Neurochaetidae, McAlpine, 1978
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https://doi.org/ 10.3853/j.0067-1975.63.2011.1585 |
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https://treatment.plazi.org/id/03C1878D-A637-917E-FF47-F9FE589491FB |
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Felipe |
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Neurochaetidae |
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The Neurochaetidae View in CoL View at ENA and Periscelididae
These families share a distinctive antennal structure including possible synapomorphies, but only if the genera Cyamops and Stenomicra are omitted from consideration. The two last genera are so different that their antennae will be described separately (as subfamily Stenomicrinae ). For comment on the recently published phylogenetic association of the Neurochaetidae with the Pallopteridae see p. 150.
Because of availability and ease of exposure of parts of segment 2, I describe the antenna of Nothoasteia clausa McAlpine first ( Figs 94–96 View Figures 94–98 ), and then draw comparisons with other taxa. Segment 2 is deflexed so that its broad distal articular surface faces downwards ( Fig. 94 View Figures 94–98 ). The rim forms a pair of dorsal lobes separated by a deep slit, or cleft, but their margins are not appressed as in the Ephydroidea . The medial lobe is larger than the lateral lobe, but the lobes are not as large and cucullate as in some related genera (e.g., Neurochaeta ), so that most details of the articular surface are exposed by disarticulation ( Fig. 95 View Figures 94–98 ). The conus is absent. The distal articular surface is extensively microtrichose, with the ventral part extensively almost flat, the dorsal part with centrally placed shallow concavity almost filled by the nearly symmetrical, distally facing, complete annular ridge. The annular ridge is armed with two to three dense irregular encircling series of incurved spinescent microtrichia. A welldeveloped button is located just outside the annular ridge slightly dorsad of a mid-lateral position. There is a welldeveloped nodulose caestus on each side between the annular ridge and the foraminal ring. The latter is rather prominent and produced into a blunt cusp dorsally and ventrally. The short oval foramen faces distally and is approximately symmetrically placed, both within the annular ridge and on the segment as a whole.
Segment 3 of Nothoasteia clausa ( Fig. 96 View Figures 94–98 ) consists of a short, stout basal stem and rounded disc. The basal foramen is on the mid-ventral surface of the basal stem, in accordance with the symmetrically placed distal foramen of segment 2. The scabrous tongue is finely, irregularly ridged and runs from the basal extremity of the medial surface of the basal stem distad into the basal caecum of the disc. The ventrobasal surface of the disc has a shallow secondary cavity or postpedicellar pouch just beyond the opening of the basal cavity. Such secondary cavity has not been observed in other genera. The sacculus opens near the centre of the lateral surface of the disc.
The arista of Nothoasteia clausa lacks any trace of segment 4. Segments 5 and 6 are symmetrical, without trace of the oblique base of segment 6 seen in Cyamops , Periscelis , and some other genera. Segment 6 and the short segment 5 are both pubescent, the hairs beyond the basal enlargement of segment 6 tending to form slightly differentiated but not seriate rays which extend to the apex. In one specimen examined segments 5 and 6 appear to be fused, leaving no visible suture under high magnification of CLM, but in other specimens there is a visible suture but no annular membrane between these segments.
In the neurochaetid Neurotexis primula McAlpine the essential structure of segment 2 resembles that of Nothoasteia with some difference in proportions. The dorsal lobes are larger than in Nothoasteia but do not conceal much of the distal articular surface. The part of the dorsal articular surface immediately below the annular ridge is almost devoid of microtrichia but bears a reticulate pattern of fine, prominent ridges, which give way to an irregular covering of separate microtrichia towards the ventral margin. The button is larger than that of Nothoasteia but similarly located. The annular ridge is more vertically elongate than in Nothoasteia but has similar armature. The caesti are more vertically elongate and diffuse, with weak, almost horizontal nodulation.
I previously mentioned (D. McAlpine, 1993) the general features of segment 3 and the arista in Neurotexis spp. , and illustrated the antenna of Neurotexis freidbergi McAlpine (D. McAlpine, 1993: fig. 8). This and N. primula have the basal stem longer than in Nothoasteia and the disc narrower and more ovate. In Neurotexis freidbergi the arista is threesegmented, with segments 4 and 5 small; in N. primula segment 5 is very short and distinct, but segment 4 is not clearly defined, perhaps fused with segment 3. Segment 6 has long dorsal and ventral rays and fewer short medial rays. It has not been possible to locate the sacculus in preparations because of the irregularly roughened cuticle of segment 3.
The antenna of Neurochaeta inversa McAlpine resembles that of Neurotexis primula in most features. The dorsal lobes of segment 2 are more deeply cucullate than in that species making examination of the dorsal part of the distal articular surface more difficult. The part of this surface ventral to the annular ridge is almost devoid of microtrichia, but has a reticulate pattern of ridges resembling N. primula . The incurved spinescent microtrichia on the annular ridge are particularly large and dense on the more ventral part of the ridge, but are less developed dorsally. The button could not be located, possibly because of difficulty in exposing the more dorsal part of the articular surface. The caesti are short, compact, and prominently raised, with relatively few nodules.
Segment 3 of Neurochaeta inversa ( Fig. 97 View Figures 94–98 ) resembles that of Neurotexis primula in most features, but the basal cavity, with its contained extension of the scabrous tongue, is deeply elongate, and none of the larger, fringing microtrichia is forked. There is a well-developed sacculus opening near the centre of the lateral surface of the disc.
