Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 61 - Lucanidae (Insecta: Coleoptera) - General morphology

Holloway, BA 2007. Lucanidae (Insecta: Coleoptera). Fauna of New Zealand 61, 254 pages.
( ISSN 0111-5383 (print), ; no. 61. ISBN 978-0-478-09395-7 (print) ). Published 21 Nov 2007
ZooBank: http://zoobank.org/References/DD20213C-BAEF-49E8-9C34-D65807AA5945

General morphology , terminology, and measurements

“In fact, many of the tiny bristles or hairs that occur to one degree or another on most insects are sense organs.” Matthews, R. W. & Matthews J. R. 1978 “Insect Behavior” p.268.

This morphological account uses New Zealand examples. For the morphology of some exotic species see Holloway (1960, 1968, 1969), Nel & Scholtz (1990), D’Hotman & Scholtz (1990), and Franciscolo (1997). Figures 1 and 2 show the basic morphology of adult lucanids and are mostly self-explanatory. Figures 3 to 74 show other morphological features that are referred to below or elsewhere in the text. Where necessary, the manner in which measurements have been taken is indicated on the figures. The terminology is mainly that used in my previous papers especially Holloway (1960, 1961, 1969) and is based to a large extent on the pioneering reference works of Snodgrass (1935) and Lindroth (1957).

HEAD The labrum (Fig. 1, 3) is by definition (Snodgrass 1935) the preoral lobe of the head. Usually it is separated from the rest of the head by the labral suture, the only visible suture on the dorsal surface of the lucanid head. This suture is obsolete or even absent in some species. While the limits of the clypeus, frons, and vertex can be determined internally from muscle attachments and tentorial pits, externally they are rather vaguely defined. I do not attempt to delimit the clypeus, by definition the facial area of the cranium just above the labrum. Instead I refer to the entire front section of the head extending from the base of the mandibles to the level of the posterior margin of the eyes as the frons, the area posterior to the frons as the vertex, and any integumental extension between the frons and the labrum as the intermandibular projection. The intermandibular projection, which almost certainly includes part of the clypeus, varies from extremely short to conspicuously long and may extend obliquely rather than horizontally to the labrum, sometimes not being visible at all in dorsal aspect (Fig. 5). The region I term the frons probably also includes part of the clypeus and should perhaps be more accurately termed frontoclypeal region. In most species the integument above the antennal insertion is raised as the supra-antennal brow (Fig. 3) which varies from slightly convex to conspicuously arched. The eyes vary greatly in size and shape and are either entire or divided. The eye is termed entire when the anterodorsal angle of the eye lies on the lateral margin of the head (Fig. 1), and divided when an integumental projection, the canthus, intrudes into the front of the eye separating the eye into upper and lower parts and displacing the anterodorsal angle from the margin to a submarginal position (Holloway 1969). Most commonly the canthus extends only partly across the eye (Fig. 2–4) but in a few species it divides the eye completely into upper and lower parts (Fig. 5). In some species a very short canthus extends forward into the eye from the postocular margin.

