Cercaria capricornia

Barnett, Leonie J., Miller, Terrence L. & Cribb, Thomas H., 2010, Two new Stephanostomum - like cercariae (Digenea: Acanthocolpidae) from Nassarius dorsatus and N. olivaceus (Gastropoda: Nassariidae) in Central Queensland, Australia, Zootaxa 2445, pp. 35-52 : 41-45

Cercaria capricornia VIII

( Fig. 2 )

Host: Nassarius dorsatus (Röding) (Gastropoda, Nassariidae ).

Other host: None.

Locality: Cawarral Creek, Keppel Sands, Queensland (23°19' S; 150°47' E).

Habitat: Intertidal mudflats.

Location in host ( redia ): Digestive gland, gonads.

Prevalence of emergence: 0.11% (2 of 1766 N. dorsatus ).

Material deposited: Queensland Museum; G231721–G231724.

Molecular sequence data: ITS2, 1 replicate; LSU, 1 replicate.

GenBank accession numbers: ITS2 ( FJ809038 ); LSU ( FJ809036 ).

MorphBank accession number: 515658.

Dates of collection: August and November 2004.

Description: Redia . ( Fig. 2c , based on 10 unflattened specimens): Body elongate,

cylindrical with posterior extremity tapering, 240–580 (416.0) long by 35–50 (41.5) wide. Mouth opens terminally. Pharynx 27–30 (28.5) long by 20–25 (23.3) wide. In reproductive and digestive glands. Cercaria . ( Figs 2a–b , based on 30 naturally emerged specimens): Body elliptical, longer than wide, widest point anterior to ventral sucker, 182–240 (205.3 ± 13.1) long by 62–83 (70.5 ± 4.7) wide; length/width ratio 2.48–3.31 (2.92 ± 1.2). Tegument spinose; spines arranged in regular rows. Tail simple, long, cylindrical, gradually tapering terminally, lacking spines, chaetae, fins, 215–270 (253.6 ± 13.4) long by 20–30 (22.1 ± 2.2) wide. Oral sucker 35–43 (38.2 ± 1.8) long by 32–38 (35.4 ± 1.9) wide. Ventral sucker 27–35 (30.6 ± 1.7) long by 27–35 (31.3 ± 1.8) wide. Mouth subterminal, opening anteroventrally, surrounded by spines; spines around mouth aperture slightly larger than on surrounding tegument. Forebody 95–138 (112.4 ± 9.8) long; forebody/ hindbody ratio 1.08–1.34 (1.21 ± 0.07). Pharynx obscured by central glands. Penetration glands in 5 pairs; 2 pairs median and immediately anterior to ventral sucker and 3 pairs lateral or anterolateral to ventral sucker. Excretory vesicle 42–55 (49.7 ± 2.8) long by 32–48 (39.3 ± 3.5) wide; V-shaped when full, Y-shaped when empty; excretory duct appears to continue length of tail. Eye-spots dense, oblong, 7–23 (14.4 ± 2.9) apart, 37– 68 (53.6 ± 6.1) from anterior end; 13 long by 10–13 wide (n=7).

Remarks: Large numbers of cercariae emerge, sometimes on consecutive days, with pauses between emergences (few days to weeks). Cercariae generally emerge before 8 am. Naturally emergent cercariae are free-swimming and strongly positively phototactic. When swimming, the hindbody is folded ventrally and the tail lashes from side to side for movement, similar to C. capricornia VII (see Fig. 1c ). When resting, the hindbody remains folded ventrally. When first emerged, cercariae swim actively towards light, frequently forming swarms near the surface. After about 24 hours, cercariae become less active. Cercariae were never observed to encyst.

Cercaria capricornia VIII can also be distinguished from S. tenue , S. cloacum , S. caducum and C. bengalensis VII by the absence of a stylet, from S. baccatum by size and the presence of lateral penetration glands, and from S. dentatum by the absence of lateral cuticular fins on the tail.

Cercaria capricornia VIII has a longer tail relative to body length than C. capricornia VII, and the eyespots are oblong in shape and larger than the spherical eye-spots of C. capricornia VII. The hindbody of C. capricornia VIII tapers inward towards the tail and the widest point of the body is anterior to the ventral sucker, while the hindbody of C. capricornia VII is broader with the widest point posterior to the ventral sucker. Morphometric comparison between C. capricornia VIII and C. capricornia VII, S. tenue , S. cloacum , S. caducum , C. bengalensis VII, S. baccatum and S. dentatum is given in Table 2.

Figures

FIGURE 2. a – c. Cercaria capricornia VIII, naturally emerged from Nassarius dorsatus. a. Body, heat-killed, in ventral view; b. Entire cercaria, heat-killed, from side view; c. Redia, fixed. Scale bars a, b, c = 50 µm.

FIGURE 1. a – d. Cercaria capricornia VII, naturally emerged from Nassarius dorsatus and N. olivaceus. a. Body, heatkilled, in ventral view; b. Entire cercaria, heat-killed, from side view; c. Live cercaria, body folded for swimming, from ventral view; d. Redia, fixed. Scale bars a, b, d = 50 µm; c not to scale.