Procladius (Holotanypus) prolongatus Roback, 1971

Egan, Alexander T. & Langton, Peter H., 2018, DESCRIPTIONS OF FOUR NEARCTIC PROCLADIUS SKUSE PUPAL EXUVIAE Abstract, CHIRONOMUS Journal of Chironomidae Research 31, pp. 30-36 : 33-34

Procladius (Holotanypus) prolongatus Roback

Material examined. USA: Alaska, Loon Pond, a tundra pond on the west edge of Prudhoe Bay , 3-VII-1980, col. Malcom Butler.

Pupa (n = 8), 4 males, 4 females. Total length 7.65-8.47, 8.02 mm (n = 8)

Cephalothorax. Light brown. Thoracic horn ( Fig. 9 ) 630-760, 682 µm long (n = 16); 240-300, 265 µm wide (n = 13); covered evenly with short teeth; no reticulation; plastron plate 140-200, 170 µm long (n = 16); 252-330, 279 µm wide (n = 13); apical constriction of horn chamber 110-148, 130 µm wide (n = 5) with a short neck often obscured by the large, dark plastron plate; an oval aperture between the neck and atrium is often elongate and distinct; length/width of horn 2.3-2.78, 2.57; width of plastron plate/width of constriction 1.89-2.35, 2.06 (n = 5). Respiratory atrium, neck and plastron plate dark brown. Plastron plate width usually equal to or wider than horn width.

Abdomen. Color pattern 3, but usually a solid light brown with no pale patches. Shagreen ( Fig. 10 ) of T IV medially with elongate (4-7 µm) single sharp points. Shagreen on T VIII similar in size, shape, and pattern, although less robust than on other tergites. LS taeniae of VII at 0.38, 0.62, 0.81, 0.96 (n = 6) segment length. LS taeniae of VIII at 0.16, 0.35, 0.57, 0.78, 0.95 (n = 6) segment length. Anal lobe ( Fig. 11 ) length 920-1000, 964 µm; 30-48, 40 (n = 16) spines on outer margin; largest spines 40- 70 µm posterolateral, with distance between spines equal or wider than width of spine bases; smallest apical and lateral spines 10-20 µm long; posterior edge indented, apical spines clustered on a projection (except one specimen with no projection and no indentation along posterior edge) .

Remarks. Roback (1980) described features that suggested subgeneric status for P. prolongatus , and he formally implemented this distinction among Holotanypus groups in Roback (1982). From associated Prudhoe Bay material, we can provide insight into the immature traits used to support the subgenus.

The anal lobes from Roback’s Barrow, Alaska, specimens were described as “unusually shaped” with a “projecting outer curve”. The Prudhoe Bay specimens usually do have a rounded lateral shape, but none are as expansive as in Roback’s description and some also have lateral edges that are straight. Based on descriptions in Roback (1980) and material from Isle Royale, Michigan, P. dentus also has a large anal lobe that can be rounded laterally. P. dentus and prolongatus can both have a fold near the respiratory organ neck, but in both species this feature is not always observed. Therefore, these two features are not diagnostic and without a series of specimens may create confusion when using the key in Roback (1980). These species may be reliably separated by tergite IV and VIII shagreen, which is elongate (4-7 µm) in P. prolongatus and short (1-4 µm) in P. dentus . In addition, the number of spines on the anal lobe will distinguish these species, with 30-48 in P. prolongatus and 56-63 (from Isle Royale) and 68 (from the single specimen reported by Roback) in P. dentus .

Larvae have one proleg that is apparently diagnostic in Procladius , with a wide, triangular base and a tight apical hook (see figure 244, Roback 1980). Prudhoe Bay tundra pond specimens have this feature. Larvae of P. dentus , though undescribed, should presumably have simple proleg claws, similar to all other known larvae in Holotanypus ( Roback 1982).

Known range is Nunavut, Canada, and Alaska, USA.

Figures

Figure 9-11. 9, Procladius prolongatus thoracic horn (Scale = 0.1 mm); 10, tergite IV medial shagreen (Scale = 0.025 mm); 11, anal lobe (Scale = 0.1 mm).