Cissidium Motschulsky, 1855

Darby, Michael, 2020, A revision of Cissidium Motschulsky (Coleoptera: Ptiliidae) with seventy seven new species, European Journal of Taxonomy 622, pp. 1-188 : 10-12

Genus Cissidium Motschulsky, 1855

Tribal placement

Grebennikov’s tribe Discheramocephalini was set up to contain six genera of Ptiliidae with perforated mesoventrites following phylogenetic analysis indicating monophly. At the same time he erected a new genus in the tribe – Dacrysoma – which like Cissidium is unique in possessing a dumb-bell-shaped antennomere XI. In separating the two genera, he pointed to the possession by Dacrysoma of a ‘clearly visible’ perforation of the mesoventral collar ( Fig. 2 A–B) whereas the perforation in Cissidium was not well developed and sometimes obscured by a membrane.

With the possible exception of C. cryptophagoides sp. nov. and C. noumeae sp. nov., this study has not found any species of the genus to possess perforated mesoventrites whether obscured by a membrane or not, and as such agrees with the descriptions of Johnson and Sawada, published before Grebennikov’s paper, which make no mention of this feature. In the unpublished manuscript of his Solomon Islands paper Johnson notices Grebennikov’s work and expresses his preference for excluding Cissidium from the new tribe on the basis that it “also includes genera with typical ptinelline hind angles to mesosternum – effaced and far removed from metasternal sides” (Johnson ms 2010). The present author’s inclination, however, after the study of many undescribed species of Ptinellini (unpublished), is to leave it where it is whilst at the same acknowledging that several of the features displayed by the genus are closely related to those in that tribe. It is also clear that Cissidium is very closely related to Dacrysoma in which mesoventral perforations are clearly present, and from the specimens in the MMUE boxes, that Johnson made no distinction between the two genera. On further aids to separating the two genera see below.

Separation of Cissidim from Dacrysoma ( Fig. 2 A–B)

The only species with which Cissidium are likely to be confused as mentioned above are those of the genus Dacrysoma which also possess a dumb-bell or hour glass like antennomere XI. Additionally, the two species also share a shallow emargination in the pronotum opposite the scutellum. The shape of the pronotum in many species of Dacrysoma is more cordate than those of Cissidium but a much clearer distinction between the two genera is provided by the form of the mesoventrite. Dacrysoma possess a wide mid-keel as a direct extension of the collar and distinct setae-fringed perforations either side of the mid-keel which are lacking in Cissidium . Additionally, the lateral margins of the mesoventrite are always effaced anteriorly in Dacrysoma , whereas the lateral margins of Cissidium are rarely effaced and then usually posteriorly.

Revised generic description to include all species in the present paper

Antennomere XI with a median restriction causing it to appear dumb-bell-shaped (though in some species the medial restriction is not clear). Dorsal surface glabrous and/or foveate and foveolate with long, fine, semi recumbent, usually overlapping, setae sometimes giving a ‘hairy’ appearance. Eyes large and prominent, smaller in the females than the males. Submentum with 4/5 setae, when four the two central setae often much longer than the outer two. mentum with sides slightly or strongly tapering to base or parallel and slightly sinuous ( Fig. 4 A–F). Pronotum glabrous or pubescent, shallowly or markedly foveolate and/or with a series of two or more foveae anterior to the posterior margin. Lateral margins rounded or angled, clearly bordered the borders sometimes running along part or all of the posterior margin, posterior margin with or without a clearly defined emargination opposite the scutellum. Hind angles rectangular, obtuse or acute. Scutellum triangular with two deep foveae at the anterior angles. Elytra leaving 2/4 posterior abdominal segments exposed; elliptical/oblong elliptical, with/without foveolae and pubescence, sometimes truncate. Legs long and narrow. Most species fully winged with wings of usual ptiliid form but microptery, macroptery and aptery are not uncommon in the genus, one species recorded as both apterous and probably blind ( C. delicatum sp. nov.). Mesoventral collar with/ without a short median extension onto the flattened median part of the mesoventral keel (mid-keel), posterior margin with shallow depressions occasionally forming deeper fossae particularly at the anterior angles; keel raised medially and extending posteriorly to between the mesocoxae; meso/metaventral suture curving anteriorly to meet collar at corners, sometimes obliterated externally in posterior half and only visible as an apodeme, with or without serrations, evenly rounded or angled. Arms of the metendosternite very long and thin reaching almost to the anterior corners of the mesoventrite. Hind coxae separated by approximately one quarter/one third of the metaventral width, coxal plates small. Metaventral margin between coxae with two pointed projections of varying length at the lateral corners. Spermathecae very small, commonly either globular or ovoid/tubular, sometimes with a small bulge on one side, occasionally in the shape of a horseshoe. Aedeagi very small, pointed or with a rounded or hooked tip, often bent giving a beak-like appearance in profile.