The mouthparts consist of the epipharynx, labium, maxillae, and mandibles. The epipharynx is the membranous or partly sclerotised inner lining of the labrum. It forms the roof of the preoral cavity and bears tactile hairs and taste organs on part of its surface (Fig. 6). The floor of the preoral cavity is formed by the labium (Fig. 7–12) consisting of the mentum, prementum, ligula, and labial palps. The mentum is a strongly sclerotised, immovable, somewhat quadrangular plate articulating on the gula (Fig. 4). On its internal surface it typically bears the prementum which provides support for the ligula and labial palps. In Lucaninae the prementum consists of a pair of pale, rather weakly sclerotised, elongate plates lying against the sides of the ligula, near the middle of the mentum (Fig. 7). Aesalinae, Lampriminae, and Syndesinae do not have these plates and therefore appear to lack a prementum but, as will be shown below, the prementum in these subfamilies is represented by a pair of sclerites at the apex of the mentum (Fig. 9–12). The ligula is variably developed but is always setose to some extent. Its apex may be deeply divided (Fig. 7), shallowly notched (Fig. 9, 10), or entire (Fig. 11). In Lucaninae the labial palps are clearly 3-segmented and the integument of their segments is smooth and sparsely setose. The base of the 1st labial palp segment in this subfamily is movable on the distal end of the prementum, concealed in ventral aspect by the mentum (Fig. 7), and the intersegmental membrane between the segment and the prementum is conspicuously broad, stiff, and transparent. Nel & Scholtz (1990) consider the labial palps to be 4-segmented in Aesalinae, Lampriminae, and Syndesinae but I disagree with their interpretation. The so-called “basal” or “first” segment in these apparently 4-segmented palps is short, broad, somewhat ring-like, immovably attached to the apical region of the mentum, and at least partly visible in ventral aspect (Fig. 8). Its integumental texture and vestiture are like those of the mentum and not at all like those of the other palp segments, its medial edge is pressed against the sides of the ligula and the intersegmental membrane connecting it to the adjoining palp segment is like the distinctive membrane between the prementum and 1st palp segment in Lucaninae. In my earlier publications (Holloway 1960, 1961, 1968) I considered this “basal segment” to be part of the mentum because of its position and appearance. Having re-examined the labium in a range of species I now consider the pair of “basal segments” in Aesalinae, Lampriminae, and Syndesinae to be the highly modified prementum, and confirm that the labial palps are 3-segmented throughout Lucanidae. The maxillae lie between the mentum and the mandibles. Several types of maxillae are shown in Fig. 13–17. The maxillary palps are always 4-segmented. Sexual and generic differences are sometimes apparent in the form of the galea and lacinia, and in the size of the palp segments. The galea always has brushes or bands of long setae on its medial edge and apically, and a few sclerotised hooklets may be present among the setae (Fig. 13). The apex of the lacinia can be developed as a strongly sclerotised hook (Fig. 13) or a blade (Fig. 14) but more commonly it is unarmed and entirely setose (Fig. 15–17). The mandibles form the outer lateral margin of the preoral cavity (Fig. 4, 6). Their exposed distal part has teeth or lobes whose shape and position provide important characters for identifying and sexing specimens. The proximal part of the mandible, partly concealed within the head capsule, may have a variably developed lobe, the mola, on its medial edge (Fig. 6). In phytophagous beetles the mola is used for crushing and grinding plant material but its function is unclear in stag beetles as they mostly feed exclusively on sap and nectar. The mandibles are almost always larger and more ornate in males than in females of the same species. However, in several New Zealand species, e.g., Holloceratognathus cylindricus (Broun) and H. passaliformis (Holloway), the mandibles in both sexes are small and extremely similar in appearance. Mandibles of some Geodorcus males are strikingly allometric, becoming disproportionately larger with the increase in body size in individuals of the same species. Short, crescentic mandibles are typical of most lucanid females (Fig. 2–4) but not all (Fig. 5).

The mouthparts of several exotic lucanids and 2 New Zealand species are described and illustrated by Nel & Scholtz (1990) in a very comprehensive survey of these structures in Scarabaeoidea.

