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Photo#1612783
Likely Ceriana ancoralis? - Ceriana ancoralis - male

Likely Ceriana ancoralis? - Ceriana ancoralis - Male
Guadalupe Canyon, Cochise County, Arizona, USA
April 30, 1972
For full-size image, click here, then click the image once more after in loads in your browser.

In the photo above, note the "peculiar lobe" at the anterior angle of the 1st abdominal segment...it has the form of a very small, round bead. Curran seemed to imply this was a distinctive character of C. ancoralis (see last sentence of initial paragraph of his discussion here...and also the 15th line from the bottom on pg. 38). However, it turns out the "peculiar lobe" is not unique to C. ancoralis...see comment near bottom of this page.

See remarks under 1st image of this series for further detailed info on this post.

Images of this individual: tag all
Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male Likely Ceriana ancoralis? - Ceriana ancoralis - male

Separating Ceriana ancoralis from Ceriana tridens
The species C. ancoralis and C. tridens are quite similar-looking and can easily be confused. But after studying the original descriptions in:

    Coquillett(1902) [based on 6 males & 5 females of ancoralis]; and
    Loew(1872) [based on one or two(?) specimens of tridens]

...as well as the treatments in:

    Williston(1886) [based on 4 specimens of tridens];
    Curran(1924) [based on 6 males & 5 females of ancoralis; and 5 males of tridens]; and
    Shannon(1925) [based on 9 males & 5 females of ancoralis, and 7 males & 3 females of tridens]

...and also scrutinizing BugGuide and iNat posts for both species...there appear to be various characters that can be used to separate the two species––although due to their subtlety (together with variation) each of the characters can sometimes be difficult to decisively interpret. The separating characters are:

1) In couplet 4 of Curran's 1924 key he used the yellow markings on the upper-back edge of the head to separate ancoralis and tridens. In ancoralis that yellow extends further to the sides and is either uninterrupted medially (as in the photo above, and in Ximo's 3rd paratype photo here) or has a fairly narrow black medial line separating the yellow markings on the hind-edge of the vertex (per Curran's 1924 description of ancoralis)...whereas in tridens there are always two separate yellow spots, with the medial black separation wider (sometimes only slightly!), and the yellow spots usually don't to extend quite as far laterally.
2) Shannon's 1925 key (shown at bottom of the 1st image of this series) states ancoralis lacks any yellow on the pteropleuron (cf. "ptp" in this labelled image); while tridens positively has a yellow spot on the pteropleuron. But Coquillett's original description of ancoralis mildly contradicts this, as it states there's a "small [yellow spot] on lower part of pteropleura, sometimes very indistinct". So this seems a somewhat ambiguous separating character...though a strongly-defined yellow spot on the pteropleuron is presumably indicative of tridens.
3) Curran's figures 10 & 11 on Plate II indicate ancoralis has narrower and more linear facial markings. Unfortunately, photos from the field often don't show the face clearly, so this may be of limited use.
4) On the 4th abdominal segment, the medial portion of the posterior yellow band projects forward less in ancoralis and has a more gradually-tapered forward edge towards the sides; whereas in tridens the yellow usually projects further and more widely forward and is more abruptly-tapered laterally. Also, in tridens the porterior portion of the 4th tergite is more abruptly and widely "depressed" (or "crimped") and there are often two small, black, indented spots on either side of the middle.
5) In tridens the 4th tergite usually has a more well-defined pair of pollinose (="wax-like dust") brown-to-yellowish markings in front of the posterior yellow band, each usually in the shape of a rectangle with a quarter-circle removed from the antero-lateral portion. In ancoralis the pollinose markings are typically smaller or more often absent than in tridens.
6) Range Considerations: All the C. ancoralis material referred to in the papers of Coquillett, Curran, and Shannon was from New Mexico...much of it (perhaps all?) from the Las Cruces area (like the paratype here). The specimen herein is from "Guadalupe Canyon, Cochise County" in the far southeastern corner of Arizona, within three miles of the New Mexico border. The Systema Dipterorum "Nomenclator" page for C. ancorals gives its range as "Arizona to Texas"...and Curran(1924) speculated that some records for C. tridens from Colorado and New Mexico were likely C. ancoralis instead. The range given for C. tridens on its Systema Diptororum page is "Washington to Idaho, s. to California"...which is consistent with current BugGuide and iNaturalist posts, which indicate its presence in British Columbia and Utah as well.
Most the current iNaturalist posts under C. ancoralis from New Mexico conform well with Curran's description thereof, though some of the characters states discussed in 1)–5) above can vary or overlap with those of C. tridens, and placing a specimen can sometimes be tricky and seem subjective (especially without a view of the thoracic pleura...where a conspicuous yellow spot on the pteropleuron is a good indicator of tridens).

"Peculiar Lobe" not(!) unique to C. ancoralis
In his 1924 original description of Ceriana ancoralis, Curran remarked on "a peculiar lobe" occupying an excavated angle on each anterior corner of the 1st abdominal segment (see last sentence of initial paragraph of his discussion here...and also 15th line from the bottom on pg. 38). An arrow points to "the peculiar lobe" in the photo at the top of this page (full-size image here)...it has the form of a very small, round bead.

In my initial reading of Curran's description, I got the impression his remarks suggested that the "peculiar lobe" was a diagnostic character unique to C. ancoralis. But upon carefully scrutinizing BugGuide & iNat posts of C. tridens, I noticed that species also has the same "peculiar lobe"...as can be seen in each of the photos below:

                           

Thus the "peculiar lobe" is not unique to C. ancoralis...it is also present in C. tridens (though the "lobe" appears to be absent in C. abbreviata).

Moved
Moved from Ceriana.

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