and can not be type species of the genus.

Sakai (2011) further complicated the issue by including Manaxius both as a junior synonym of Calaxius (p. 84) and as a separate genus (p. 131), but it is assumed that Sakai’s intention was the reinstatement of Manaxius as a valid genus. Sakai’s (2011: 131) Manaxius includes vast majority of species previously assigned to Calaxius , but his logic is very difficult to trace: Calaxius was compared only with Eutrichocheles modestus ( Herbst, 1796) ( Sakai 2011: 84) , whereas Manaxius was compared only with Calocarides Wollebaek, 1908 ( Sakai 2011: 131) . On the other hand, in the key to the genera (p. 17), Calaxius is placed close to Albatrossaxius Sakai, 2011 and Manaxius . In his key, Sakai uses only the armature of the gastric median carina in differentiating Calaxius (“Gastric median carina linear”) and the latter two genera (“Gastric median carina tuberculate), but in C. acutirostris , the type species of Calaxius , the gastric median carina is actually denticulate (cf. Sakai & de Saint Laurent 1989; Poore & Collins 2009). Comparison of his (2011) diagnoses of the two genera shows them to differ only in the postcervical carina being present in Calaxius , absent in Manaxius , the anterolateral margin of the carapace with a spine in Calaxius , absent in Manaxius , and the scaphocerite protruded straight forward in Calaxius , ‘horn-shaped’ in Manaxius . None of these features are of generic value if real. The development of the postcervical carina appears variable in species Sakai referred to Manaxius : a trace of a postcervical carina is discernible at least in the posterior part in C. mimasensis and C. izuensis (cf. Komai et al. 2002; Komai 2011). The extent of a protrusion on the anterolateral margin is also variable and the scaphocerite is straight to slightly curved downwards (the contrast between “protruded forward” versus “horn-shaped” does not make sense). The lateral spine on the cheliped palm that characterizes all species of Calaxius-Manaxius complex was not mentioned in either diagnosis. Sakai (2015) finally recognized Manaxius as a junior synonym of Calaxius , but his argumentation was based only on comparison of the respective type species (he did not realize that his M. aganaesis was not available). Here the synonymy of Manaxius with Calaxius proposed by Clark et al. (2007) is fully confirmed.

Sakai (2014) established a new monotypic genus Calaxidium to accommodate Calaxius izuensis . His argumentation ( Sakai 2014: 887) is directly quoted below: “However, the characters presented for Calaxius izuensis by Komai indicate that C. izuensis should not be included in the genus Calaxius , because the genus Calaxius is characterized as follows ( Sakai, 2011): (1) the P1 are subequal in size and shape, both chelae are rather elongate, and the fingers of both larger and smaller chelipeds are longer than the palm (vs. in Komai’s Calaxius izuensis the P1 are unequal, both chelae are stout, and the fingers of the larger cheliped are shorter than the palm, and those of the smaller cheliped are as long as the palm); (2) the abdominal pleura 1-6 are sharply pointed ventrally (vs. the abdominal pleuron 1 is sharply pointed, the abdominal pleuron 2 is truncate, and the abdominal pleura 3-6 are rounded ventrally); (3) the male Plp1 is absent, the Plp2 endopod bears mesially articulated appendices masculina and interna at the proximal third (Poore & Collins, 2010 [sic], fig. 19h) (vs. the male Plp1 is absent, the Plp2 endopod bears mesially an appendix masculina fused proximally with an appendix interna (Komai, 2011, fig. 21f)); and (4) the postcervical carina is distinct (vs. the postcervical carina is not distinct, but its trace is discernible). Hence, a new genus, Calaxidium gen. nov. is here established for Calaxius izuensis Komai, 2011 .”

As noted above, three of the four features cited by Sakai (2014) for diagnosing Calaxidium are seen also in the species transferred to Manaxius by Sakai (2011), although Sakai (2014) did not mention Manaxius sensu Sakai (2011) in comparison with Calaxidium at all. With regard to the character of the appendix masculina on the second pleopod, the basal articulation of it has never been considered as of taxonomic significance in taxa with a nonmodified second pleopod. In fact, the lack of the basal articulation in Komai’s ( Komai 2011: Fig. 21F) figure is merely an artistic omission. Komai (2011) discussed on the close similarities between C. izuensis and the other three Calaxius species, C. kensleyi , C. pailoloensis and C. sibogae , which were all transferred to Manaxius by Sakai (2011), but Sakai (2014) completely ignored Komai’s (2011) indication. Calaxidium cannot be distinguished from Manaxius sensu Sakai (2011) . In conclusion, Calaxidium is also here synonymized under Calaxius , and C. izuensis is returned to Calaxius .