The antennae are set in the antennal fossae located ventrally between the eye and the outer margin of the mandible (Fig. 2, 4). They are 10-segmented in all the New Zealand species (Fig. 1, 18–20) and in most other lucanids. Depending on the way in which the 2nd segment (pedicel) articulates on the 1st segment (scape), the antennae are termed geniculate, non-geniculate, or partially geniculate (Holloway 1960). In geniculate antennae (Fig. 18) the scape is almost straight not arched, considerably widened distally, and the pedicel articulates dorsally a short distance from the distal end of the scape and can be held at a right angle to it. In non-geniculate antennae (Fig. 19) the scape is strongly arched, approximately uniformly wide throughout its length, and the pedicel articulates on the whole distal end of the scape and cannot be held at a right angle to it. The scape of this type of antenna frequently has on its dorsal or posterodorsal surface a row of long setae and an associated short groove. Partially geniculate antennae (Fig. 20) have a slightly arched scape that is not conspicuously widened distally, and the pedicel articulates somewhat dorsally on or very close to the oblique distal end of the scape and can be held almost at a right angle to it. In this type of antenna the scape may have a row of setae and an associated groove on its posterodorsal surface. The antennal club consists of 3–7 segments which are recognisable as belonging to the club by their partially or completely pubescent or densely setose surface and not necessarily by being different in shape and size from the preceding segments. Club segments may be stout to slender, rather rigidly opposed or loose and free, but never lamellate. Males usually have larger club segments than females and in some e.g. Mitophyllus irroratus Parry the segments have spectacularly long setae. The 5 segments between the pedicel and club comprise the funicle.

THORAX External thoracic structures are shown in Fig. 1 and 2. The discal surface of the pronotum and elytra occasionally has tubercles but mostly the integument is smooth. A broad horizontal or reflexed brim is present on the lateral margin of the pronotum in some species and there may be a narrower brim on the sides of the elytra. The pronotal and elytral integument in lucanids always has some punctures and usually setae or scales on it. Punctures in the brim are often larger than those elsewhere on the body and are the best ones for showing the floor and wall structure, under a stereomicroscope. The density and size of the punctures and the colour pattern and angle of inclination of the vestiture are usually distinctive for species. The ultrastructure of the elytral vestiture and of the associated pits (punctures), pores, and adjacent integument includes characters that can be used to define genera and even one of the subfamilies (Lampriminae). Examples of the diverse elytral ultrastructure found in Lucanidae are shown in Fig. 21–42. The micrographs (Fig. 31–42) are of the elytral surface immediately anterior to the elytral declivity, and the drawings (Fig. 21–30) are of vestiture also from this part of the elytra.

A typical lucanid wing is shown in Fig. 43. The terminology applied to the veins is that used in my paper on New Zealand lucanid wings (Holloway 1963b). In flying species the wings range from 1.6–2.1× the elytral length. All the species of Geodorcus and Paralissotes have vestigial wings ranging from 0.2–0.8× the elytral length (Fig. 46–49), depending on the species. Mitophyllus fusculus (Broun),is the only flightless species in the genus and only its females are vestigial winged. The wings are 1.7× longer than the elytra in the males but in the females they are the same length as the elytra (Fig. 45). The actively flying species Holloceratognathus cylindricus (Broun) and H. helotoides (Thomson) have “normal” wings that are respectively about 1.8× and 1.6× the elytral length and have a “normal” anal area while those of H. passaliformis (Holloway) which is found in ants nests are about 1.5× the elytral length and have shortened anal veins (Fig. 44).

