Rediscovery of the enigmatic Stenosternus costatus from São Tomé Island

Figures 1–2. Stenosternus costatus Karsch, habitus in dorsal view and abdomen in ventral view. 1 — female, 2 — male.

Frolov, A. V. & Akhmetova, L. A. 2015. Rediscovery of the enigmatic Stenosternus costatus Karsch (Coleoptera: Scarabaeidae: Orphninae) from São Tomé island. Zootaxa, 4007, 440–444.

Stenosternus Karsch, 1881 is one of the least-known genera of the Orphninae scarab beetles. It was described from a single specimen of the odd-looking S. costatus Karsch, 1881, from the island of São Tomé, Gulf of Guinea, West Africa. Since then, no more findings of S. costatus have been reported... We discovered additional specimens of both sexes of S. costatus housed in the Museo Civico di Genova, Genova, Italy (MCGI) and California Academy of Sciences, San Francisco, California, United States of America (CASC). In this note we describe a female of S. costatus and discuss the species distribution and the taxonomic position of the genus.

Stenosternus Karsch, a possible link between Neotropical and Afrotropical Orphninae

1–3 Habitus of males 4 punctation of elytral disc 5 aedeagus in lateral view and parameres in dorsal view 6 serration of medial margins of parameres 7–10 aedeagus in ventral view 1, 4–7 Stenosternus costatus Karsch, holotype 2 Aegidium colombianum Westwood 3 Orphnus macleayi Laporte de Castelnau 8 Hybalus cornifrons (Brullé) 9 Aegidium parvulum Westwood 10 Orphnus compactus Petrovitz.Frolov, A.V. 2013. Stenosternus Karsch, a possible link between Neotropical and Afrotropical Orphninae (Coleoptera, Scarabaeidae). ZooKeys, 335: 33-46.   PDF (2.41 MB)

Abstract. The monotypical orphnine genus Stenosternus Karsch is known from a single specimen of Stenosternus costatus collected on the São Tomé island (Gulf of Guinea). The holotype of Stenosternus costatus Karsch is re-examined and its characters are discussed and illustrated. Although the genus was implicitly placed by Paulian (1984) in the Old World tribe Orphnini Erichson, re-examination of the holotype of Stenosternus costatus shows that it has characters similar to those of the members of the New World tribe Aegidiini Paulian. Placement of Stenosternus in the Aegidiini is supported by the metepisternum widened posteriorly (forming posterior metepisternal lock for closed elytra) and a keel separating basal and anterolateral parts of propleurae. Relationships of Stenosternus with other orphnine taxa and possible ways of origin of São Toméan orphnine fauna are discussed.

Genus Stenosternus (Scarabaeidae, Orphninae)

Orphninae, Stenosternus costatus Karsch, 1881

Body mid-sized (length 16.1 mm, pronotum width 7.3 mm, elytra width 7.6 mm), uniformly dark-brown with slight bronze and greenish tint. Mandibles subsymmetrical. Clypeus emarginate anteriorly, with crenate margin, without tubercles. Pronotum trapezoidal, elongated, with distinct longitudinal middle depression from base to almost anterior margin. Propleurae with fine carinae separating anterolateral areas from basal area adjacent to bases of elytra. Scutellum 1/20 length of elytra, narrow, rounded apically. Elytra somewhat oblong, 1.2 times longer than width, without striae but each elytron with low longitudinal ridge from base to about 5/6 its length. Wings vestigial, about 1/2 length of elytra. Metepisternon narrow, almost parallel-sided, with rounded distal part which somewhat overlaps epipleuron. Anterior tibiae relatively slender, almost parallel-sided, with 2 short lateral teeth and a smaller medial tooth; protarsi absent. Middle and hind tibiae with modified spur-like basal tarsomere. Phallobase symmetrical, with sclerotized ventral plate separated by weakly sclerotized membranous areas. Apices of parameres with tooth-like rounded processes directed anterolaterally and relatively long and dense pale setae. Lateral sides of parameres with short, sparse, mostly abraded setae. Medial sides of each paramere without membrane in apical 2/3 but with dense, scale-like teeth directed apically. Endophallus with about 15 small, tooth-like spinules, without larger sclerites...

Diagnosis, classification, and phylogenetic relationships of the orphnine scarab beetles

Fig. 1. Orphnus spp. and Allidiostoma spp.

Frolov, A.V. 2012. Diagnosis, classification, and phylogenetic relationships of the orphnine scarab beetles (Coleoptera, Scarabaeidae: Orphninae). Entomological Review, 92, 782-797. PDF (1.07 MB)

Abstract — Orphnine scarab beetles (Orphninae) are widely distributed in tropical and subtropical regions of southern continents except for Australia. Catalogue of nominal taxa of orphnines includes 2 tribes, 15 genera, and 193 species. Diagnosis of the group, based on adult morphological characters, is as follows: antennae 10-segmented with 3-segmented club; mandibles with 2-4 scissorial teeth and well developed mola; labrum and mandibles protruding past clypeus and can be seen from above; scutellum well developed in winged species, reduced but distinct in wingless species; wings with distinct anal area; apices of anterior tibia in males without spur but normally with a few robust setae; anterior coxa with longitudinal hollow on anterior surface; tarsi with 2 similar claws; middle and hind tibiae with 2 apical spurs; 2 abdominal sternite with sub-triangular to rounded plectrum; dorsal surface of hind coxae with oval flat stridulatory file; pygidium partly hidden under elytra; parameres symmetrical; ...