The arista of Neurochaeta inversa resembles that of Neurotexis spp. in general features. Segments 4 and 5 are both very short, microtrichose, and approximately symmetrical.
I have examined segments 2 and 3 in Periscelis fasciata Mathis , and segment 3 and the aristal segments in Periscelis annulata (Fallén) . Segment 2 of P. fasciata ( Figs 99, 100 View Figures 99–104 ) has much in common with that of the neurochaetids described above. The paired dorsal lobes are subequal, large and appressed, so that part of the distal articular surface is sunk in a cup, which is well differentiated from the rest of the distal articular surface. The part of the distal articular surface ventral to the annular ridge is clothed with many simple irregularly placed microtrichia and has no ridges. The structures on the distal articular surface are approximately symmetrical and symmetrically placed. The annular ridge resembles that of Nothoasteia and other neurochaetids, but its dorsal part is not visible in the preparation. The button is small and located near the outer lateral side of the ridge. The caesti are present, but elongate and not very prominent.
In both Periscelis fasciata ( Fig. 98 View Figures 94–98 ) and P. annulata the basal stem of segment 3 is more abruptly narrowed and set off from the disc than in Neurotexis and Neurochaeta . The sacculus is located very near the ventral base of disc in both species (as it is also in Scutops fascipennis Coquillett ), instead of the more central position on the lateral surface as in the other periscelidid taxa studied and in the neurochaetids.
As previously pointed out (D. McAlpine, 2002) the arista of the more typical Periscelidinae (e.g., Periscelis and Scutops ) is three segmented with asymmetrical segment 5, and the base of segment 6 is obliquely fitted to the distolateral surface of segment 5 ( Fig. 110 View Figures 105–111 ). I have noted also that in a paratype of the periscelidid Diopsosoma primum Malloch (in BMNH) segment 6 is asymmetrical basally.
The genus Planinasus is placed in the Periscelididae in most recent literature, and sometimes in the subfamily Stenomicrinae (e.g., Grimaldi & Mathis, 1993). I find the antennal structure of Planinasus sp. (N. Friburgo, Brazil) to resemble more closely that of the subfamily Periscelidinae ( Figs 101, 102 View Figures 99–104 ). Segment 2 shows most of the features seen in the Periscelidinae and Neurochaetidae . These include the pair of large, cucullate dorsal lobes, the nearly symmetrical structure of the distal articulatory surface and annular ridge, the pair of prominent caesti, and the centrally located, distally facing foramen. The part of the distal articulatory surface below the annular ridge has many, more or less transverse ridges supporting many microtrichia. The button is present just outside the lateral part of the annular ridge. The basal cavity of segment 3 opens obliquely along the basal stem ( Fig. 102 View Figures 99–104 ). It thus contains the elongate, somewhat obliquely facing basal foramen and the greater part of the scabrous tongue. The sacculus is located near mid-length of the disc.
The arista of Planinasus ( Fig. 111 View Figures 105–111 ) lacks segment 4. Segment 5 is dilated to cover much of the membranous socket of segment 3. It is asymmetrical and partly microtrichose. Segment 6, with its complex branching, is bifurcate from the base which is oblique—desclerotized on its medial side—to fit the oblique distal articular foramen of segment 5.
The most typical genera of the subfamily Stenomicrinae here considered are Stenomicra and Cyamops ( Figs 103–109 View Figures 99–104 View Figures 105–111 ). In these segment 2 has the distal articular foramen and associated parts much more asymmetrical than in the Periscelidinae and Neurochaetidae , and more like that of the ephydrid genera Hydrellia and Paralimna . The reduced conus is present only on the medial side of the foramen as an irregularly rounded ridge, and the foramen faces laterally from inside this conus-remnant. The annular ridge with its dentate armature is variably developed, and is concealed by the conus-remnant from most angles. The button is located near the lateral margin of the foramen. Caesti are absent. Segment 3 has a very prominent basal stem (when disarticulated), with its basal foramen located asymmetrically on its lateral surface ( Figs 103, 104 View Figures 99–104 ). Some Stenomicra spp. have the annular ridge and button more deeply recessed than in Figs 105–107 View Figures 105–111 and difficult to examine.
These facts suggest that a rearrangement of genera within the currently recognized taxa Stenomicrinae (sensu Grimaldi & Mathis, 1993) , Periscelidinae , and Neurochaetidae may be necessary. I do not formally make this reclassification because (1) I do not have access to a wide enough range of material, (2) the degree of symmetry in the articulation between segments 5 and 6 suggests a different segregation of taxa from that indicated by the structure of segment 2, (3) some other schizophoran families (e.g., Ephydridae ) possess a comparable range of variation to that of Periscelididae s.l., (4) some of the distinctive features shared by Neurochaetidae and Periscelididae appear in other acalyptrate families (e.g., the Psilidae , see below), and (5) any major reclassification should take into consideration further evidence in addition to antennal morphology. Also, the Neurochaetidae should perhaps retain family status as a derivative or close relative of the Eocene genus Anthoclusia , possessing a more complete series of fronto-orbital bristles and a symmetrical antennal segment 5, in contrast to the genera recently placed in both the Periscelidinae and Stenomicrinae (see D. McAlpine, 1983).
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