Features of the ventral surface of the thorax are shown in Fig. 2 and Fig. 50–52. The prosternal process is on the midline of the prosternum, between the coxal cavities. In the New Zealand lucanines this process is very broad, widely separating the coxae (Fig. 2, 50). In the New Zealand examples of the other subfamilies the process is narrow and the medial edges of the coxae almost touch on the midline (Fig. 51, 52). I refer to the legs on the pro, meso-, and metathorax as the fore or front, middle, and hind legs respectively but when appropriate I apply the prefixes pro-, meso-, and meta- to parts of the legs. The procoxal process is a ventrally directed lobe on the anteromedial edge of the procoxa. In general, species with a broad prosternal process lack a procoxal process (Fig. 50) while those with a narrow prosternal process may have either a large procoxal process (Fig. 51) or one that is quite small (Fig. 52). The profemur in all lucanids has a conspicuous patch of orange or yellow setae on its anterior surface. I refer to this as the femoral setiferous patch. Some other scarabaeoids also have this patch, usually in a reduced form. Associated with the femoral setiferous patch is a broad band of setae, here termed the procoxal fringe patch, which is on the posterior surface of the opposing procoxa. The fine structure of both patches seems not to have been investigated previously so I have included details of these as seen with a scanning electron microscope (Fig. 53–58) and with a stereomicroscope (Fig. 59–62). Most commonly the femoral patch is on the proximal half of the femur and is about half its length (Fig. 53, 59) but it may be considerably larger (Fig. 61) or smaller (Fig. 62). Its setae are long, soft, appressed, overlapping, and directed ventrally (Fig. 53). Their bases are set in sockets (Fig. 54) and throughout their length the setae are grooved (Fig. 55). No glandular openings are present on the floor of the patch (Fig. 54). The procoxal fringe patch is a rather broad band of setae located close to the ventral margin on the posterior surface of the procoxa (Fig. 56, 60). The band is similar in length to that of the associated femoral patch. The apices of some of the procoxal patch setae project beyond the ventral margin to form a distinct fringe (Fig. 56, 59–62). In colour, length, and angle of inclination the procoxal fringe and patch setae are like those in the femoral patch except that in addition to being grooved they are barbed, sparsely on their basal and middle regions (Fig. 57) and densely towards the apex (Fig. 58). No glandular openings are present on the floor of the procoxal fringe patch (Fig. 58). When the profemur is extended outwards at a right angle to the ventral midline of the body its anterior surface is pressed against the posterior surface of the procoxa. In this position the barbed setae of the coxal fringe spread across the grooved setae of the femoral patch and the apices of both types of setae are directed ventrally. Whether the setae interlock in a “velcro” type of arrangement has not been determined. As there are no glandular openings associated with their bases both types of setae are unlikely to be involved in dispersing chemicals. Perhaps their role is to position the procoxa against the profemur, e.g., during walking, although why a special mechanism should be required is not clear. The procoxae of Holloceratognathus passaliformis are unusual in having a crescentic integumental flange that covers the fringe patch (Fig. 62) and also overlies the femoral patch when the femur is extended outwards.

In the New Zealand lucanids the protibiae have 2 main dentition patterns, either with numerous variably or similar-sized small teeth, a large apical tooth, and a somewhat smaller mid dorsal tooth (Fig. 1), or with fewer teeth, all rather broad-based, which increase in size from the proximal end of the tibia to its apex (Fig. 59, 63). The mid dorsal tooth is often located near the middle of the protibia but sometimes lies closer to the apex. Some species have a mid dorsal tooth as well on the tibiae of the middle and hind legs (Fig. 1). If the tibial teeth are sharply pointed they look like spines and may be referred to by that term. Structurally they are rather plate-like, often curved, with their underside concave at the base and overhanging a shallow depression containing a small seta or scale. I am unaware of any detailed study that has been made on the tibial teeth in lucanids and other scarabaeoids but in some Diptera very similar looking tibial units have a glandular opening in the concave floor and are known to be sites of pheromonal release (Schlein et al. 1980).

The tarsi of all the legs have 5 tarsomeres and a pair of claws. The arolium (Fig. 63) lying between each pair of claws consists of a long or short rod with 2 or more setae arranged on either side of its apex.

ABDOMEN There are 5 visible ventrites (Fig. 2). The 5th ventrite in males differs in length from that in females and its apex is notched, truncate, or narrowly convex, not broadly convex as it usually is in females.

