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: 29-31
treatment provided by
Cercaria capricornia IV
( Fig. 4 View Figure )
Host: Nassarius olivaceus (Bruguière) (Gastropoda, Nassariidae ). Locality: Sandy Point, Corio Bay (22 ° 58 ' S, 150 ° 46 ' E). Habitat: Amongst and immediately adjacent to mangroves on intertidal mudflats. Other localities: Ross Creek, Yeppoon (23 ° 8 ' S, 150 ° 45 ' E), Cawarral Creek, Keppel Sands, Queensland
(23 ° 19 ' S, 150 ° 47 ' E).
Prevalence of emergence: 0.31 % (6 of 1908 N. olivaceus ). Material: South Australian Museum, AHC 29314 – AHC 29316, AHC 34554 – AHC 34564. Dates of collection: August 2004, May/ August 2005 and February 2006. Description:
Site. Reproductive and digestive glands.
Structure. Body elongate, cylindrical with posterior extremity tapering to point ( Figure 4 e View Figure ). Mouth opens terminally; pharynx spherical. Cercariae in various stages of development.
Dimensions. Based on 10 unflattened rediae.
Length: 400–510 (468.0)
Width: 70–110 (86.0)
Pharynx: 20–23 (21.0) x 17–23 (20.5)
Naturally emerged cercaria
Body. Flattened, with conspicuous constriction immediately posterior to ventral sucker ( Figure 4 a View Figure ). Forebody reduced, arched ventrally; body anterior to constriction pyriform, widest at level of anterior margin of ventral sucker. Hindbody posterior to constriction expanded, large, broadly ovate, extremely flattened, extending backwards beyond tail junction on both sides, with very deep ventral keel longitudinally between constriction and midpoint of excretory vesicle; keel oblong in profile, deepest at anterior margin of excretory vesicle ( Figure 4 b View Figure ). In life, body bent dorsally at constriction (~ 90 °), forebody bent forward ventrally at eyespots; fleshy portion around ventral sucker extremely expanded; hindbody bent ventrally (~ 120 °) at level of anterior margin of excretory vesicle; sides of hindbody anterior from this point flexed dorsally in a shallow V; sides of posterior hindbody curving ventrally, bowl shaped ( Figure 4 c, 4 d View Figure ).
Appendages: Long tubular filament-like appendages arising from dorsal surface of hindbody at level slightly forward of anterior margin of excretory vesicle and near to margin of body. Extremely extensible, more extended in live cercariae.
Tegument. Spines anterior to constriction, arranged in regular rows in anterior forebody, longest in anterior two-thirds forebody, decreasing in size towards constriction.
Suckers. Oral sucker opening ventrosubterminally, spinose, lacking stylet. Ventral sucker round, row of 87–98 inward pointing spines at aperture, several rows of spines bordering cavity.
Eye-spots. Round, dense, lateral on either side of prepharynx.
Pigment. Variable, faint to dark golden brown or red brown shading throughout body; often darker anterior and posterior to ventral sucker and along fold of keel; conspicuous red brown rectangular patches on hindbody beside base of tail may be present. In life, translucent to bright pinkish/orange; blue pigmentation on keel and fleshy portion around ventral sucker may be present.
Penetration glands. Possibly two pairs of small central glands; ducts run anteriorly either side of pharynx, continue forward medially; possibly three pairs of large lateral glands present, anterolateral to ventral sucker; ducts run anteriorly on lateral edges of body; difficult to determine; all anterior to constriction.
Digestive system. Mouth opens anteroventrally. Prepharynx long, narrow. Pharynx pyriform, small. Pharynx difficult to determine in specimens from one host, obscured by dark pigmentation.
Excretory system. Excretory vesicle I-shaped, cylindrical, turgid, thin-walled, slightly longer than onethird length hindbody. Two lateral ducts open into anterior extremity of vesicle, continue in close association with vesicle towards posterior extremity. Flame cells difficult to discern, formula not determined.
Tail. Simple, long, cylindrical, gradually tapering terminally; lacks spines, setae or fins.
Dimensions. Based on 83 naturally emerged specimens.
Total length body: 580–870 (728.6 ± 75.4)
Length anterior end to tail base: 540–810 (675.8 ± 72.7)
Maximum width hindbody: 280–400 (342.7 ± 33.5)
Maximum width forebody: 125–215 (173.3 ± 14.0)
Width at constriction (n= 68): 55–138 (103.3 ± 20.3)
Length forebody: 137–218 (175.7 ± 21.4)
Oral sucker: 47–60 (52.1 ± 2.9) x 45 –63 (52.6 ± 4.2)
Ventral sucker: 82–113 (100.4 ± 6.0) x 82 –105 (94.8 ± 5.2)
Prepharynx (n= 63): 90–140 (118.5 ± 11.0)
Pharynx (n= 62): 17–30 (24.0 ± 2.4)
Excretory vesicle: 175–270 (224.3 ± 20.0) x 22–38 (28.2 ± 3.4)
Tail (n= 80): 690–990 (824.9 ± 81.6) x 42 –68 (51.6 ± 5.5)
Appendage (n= 163): 155–790 (453.6 ± 127.9) x 12–28 (18.4 ± 2.9)
Cercarial emergence: rhythm and variation. Few to large numbers emerged between 7 pm and 8 am; 1–6 days between periods of emergence, emerged on consecutive days (recorded for 9 consecutive days with only 5–42 cercariae emerging for last 4 days).
Behavior. Naturally emerged cercariae are free-swimming and swim actively toward light. When swimming, the hindbody is folded ventrally and forebody contracted longitudinally; the tail lashes from side to side for movement. When resting, the hindbody is held in three-dimensional shape, tail extends backwards dorsally from hindbody, curves ventrally ( Figure 4 c View Figure ). When first emerged, cercariae swim actively towards light and frequently rise to surface, float in water column, slowly settle. After about 24 hours, cercariae become less active, may attach to the substrate at tip of tail, decaudation may occur and they start to die. The cercariae never encyst.
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