Dineutus emarginatus (Say, 1825)

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 : 41-43

Dineutus emarginatus (Say, 1825) Figures 16, 17, 53

Gyrinus emarginatus Say 1825: 108, [ Dineutes americanus : Aubé 1838 b: 777 misidentified], Dineutus emarginatus : LeConte 1863: 18, Dineutes emarginatus : Régimbart 1882: 366, Dineutes emarginata Kellog 1905: 257, Dineutus (Cyclinus) emarginatus : Ochs 1926a: 136, Dineutus (Cyclinus) emarginatus floridensis Ochs, 1929 [synonymy by Cook et al. 2006], Dineutus emarginatus : Ciegler et al. 2003: 15.

Type locality.

None given.

Specimens examined.

75

Type material examined.

None examined, none available. The Thomas Say entomology collection is known to have suffered substantial damage with portions of his type collection having been destroyed ( Mawdsley 1993). Mawdsley (1993) provided a list of the surviving type specimens, but none of Say’s gyrinid species appear to remain. The MCZ online type database lists the following specimen as being a “Neotype”: (♀, pinned) "340/ ♀/ A. [brown label, handwritten in black ink]// NEOTYPE/ Dineutus emarginatus / Desig. R.P. Withington III/ 1999 [red label, handwritten in black ink, handwriting unknown]// Dineutus ♀/ emarginatus (Say)/ Det. 1998 1999/ RP Withington III [white label, typed black ink, except cross through 1998, 1999, and female symbol, handwritten in black ink]// emarginatus 5 [white label, handwritten in black ink, unknown handwriting]// MCZ TYPE/ 34947 [red label, MCZ TYPE typed in black ink, 34947 handwritten in black ink]//." As with all other R.P. Withington III designations for North America Dineutus , they were never published and are invalid, thus this specimen has absolutely no type status. As there is no question as to the identity of Dineutus emarginatus Say, no "exceptional need" exists for the designation of a neotype as per Article 75.3 of The Code ( ICZN 1999), and we refrain from designating a neotype.

Material examined.