Establishment of species groups

Earlier work by the author on Cissidium ( Darby 2013, 2015, 2019) emphasised the importance of the pronotum and in particular the mesoventrite in the separation and determination of species, and these were examined in an attempt to establish the validity of dividing the material into subgenera. Study of the mesoventral characters in particular was regarded as likely to provide a better indication of phylogenetic development than pronotal characters, and 17 character states were analysed using an Excel Pivot Table with data extracted from all the species. However, this produced many small groups of species varying too slightly to justify subgeneric classification, and it was decided to rely instead on the more easily recognisable features of the pronotum to establish species groups, rather than subgenera, and to use the mesoventral and other characters for the separation of individual species within each group. This approach appears to have followed that of Johnson (although he did not examine the undersides), who included some small sketches of pronota amongst some of the insects in the MMUE drawers. Five groups resulted, with one group split into two halves, as set out below.

Group 1 = species with pronotum entirely glabrous

Group 2 = species with pronotum foveate but lacking distinct foveolae

Group 3 = species with pronotum distinctly foveolate but lacking foveae

Group 4A = species with pronotum lacking both foveolae and foveae, and with rounded sides Group 4B = species with pronotum lacking both foveolae and foveae, and with angulate sides Group 5 = species with pronotum with both foveae and distinct foveolae

The important distinction between ‘distinct’ foveolae and other foveolae, usually described as shallow foveolae, is made clear in Fig. 2C, E .

Apart from the species in the aforementioned groups are several specimens in the MMUE boxes either with insufficient data or in very poor condition preventing them being placed accurately. With one exception, Cissidium adustipenne (Motschulsky, 1869) described below, these have been omitted from this paper. The specimen of Cissidium rufulum Motschulsky, 1855 ( Cissidium rufescens Motschulsky, 1868 ) from Panama, briefly noted by Motschulsky at the time of describing Cissidium basale Motschulsky, 1855 as “ Une seconde espèce est plus courte et de couleur rouse ” to which he added in 1868 “... et taille d’un tiers plus petite, d’un testacé roussâtre, un peu rembruni sur le milieu des élytres ” has been located in ZMUM, but a loan has not been possible because retrieving the specimen from an earlier loan has failed.

Figures

Fig. 2. A–B. Mesoventra of two species of Dacrysoma Grebennikov, 2009 to show form of mid-keel and perforation fringed by setae. C–E. Figures to explain use of the terms foveae, distinct foveolae and shallow foveolae in distinguishing the main species groups. C. Distinct foveolae, showing setae arising from the anterior margin of the depressions. D. Foveae and foveolae, showing setae randomly associated with foveae. E. Shallow foveolae, many setae rubbed off, but insertion points marked by punctures with slightly raised circular rims. F–I. Figures to show different forms of antennae. F. Elongate antenna of Cissidium lisae Darby, 2015. G. Globular antennomere of Cissidium globosum Darby, 2015. H. Female and male antennae of Cissidium petri Darby, 2015. I. Abnormal antennomere XI of Cissidium tigrum Darby, 2015.

Fig. 4. Menta and submenta. A. Cissidium petri Darby, 2015, × 1380. B. Cissidium tigrum Darby, 2015, × 1220. C. Cissidium amboroense Darby, 2015, × 1260. D. Cissidium losbanos sp. nov., × 1100. E. Cissidium triangulum Darby, 2019, × 650. F. Cissidium pilosellum sp. nov., × 1420.