Coelostoma (s. str.) nostocinum, Sheth & Ghate & Fikáček, 2020

Sheth, Sayali D., Ghate, Hemant V. & Fikáček, Martin, 2020, Review of Coelostoma of the Indian subcontinent (Coleoptera: Hydrophilidae) Part 1: Coelostoma s. str. and Holocoelostoma, European Journal of Taxonomy 690, pp. 1-32 : 12-14

Coelostoma (s. str.) nostocinum sp. nov.

urn:lsid:zoobank.org:act:B069E8DC-6096-4292-B70D-93D6C5CB7337

Fig. 5 A–K

Differential diagnosis

Coelostoma nostocinum sp. nov. is characterized by smaller body size, by which it especially resembles C. vividum . Its male genitalia with the triangular median lobe easily distinguish it from all species except C. fallaciosum and C. aeneolum . The species may be distinguished from C. fallaciosum by its much shorter median lobe (compared to parameres) with straight lateral margins (concave in C. fallaciosum ) and wider apex, and by the more or less symmetrically pointed apex of the paramere (strongly asymmetrical in C. fallaciosum ). Coelostoma nostocinum sp. nov. is very similar to C. aeneolum , but may be distinguished from it by its (1) smaller body size (3.5–4.5 mm, compared to 4.6 mm in C. aeneolum ), (2) larger aedeagus (0.7 mm, compared to 0.4 mm in C. aeneolum ), (3) relatively longer apodemes of the median lobe (longer than half of the length of the apical triangular part of the median lobe, compared to much shorter than half the length in C. aeneolum ) and (4) paramere distinctly concave on outer margin subapically and pointed apically (compared to evenly arcuate on whole outer margin and more less rounded apically in C. aeneolum ).

Etymology

The species name refers to the finding of the holotype of this species in association with Nostoc Vaucher ex Bornet & Flahault (see Biology).

Material examined

Holotype

INDIA • ♂; “ GOA province, 30 km S of MARGAO (Madgaon), Palolem env., INDIA 2002 exped; 15º00.47ʹN 74º01.56ʹE ” [15º00ʹ38.37ʺ N, 74º01ʹ23.76ʺ E]; 0–20 m a.s.l.; 12–14 Aug. 2002; P. Šípek and M. Fikáček leg; found in Nostoc -like algae; NMPC.

Paratypes

INDIA – Goa • 11 specs; same collection data as for holotype; NMPC • 2 specs; same collection data as for holotype; BMNH • 1 spec; same collection data as for holotype; UASB 01923074 • 1 spec; same collection data as for holotype; ZSI • 3 specs; “ 30 km S of Margao, Palolem env.; 15º00.47ʹ N, 74º01.56ʹ E ” [15º00ʹ38.37ʺ N, 74º01ʹ23.76ʺ E]; 0–20 m a.s.l.; 12–14 Aug. 2002; M. Fikáček and P. Šípek leg.; NMPC . – Maharashtra • 1 ♂, 33 specs; “ 4 km W of Lonavala, Bushi dam env.” [Bhushi dam]; [18º45ʹ22.31ʺ N, 73º24ʹ32.95ʺ E]; 500 m a.s.l.; 24–28 Oct. 2005; J. Bezděk leg.; at light; NMPC • 3 specs; same collection data as for preceding; SMNS • 1 ♂, 1 spec.; “ 4 km S of Lonavala, Bushi dam env.” [Bhushi dam]; [18º43ʹ24.35ʺ N, 73º23ʹ49.43ʺ E]; 500 m a.s.l.; 12–15 Oct. 2005; J. Bezděk leg.; NMPC • 1 spec.; same collection data as for preceding; NCBS BL020 • 2 ♂♂, 3 specs; Lonavala , 80 km E of Bombay; [18º45ʹ21.96ʺ N, 73º24ʹ32.40ʺ E]; [630 m a.s.l.]; 13 Sep. 1991; R. Schuh leg.; NHMW . – Karnataka • 1 spec.; Udipi distr., E of Bhatkal, Kollur ; [13º51ʹ48.71ʺ N, 74º48ʹ37.46ʺ E]; [80 m a.s.l.]; 26–29 May 2006; Z. Kejval leg.; UASB 01923075 . – Kerala • 6 specs; Cardamon Hills, 50 km NW of Pathanamhitta, Pambaiyar River ; 9º25ʹ N, 77º05ʹ E; 300 m a.s.l.; 6–9 May1994; Z. Kejval leg.; at light; NHMW • 1 spec.; same collection data as for preceding; NMPC .

