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 : 39-41

Cercaria capricornia VII

( Fig. 1 )

Host: Nassarius dorsatus (Röding) , (Gastropoda, Nassariidae ). Other host: Nassarius olivaceus (Bruguière) , (Gastropoda, Nassariidae ). Locality: Cawarral Creek, Keppel Sands, Queensland (23°19' S; 150°47' E). Habitat: Intertidal mudflats.

Stephanostomum -like cercariae ( Gnana Mani 1994; Køie 1978; Madhavi & Shameem 1993; Martin 1939; Stunkard

1961; Wolfgang 1955).

C. capricornia S. dentatum S. tenue S. caducum S. cloacum S. baccatum C. bengalensis VII VII VIII

Other locality: Sandy Point, Corio Bay (22°58' S, 150°46' E), Ross Creek, Yeppoon, Queensland (23°8' S, 150°45' E).

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

Prevalence of emergence: 0.57% (10 of 1766 N. dorsatus ), 0.21% (4 of 1908 N. olivaceus ).

Material deposited: Queensland Museum; G231698–G231720.

Molecular sequence data: ITS2, 6 replicates; LSU, 6 replicates.

GenBank accession numbers: ITS2 ( FJ809039 ); LSU ( FJ809037 ).

MorphBank accession number: 515656.

Dates of collection: August/ November 2004, February/May–June/ November 2005 and March/ May 2006.

Description: Redia . ( Fig. 1d , based on 10 unflattened specimens): Body elongate, cylindrical with posterior extremity tapering, 530–1210 (703.0) long by 60–120 (75.5) wide. Mouth opens terminally. Pharynx 25–32.5 (29.3) long by 20–25 (23.8) wide. In reproductive and digestive glands.

Cercaria . ( Figs 1a–c , based on 140 naturally emerged specimens): Body elliptical, longer than wide, widest point posterior to ventral sucker, 155–250 (195.2 ± 16.1) long by 50–85 (69.2 ± 5.9) wide; length/ width 2.27–4.17 (2.84 ± 0.3). Tegument spinose; spines arranged in regular rows. Tail simple, long, cylindrical, gradually tapering terminally, lacking spines, chaetae, fins, 142–210 (175.6 ± 15.2) long by 17–28 (20.6 ± 2.1) wide. Oral sucker 30–40 (34.4 ± 2.2) long by 27–38 (33.4 ± 2.0) wide. Ventral sucker 17–33 (29.1 ± 2.2) long by 20–35 (30.4 ± 1.9) wide. Mouth subterminal, opening anteroventrally, surrounded by spines; spines around mouth aperture slightly larger than on surrounding tegument. Forebody 75–125 (97.2 ± 8.9) long; forebody/hindbody 0.80–1.34 (0.99 ± 0.07). Pharynx generally obscured by central glands, pyriform, 10 long by 12 wide (n=1). 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 37–75 (52.1 ± 6.1) long by 32– 58 (45.1 ± 4.7) wide; V-shaped when full, Y-shaped when empty; excretory duct appears to continue length of tail. Eye-spots dense, spherical, 12–28 (20.3 ± 2.9) apart, 32–55 (46.6 ± 5.0) from anterior end; 7–10 diameter (n=24).

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 ( Fig. 1c ) and the tail lashes from side to side for movement. 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 VII can be distinguished from the cercariae of S. tenue , S. cloacum , S. caducum and C. bengalensis VII by the absence of a stylet ( Gnana Mani 1994; Køie 1978; Madhavi & Shameem 1993; Martin 1939). Stephanostomum baccatum is larger and has no lateral penetration glands ( Wolfgang 1955). Stephanostomum dentatum has a tail with lateral cuticular fins and is photonegative ( Stunkard 1961). Morphometric comparison between C. capricornia VII and C. capricornia VIII, S. tenue , S. cloacum , S. caducum , C. bengalensis VII, S. baccatum and S. dentatum is given in Table 2.

Figures

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.