Megischus spp.
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publication ID |
https://doi.org/ 10.1080/00222930802105155 |
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persistent identifier |
https://treatment.plazi.org/id/475687B5-1051-DD64-8E7B-FB6625CBE85C |
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treatment provided by |
Felipe |
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scientific name |
Megischus spp. |
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( Figures 3A–D View Figure 3 , 4A–C View Figure 4 , 5A–F View Figure 5 )
Fore leg
The tibia is shorter than the femur ( Figure 3A View Figure 3 ). In females, it is distinctly swollen approximately one-third from its base, with an oblique depression laterally in this position ( Figure 3B View Figure 3 ) and a small dome with reduced microsculpture just anterodorsad of the depression. The tibia is not expanded distad of the swelling and tapers slightly towards its apex. A row of apically expanded setae extends along the distal two-thirds of the median side. A single modified apical spur, the calcar, is present; a distinct cone-shaped sensillum is present at the apex of the tibia opposite the calcar ( Figure 3B View Figure 3 ). The lateral depression on the tibia is less developed in the males, sometimes being hardly discernible.
The SGO is situated inside the proximal swelling, where the tibia is widest. It is suspended between a distinct spine ( Figure 5A View Figure 5 ) laterally and a low swelling ( Figure 5B View Figure 5 ) medially on the median tibial wall. The thickness of the tibial wall is not reduced in any region except for the area around the base of the spine.
The tarsus is five-segmented in both sexes and approximately 1.7 times as long as the tibia, with the basitarsus making up less than half of its length. A slight extension with setae is present distally on tarsomere 3. Tarsomere 4 is very short, but equipped with an elongate distal flange with a dense tuft of setae at the apex ( Figure 3A View Figure 3 ).
Mid leg
The tibia is slightly longer than the mid femur ( Figure 3D View Figure 3 ) and of about equal width along most of its length, except for its slender base; it is, at most, slightly swollen proximally approximately one-quarter of the total length from its base; no distinct depression is present in the region of the SGO. Scattered elongate setae are present on the lateral side. Apical spurs are absent; a distinct cone-shaped sensillum is situated posteriorly at the apex ( Figure 3C View Figure 3 ).
A small spine ( Figures 5C and D View Figure 5 ) projects from the inner mesal wall of the tibia at the level of the swelling; the spine bends anteriorly towards its apex; opposite the spine on the inner lateral wall a low ridge is present ( Figure 5C View Figure 5 ); the SGO is suspended between the spine and the ridge. The wall of the tibia posterad of the spine and the ridge is somewhat thinner than the rest of the wall ( Figures 5C and 5D View Figure 5 , right).
The tarsus is five-segmented in both sexes and less than twice as long as the tibia, with the basitarsus making up almost half of its length. A setose extension is present distally on tarsomere 3. Tarsomere 4 is very short proximally, but an elongate distal flange with a dense tuft of setae is present at the apex ( Figure 3D View Figure 3 ).
Hind leg
The tibia is distinctly longer than the femur, including the trochantellus ( Figure 4A View Figure 4 ). The proximal part is slender, tubular and the walls are comparatively thick. An external longitudinal carina extends along the anterior part from the base about halfway to the apex ( Figure 4B View Figure 4 ). Approximately one-third from its base, the tibia expands medially and also laterally a bit further down; the distal part appears distinctly swollen compared to the tubular proximal part. A shallow, inverted Vshaped furrow is present on the mesal side at the proximal end of the swelling. A small dome with less distinct microsculpture is present posteriorly on the tibia close to the apex of the furrow ( Figure 4B View Figure 4 ). On the distal half of the mesal side of the tibia a brush composed of distally expanded setae is present; the setae are more densely arranged towards the tibial apex ( Figure 4A View Figure 4 ). A pair of short apical spurs is present on the anterior part of the tibia.
The SGO is situated proximally in the expanded part of the tibia, as indicated externally by the smooth dome; two tracheae, one with a small and one with a large diameter, pass along the anterior side of the SGO, and a ganglion is present posterad and slightly proximad of it ( Figure 5E View Figure 5 ). The posterior wall of the tibia is distinctly thinner than the rest of the wall in the region of the SGO ( Figures 5E and F View Figure 5 , right). A distinct internal spine extends anteriorly from the median wall of the tibia ( Figures 5E and F View Figure 5 ). A sheet of cap cells containing the scolopales is suspended between the spine and the opposite, lateral tibial wall ( Figure 5E View Figure 5 ). A low ridge is developed anteriorly on the lateral wall, posterad of the smaller trachea. A sheet of modified epidermal cells extends posteriorly on the lateral wall of the tibia from the ridge to the thin posterior wall ( Figure 5F View Figure 5 ); a direct contact of the epidermal cells with any of the cap cells was not observed. Attachment cells connecting the cap to the spine could not be identified with certainty. Slender dendrites extend between the SGO and the ganglion posterad of it ( Figure 5E View Figure 5 ). A membrane enveloping the SGO was not observed. Distad of the SGO the tarsal muscles are attached to the lateral wall of the tibia, occupying up to one-third of the tibial diameter.
The tarsus is three-segmented in the females and shorter than the tibia ( Figure 4A View Figure 4 ). The basitarsus is of variable length (compare Figures 4A and C View Figure 4 ), but always at least as long as the two other tarsomeres; it bears a short lobe anteroventrally with a dense tuft of stout setae. Tarsomere 2 is very short proximally, but an elongate anteroventral flange with a dense tuft of stout setae is present adjacent to the tuft on the basitarsus ( Figure 4C View Figure 4 ); together, they form a common setal brush. Tarsomere 3 is longer than tarsomere 2. In males, the hind tarsus is fivesegmented and longer relative to the tibia; the basitarsus is at most slightly longer than the remaining tarsomeres combined. Tarsomere 3 and especially tarsomere 4 bear distinct distal lobes, but are not as setose as in the females.
Additional taxa examined
In general, among the additional taxa examined, tibial and tarsal structures of Stephanus serrator mostly resemble those of Schlettererius cinctipes , whereas the other taxa show more affinities with Megischus spp. Only the most important differences are reported here to avoid repetition.
Fore leg
A shallow concavity on the lateral side of the tibia is present in S. serrator , whereas a more prominent groove is developed in females of the other stephanid taxa; the groove is generally less strongly developed in males. A distinct spine situated posteriorly at the apex of the tibia could be observed in most taxa.
Mid leg
A shallow concavity approximately halfway down the median side of the tibia is present in S. serrator . A distinct spine situated posteriorly at the apex of the tibia could be observed in most taxa.
Hind leg
A small dome is situated approximately halfway down the posterior side of the tibia in all taxa examined. All taxa except S. serrator display an inverted V-shaped groove on the mesal side and the tibia is substantially swollen distad of the groove; in S. serrator the groove is absent and the tibia expands more gradually. The tarsus is fivesegmented in S. serrator females and three-segmented in the females of all other species examined, with distal flanges on tarsomeres 4 and 2, respectively. Dense setal tufts are developed on the basitarsus and tarsomere 2, forming a continuous brush, in the females of all taxa except S. serrator .
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