Description

FORM AND COLOUR. Body length 3.3–4.5 mm (3.8 mm in holotype), body width 2.2–2.5 mm (2.4 mm in holotype). Body oval in dorsal view, moderately convex in lateral view. Head black, dark brown clypeus; pronotum and elytra uniformly dark brown to black; ventral surface pale to dark brown. Femora and tarsi yellowish brown, tibia dark reddish brown, tarsi pale brown. Mouth parts and antennae yellowish, antennal club brown.

HEAD. Dorsal punctation dense, consisting of simple punctures without associated ridges; trichobothria present; surface between punctures smooth. Anterior margin of clypeus non-arcuate. Eyes large, interocular distance ca 4.0 × the width of one eye in dorsal view; eye emarginate anteriorly. Labrum moderately sclerotized, largely exposed anterior of clypeus. Antenna with 9 antennomeres, club loosely segmented. Second maxillary palpomere markedly wide.

PROTHORAX. Pronotum bisinuate anteriorly, anterolateral corners obtuse; posterior margin moderately bisinuate, posterolateral corners rectangular. Anterior and lateral margins with distinct bead not extending to posterior margin. Pronotal punctation finer than on head, consisting of simple punctures

without associated ridges; surface between punctures smooth. Prosternum nearly straight on anterior margin, gently carinate mesally.

MESOTHORAX. Elytral punctation dense and moderately coarse, consisting of punctures without transverse ridges. Weakly developed series of impressed punctures present along suture and laterally. Sutural stria well impressed, present in apical half, extends beyond middle; lateral elytral margins with sculpture. Mesoventral plate as long as wide, arrowhead-shaped, bluntly pointed anteriorly, posteriorly widely attached to metaventrite.

METATHORAX. Metaventrite raised medially, completely glabrous on median elevation, lateral portions pubescent. Anterior metaventral process narrowly projecting between mesocoxae; posterior process bifid. Wings well-developed (macropterous).

LEGS. Profemur with dense pubescence except in apical fifth; mesofemur and metafemur with sparsely arranged short setae only.

ABDOMEN. All ventrites densely pubescent. First ventrite without carina. Posterior margin of last ventrite entire, without stout spines mesally.

AEDEAGUS ( Fig. 5 J–K). 0.7 mm long. Median lobe broad at base, slightly tapering towards widely rounded apex; gonopore situated at apex, widely semicircular. Parameres longer than median lobe; weakly arcuate on outer margin, narrowed in apical fourth; apex bluntly pointed; inner margin of parameres with long setae. Phallobase small, slightly wider than long.

Variation

Specimens from Maharashtra are slightly smaller than those from more southern areas. The aedeagus varies slightly in the shape of the parameres, the apical part of which is slightly wider in the specimens from Kerala; in all other aspects these specimens agree with those from Goa and hence we consider them conspecific.

Remarks

Coelostoma nostocinum sp. nov. and C. aeneolum are very similar in all characters including the morphology of the male genitalia, and both species seem to have very similar (and overlapping) distribution ranges. We were hence working with the hypothesis that they may be conspecific for some time, with the observed variation in body size and aedeagus morphology being an intraspecific variation. The examination of all available material, however, indicates that this is not the case, and that we really have two distinct morphotypes without intermediate characters: the species with larger body and smaller aedeagus with more or less rounded apices of parameres ( C. aeneolum ) and the smaller species with larger aedeagus with narrower and apically pointed paramere ( C. nostocinum sp. nov.). Based on the material examined, both morphotypes are constant in the characters listed in the differential diagnosis across the distribution range (i.e., from Maharashtra to Kerala in both). For these reasons, we are treating them as separate species, with the smaller species described here as C. nostocinum sp. nov.

Biology

The specimens from Goa were collected under ‘ballsʼ of Nostoc blue-green algae growing on wet sandy places on rock cliffs at the sea coast. Specimens from Maharashtra were collected at light.

Distribution

Only known from the western coast of India and adjacent parts of the Western Ghats Mts, from Maharashtra to Kerala.

Figures

Fig. 5. Coelostoma (s. str.) nostocinum sp. nov. A. Dorsal habitus. B. Lateral habitus. C. Frontal view. D. Thorax in ventral view. E. Dorsal punctation of head. F. Dorsal punctation of pronotum. G. Dorsal punctation of elytron. H. Abdominal ventrites. I. Detail of abdominal apex. J–K. Aedeagus: ventral (J) and dorsal (K). Photographs based on: A–G. Paratype from Lonavala, Bhushi dam (NMPC). H–K. Holotype, ♂ (NMPC).