Fauna of New Zealand 71: Fanniidae (Insecta: Diptera) - Morphology
Domínguez, MC; Pont, AC 2014. Fauna of New Zealand. 71, 91 pages.
( ISSN 0111-5383 (print), ISSN 1179-7193 (online) ; no. 71. ISBN 978-0-478-34745-6 (print), ISBN 978-0-478-34746-3 (online) ). Published 30 Jun 2014
Head. The head is semicircular and concave posteriorly in males, ovoid and convex in females. Males holoptic (Fig. 3, 4); females of the genus Fannia, both sexes of the species of Euryomma, Australofannia Pont, Zealandofannia new genus, some Piezura Rondani, and two of the newly described species of Fannia from New Zealand have the head dichoptic with the eyes well separated (Fig. 5). The eyes are mostly bare, but are sparsely to densely setulose in a few species.
On the frons, the eyes are bordered by a relatively narrow or broad fronto-orbital plate (Fig. 3). The fronto-orbital plate and the frontal vitta (interfrontalia) occupy the central line of the head, between the ocellar triangle and the lunula. In males of the genus Fannia, this area is generally narrow to very narrow, so that the eyes appear almost to touch for part of their length (Fig. 3). Usually the female fronto-orbital plates have a convex inner median margin, which is an autapomorphic character of the family (Hennig 1965; McAlpine 1989) (Fig. 5). The fronto-orbital plates in males and females have a row of frontal setae that vary in number, length, and strength (Fig. 3, 5). Females of the genus Fannia, and both sexes of Australofannia, Zealandofannnia, Euryomma, and some Piezura have 1 upper reclinate and 1 lower exclinate orbital setae (autapomorphy), as well as a variable number of rows of setulae along the whole length of the fronto-orbital plates (Fig. 5). Males of the canicularis-group of the genus Fannia and some species of Piezura have the upper (reclinate) orbital seta strongly developed.
The ocellar triangle on the vertex is very distinct and all three ocelli are developed. On either side of the ocellar triangle are the outer and inner vertical setae, best developed in females, followed by a row of post-ocular setulae which is generally simple (Fig. 4), but can be double or irregular in arrangement.
The face is the part of the head, below the antenna. It is separated from the eye margins by a parafacial (Fig. 3). The parafacial is generally bare, but it may have rows of setulae (as in females of the groups of canicularis) or rarely a row of setae. The mouth margin is produced anteriorly only in the Fannia mollissima-subgroup(Chillcott 1961; Pont 1965; Wang et al. 2008). At the side of the lower part of the face, a pair of strong and usually crossed setae is present at the vibrissal angle. The gena is generally narrow, with the width below lowest eye-margin less than twice the width of postpedicel, but it may be broad as in the species from New Zealand that have a broad frontal vitta. The antenna consists of two short basal segments (scape and pedicel) and a third longer segment, the postpedicel which is almost always shorter than the face (Fig. 4, 5). The antenna may vary in colour from black or brown to yellow. The postpedicel bears an arista in the usual dorsal position. The arista is bare or short-pubescent, but may be plumose, as in the genus Piezura, or sub-plumose, as in Australofannia and the South American Fannia admirabilis-group (Chillcott 1961; Pont 1977a; Albuquerque et al. 1981).
The mouthparts consist of a sucking type of proboscis (Fig. 4). The short tubular part of the proboscis is formed from the sclerotised labium. The prementum may be conspicuously shining or dusted on the ventral side. The apical part of the proboscis terminates in two labella. The maxillary palpi are usually well developed but may be strongly reduced in size, and may be filiform to expanded and spatulate in shape. They vary in colour from dark brown to yellow, and in the New Zealand species there is a slight variation in shape from slender to weakly spatulate.
Thorax. The thorax is as in most calyptrate Diptera.
The postpronotum is well developed and is closely associated with the mesonotum (scutum); its posterolateral margins form the postpronotal lobes (Fig. 6). This lobe in Fanniidae has three setae (two strong and one weaker) and a variable number of setulae.
Laterally the propleuron is divided into an anterior portion, the proepisternum, and a smaller posterior portion, the proepimeron (Fig. 6). These two sclerites form an arch over the anterior coxa, being placed below the anterior spiracle. The proepisternum has 2 setae and the proepimeron 1 seta, each with a variable number of setulae.
