Dineutus americanus (Linnaeus, 1767)

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 : 21-22

Dineutus americanus (Linnaeus, 1767) Figures 4, 5, 55

Gyrinus americanus Linnaeus 1767: 568, Dineutes metallicus Aubé 1838: 781 [synonymized by Schaum 1848], Dineutes americanus : Schaum 1848: 337, Dineutus (Cyclinus) metallicus : Ochs 1926a: 137.

Type locality.

“America”.

Specimens examined.

8

Type material examined.

Gyrinus americanus Linnaeus, 1767: syntype (1 ♀ card mounted) "2 [white label typed black ink]// americanus [beige lable, handwritten in black ink]//" examined online through the Linnaen Society of London’s Linnean’s Insect Collection.

Dineutus metallicus Aubé, 1838: lectotype, here designated (1 ♀ pinned) "MUSEUM PARIS/ CUBA/ M. De LA SAGRA 764-36 [beige label with thin black border, typed black ink]// green circle [underneath is 764/ 36 handwritten in black ink]// metallicus au [beige label, handwritten in black ink, handwriting appears to be Aubé’s, author is partially cut off]// PARATYPE [red label, typed black ink]// LECTOTYPE [red label, typed black ink]//" deposited in the MNHN. Paralectotype (1 ♀ pinned missing right mesothoracic leg past the femur and entire right metathoracic leg) same data as previous except without Aubé’s handwriting label and with "PARALECTOTYPE [red label, typed black ink]//" deposited in the MNHN.

Material examined.

BAHAMAS: Great Exuma: Simons Pt., " 23.31.50 75.37.30 ", 26.i.1980, leg. S.A. Teale (1 ex. KSEM); Mayaguana Island: 3.viii.1963, leg. C.M. Murvosh, BLT (1 ex. FSCA). CUBA: Holguín river near Biological Station of PN La Mensura, Piloto, 657 m, 11.v.2013, 20.48640N, 75.779134W, leg. A. Deler-Hernández (1 ex. NMPC). DOMINCAN REPUBLIC: La Altagracia: Nisibón, 3.v.1978, leg. R.E. Woodruff & G.B. Fairchild, (1 ex. FSCA); Monte Cristi: 5 km N Villa Elisa, 10-18.v.1985, leg. E. Giesbert (1 ex. FSCA). PUERTO RICO: Almirante Rd., “K.B.Y.”, 9.iii.1935, leg. J.G. Needham (1 ex. MSBA). U.S.A.: The Virgin Islands: St. Thomas, 27.ii.1925, WIBF 011217 (1 ex. WIBF).

Diagnosis.

Male (Fig. 4C-D): Size: 8.7-9.3 mm. Body form elongate oval; elytral apices with sutural angle produced to a point, with serrations and irregularities present apically, elytra with reticulation very strong laterally, medial disc with reticulation sparse or absent, striae often not apparent, lateral marginal depression of elytra not present; profemora with small sub-apicoventral tooth; protibiae club-shaped with apicolateral margin obliquely angled; mesotarsal claws (Fig. 5C) with ventral margin weakly rounded; venter darkly colored, reddish brown to black, weakly metallic, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 5A, B, D) median lobe in dorsal view shorter than parameres, nearly parallel sided, narrowed in apical 1/6; parameres weakly expanded laterally in apical 1/3, medially weakly curved, flatly rounded apically.

Female (Fig. 4A-B): Size: 8.9-9.1 mm. Body form elongate oval; elytral apices with sutural angle produced, with serrations and irregularities present apically, apicolateral sinuation present, elytra with reticulation strongly present laterally, medial disc with reticulation sparse or absent, striae often not present, lateral marginal depression of elytra absent; profemora without sub-apicoventral tooth; protibiae club-shaped with apicolateral angle rounded; venter darkly colored, reddish brown to black, weakly metallic, mesothoracic and metathoracic legs and apex of abdomen usually lighter in coloration.

Differential diagnosis.

