Cymonomus A. Milne-Edwards, 1880

Ahyong, Shane T., 2019, The Cymonomid Crabs of New Zealand and Australia (Crustacea: Brachyura: Cyclodorripoida), Records of the Australian Museum 71 (2), pp. 33-69 : 34-35

Cymonomus A. Milne-Edwards, 1880

Remarks. Cymonomus now comprises 43 species including the eight new species described herein. Two broad species groups within Cymonomus have been recognized in older literature: the C. granulatus group and the C. quadratus group, distinguished by whether the rostrum is longer or shorter than the eyestalks, respectively ( Dell, 1971). This division follows the early taxonomic history of the genus in which most new taxa were described as subspecies of either C. granulatus (Norman in Wyville Thomson, 1873) (rostrum longer than the eyestalks) or C. quadratus A. Milne-Edwards, 1880 (rostrum shorter than the eyestalks) ( Dell, 1971). This binary division based on rostral length, however, does not adequately reflect the morphological diversity within the genus.Among the Indo-West Pacific species of Cymonomus , multiple groups have been recognized and additional groups are delineated below for species from the study area.Atlanto- East Pacific species of Cymonomus may also belong to these groupings, which may or may not represent natural groups. Whether these informal species groups are natural or artificial is currently under study and contingent on evaluation of the Atlanto-East Pacific species of Cymonomus (currently under revision by M. Tavares). They are used here for taxonomic utility pending revision of the cymonomid generic system in collaboration with M. Tavares, currently underway. For species of Cymonomus from New Zealand and Australia, the following informal groups are delineated herein:

• Cymonomus bathamae group (recognized herein): includes species having the outer orbital processes inclined anterolaterally, straight rather than curved eyestalks, and the anterior margin of the carapace lateral to the outer orbital processes curving inwards and sloping posteriorly towards the midline. In other species of Cymonomus , the anterior margins are transverse or slope posterolaterally. The C. bathamae group includes: C. bathamae Dell, 1971 , C. umitakae Takeda, 1981 , C. brevis sp. nov., C. confinis sp. nov., C. triplex sp. nov., C. espinosus sp. nov., and C. valdiviae Lankester, 1903 , and might also include C. guillei Tavares, 1991 from Brazil. Of these, the eyestalks

are fused basally and immovable in C. bathamae , C. espinosus , C. brevis , and C. confinis , all from the Indo-West Pacific; the eyestalks are slightly movable

in others of the group. Of those species with slightly movable eyestalks, the rostrum is shorter than the eyes in the three Indo-West Pacific species ( C. umitakae , C. valdiviae , C. triplex ), and as long as or longer than the eyes in the Western Atlantic species, C. guillei .

• Cymonomus curvirostris group ( Ahyong &

Ng, 2017): includes species adorned with large, pedunculate, globose tubercles on the carapace and pereopods: C. curvirostris Sakai, 1965 ( Japan) , C.

liui Ahyong & Ng, 2011 ( Philippines), C. mariveneae Ahyong & Ng, 2009 ( Philippines) , and C. trifurcus Stebbing, 1920 ( South Africa). These are among the smallest species of Cymonomus , with the maximum pcl of adults ranging from 2.0 to 3.1 mm.

• Cymonomus delli group ( Ahyong & Ng, 2017): includes species with short, stout, relatively broad, ventrally flattened eyestalks; a small, triangular rostrum that is distinctly shorter than the eyestalks;

a relatively swollen carapace with a finely granulate surface and margins, rounded anterolateral margins; and a pleotelson with a partial to full demarcation between abdominal somite 6 and the telson (yet to

be confirmed in C. andamanicus Alcock, 1905 ). The C. delli group includes C. cognatus Ahyong & Ng, 2017 , C. cubensis Chace, 1940 , C. delli Griffin & Brown, 1976 , C. diogenes Ahyong & Ng, 2009 , and C. andamanicus Alcock, 1905 . The demarcated telson and abdominal somite 6 in the C. delli group is similar to that of the American Cymonomoides Tavares, 1993a (to which C. cubensis and C. delli were previously assigned). Apart from the abdominal segmentation, however, Cymonomoides guinotae ( Tavares, 1991) , the type species of the genus, appears to have few obvious similarities to members of the C. delli group.

• Cymonomus granulatus group ( Dell, 1971): includes species with the combination of a long rostrum that overreaches the eyestalks and well-developed outer orbital processes, namely, C. aequilonius Dell, 1971 ( New Zealand), C. alius sp. nov. ( New Zealand), C. granulatus (Norman in Wyville Thomson, 1873) (northeast Atlantic), C. indicus Ihle, 1916 ( Indonesia) , C. japonicus Balss, 1922 ( Japan) , and C. magnirostris Tavares, 1991 ( Brazil) .

• Cymonomus karenae group (recognized herein): includes only C. karenae sp. nov., in which the eyes are stout and widely divergent with well-defined, transparent corneal surfaces, and in which the telson and abdominal somite 6 are separated by a distinct groove except on the central one-third, which is indistinguishably fused.

• Cymonomus soela group (recognized herein): includes species in which the anterolateral margins of the carapace are transverse or slope posteriorly, the

outer orbital processes and rostrum are well-developed and of similar length (but distinctly shorter than the eyestalks), and in which the pleotelson shows no evidence of a demarcation between somite 6 and the telson. The C. soela group includes C. soela Ahyong & Brown, 2003 , C. clarki Ahyong, 2008 , C. deforgesi Ahyong & Ng, 2009 , C. dianae sp. nov. and C. tesseris sp. nov. from the Indo-West Pacific, and possibly also C. menziesi Garth & Haig, 1971 , from the eastern Pacific, and C. caecus Chace, 1940 , from the Western Atlantic.