The scutum is provided with a variable number of longitudinal rows of acrostichal setulae (Fig. 7). The number of rows is usually constant in the different species groups. Five pairs of dorsocentral setae (Fig. 7), two in front and three behind the transverse suture (Fig. 6), apparently belong to the ground-plan of the family. Only Fannia abnormis (Stein) lacks the presutural dorsocentral setae (Stein 1911), and in Euryomma and Zealandofannia the anterior presutural dorsocentral is reduced. Lateral to the dorsocentral rows are the intraalar setae (Fig. 7), of which there are usually one presutural and two postsutural pairs, but there is only one postsutural pair in Zealandofannia. The postalar and supraalar (presutural and postsutural) setae are usually distinct (Fig. 7).
Behind the lateral margin of the transverse suture and in the anteromedial region of the notal alar process is the prealar area (Fig. 7). Here are the prealar setulae, which are of great toxonomic importance. The name ‘prealar’ was introduced by Stein (1898: 164) to designate the first and second supraalar setae/setulae immediately behind the suture. In Fanniidae the setulae may be absent or reduced or duplicated. Their position may also vary, as they may be closer to the supraalar seta or to the suture.
The scutellum (Fig. 6), placed posterior to the scutum, bears two pairs of strong and one to two pairs of fine marginal setae, a pair of discals before the tip, and a few to several additional discal setulae. The lateral margins below the strong setae and the ventral surface are bare.
The mesopleuron is divided by the pleural suture into an anterior episternum and a posterior epimeron. The episternum is transversely divided by a suture into a superior area, the anepisternum, and an inferior area, the katepisternum (Fig. 6). Anepisternal setulae cover the greater part of the anepisternum, and usually form a row of setae along its posterior margin. The katepisternum usually has two strong setae in addition to some fine setulae, but there is a second (lower) posterior seta in Zealandofannia. Similarly, the epimeron is transversely divided into an anepimeron and a katepimeron, which are always bare in Fanniidae (Fig. 6). Below them is the meron, which is also bare in Fanniidae (Fig. 6).
The wing has a conspicuously uniform venation in virtually all species. The shape of the subcosta and of the first and second anal wing veins are apomorphies of the family (Fig. 8). The subcosta runs straight in its apical half, without any sinuous bend. The first anal vein is remarkably shortened, and the second anal vein is fine and bow-shaped. In Euryomma the second anal vein is longer, but its imaginary extension would still intercept an imaginary extension of the first anal vein before the wing margin. The wings may vary in colour, from translucent to heavily smoky. The membrane is always completely covered with tiny microtrichia. The calypters are mostly of the same size, so that the outer margin of the lower one is clearly visible. However, the lower calypter may vary in its shape, from rounded as in Euryomma and the Fannia canicularis-group, to slightly oval as in the majority of the species of Fannia; or it may be very narrow and almost strip–like, as in Australofannia and the Fannia serena-group, or elongated and tongue-like, as in Fannia australis Malloch. The calypters are generally white, but may be brown on the outer margin. The halteres (Fig. 6) are mostly yellowish-white, but are brownish to blackish in males of some groups.
The legs provide a series of valuable diagnostic characters, with some striking structural modifications in males as well as variable arrangements of setae and hairs.
Fore leg. The fore femur may be slender or swollen, generally bare on the anterior surface and with a variable number of rows of setae on posterodorsal, posterior, and posteroventral surfaces. The fore tibia has a preapical posterodorsal seta, and apical setae on ventral and posteroventral surfaces; and some species have a short seta or a row of short setae on the anterodorsal surface; a few males have a submedian posterior seta, or fine setae on the posteroventral surface. The fore tarsomeres are usually dark and normal in shape, but can be strikingly modified in shape and colour in a few males, as in the Fannia anthracina-groupwhere they are flattened and expanded and partially to totally whitish-yellow (Fig. 9, 10); in males of a few species they are ornamented with fine hairs.