Male genitalia.The terminology applied to the various structures is that used in my previous papers (Holloway 1960, 1961, 1998). Terms in parentheses are those used by D’Hotman & Scholtz (1990). The male genitalia consist of the 9th abdominal segment (genital segment) and the aedeagus. The 9th abdominal segment comprises a stalked sternite (ventral plate), a sessile tergite (dorsal plate), and a pair of stalked pleurites (lateral plates) (Fig. 64, 67) that together form a cylinder around the aedeagus when it is in repose. Most commonly the 9th abdominal segment is bilaterally symmetrical (Fig. 64), but in a few species it is asymmetrical (Fig. 67). The aedeagus is composed of a basal piece, a pair of parameres, the penis (median lobe), an internal sac continuous with the ejaculatory duct and, in some species, a pair of struts (temones) which articulate on the base of the penis. The basal piece and parameres together comprise the tegmen. In Lucaninae (Fig. 65, 66) the penis rests on the distal end of the basal piece and a pair of struts articulates on a dorsal or dorsolateral cross bar at its base (Fig. 66). The internal sac in this type of genitalia is permanently everted and has the form of either a strap-shaped or lobed structure (Fig. 65) or terminates in a flagellum. In the other subfamilies the penis does not rest on the end of the basal piece but instead is enclosed to some extent within it (Fig. 68), a pair of struts may be present or absent (Fig. 68) at the base of the penis, and the internal sac is eversible, lying within the penis when in repose but emerging through the aperture (ostium) at the distal end of the penis during copulation. The form of the male genitalia is constant within genera and is also indicative of subfamilies. Illustrations and descriptions of the male genitalia in a range of lucanids are available in Holloway (1960, 1968, 1969, 1998) and in the comprehensive paper on the male genitalia of Scarabaeoidea by D’Hotman & Scholtz (1990) who consider the function and phylogenetic significance of the various components.

Female genitalia.These consist of the well sclerotised tergite, paired pleurites, and divided sternite of the 9th abdominal segment, the strongly sclerotised hemisternites of the 10th abdominal segment, and the weakly sclerotised internal genitalic structures. Two types of genitalia, depicted in the customary ventral aspect, used throughout this revision, are illustrated in Fig. 69 and Fig. 70. Unfortunately, important specific and generic features of the tergite and pleurites of the 9th segment (Fig. 71–74), visible dorsally, cannot be seen in this aspect, and probably warrant a separate study at a later date. The 9th abdominal segment and hemisternites are always bilaterally symmetrical even in species whose males have asymmetrical genitalia. The shape and configuration of the softer internal structures are extremely important for delimiting species and genera but seem not to be useful for distinguishing subfamilies. The spermatheca, spermathecal gland, and spermathecal duct are easily recognised (Fig. 69, 70). The bursa copulatrix may be large and saccate, or bilobed, or developed as a small pouch but regardless of its shape it is recognisable because the spermathecal duct inserts on its wall. Very rarely, as in Dendroblax earlii, the bursa copulatrix is developed only as a tube continuous with the spermathecal duct from which it is indistinguishable. The bursal duct is joined to the vagina and extends from the base of the median oviduct to the bursa copulatrix. It may be very much narrower than the vagina (Fig. 70) or equal in width to it (Fig. 69). An accessory gland if present arises on the side of either the vagina (Fig. 69) or the bursal duct. The genitalia shown in Fig. 70 lack an accessory gland. The vagina continues distally to the vulva, a transverse slit in the membrane between the hemisternites.

Terminology of the vestiture and punctures The curvature and angle of inclination of the setae and scales are shown in Fig. 75. I refer to elements of the vestiture that are approximately circular in cross section as setae and those that are either laterally compressed or dorsoventrally flattened as scales. In descriptions of the gross morphology of the integument it is customary to refer to the depression surrounding the socket in which a seta or scale is located as a puncture. At the ultrastructural level punctures are more accurately termed pits to give recognition to their physiological significance (Holloway 1997). In referring to the size of punctures and vestiture and their density I have used vernacular terms, small, short, dense, etc. The approximate measurements that these translate into, using a calibrated ocular micrometer, are given below.

Puncture diameter: minute, less than 0.02 mm; small, 0.02–0.1 mm; moderately large, 0.1–0.2 mm; large, more than 0.2 mm.

Puncture density (distance between margins of adjacent punctures): very dense, less than 0.02 mm; dense, 0.02–0.1 mm; moderately dense, 0.1–0.2 mm; sparse, more than 0.2 mm.

Seta/scale length: minute, less than 0.02 mm; short, 0.02–0.1 mm; moderately long, 0.1–0.2 mm; long, more than 0.2 mm.

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