FNZ 3 - Anthribidae (Insecta: Coleoptera) - Morphology
Holloway, BA 1982. Anthribidae (Insecta: Coleoptera). Fauna of New Zealand 3, 272 pages.
(
ISSN 0111-5383 (print),
;
no.
03.
ISBN 0-477-06703-4 (print),
).
Published 23 Dec 1982
ZooBank: http://zoobank.org/References/AC1DC576-5021-40DE-9BD7-0F7C591C6521
Morphology and Terminology
In this section emphasis is placed on the morphology of the New Zealand species. A more general treatment is available in Valentine (1960) and Arnett (1963).
Head
The head (Figures 1-7) lacks longitudinal sutures on the gula (Figure 2) and is not conspicuously retracted into the prothorax. Throughout the text the upper surface is referred to as dorsal even when the head is directed anteroventrally in relation to the pronotal surface.
Rostrum. This is depressed and never cylindrical, rarely moderately long and slender (Figures 3 and 4) but more commonly short and broad (Figures 5 and 6) or indistinct (Figure 7). Its dorsal surface often has pits (Figure 1), tubercles (rounded or conical elevations), longitudinal carinae (keels) (Figures 3 and 4), or depressed areas (Figure 6), or a combination of these (Figure 5). The presence, form, and disposition of depressions and carinae is constant within genera. The rostrum is often longer, larger, and more conspicuously contoured on the dorsal surface in males than in females.
Antennae (Figures 1, 2, and 5-11). These are 11-segmented, short to very long, and not elbowed, except in large males of Hoherius (Figure 194). The scape (segment 1) is cylindrical, almost bilaterally symmetrical, and has a basal stalk in about the same plane as the rest of the segment (Figures 3 and 9 - Anthribinae); or is somewhat pear-shaped, obliquely truncate at the base, and has the stalk inserted at right angles to the rest of the segment (Figure 10 - Anthribinae); or is arched, with the external margin much more convex than the internal margin (when the antenna is folded against the body), and has the stalk almost in the same plane as the rest of the segment (Figures 7 and 11 - Choraginae). The pedicel (segment 2) is shorter or longer than the scape and is either cylindrical and almost bilaterally symmetrical (Figures 9 and 10 - Anthribinae) or arched, with the external margin more convex than the internal margin (Figures 7 and 11 - Choraginae). The funicle comprises 6 rather similar, usually symmetrical segments. The club is composed of 3 segments most commonly broad and compact, but sometimes narrow and loosely articulated, or with the first segment not very different from the funicle segments. Relative proportions of the scape and pedicel, and the overall appearance of the antenna, are constant within genera. Males usually have longer antennae than females.
Mouthparts. The labrum (Figures 1, 3, and 4) is separated from the rostrum by a groove. The mandibles (Figures 1-3) are large and exposed. The maxillae (Figure 2) consist of a pair of laciniae and a pair of 4-segmented, slender, flexible palps which have their basal segment concealed by the mentum. The labium (Figure 2) is composed of an exposed, bilobed, sclerotised ligula, a pair of 3-segmented, slender, flexible palps, and a large, strongly sclerotised, bilobed mentum.
Eyes. These are lateral (Figures 1-7) or rarely dorsolateral (Figure 107), round (Figure 7), oval (Figure 1), kidney-shaped (Figure 152), or horseshoe-shaped (Figure 207), with the anterior margin entire (Figure 4), truncate, notched (Figure 6), or deeply incised (Figure 203). They are often reduced in size in flightless species (Figure 6). The hairs between the facets are usually visible at low magnifications (about x50). Males often have more closely approximated and more deeply notched eyes than females. The general shape of the eyes is diagnostically useful at the generic level.
Antennal Scrobes. These are grooves on the side of the rostrum that contain the base of the scape. They may be lateral (Figures 1-4 - Anthribinae), with no part of their floor or walls visible in dorsal aspect; or dorsolateral (Figure 6 - Anthribinae), with part of their floor and walls visible in dorsal aspect; or dorsal (Figure 7 - Choraginae), with their floor and walls almost totally visible in dorsal aspect. The interscrobal distance compared with the interocular distance is important for separating genera.
Thorax
Prothorax. The pronotum (Figure 1) usually has a transverse carina near the base and lateral carinae at the sides. The transverse carina may be basal (Figure 12), subbasal (Figure 13), or antebasal (Figure 14), and either entire (Figures 12 and 13) or fragmented (Figure 14). The lateral carinae are variably developed but rarely extend anteriorly beyond the pleural suture. The disc (central part) of the pronotum sometimes has tubercles, and the declivity behind the transverse carina may have denticles (Figure 13) or secondary carinae (Figure 14). The position of the transverse carina varies within genera but not within species; its curvature may vary slightly within species. Fragmentation of the transverse and lateral carinae occurs commonly but not exclusively in flightless species. The prosternum (Figure 19) has a pleural suture - perhaps more correctly termed a pleural apophyseal invagination (Hlavac 1972) - running forward obliquely from the outer edge of the coxal cavity to the sides or dorsal surface of the prothorax.
