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: 25-27
treatment provided by
Cercaria capricornia II
( Fig. 2 View Figure )
Locality: Cawarral Creek, Keppel Sands, Queensland (23 ° 19 ' S, 150 ° 47 ' E).
Habitat: Amongst and immediately adjacent to mangroves on intertidal mudflats.
Other localities: Sandy Point, Corio Bay, Queensland (22 ° 58 ' S, 150 ° 46 ' E), Ross Creek, Yeppoon (23 ° 8 ' S, 150 ° 45 ' E).
Prevalence of emergence: 1.26 % (24 of 1908 N. olivaceus ).
Material: South Australian Museum, AHC 29308 – AHC 29311, AHC 34518 – AHC 34548.
Dates of collection: August/ November 2004, February/May-June/August/ November 2005 and March/ May 2006.
Site. Reproductive and digestive glands.
Structure. Body elongate, cylindrical with posterior extremity tapering to point ( Figure 2 f View Figure ). Mouth opens terminally; pharynx spherical. Cercariae in various stages of development.
Dimensions. Based on 12 unflattened rediae.
Length: 290–420 (344.2)
Width: 50–100 (72.5)
Pharynx: 17–33 (22.9) x 17–30 (22.1)
Naturally emerged cercaria
Body. Flattened, with conspicuous constriction at level of ventral sucker ( Figure 2 a View Figure ). Forebody reduced, slender, arched ventrally, widening medially at about level of pharynx. Hindbody posterior to constriction expanded, large, broadly ovate, extremely flattened, extending beyond tail junction on both sides, with deep ventral keel longitudinally between posterior margin of ventral sucker and anterior margin of excretory vesicle; keel roughly triangular in profile, deepest midway between constriction and anterior extremity of excretory vesicle, ventral margin varies from sharp angle to broadly rounded ( Figure 2 b View Figure ). In life, anterior end of forebody reflexed dorsally and angled forward posterior to eye-spots; hindbody slightly arched ventrally, sides reflexed dorsally on either side of keel in V formation ( Figures 2 d, 2 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 71–85 inwardly facing spines.
Eye-spots. Oblong, dense, lateral on either side of prepharynx.
Pigment. Golden-brown, variable: sides of keel sometimes with 4 conspicuous spots – one pair laterally each side of tail base, one pair about level with midpoint of excretory vesicle, laterally about midway between midline and margin; some with regions on anterior edge of expanded hindbody; some with region anterior to ventral sucker. In life, orange brown shading on anterior part of hindbody and keel; small orange brown spots on posterior hindbody sometimes present.
Penetration glands. Three pairs of long, elongate and folded saccular glands, extend from posterior margin of ventral sucker to excretory vesicle, longest often extending almost half length 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, onethird length hindbody. Two lateral ducts open into anterior extremity of vesicle, anterior extremity often obscured by glands. Flame cells difficult to discern, formula not determined.
Tail. Simple, long, cylindrical, gradually tapering terminally; lacks spines, setae or fins. Dimensions. Based on 249 naturally emerged specimens. Total length body: 380–710 (553.9 ± 63.2)
Length anterior end to tail base: 360–660 (524.7 ± 58.3) Maximum width hindbody: 212–340 (267.8 ± 24.6)
Maximum width forebody: 75–138 (111.7 ± 11.0)
Width at constriction: 65–133 (94.3 ± 11.7)
Length forebody: 130–235 (197.4 ± 19.8)
Oral sucker: 37–55 (45.6 ± 3.3) x 37 –60 (46.8 ± 3.6)
Ventral sucker: 57–83 (69.3 ± 4.6) x 57 –83 (66.3 ± 3.8)
Prepharynx (n= 246): 75–148 (120.5 ± 13.1)
Pharynx (n= 246): 17–28 (23.6 ± 2.0)
Excretory vesicle: 85–150 (115.4 ± 12.8) x 37 –63 (49.7 ± 4.2)
Tail (n= 173): 510–950 (708.6 ± 79.3) x 27–53 (38.3 ± 5.1)
Cercarial emergence: rhythm and variation. Large numbers of cercariae emerged every 2–5 days, sometimes 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 toward the light source. When swimming, the hindbody is folded ventrally and the forebody is contracted longitudinally; the tail lashes from side to side for movement ( Figure 2 c View Figure ). When resting, the hindbody is slightly flexed ventrally; tail extends forwards and angled dorsally from hindbody, may be held close to hindbody ( Figures 2 d View Figure ). When first emerged, cercariae swim actively towards light and frequently rise to surface; then settle characteristically on their side. After about 24 hours, cercariae become less active, decaudation may occur and they start to die. The cercariae never encyst.
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