U.S.A.: Alabama: Monroe Co., 10km W Bowles, 31°33.094'N, 86°59.956'W, 11.v.2006, leg. K.B. Miller (9 ex. MSBA); Connecticut: New London Co., Ledyard, pond, 1.vi.1995, leg. K.B. Miller (2 ex. MSBA); Florida: Alachua Co., 2.ii.1949, leg. S.B. Mansell, (1 ex. FSCA); same as previous except: 23.iii.1949, leg. B.W. Cooper (1 ex. FSCA); same as previous except: 8.iv.1949, leg. E.H. McConkey (1 ex. FSCA); same as previous except: 30.iv.1949, leg. O.S. Russell (1 ex. FSCA); same as previous except: 15.iv.1950, leg. J.T. Darlington, (2 ex. FSCA); Alachua Co., Hatchet Creek, 25.vii.1975, leg. J.B. Heppner (4 ex. FSCA); Alachua Co., Gainesville, 6 mi. SW, 12.iii.1975, leg. L.R. Davis Jr., Blacklight trap (2 ex. FSCA); Clay Co., Camp Blanding Training Site, INSECT SURVEY SITE 11, Sand Pine Scrub, 29°55.599'N, 81°59.914'W, 24.ix.1999, leg. M. & M. Minno, Light trap (1 ex. FSCA); Hernando Co., Weekiwachee Spring, 5.iii.1953, leg. W.C. Sloan (1 ex. FSCA); Highlands Co., Archbold Biol. Sta., 7.iv.1975, leg. L.L. Lampert, UVL (2 ex. FSCA); Highlands Co., Highlands Hammock State. Prk., 11.iv.1964, leg. J. Waters (2 ex. FSCA); Collier Co., Immokalee, 23-28.iii.1960, leg. A.F. Wilson, Blacklight trap (1 ex. FSCA); Liberty Co., Yellow Creek SE of Telogia, 7.x.1992, leg. F.N. Young, #3503 (5 ex. FSCA); Walton Co., Eglin AFB., Range Rd. 205, 4.5 mi W. Hwy-331, 16.vi.1995, leg. P.E. Skelley et al., MV & blacklight (1 ex. FSCA); Georgia: Okefenokee Swamp, 1.iv.1969, leg. T.E. Rogers (1 ex. FSCA); Bibb Co., Macon, 20.v.1969 (1 ex. FSCA); Lowndes Co., 6.v.1963, leg. E.I. Hazard (1 ex. FSCA); Louisiana: West Feliciana, St. Francisville, 17.vi.1955 (1 ex. FSCA); Maryland: Charles Co., Allen’s Fresh, 15.viii.1984, leg. C.L. Staines Jr. (1 ex. FSCA); Prince George’s Co., Blue Pond, 29.ix.1949, leg. H.L. Dozier (1 ex. FSCA); Prince George’s Co., Greenbelt, 4.ix.1954, leg. H.L. Dozier, still pond in woods (1 ex. FSCA); Mississippi: Hancock Co., Turtleskin Creek, 25.iv.1965, leg. R. Hepburn (2 ex. FSCA); New Jersey: Bergen Co., Dumont Woods, 9.iv.1931, leg. C.L. Ragot, (5 ex. FSCA); New York: Queens Co., Corona, Long Island, 16.iv.1927, leg. C.L. Ragot (1 ex. FSCA); North Carolina: Wake Co., Raleigh, Yates Pond, 12.ix.1970, leg. L.L. Lampert (14 ex. FSCA); Ohio: Fairfield Co., Barnebey Center, 31.vii.1978, leg. D. Streett, sweeping net (4 ex. MTEC); Oklahoma: Latimer Co., 3.vii.1987, leg. K.E.M. Galley, at black light (2 ex. FSCA); South Carolina: Aiken Co., Jackson, 4 mi NW at hwy 125 bridge, Holley Creek, 26.iii.1980, leg. D. Huggins, S. Hamilton, SEMC 1054963 (1 ex. KSEM); Texas: Kinney Co., 17m NW Bracktville, 30.x.1997, leg. J.E. Wappes, MV/UV (1 ex. FSCA); La Salle Co., vic. Los Angeles, 11.ix.1993, leg. J.E. Wappes, (1 ex. FSCA); No locality info: “Station”, 8.v.1901, "Hatch Ex.", (1 ex. MTEC).

Diagnosis.

Male (Fig. 16C-D): Size: 8.6-11.0 mm. Body form elongate oval; elytral apices regularly broadly rounded, with serrations and irregularities absent apically, elytra with fine reticulation covering its entirety, striae very faintly present, most evident medially on elytral disc, lateral marginal depression of elytra broad, usually extending to lateral elytra apex; profemora with large triangular sub-apicoventral tooth; protibiae subsinuate; mesotarsal claws (Fig. 17C) with ventral margin straight; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 17A, B, D) median lobe in dorsal view shorter than parameres, medially slightly constricted, acuminate in apical 1/5 producing a strong point, apex very shortly rounded, in lateral view median lobe weakly curved dorsally in apical half, ventrally median lobe with large rounded sperm-groove, parameres in dorsal view rounded laterally at apical 1/3, narrowly rounded apically.

Female (Fig. 16A-B): Size: 8.9-10.1 mm. Body form elongate oval; elytral apices regularly broadly rounded, with serrations and irregularities absent apically, apicolateral sinuation usually absent, rarely developed, elytra with fine reticulation covering most of its entirety, striae very faintly present, most evident medially on elytral disc, lateral marginal depression of elytra broad; profemora without sub-apicoventral tooth; protibiae club-shaped; venter darkly colored, usually black to very dark brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.

Differential diagnosis.