Mesothorax. The scutellum (Figure 1) is usually visible and always small. The elytra (Figure 1) do not completely cover the pygidium (last abdominal tergite). They usually have a scutellary striole and other striae (depressed lines often containing punctures) (Figure 15); sub-basal, median, and preapical tubercles and a humeral callus may be present in fully winged species (Figure 1). The outer edge of the elytron is bent under to form an epipleural fold (Figure 20), which is narrow except near the base; also on the underside is a supra-costal flange (Figure 15). The mesepisternum and mesepimeron do not reach the middle coxal cavity, which is closed outwardly by the junction of the mesosternum and metasternum (Figure 20).
Metathorax. The hindwings are fully developed (Figures 16-18), vestigial (Figures 277-290), or absent. Veins of fully developed wings vary from moderately complete and strongly sclerotised (Figures 16 and 17) to very incomplete and weakly sclerotised (Figure 18). The metepisternum (Figure 20) is broad, elongate, and partly covered by the elytral margin; the metepimeron (Figure 20) is narrow, elongate, and almost entirely obscured by the elytral margin.
Legs. The front and middle coxae are globular and the hind coxae are transverse (see coxal cavities, Figures 19 and 20) . The femora and tibiae (Figure 1) lack spurs and spines; they often have conspicuous transverse rings or bands of vestiture whose colour and position are important for separating genera. The tarsi (Figure 21) are 5-segmented but with the fourth segment very small and often hard to see; the second segment is almost always emarginate at the apex; the third is bilobed; and the fifth bears a pair of apical claws with a variably developed tooth on their inner edge.
Abdomen
Dorsal Surface. There are 7 tergites (segmental plates), of which the first to sixth are covered by the elytra and the seventh (pygidium) is partly exposed (Figure 1). There are usually marked sexual differences in the shape, surface texture, and vestiture of the pygidium.
Ventral Surface (Figure 20) . There are 5 ventrites (segmental plates); the first 4 are fused together but have the sutures showing, and the fifth is slightly movable on the fourth. Sexual differences may be apparent in the surface contours of the ventrites; the fifth ventrite of females is often longer and more strongly deflected than in males, and frequently has asperities (dot-like swellings) on part of its surface.
Vestiture This consists of variably developed fine hairs and small, usually linear scales or thickened scale-like hairs. The angle of inclination of the vestiture (Figure 22) varies from appressed to erect, and the scales or hairs may be straight or curved. Any vestiture that is not pressed against the integumental surface may be referred to as standing vestiture. In all the New Zealand species the tips of the scales and hairs are directed forwards on the head and pronotum and backwards on the elytra.
Genitalia
These include the modified eighth and ninth abdominal segments. In repose they are contained within the abdomen.
Male. Segment 8 (Figure 23) consists of a variably developed tergite and a pair of sternal lobes. A short apodeme (a rod for the attachment of muscles) belonging to sternite 8 may be present. Sternite 9, sometimes called the spiculum gastrale (Figure 23), is represented by a long apodeme which is usually divided distally into two short arms. The tegmen (Figures 24 and 25) consists of a ventral, proximal apodeme and a large sclerotised ring which is divided dorsally near the apex by a transverse preapical flange. The tapering part beyond the flange bears stiff hairs at its apex; it represents the fused parameres of other Curculionoidea. In repose the ring encloses the aedeagus (Figures 26 and 27), which consists of a body, a pair of apodemes, and an eversible internal sac. The body is beak-like and comprises a ventral plate (pedon) and a dorsal plate (tectum) joined by lateral membranes. Jordan (1942) has used the term hypophallite and epiphallite respectively for these plates, but I consider the terms pedon and tectum, used in one of my earlier papers (Holloway 1970), to fit in better with the terminology recommended by Lindroth (1957) for the male genitalia of Coleoptera. The apodemes are usually connected dorsally by a cross-piece (bridge), and are continuous with - or, rarely, articulated on - the pedon. The male genitalia embody many important specific and generic characters.