Mid leg. The mid femur in males does not show great variation in shape although it may be slightly curved or indented in the apical part. Distinct rows of anteroventral and posteroventral setae are usually present, and may be thickened and/or duplicated in males; sometimes a preapical comb of setulae is formed. In males, the swelling of the mid tibia in its apical portion (except in the Fannia canicularis-group) and the pubescence on the ventral surface are apomorphies for the family (Chillcott 1961; Hennig 1965; McAlpine 1989). The male mid tibia can also be indented twice in its basal half, as in the Fannia anthracina-group. The disposition of the setae is rather uniform, but the anterior, anterodorsal and posterodorsal setae may be doubled or tripled in some species; the females of some species have anteroventral and posteroventral setae. On the mid tarsomeres the basal tarsomere may be armed in some males with a ventral hook-like or rod-shaped spine or a group of short and dense setulae forming a crest at its base (Fig. 11).
Hind leg. The hind coxa is bare or bears 1–3 short setae on its posterior inner margin (Fig. 12). The hind femur may vary in shape from slender to swollen, and it may have a preapical ventral swelling (Fig. 9, 13, 14). Rows of anteroventral and posteroventral setae in the males may be developed or reduced to a varying extent, or they can be completely absent. The hind tibia does not show variation in shape in New Zealand species. The hind tibia has a submedian seta on the true dorsal surface, in line with the apical dorsal seta, which is an apomorphy for the family (Fig. 15). There are varying numbers of anterodorsal, anteroventral, and sometimes also posteroventral setae and setulae; some setae are occasionally elongated and hair-like or are grouped in various ways in the males (Fig. 14).
Abdomen. The abdomen is mostly uniform in structure except for the terminal segments (Fig. 16). In dorsal view the five main segments are visible (Fig. 16). In the males it is broadest at the level of segment 2, but at the level of segment 4 in the Fannia mollissima-subgroup. A more or less distinct pattern is usually present on the dusted dorsal surface of the male abdomen, in the form of a dark middle line or of dark triangular markings on each tergite, rarely of symmetrical lateral patches; the female abdomen is usually uniformly dark, with some exceptions. Sternite 1 is broad and densely setulose, especially in males. Sternite 5 (Fig. 17) differs from the preceding sternites, and is usually broadened and with stronger setae along the posterior margin, but often with other species-specific modifications.
The male terminalia includes the postabdominal segments and the hypopygium. The cerci are fused into a median cercal plate which is extremely variable and is frequently species-specific in shape (Fig. 18). The epandrium is hemispherical in form and has a pair of surstyli on its posteroapical margin (Fig. 18). The surstyli are frequently species-specific in shape and may be stout, slender, bent, bifid, etc., but they are rather uniform in the Fannia canicularis-group. The slender, sabre-shaped, or spirally-coiled paired bacilliform sclerites usually originate on the inner basal part of the cercal plate (Fig. 18, 19). The hypandrium is semicircular, connected with the aedeagal base by means of a sclerotised bridge (Fig. 19, 20). The pregonite (gonopod) is absent in the family, and the narrow postgonite (paramere) is closely attached to the phallus. The phallus itself is mostly membraneous, more sclerotised in some species (Piezura, Euryomma, and some species of Fannia).
The female terminalia (Fig. 21, 22, 23) is in the form of an elongate and telescopic oviscapt, without specialised structures; only in Australofannia and Fannia capitalis Pont (Australia) is the oviscapt remarkably shortened. It consists of the 6th to 9th abdominal segments, sheathed within the 5th segment (Fig. 21, 22). The tergites and sternites are sclerotised to a variable extent. The cerci and the two anal plates (the dorsal epiproct and the ventral hypoproct) are mostly simple, covered with fine setulae; the hypoproct has a pair of short lingulae in each anterior corner. Some distinguishing characters are to be found in the position of the two pairs of postabdominal spiracles (Fig. 21), and in the number and shape of the spermathecae which may be two or three, spherical, pear-shaped or elongated in form, with a smooth or sculptured surface (Fig. 23).
Larvae of fanniid flies are the most easily recognised maggots of any family of the so-called higher Diptera (Roback 1951). All three instars, and therefore the puparia too, have conspicuous feathery, forked, tufted, or button-like processes distributed in 4 or 6 longitudinal rows over most of the dorsal surface of the body, and the posterior spiracles are on a pair of stalks that are always widely separated. As well as being diagnostic at the family level, the larval morphology is distinctive for each species. Indeed, for the non-specialist, fanniid species are easier to identify as third instar larvae or puparia than as adults.
