Rhithrodytes minimus, Fery, 2016

Fery, Hans, 2016, Notes on Rhithrodytes BAMEUL, 1989, with the description of R. minimus nov. sp. from Algeria (Coleoptera, Dytiscidae. Hydroporini, Siettitiina), Linzer biologische Beiträge 48 (1), pp. 431-450 : 433-439

Rhithrodytes minimus nov.sp.

T y p e l o c a l i t y: " Algeria "; exact locality unknown.

T y p e m a t e r i a l: H o l o t y p e: Ƌ, " Algeria " [green label with black margin, hw Wehncke ], "Fairmaire" [white label with black margin, hw Wehncke], "Museum Paris, ex Coll. R. Oberthur, ex Wehncke" [printed], " Holotype, Rhithrodytes minimus sp. n., Fery det. 2016" [red, printed] ( MNHN) (see Fig. 2 for scans of the labels). N o t e s: The holotype lacks the entire left fore-leg, the last three tarsomeres of the right fore-leg and the tibia and tarsi of the left hind-leg. The head, the prothorax and the pterothorax are only very delicately attached to each other. The left side of the pronotum, the left elytron in its anterior half and the right elytron in its posterior half are somewhat torn. The two last abdominal ventrites have been removed (because of dissection of the aedeagus) and glued onto the card behind the specimen ; same was done with the aedeagus. The holotype of the new species was found in drawer No. 11 of the water beetle part (former coll. E. Wehncke) of the coll. Oberthür in the Paris Museum ( MNHN) ; a photo of the respective part of this drawer is given in Fig. 3 . Originally , the holotype was glued onto a point (small triangular card) ; we have glued it onto a new bigger rectangular card.

Description: H a b i t u s: Body elongate oval, not appearing parallel-sided, rather flat ( Fig. 1 ); in dorsal view lateral outline with a very slight discontinuity at posterior angles of pronotum and base of elytra. Dorsal surface rather shiny due to weakly impressed reticulation and sparse punctation; with brownish to almost blackish background colour, lighter brownish pronotal sides and yellowish brown elytral pattern.

H e a d: Dark brownish, but lighter and more reddish near anterior margin. Between margin and eyes with two impressions (clypeal grooves); beside inner margin of eyes with distinct line of impressed punctures. Entire surface distinctly reticulated, but reticulation weakly impressed; meshes polygonal and more or less isodiametric, near anterior margin smaller and transverse, on frons lager and not transverse; in clypeal grooves and near eyes meshes rather small. Punctation very sparse and fine behind anterior margin, becoming progressively denser and larger posteriad; on frons diameter of most punctures slightly smaller than that of meshes, distance between punctures about three diameters of meshes; punctation on frons interspersed with a few larger and some smaller punctures; on vertex punctation again sparser and finer. Setation on head absent, except very few setae in clypeal grooves and in puncture lines along inner margin of eyes. Antennomeres yellowish brown, progressively somewhat darkened distally beginning with sixth antennomere; palpomeres uniformly yellowish. First and second antennomeres (scape and pedicel, respectively) relatively long, third distinctly shorter, fourth still shorter; fifth as long as third; sixth to ninth again longer and slightly broadened (see arrow "a" in Fig. 4 ), elliptical in cross-section; tenth as long as ninth, but scarcely broadened; eleventh flattened and almost twice as long as tenth. Antennomeres reticulate, fifth to tenth anterodistally with two large punctures. Apex of eleventh antennomere shortly truncate and with very short bristle. Apex of last labial and maxillary palpomeres incised.

P r o n o t u m:Withverydistinctsublateralstriaoneach side, reaching from anterior to posterior margin. Colour dark brownish as on most parts of head, interspace between stria and margin lighter brownish. Base of pronotum more less as wide as base of elytra; maximum width at posterior angles; lateral margins straight in posterior half, here slightly converging anteriad; in anterior half slightly curved; posterior angles shortly truncate. Rim at sides of pronotum distinct, becoming smaller near anterior and posterior angles. Entire surface reticulated; meshes slightly larger than those on frons; on interspace between stria and margin shape of meshes more longitudinal. Behind anterior margin with a row of very coarse punctures; before posterior margin with a more irregular puncture line, here punctures sparser. Disc only with very few very small punctures, centre of disc with a small longitudinal scratch. More laterally with a few larger punctures and additionally with very small punctures in intersections of meshes. Setae not found.