Female. Segment 8 (Figure 28) consists of a variably developed tergite and a sternite which has a proximal apodeme. Tergite 9 is represented by a weakly sclerotised plate which is associated with the rectum. The hemisternites (Figures 29 and 30) are composed of a somewhat cylindrical distal body and two pairs of apodemes, the lateral and median rods. The lateral rods either articulate on a transverse bar on the ventral surface of the body of the hemisternites (Figure 29 - Anthribinae) or are continuous with the body (Figure 30 - Choraginae). Each hemisternite usually has a strongly sclerotised, articulated, apical toothed plate which partially encloses a small, lateral, setose stylus. Gynarchaeus (Figure 31) has retained the unmodified curculionid type of hemisternite which lacks sclerotised teeth and has a large apical stylus. Other forms of anthribid hemisternite apex are shown in Figures 32- 38, which depict the sequence of changes that can occur in the teeth and stylus; the latter is reduced to a single long bristle in Notochoragus (Figure 38). The vulva is usually enclosed by a dorsal and two ventral membranous lobes, though these are reduced or absent in some genera, of Choraginae especially. The vagina extends from the vulva to the level of entry of the median oviduct. The bursa copulatrix is a simple or lobed sac often with sclerites or patches of spinules near the insertion of the spermathecal duct. The spermatheca is strongly sclerotised and usually sickle-shaped, rarely annulate. The spermathecal gland duct enters the spermatheca through a small atrium - or rarely a slit - at its base or outer basal edge. The spermathecal duct inserts on this atrium or slit. The genitalia of females have very distinctive features, especially at the generic level.
Form and function of some integumental structures
Sensory structures of several kinds are obvious on the body surface of many anthribids, but virtually nothing is known of their fine structure or function. Those occurring only in males can be assumed to have a purely sexual function, but some of those found in females could be involved in oviposition as well as mating behaviour. The most conspicuous sensory structures in males are oval or circular pits bordered by a shiny rim and containing dense, erect, pale hairs. These are very likely to be sites for the production and release of sex pheromones. An oval pit of this type is present on the underside of the hind femur in males of Androporus discedens (Figure 176), and an undescribed New Caledonian species of this genus has a smaller circular pit on the hind femur.
Keels and tubercles on the midline of some abdominal ventrites in males of several species are also likely to be involved in the dispersal of sex attractants. The tubercles in Sharpius chathamensis (Figure 91) are conical and rather small, but in Liromus pardalis (Figure 216) they are large and have a conspicuous concavity on the posterior face. Males of all species of Dysnocryptus have a narrow, often deep keel on the midline of several of the ventrites. These keels are capped by a tuft or row of erect hairs, and are distinctive for each species (Figures 223, 227, 231, 235, 239, 243, 247, 251, and 255) .
Females of many species have part or all of the surface of the pygidium covered with conspicuous asperities, each one usually bearing a very small scale or short hair. Asperities and dense tufts of hairs are present on the fifth abdominal ventrite in both sexes of many species. In the males and females of a given species they are always differently developed. The tubercles, ridges, pits, pores, grooves, and depressed areas that are variously distributed over the integument form part of what Lawrence & Hlavac (1979) refer to as the "family of adaptations for controlling the flow and storage of materials on cuticular surfaces". The functions of cuticular secretions are diverse; they include defence against bacteria and fungi and protection from water loss as well as sexual attraction. Tubercles (Figure 181), ridges (Figure 177), and grooves (Figure 186) on the upper surface of the head and rostrum of anthribids, particularly males, almost certainly serve to channel the flow of secretions. Because of the downward tilt of the head in most species, and the direction of the vestiture, the substances will move towards the anterior margin of the head. In males of Lawsonia variabilis (Figure 202) the base of the mandible has a small, deep pit in which these materials could be trapped. Both males and females of Gynarchaeus ornatus (Figure 67), Garyus altus (Figure 128), and Euciodes suturalis (Figure 207) have small, deep, shiny pits along the dorsal midline of the rostrum, often with a groove opening into them from behind, and these too perhaps serve as reservoirs for surface secretions.
The fine structure and function of the transverse and lateral carinae margining the pronotum (Figure 69) have not been studied. In some species, especially those with fully developed wings, the carinae consist of a row of small, similar-sized, contiguous asperities which usually bear a minute apical scale or hair. On the transverse carina the asperities are directed upwards or slightly forwards, and those of the lateral carinae lean slightly towards the midline of the pronotum. Cuticular secretions originating from in front of the transverse carina would therefore be confined to the anterior part of the pronotum, and would tend to flow towards the head because of the direction of the vestiture. The surface of the pronotal disc is often moulded into tubercles (Figure 69) or quite deep depressions which could also assist in channelling or retaining these substances. Why the transverse carina should tend to fragment or disappear entirely in flightless species is not clear.
In many species the elytra have tubercles, swellings, and sunken areas similar to those on the pronotum, equally developed in males and females. The tubercles are evaginations of the cuticle, and usually are capped by a tuft of erect, black hairs. When more than one pair of tubercles is present (excluding the humeral callus), the anterior ones are the larger (Figure 190). In general, all elytral tubercles have the apices directed posteriorly (Figure 195). As the tips of the scales and hairs also point in this direction the flow of cuticular secretions on the elytra will be towards the pygidium.