Barnett, Leonie J., Smales, Lesley R. & Cribb, Thomas H., 2008, A complex of putative acanthocolpid cercariae (Digenea) from Nassarius olivaceus and N. dorsatus (Gastropoda: Nassariidae) in Central Queensland, Australia, Zootaxa 1705, pp. 21-39: 22-24
treatment provided by
Cercaria capricornia I
( Fig. 1 View Figure )
Host: Nassarius olivaceus (Bruguière) (Gastropoda, Nassariidae ). Locality: Ross Creek, Yeppoon, Queensland (23 ° 8 ' S, 150 ° 45 ' E). Habitat: Amongst and immediately adjacent to mangroves on intertidal mudflats. Other locality: Cawarral Creek, Keppel Sands, Queensland (23 ° 19 ' S, 150 ° 47 ' E). Prevalence of emergence: 0.16 % (3 of 1908 N. olivaceus ). Material: South Australian Museum, AHC 29306 – AHC 29307, AHC 34513 – AHC 34517. Dates of collection: May 2005 and February 2006.
Site. Reproductive and digestive glands.
Structure. Body elongate, cylindrical with posterior extremity tapering, rounded ( Figure 1 f View Figure ). Mouth opens terminally; pharynx spherical. Cercariae in various stages of development. Dimensions. Based on 10 unflattened rediae.
Length: 400–580 (478.0)
Width: 65–120 (89.0)
Pharynx: 20–28 (23.3) x 20–25 (23.5)
Naturally emerged cercaria
Body. Flattened, with conspicuous constriction at level of ventral sucker ( Figure 1 a View Figure ). Forebody reduced, slender, arched ventrally, widening medially. Hindbody posterior to constriction expanded, large, broadly ovate, extremely flattened, extending beyond tail junction on both sides, with deep ventral keel longitudinally between constriction and posterior hindbody; keel deepest between constriction and anterior extremity of excretory vesicle; ventral margin broadly rounded in profile ( Figure 1 b View Figure ). In life, forebody reflexed dorsally at ventral sucker and curved ventrally, fleshy portion around ventral sucker expanded; hindbody slightly arched dorsally; sides reflexed dorsally on either side of keel in V formation ( Figures 1 d, 1 e View Figure ).
Tegument. Spines anterior to constriction, arranged in regular rows in anterior forebody, longest in anterior half forebody, decreasing in size towards constriction.
Suckers. Oral sucker opening ventrosubterminally, spinose, lacking stylet. Ventral sucker round; aperture surrounded by single row of approximately 76–82 inwardly facing spines.
Eye-spots. Oblong, dense, lateral on either side of prepharynx.
Pigment. Dark brown-black, dense, conspicuous, in forebody medially between eye-spots and pharynx; brown-black, diffuse, may be present between pharynx and ventral sucker; brown-black lines may be present on hindbody along ventral margin of keel and in two longitudinal lines lateral to keel on each side; golden brown, oblong, either side of tail base ( Figure 1 a View Figure ). In life, pigment in forebody and lines on hindbody blueblack.
Penetration glands. Three pairs of long, elongate and folded saccular glands, extend from posterior margin of ventral sucker to excretory vesicle, longest may extend past anterior extremity of excretory vesicle; ducts run anteriorly on lateral edges of body. Central glands not evident in forebody.
Digestive system. Mouth opens anteroventrally. Prepharynx long, narrow. Pharynx pyriform, small.
Excretory system. Excretory vesicle I-shaped, cylindrical, turgid, thick-walled, with columnar cells, almost one-third length hindbody. Two lateral ducts open into anterior extremity of vesicle. Flame cells difficult to discern, formula not determined.
Tail. Simple, long, cylindrical, gradually tapering terminally; lacks spines, setae or fins.
Dimensions. Based on 86 naturally emerged specimens.
Total body length: 580–800 (717.0 ± 48.6)
Length anterior end to tail base: 530–750 (665.6 ± 45.9)
Maximum width hindbody: 260–360 (313.3 ± 23.2)
Maximum width forebody: 100–155 (123.6 ± 10.7)
Width at constriction: 75–133 (106.6 ± 12.8)
Length forebody: 185–240 (215.0 ± 13.8)
Oral sucker: 42–58 (49.3 ± 2.8) x 45 –60 (51.7 ± 4.0)
Ventral sucker: 65–88 (78.0 ± 3.8) x 65 –83 (72.9 ± 4.8)
Prepharynx (n= 83): 120–158 (135.9 ± 8.6)
Pharynx (n= 82): 20–38 (25.5 ± 3.6)
Excretory vesicle: 115–168 (141.8 ± 11.0) x 47 –75 (56.3 ± 5.3)
Tail (n= 42): 690–890 (829.0 ± 40.7) x 30–55 (42.7 ± 5.3)
Pigment on forebody: 35–65 (47.6 ± 7.6) x 20–33 (25.7 ± 2.7)
Cercarial emergence: rhythm and variation. Cercariae emerged in large numbers with variable periods between emergences (few days to weeks), sometimes emerging on consecutive days; emergence generally between 7 pm and 8 am.
Behavior. Naturally emerged cercariae are free-swimming and swim actively toward light where they orient themselves facing away from the light source. When swimming, the hindbody is folded ventrally and the forebody is highly contracted longitudinally ( Figure 1 c View Figure ); the tail lashes from side to side for movement. When resting, the hindbody is slightly flexed dorsally; tail extending backwards and angled ventrally from hindbody ( Figure 1 d View Figure ). When first emerged, cercariae swim actively towards light and frequently rise to the surface after which they settle on their side or ventral side up. After about 24 hours cercariae become less active, decaudation may occur and they start to die. The cercariae never encyst.
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