Cryptochironomus digitatus Malloch

Cryptochironomus digitatus (Malloch)

(Fig. 3 C–G)

Material examined. CANADA: British Columbia, Marion Lake, pupal exuviae, 1964, A.L. Hamilton. Lake Winnipeg records: Victoria Beach, 219 males, 9. & 25.vii. 1969; Pine Dock, 6 males, 10. & 31.vii. 1969; 0.5 km off George Island, 10 males, 11.vii. 1969; 3 km off Grand Rapids, 28 males, 13.vii & 4. x. 1969; 10 km off (Sturgeonskin) Long Point, 22 males, 14.vii. 1969; 3 km off McCreary Island, 14 males, 15.vii. 1969; Gull Harbour, 5 males, 1 female, 16.vii. 1969; Gimli Government Wharf, 3 males, 24.vii. 1969; Matheson Island Government Wharf, 1 male, 26.vii. 1969; 3 km off George Island, 46 males 27.vii. 1969; Grand Rapids Government Wharf, 16 males, 28.vii. 1969; 5 km of Selkirk (Horse) Island, 58 males, 29.vii. 1969; McBeth Harbour, 123 males, 7.ix. 1969; 15 km east of Long Point, 1 male, 6.ix. 1969; 20 Mile Creek, 1 male, 1.ix. 1971; Old Fishing Dock, 9males, 21.vii. 1971; Calder’s Dock, 22 males, 6. & 14. vi. 1971; Hecla Island, 10 males, 27. vii. & 11.viii. 1971; Beaver Creek, 1 male, 13.vii. 1971; South Basin, 31 larvae, 4.vi.–31.x. 1969; Narrows, 9 larvae, 4. vi.–31.x. 1969; North Basin, 41 larvae, 1 pupa, 4.vi.–31.x. 1969.

The Lake Winnipeg males have an AR of 3.54–4.03, 3.80 (10); a LR1 of 1.23–1.39, 1.30 (10); 9–24, 14(10) sensilla chaeticae on mid leg, none on hind leg; and 24–40, 32(10) setae on squama.

A female has 75 sensilla chaeticae on mid leg, 34 on hind leg. Its genitalia are illustrated in Saether (1977b fig. 90 A, B).

Pupa (n=1–2, tentatively associated and not reared)

Total length 10.34–10.84 mm.

Cephalothorax. Cephalic tubercle (Fig. 3 C) 270–285 µm long, 46 µm wide 1/3 from base, 40 µm wide 2/ 3 from base, with or without a 20 µm long frontal seta.

Abdomen. T I–V, anterior portion of T VI, S I–V and margins of S VI–VIII with reticulation. Caudal margin of T II with 31–43 hooklets on each side of 90–1601,wide interruption. Pedes spurii A present on S IV–VII, spinules 36–40 µm long on IV, 14–18 µm long on V–VII. Caudal margin of 25 T I–VII respectively with following numbers of spines (lengths in parentheses): 32–56 (20–34 µm), 50–52 (24–30 µm), 17–26 (48–50 µm), 15–29 (32–50 µm), 18–25 (50 µm), 21 (42–52 µm), 17–43 (30–36 µm). Caudal margins of S I– VII respectively with following numbers of spines (lengths in parentheses): 27–60 (35–38 µm), 12–17 (20–30 µm), 21–28 (40–50 µm), 15–26 (20–38 µm), 7–30 (24–28µm), 0–38 (0–34 µm), 0–26 (0–18 µm). Caudomedian projection of anal lobe 282–442 µm long, 276–313 µm wide; with 88–130 µm, long, 22 µm wide branches. Genital sac of male with 54–74 µm long, 44–54 µm wide apical point. Fringe of anal lobe with 99–106 filaments.

Fourth instar larva (n = 9–10, except when otherwise stated, tentatively associated)

Total length 7.99–12.67, 10.04 mm. Head capsule length 0.66–0.77, 0.71 mm (23).

Head. Antenna as in Fig. 3 D. Lengths of antenna] segments (in µm): 82–98, 90; 28–35, 32; 16–20, 19; 2– 4, 2; 2–4, 4. AR 1.41–1.72, 1.56. Basal antennal segment 35–39, 37µm wide; 2.45–3.29, 2.80 times as long as second segment; ring organ 50–70, 62 µm from base. Style of second segment 10–12, 11 µm long. Labrum (Fig. 3 E) with 35–40, 38 µm(8) long labral sensilla; S I 26–42, 33 µm (6); S II 50 –60, 54 µm (4) long. Premandible 148–180, 160 µm long. Mandible (Fig. 3 F) 190–220, 210 µm long; with 43–55, 50 µm apical tooth which is 0.20–0.26, 0.24 times as long as mandible. Basal segment of maxillary palp 58–76, 70 µm long; 26–30, 28 µm wide. Median tooth of mentum (Fig. 3 G) including darker lateral accessory teeth 62–68, 65 µm wide. Ventromental plate 190–220, 201 µm wide; 50–60, 57 µm long; 3.28–3.80, 3.51 times as wide as long. Postmentum 250–308, 267 µm long.

Abdomen. Procercus 42–52, 49 µm high; 39–46, 43 µm wide; with 552–761, 677 µm long anal setae. Supraanal seta 330–435, 400 µm (7); supraanal seta/anal setae 0.57–0.70, 0.61(7). Anal tubules triangular 192–250, 222 µm (5) long; 100–130, 112 µm (5) wide at base. Posterior parapods 368–515, 436 µm long.

Third instar larva

Head capsule length 0.40–0.48, 0.44 mm (44) (See Fig.)

Second instar larva

Head capsule length 0.26–0.29, 0.28 mm (5) (See Fig.)

Distribution and ecology. The species was previously known from Yukon to New Foundland and south to California, New Mexico, Texas and Florida (Townes 1945:100, Sublette and Sublette 1965:167, Oliver et al. 1990: 44, Epler 2009). Mozley (1975: 102, 104) found the species in the sandy littoral (down to 8 m) in Lake Michigan. This and other observations indicate that C. digitatus has an ecology conforming to that of other numbers of the Harnischia -complex living in the sandy littoral of large lakes and rivers.