E l y t r a: Dark brownish with yellowish brown pattern; pattern diffusely delimited ( Fig. 1 ). Dark brownish parts somewhat lighter than on head and pronotum. Yellowish brown pattern consisting of broad band in anterior quarter and two spots in posterior half. Base of elytra narrowly and suture broadly dark brownish. Along lateral elytral margin narrowly yellowish brown; epipleura of same colour. Outline of elytra in dorsal view almost straight in anterior quarter, behind evenly rounded, in posterior quarter progressively more curved. Maximum width somewhat before mid-length of elytra. Sides of elytra with distinct rim. In lateral view margin of elytra almost straight, only very weakly ascending to humeral angles in anterior quarter; angle between elytral margin and straight margin of pronotum about 170°; epipleura not visible until shoulders. Entire elytral surface reticulated, meshes isodiametric, very slightly smaller than those of pronotum; near apex still smaller. Punctation sparse, diameter of punctures more or less equalling diameter of meshes; distance between punctures about that of five meshes; in posterior quarter punctures still sparser. Very small punctures at intersections of meshes relatively numerous. Two puncture lines perceptible if observed in adequate direction, consisting of rather irregularly arranged punctures; in anterior third more distinct than posteriorly. Setation very thin, transparent and indistinct, restricted to sides and posterior third. Sutural puncture line absent.

V e n t r a l s u r f a c e: More or less entirely reddish brown; only very few parts slightly darker brownish: trochanters, large parts of prosternum including prosternal column and prosternal blade, anteromedial metaventral process, metacoxal processes, second abdominal ventrite centrally and outer margin of epipleura. Genae and gula of same colour. All parts of ventral surface more or less appearing transparent although specimen not immature.

Head behind eye with distinct crease ( Fig. 4 , arrow "c"); between mouthparts and eyes with one distinct and one weak wrinkle; genae reticulate, between eye and crease with relatively large transverse meshes, behind crease meshes distinctly smaller; gula anteriorly weakly reticulate, behind smooth, sublaterally with line of coarse punctures near each side.

Hypomeron (= pronotal or prothoracic epipleuron) near anterior angle distinctly flattened in a more or less triangular area ( Fig. 4 , arrow "b"), here with some coarse punctures and few longitudinal wrinkles. Anterior angle provided with two distinct forwards directed short bristles. Base of prosternum anterior to procoxae distinctly elevated, here strongly sculptured; prosternal column near middle of procoxae with weak protuberance. Prosternal process narrowly lanceolate, in cross-section tectiform, apex shortly rounded; sides with distinct rim, here with very few punctures and setae; process weakly inclined against prosternal column. Tip of prosternal process (blade) reaching anteromedial metaventral process.

Apex of anteromedial metaventral process narrower than mesotrochanter; tip inclined against metaventrite, most probably contacting mesosternal fork (difficult to observe without further dissection); provided with flat furrow for reception of prosternal process. Structure of mesocoxal cavities not studied. Epipleuron becoming narrower near midlength, but not as abruptly as e.g. in species of Graptodytes (cf. fig. 12 in FERY & BOUZID 2016); with distinct oblique carina near shoulder ( Fig. 5 , arrow "a"). Metaepisternum more or less triangular in shape ( Fig. 5 ). Ratio of width of metacoxal plate (WC) and width of metaventral wings (WV): WC/WV ca. 2.4/1 (cf. fig. 3 in PETROV et al. 2010: 43). Metacoxal lines very distinct, slightly diverging anteriad, reaching posterior margin of metaventrite; joint hind margin of metacoxal processes incised; lobes of processes rounded ( Fig. 5 , arrow "c"), but not as broadly as in Graptodytes (cf. fig. 14 in FERY & BOUZID 2016); interlaminary bridge not concealed. Hind margin of last ventrite appearing on first glance as being evenly rounded, but left and right margins of last abdominal ventrite in fact forming a very large angle, thus apex very slightly pointed; pre-apically without impression.