Dineutus americanus is unique among all other species of Dineutus in North American in having an elongate oval body form (Fig. 4A, C), elytra without a well defined marginal depression, strong lateral reticulation, with striae mostly absent, the elytral apices with the sutural angle produced to a point with apical serrations and irregularities present, in the male having the profemora with a small sub-apicoventral tooth, protibiae that are club-shaped, and in the form of the male aedeagus (Fig. 5A). This species is also unique in being small in size and endemic to the Caribbean, reaching the Florida Keys (Fig. 55A). The species most similar to Dineutus americanus is Dineutus carolinus .

Both sexes of Dineutus americanus can be distinguished from Dineutus carolinus in having the sutural angle of the elytra produced to a point and being generally smaller in size. However, this production can sometimes be highly reduced to only a small point at the sutural angle, especially in males. Both sexes of Dineutus americanus can further be separated from Dineutus carolinus in lacking the marginal depression of the elytra seen in Dineutus carolinus . The absence of the elytral marginal depression is most evident in the humeral region of the elytra, where in Dineutus carolinus it is steep and narrow, becoming larger and shallower posteriad. Dineutus americanus has the elytra more evenly convex with the lateral portions of the disc with a very strongly impressed reticulation, producing a bronzy green appearance. The elytra also often do not have the striae very apparent due to the strong reticulation, whereas the striae are often faint but evident in Dineutus carolinus .

The aedeagus (Fig. 5A) will unambiguously distinguish males of Dineutus americanus from Dineutus carolinus . In Dineutus americanus the median lobe (Fig. 5A) is weakly constricted medially, and only narrowed in the apical 1/6 of its length, whereas that of Dineutus carolinus (Fig. 11A) is parallel sided for much of its length, fairly evenly narrowed in the apical 1/3, and is much more narrow overall. The parameres also differ, with those of Dineutus americanus more curved along both lateral and medial margins.

Females of Dineutus americanus can be distinguished from Dineutus carolinus by several of the above described differences, but also the elytra are much more noticeably lacking the marginal depression.

Whereas other small, elongate-oval species may be confused with Dineutus americanus (e.g. Dineutus emarginatus , Dineutus solitarius and possibly Dineutus assimilis , since the elytral apices are similar) it should again be noted that Dineutus americanus is a Caribbean endemic and its range should limit confusion with all other species except for Dineutus carolinus which is also found in the Bahamas (Fig. 53C).

Distribution

(Fig. 55A). From the Big Pine Key (Florida Keys, U.S.A.) ( Wood 1962), through the Caribbean from the Bahamas to Cuba ( Blackwelder 1944; Leng and Mutchler 1914a; Peck et al. 1998), Isle de Pinos ( Blackwelder 1944), Jamaica (Blackwelder 1994; Leng and Mutchler 1914b), Dominican Republic ( Blackwelder 1944), Puerto Rico, St. Thomas, St. John ( Blackwelder 1944), Antigua ( Blackwelder 1944; Leng and Mutchler 1914a), to Guadeloupe ( Blackwelder 1944; Leng and Mutchler 1914a; b; Peck 2011).

Habitat.

Lentic species (M. Fikáček pers. com.), also an accidental inhabitant of caves in Cuba ( Peck et al. 1998).

Discussion.

Many specimens have been misidentified as Dineutus americanus due to a long persisting synonymy issue (see the discussion under Dineutus assimilis ). Mistaken records of Dineutus americanus include Ciegler et al. (2003) and Zuellig et al. (2002) for Wyoming and, most likely, the key to larvae provided by Hatch (1927). The true Dineutus americanus is only found in the Caribbean and the Florida Keys (Fig. 55A).

Type designation.

Aubé (1838) does not give any exact label data, nor does he mention whose collection the types came from. The syntype series was identified by the presence of a disc on the specimen, which was checked with the registrar present at the MNHN to ensure dates were prior to the description by Aubé. The other specimens present either did not provide dates or had dates after Aubé’s (1838) publication. The lectotype (Fig. 51D) here designated was selected as it had a label present with Aubé’s handwriting and identification as " metallicus ". We here also confirm that Dineutes metallicus is a synonym of Dineutus americanus as proposed by Schaum (1848).