The body is somewhat dorsoventrally flattened, cream or brown, and ranges in length from 0.9 mm in first instar larvae to 10 mm in third instar larvae. The head is very small and is usually concealed inside the thorax in preserved specimens. Holloway (1985) did not study this character, which is not an important diagnostic feature, and nor did we. The 3 thoracic and 8 abdominal segments bear conspicuous integumental outgrowths referred to as paired segmental processes.
Paired segmental processes (Fig. 24–41, 43–60). Consisting of either a stalk bearing lateral projections or a cluster of very short projections, the processes are continuous with the integumental surface and contain soft tissue (Fig. 34, 39). They are not fully extended in first and early second and third instar larvae (Fig. 40). In older second and third instar larvae they open out and remain flexible (Fig. 41). At pupariation they harden and usually darken. The terminology applied to the processes largely follows Lyneborg (1970).
In most species the dorsal surface of all but the first thoracic and last abdominal segments bears 3 pairs of processes (Fig. 24): the laterodorsals on the lateral margin; the dorsomedians on either side of the midline; and the dorsolaterals which are between the other 2 series but are usually close to the laterodorsals. There are 3 similar but less conspicuous series on the ventral surface (Fig. 25): the lateroventrals on the lateral margin; the ventrolaterals which are mesad to the lateroventrals; and the ventromedians which consist of 1 or 2 pairs of very small processes on either side of the midline. The ventromedians may be arranged in a transverse row near the posterior margin of each segment or be grouped as an anterior pair and a posterior pair.
The first thoracic segment (Fig. 24) has a pair of simple, forwardly directed anterior processes dorsally, close to the anterior margin. Each anterior process has a conspicuous, elongate sensillum embedded in its dorsal wall. There are 1 or 2 minute, lateral processes near the base of the anterior spiracle (Fig. 35, 37, 52–60). They consist of a ring of simple projections enclosing a circular, integumental sensillum (Fig. 24).
The last abdominal segment or anal division (Fig. 26, 36, 38) has 3 pairs of marginal processes, referred to as laterals (anteriormost pair), sublaterals (following pair), and subapicals (terminal pair). On its ventral surface (Fig. 27) this segment has a single pair of ventrolateral processes and a median anal slit.
Several small, pointed projections and 1 or 2 round sensilla are present on the integumental surface immediately anterior to the base of each laterodorsal and there are similar projections between the laterodorsals and lateroventrals. The dorsomedians have several associated, conspicuous, round sensilla in the integument anterior to their base and at least 1 such sensillum in their stalk (Fig. 24, 28). The dorsolaterals are often much smaller and quite different in form from the other dorsal processes. On the second and third thoracic segments they are near the anterior margin and are closely associated with a conspicuous, circular, integumental sensillum. On the abdominal segments they are closer to the posterior margin and widely separated from the corresponding sensillum (Fig. 24). Euryomma peregrinum is unusual in lacking abdominal dorsolaterals (Fig. 43). In some species the dorsolaterals of the second and third thoracic segments consist merely of a ring of small projections surrounding a circular sensillum, but the abdominal dorsolaterals always have a distinct stalk bearing at least 3 projections and containing a circular sensillum (Fig. 34, 39). The sensillum in the stalk is probably homologous with that surrounded by a ring of projections on the thoracic segments.
The lateroventrals of the third thoracic and the abdominal segments are similar in shape to the laterodorsals, but are shorter. In F. albitarsis the second thoracic segment has a small, but distinct, lateroventral process composed of several concentric rings of pointed projections on a low callus, enclosing a circular sensillum (Fig. 25, 33). In the other New Zealand species these projections are absent and the lateroventral of this segment is represented by a conspicuous, round sensillum which is usually on a distinct callus.
The ventrolateral processes of the second and third thoracic segments are filiform in E. peregrinum, composed of a ring or tuft of small projections in F. canicularis and F. hollowayae and represented only by integumental sensilla lacking associated projections in F. albitarsis (Fig. 25, 29) and the remaining New Zealand species. Depending upon the species, the abdominal ventrolaterals may be tufted, stalked, filiform, or rosette-shaped.