Venter smooth in part or with weakly impressed reticulation, thus mostly distinctly shiny. Mesoepimeron and mesoepisternum shiny, very weakly reticulate; impunctate except line of coarse punctures behind anterior margin of mesoepisternum. Metaventrite centrally with three irregular puncture lines on each side; metaventral wings with line of coarse punctures behind anterior margin and another line before posterior margin and few further coarse punctures; wings laterally strongly bent backwards and here rather narrow; reticulation on metaventrite almost absent, only laterally with few very weakly impressed and incomplete meshes; metacoxal processes sublaterally with puncture line, elsewhere with few additional punctures; reticulation absent. Metacoxal plates with sparse, but large flat punctures; additionally, lateral half with numerous obliquely oriented long scratches, each arising from a large flat puncture ( Fig. 5 ); scratches at first glance resembling long setae. (N o t e s: Possibly, each scratch serves to receive a rather long seta, these setae, however, being lost in the holotype by any kind of mechanical destruction.) Reticulation on metacoxal plates mostly distinct; before hind margin with stripe of short longitudinally oriented lines ( Fig. 5 , arrow "b"). First five abdominal ventrites centrally with sparse and small punctation, more laterally punctures somewhat coarser and denser. Some scratches (like on metacoxal plates) near posterior margins; last abdominal ventrite with few small punctures. Reticulation on first five abdominal ventrites centrally very weak, almost imperceptible; more laterally becoming more distinct; last ventrite without reticulation. Epipleura distinctly reticulate, thus surface rather matt; almost impunctate. Underside of elytra sublaterally in posterior third with distinct carina; carina progressively becoming more elevated in posterior third and then abruptly ending short before apex of elytron; without ligula. Legs without conspicuous features. Anterior and posterior claws of fore- and mid-legs short, evenly curved and similar (most probably also those of hind-legs, but only one claw of one leg present). Metafemur with about six coarse punctures, not arranged in a clear line; trochanter also with some irregularly distributed coarse punctures. Metatibia with line of five spiniferous punctures and few additional ones. Metatarsomeres impunctate, first longer than second, second and third more or less of equal length, fourth still shorter; fifth slightly shorter than first and also shorter than third and fourth together. Setation on venter very sparse, perceptible only near sides of metacoxal plates and on sides as well as near hind margin of abdominal ventrites.

G e n i t a l i a: The median lobe and the left paramere of the male holotype are given in Figs 20 and 24 , respectively. The median lobe has the apex distinctly curved to the ventral side (to the left in Fig. 20 ), as it is typical for all members of the genus Rhithrodytes . According to the short TL of the species, the lobe is considerably shorter than that of all other species. The tip of the median lobe is distinctly pointed in lateral view as well as in perpendicular view onto the tip.

M e a s u r e m e n t s: Holotype: TL: ca. 2.3 mm, MW: ca. 1.2 mm; both values are somewhat inexact because of the bad state of the specimen.

D i s t r i b u t i o n: So far R. minimus nov.sp. is known only from " Algeria "; exact data are lacking. I assume, however, that the species occurs in the mountainous regions of northern Algeria.

E t y m o l o g y: The specific name minimus refers to the fact that the new species is the smallest of all members of the genus; it is an adjective in the nominative singular.

E c o l o g y: Nothing is known about the ecology of the new species and our knowledge of the ecology of the other two North-African species of the genus is also practically non-existent. However, if we consider the habitats of R. argaensis , R. agnus , and R. bimaculatus (DUFOUR, 1852) one might assume that the new species lives interstitially in small mountainous brooks between gravels, probably near sources. Rhithrodytes sexguttatus occurs in small streamlets, but can be found – at least on Corsica – in rather broad rivers as well, from high mountain passes to sea level.

Figures

Figs 1-2: Holotype of Rhithrodytes minimus nov.sp.: (1) habitus; (2) labels (scale bar 2 mm).

Fig. 3: Part of drawer No. 11 of the coll. E. Wehncke (in coll. R. Oberthür, MNHN) in which the holotype of Rhithrodytes minimus nov.sp. was found.

Figs 4-5: Ventral surface of Rhithrodytes minimus nov.sp.: (4) head; (5) part of metathorax and abdomen (significance of arrows explained in text).

Figs 20-27: Male genitalia of: (20, 24) Rhithrodytes minimus nov.sp.; (21, 25) R. dorsoplagiatus; (22, 26) R. numidicus; (23, 27) R. sexguttatus: Median lobe in ventral and lateral view and perpendicular view onto tip (20-23), left paramere (24-27).