Dineutus emarginatus is unique among all other species of North American Dineutus in being elongate oval in body shape, having the elytral apices broadly rounded, without serrations and/or irregularities present apically, males with profemora possessing a large triangular sub-apicoventral tooth, and the shape of the aedeagus (Fig. 17A). The species most similar to Dineutus emarginatus are Dineutus carolinus and Dineutus solitarius . In general Dineutus emarginatus can be distinguished from Dineutus solitarius in being more elongate oval in body form, as opposed to being more regularly oval. This difference is especially evident in the pronotum. Dineutus emarginatus has the lateral margin of the pronotum more straightly angled posteriorly to anteriorly, while in Dineutus solitarius the pronotal lateral margin is more obtusely angled. The shape of the posterior margin of the pronotum differs between the two species, being more sinuate with the lateral portion of the posterior margin of the pronotum angled towards the posterolateral corners in Dineutus emarginatus as compared to the posterior margin being much more straight and less sinuate in Dineutus solitarius . Dineutus emarginatus in general also has a more evident lateral marginal depression of the elytra compared to Dineutus solitarius .

Males of Dineutus emarginatus have a much larger profemoral sub-apicoventral profemoral tooth than do those of Dineutus solitarius , but the species can be unambiguously separated based on the aedeagus. Both species have the median lobe acuminate, however, the acumination differs between the two species. In Dineutus emarginatus the apex of the median lobe is more rounded (Fig. 17A), with the acumination present as a strong point, whose apex is narrowly rounded. The apex of the median lobe of Dineutus solitarius (Fig. 43A) is narrowed towards the acumination, with the acumination also evenly narrowed and highly pointed, with the apex of the acumination appearing sharp and narrow. In overall appearance the median lobe of Dineutus emarginatus is more broad with a shallow medial constriction giving the basal and apical margins of the aedeagus a more sinuous feel, while in Dineutus solitarius the median lobe is more parallel sided and slightly narrowed apically, becoming slightly broadened just before the acumination.

The females of Dineutus emarginatus are primarily distinguished from females of Dineutus solitarius by the general differences listed for separating the two species.

Dineutus emarginatus can be separated from Dineutus carolinus by the differences listed in the differential diagnosis for Dineutus carolinus .

Distribution

(Fig. 53D). Most of the eastern half of the United States ( Régimbart 1907; Young 1954; Wood 1962; Malcolm 1971; Folkerts 1978; Sanderson 1982).

Habitat.

Dineutus emarginatus can be found in both lotic and lentic habitats ( Young 1954). In Florida Dineutus emarginatus is often found at the mouths of slow moving streams or in lakes in regions where wave action is present ( Young 1954). This species can also be found in swamp streams, small sand bottomed streams, and canals with running water ( Young 1954). The first author has collected this species form a large man-made lake in the Ozarks of Arkansas, as well as in a large slow moving tributary of a mud-bottomed stream (see the discussion under Dineutus amazonicus ).

Discussion.

In the past Dineutus emarginatus was divided into two subspecies by Ochs (1929), Dineutus emarginatus s. str. and Dineutus emarginatus floridensis Ochs, 1929. Ochs (1929) based this subspecies on the smaller size of Dineutus emarginatus floridensis from that of the typical form and on the difference in the number of setigerous punctures of the profemora, as well as some minor differences in the body form and elytral shape. This subspecies was also stated to be restricted to peninsular Florida ( Ochs 1929; Young 1954) with other populations outside of northern and central Florida being a part of the Dineutus emarginatus s. str. subspecies. Cook et al. (2006) performed a morphometric analysis of several populations of Dineutus emarginatus to assess the claims of a significant difference in size, as that being the main basis for the subspecies Dineutus emarginatus floridensis . Cook et al. (2006) were unable to discriminate between the two subspecies via a morphometric analysis and suggested the synonymy of Dineutus emarginatus floridensis . Ochs (1929) did also mention a difference in the setigerous punctures of the profemora, however as discussed elsewhere, this character is known to be variable.

In a study of gyrinid aggregations at East Texas Primitive Big Thicket by Realza et al. (2007), Dineutus emarginatus was most commonly collected with Dineutus carolinus and also with Dineutus serrulatus analis , but to a lesser extant, but the authors observed that at a given locality both species compositions and proportions were subject to change.