Dineutus sp. near mexicanus

Gustafson, Grey T. & Miller, Kelly B., 2015, The New World whirligig beetles of the genus Dineutus Macleay, 1825 (Coleoptera, Gyrinidae, Gyrininae, Dineutini), ZooKeys 476, pp. 1-135 : 87-90

Dineutus sp. near mexicanus

Material examined.

"Tapanatepec 7 mi [black ink smudge]/ N.E. Oax. Mex [handwritten in black ink] 48/ 7-9-53 1300 ft. [black handwritten in ink] S// Univ.Kans/ Mex./ Expedition" deposited at the KSEM.

Diagnosis.

Male (Fig. 49A-B): Size: 17.45 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, blunt irregularities present apically, apicolateral margin weakly sinuate, elytral striae faint, elytra microreticulation present, apicolaterally with slightly bronzy appearance; ulimate protarsus (Fig. 30B) less than ca. 2 × as long as wide, with angled lateral margin after basal 1/3, remaining protarsi with rounded lateral margins; protibiae club-shaped; profemora with small acute sub-apicoventral tooth; anterior mesotarsal claw (Fig. 50C) with ventral margin expanded into weak denticle; venter darkly colored, reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Figs 50A, B, D) with median lobe in dorsal view parallel sided, weakly laterally expanded in apical 1/4, apex shortly acuminate, ventrally with parallel sided sperm-groove, parameres noticeably laterally expanded in apical 1/3, asymmetrical, in lateral view parameres constricted near mid-length.

Differential diagnosis.

This specimen is different from all other New World Dineutus species examined in having truncate elytra with the lateral angle rounded, with weak sinuation apicolaterally, and blunt irregularities present, the protarsus (Fig. 30B) has the lateral margin rounded, the ultimate protarsomere angled apically after the basal 1/3, and the form of the aedeagus (Fig. 50A). The aedeagus of this specimen is unique among all known world species of Dineutus in having parameres that are medially strongly constricted in lateral view. Externally, however, the specimen is most similar to the North American species Dineutus truncatus and Dineutus mexicanus . It can be separated from Dineutus truncatus by the shape of the elytral truncature and the shape of the male protarsi (Fig. 30). In this specimen the elytral truncature has the lateral angles rounded and the apex with blunt irregularities, instead of the lateral angles of the truncature acute, with fine serration present at the elytral apices as in Dineutus truncatus . The length of the ultimate protarsomere is less than 2 × the width, whereas in Dineutus truncatus the length is approximately 2 × the width.

This specimen and Dineutus mexicanus have similar elytral truncature, and similar ultimate protarsomere size ratios, however the shape of the protarsus is very different. It (Fig. 30B) has the lateral margin of protarsomeres II-IV broadly rounded, whereas in Dineutus mexicanus (Fig. 30A) they are more flatly rounded to subtruncate. The ultimate protarsomere of this specimen is strongly angled apically after the basal 1/3 (Fig. 30B), whereas in Dineutus mexicanus it is evenly tapered basally to apically (Fig. 30A). Also, in this specimen the frontoclypeal suture is sinuate medially with a rounded posterior expansion, whereas in Dineutus mexicanus the suture is mostly flat and only weakly angled medially. The mesotarsal claws are also slightly different, with those of of this specimen having a slightly more developed denticle.

Discussion.

There are several characters that suggest this specimen represents a species distinct from Dineutus mexicanus (see the diagnosis and differential diagnosis section above). The aedeagus of this specimen is strange, even among the world Dineutus fauna, as discussed above. While the aedeagus does appear to be asymmetrical in the parameres, suggesting a malformation, the rest of the body is highly symmetrical, without any noticeable deformities. Other specimens encountered that were clearly aberrant in some way, had asymmetrical features in the body, usually the prothoracic legs. Given the distinct characters discussed we have included the specimen here without placing it among any of the known species. However, as we only have a single specimen, and given its very odd genitalia, we have decided not to formally describe this species due to lack of additional material. Other Dineutus specimens examined from western and north central Oaxaca (IEXA) belonged to Dineutus mexicanus . However, this specimen comes from a locality to the south separated by a mountain range, again suggesting it may indeed represent a species other than Dineutus mexicanus . Hopefully future collecting near Tapanatepec, Oaxaca, Mexico will allow placement of this enigmatic specimen.