The ventromedians are small and difficult to study. In most of the New Zealand species they are represented by 2 pairs of processes. Each process consists of a ring or several concentric rings of short projections surrounding a circular sensillum (Fig. 25, 31, 32). The posterior ventromedians of the thoracic segments usually lack projections and are represented only by sensilla (Fig. 25, 30). It is not unusual for the projections to be absent from 1 of the 4 ventromedians of any abdominal segment. The manner in which the projections originate from the integument and eventually surround a sensillum, forming progressively more complex ventromedians and other processes in F. albitarsis,is depicted in Fig. 30–33. The sensilla incorporated in the stalked processes of various species (Fig. 28, 34, 39) are probably homologous with simple surface sensilla, and have changed their position as the processes have become more complex.
Anterior spiracles (Fig. 24, 25, 37, 52–60). It was not possible to determine with the light microscope whether anterior spiracles occur in first instar larvae (Fig. 35), but recent SEM images of F. canicularis show that an anterior spiracle is indeed present on each side as a simple respiratory aperture (Grzywacz 2011). In second and third instar larvae they are lateral near the middle of the first thoracic segment and consist of a number of finger-like lobes (4–20 in the New Zealand species) arranged in a semi-circle. Each lobe has an apical spiracular opening. The length of the lobes is constant for each species but the number varies, sometimes even between the right and left spiracles of the same specimen. In general, the length of the lobes is inversely proportional to their number in the New Zealand species (compare Fig. 52–60). The presence of up to 20 lobes in Fannia laqueorum from The Snares Islands is exceptional and the number considerably exceeds the greatest (12) recorded for northern hemisphere fanniids (Chillcott 1961, Lyneborg 1970).
Posterior spiracles (Fig. 26, 36, 38, 61–69). These are on the dorsal surface of the last abdominal segment or anal division. Each consists of a stalk bearing 2 or 3 spiracular apertures at its apex. In first instar larvae (Fig. 36) the stalk is conical, massive in relation to the size of the segment, and has 2, partially contiguous, minute apertures. Second (Fig. 38) and third (Fig. 26) instar larvae have a more cylindrical stalk with 3 spiracular apertures distributed on a distinct spiracular plate. Chillcott (1961) considered second instar larvae of Fanniidae to have only 2 apertures on the posterior spiracle, but the second instar larvae of New Zealand species (7 species, including F. canicularis) all have 3 spiracular openings and a scar. A trilobed spiracular plate has, in the past, been regarded as a diagnostic character for Fanniidae (Roback 1951), but 3 species occurring in New Zealand have a plate that lacks lobes (Fig. 62, 64, 67). The circular plate with a typically cyclorrhaphous arrangement of apertures which occurs in Z. mystacina (Fig. 62) is primitive for the family, and no similar structure is known in other fanniids. In 3 of the endemic species the surface of the plate is composed of small, raised, polygonal elements and has several conspicuous circular sensilla (Fig. 65, 68, 69).
Integumental sculpture (Fig. 70–78). This is most strongly developed in third instar larvae and puparia and is always more apparent on the dorsal surface. The integument is broken up into numerous small, circular or polygonal elements which are sometimes grouped in larger polygonal areas or on plates (Fig. 70, 71), or coalesce to form irregular crescents and rings (Fig. 74, 75). Some of the elements may be produced into domes (Fig. 76) or spiny processes (Fig. 78). Conspicuous round sensilla, indicated in the figures by black circles and ovals, are present among the polygonal elements in all species studied.
Cephaloskeleton (Fig. 79–87). This comprises the mouth-hooks and associated sclerites. In Fanniidae, the mouth-hooks are completely separated from one another and the pharyngeal sclerites do not spread apart vertically (Roback 1951). The dorsal and ventral arms of the pharyngeal sclerites are developed differently in the various species. Roback (1951) and Chillcott (1961) considered the pharyngeal arms of fanniids to lack windows, but weakly sclerotised areas, undoubtedly vestigial ventral windows, are present in all the New Zealand species, and 2 of the species have membranous dorsal windows (Fig. 80, 87).