Among 11 species referred to Manaxius by Sakai (2011; except for the nomen nudum M. aganaensis ), two species do not fit the generic diagnosis of Calaxius . “ Manaxius ” angulatus ( Coelho, 1973) , originally described from Brazil under Calastacus Faxon, 1893 , is not consistent with the generic diagnosis of Calaxius in having elongate eyestalks overreaching the rostral apex ( Coelho & Ramos-Porto 1991). Coelho et al. (2007) had assigned this species to Acanthaxius Sakai & de Saint Laurent, 1989 . Reexamination of the type material, the sole representative of the species, is necessary to determine the generic status of Calastacus angulatus . Manaxius thailandensis Sakai, 2011 was founded on the basis of two specimens (holotype male and one paratype female) from the Gulf of Thailand, originally identified as Eutrichocheles sp. by Sakai (1992). This species better fits Paraxiopsis de Man, 1905 in having a small, bispinose antennal scaphocerite and the slender cheliped with nonsetose chela lacking dorsal spines on the palm (cf. Kensley 1996). Sakai’s (2011) interpretation on the structure of the antennal scaphocerite is not consistent with his previous description ( Sakai 1992). The lack of a supraocular spine also excludes Manaxius thailandensis from Calaxius . Manaxius ohsumiensis , described from Ohsumi Islands, located to the north of the Ryukyu Islands, Japan, appears very similar to Manaxius pitatucensis sensu Kensley (2003) , and it is likely that the two taxa are conspecific. Nevertheless, it is advisable to reexamine the material studied by Kensley (2003) and Sakai (2011) to reach final conclusion. Here I tentatively include M. ohsumiensis as a valid species in Calaxius .

Coelhocalaxius Sakai, 2011 , which was established to accommodate Calastacus spinosus with C. oxypleura as a junior synonym, was said to differ from Calaxius in having a narrow rather than a triangular rostrum and more elongate eyestalks. However, the rostrum varies considerably between species. Sakai & de Saint Laurent (1989) noted that the eyestalks of species of Calaxius were ‘rather elongate’, another variable character of little generic value. Spination of the cheliped palm is the same in both genera. The only species included, Calastacus spinosus , has a postcervical carina, said by Sakai (2011) to set it apart from Calaxius but as shown above it is not the case. Nevertheless, Calastacus spinosus seems to differ from any species assigned to Calaxius in the lack of conspicuous supraocular spines and the presence of two pairs of lateral longitudinal carinae on the second to fifth pleomeres ( Sakai 2011). Consequently, Coelhocalaxius is maintained as a valid genus. The synonymy between Coelhocalaxius spinosus and C. oxypleura is not very convincing, because the latter differs from the former in having broader telson and uropods.

Heterocalaxius Sakai, 2011 , which was established for Calaxius carneyi , was said to differ from Calaxius in the lack of an appendix masculina on the male second pleopod, the lack of a postcervical carina on the carapace, the short scaphocerite, the major cheliped palm and carpus weakly tuberculate dorsally, the minor cheliped palm and carpus more tuberculate dorsally than in the major cheliped, the cheliped fingers being shorter than the palms, and the triangular telson ( Sakai 2011). Of these characters, the development of the postcervical carina and the length of the cheliped fingers are variable characters of little generic value, as discussed above, but the other characters seem to be still significant in recognizing Heterocalaxius . With regard to the statement on the armature of the cheliped palms and carpi by Sakai (2011) is not specific; the lack of conspicuous spines on the dorsal margins of the cheliped palms and carpi, not the condition of tuberculation, is significant in differentiating Heterocalaxius from Calaxius .

In conclusion, the following 14 specific taxa are recognized in Calaxius for the time being: C. acutirostris , C. euophthalmus , C. galapagensis , C. inaequalis , C. izuensis , C. jenneri , C. kensleyi , C. manningi , C. mimasensis , C. poupini n. sp., C. ohsumiensis n. comb., C. pailoloensis , C. sibogae , and C. tungi . As discussed by Sakai (2011), however, relationship between C. manningi and C. tungi is not clear, and further comparison would be necessary to establish the identity of these two taxa.