A Contribution to the Life History of Bucephalus longicornutus (Manter, 1954)

Summary

Summary

1.	With this contribution to the life history of Bucephalus longicornutus (Manter, 1954), of which the sporocyst, cercaria, metacercaria and adult are described, life history studies on marine, digenetic trematodes are introduced to New Zealand workers, and life history studies of the economically important family Bucephalidae Poche, 1907, are reintroduced to overseas workers.
2.	An analysis of previous life history studies of marine members of the family reveals that, hitherto, the experimental proof of the adult status of bucephalid sporocysts infecting bivalve molluscs has not been achieved. The major features of the bucephalid life history, ascertained previously from experimental studies of fresh-water species, are herein confirmed in a marine species for the first time.
3.	Sporocysts of B. longicornutus infect the visceral mass, pericardium and gills of the mud-oyster, Ostrea lutaria Hutton, 1873. Terminal regions of the sporocyst are found on the gills adjacent to the visceral mass. It was not possible to isolate a complete sporocyst and therefore the number infecting an individual oyster can only be speculated.page 38
4.	The structure of the sporocysts of many species of bucephalid are imperfectly known. The nucleated layer of those species for which histological details are available and the present species is syncytial and contains one or two types of mesenchymal nuclei in addition to germinal nuclei. The former occur throughout the sporocyst wall while the latter are only in or near the terminal regions or growing points.
5.	All previous reports of bucephalid cercariae are listed and it is considered that many descriptions of these are inadequate for comparative purposes. Cercariae described as species of Bucephalus or Prosorhynchus without experimental proof are herein transferred to the group name Cercaria. Bucephalopsis is valid only for B. haimeanus (Lacaze-Duthiers, 1854) and therefore B. modiolae Faust, 1928, becomes C. modiolae (Faust, 1928).
6.	Upwards of 10,000 cercariae may be liberated from an infected oyster over a 24-hour period; over several weeks, peak liberations of cercariae occur intermittently with lulls of varying duration during which few or no cercariae are liberated. Cercariae do not actively swim but can remain suspended in calm water for at least an hour. They depend on turbulence in the water for initial dispersion from a resting position in the bottom of a finger bowl. Lateral movement is achieved by flexure of one of the furcae. It is postulated that the behaviour of the furcae (which in this species resembles B. polymorphus and B. elegans and contrasts with C. apalachiensis) may reflect the generic identity of the cercaria.
7.	The method of attachment and penetration of the cercaria into the second intermediate host depends initially on accidental contact of the furcae with the body of the host; the cercaria drifts in the current and the tail stem attaches to the skin; a point of penetration is eroded with the aid of acidic and enzymic secretions of the cystogenous organ. The method of cyst wall formation from cystogenous granules (which are broken down and exuded through the cuticle), is governed by osmotic phenomena.
8.	Encystment in experimental hosts occurs in the web of all fins, in the extrinsic muscles at the base of the fins, body wall muscles, under the skin of the head and branchial chamber and rarely in the conjunctiva of the eye. Acanthoclinus quadridactylus (Forster) and various unidentified species of Tripterygion were successfully infected with metacercariae. Age immunity is exhibited by some specimens of these hosts. Host specificity of the cercaria towards Trachelochismus sp. is recorded. The natural hosts of the metacercaria were not discovered.
9.	Metacercariae are host specific against Helcogramma medium (Gunther), in which development does not proceed beyond 20 days after exposure to cercariae. The majority of cysts are resorbed after 35 days.
10.	Invertebrates are unlikely hosts of the metacercariae.
11.	Metacercariae reach maximum development after approximately 80 days in both experimental hosts. Spontaneous excystment of at least some mature metacercariae occurs. Cysts in Tripterygion sp. tend to become pigmented after 85 to 90 days and are either dead or degenerate after 110 days. Cysts from A. quadridactylus do not become pigmented and the metacercariae are still active after 120 days. It is suggested that A. quadridactylus is more closely related to the natural host or hosts of the metacercaria than Tripterygion sp. Mature metacercariae bear an anterior sucker (devoid of tentacles) whose scoop-shaped musculature is characteristic of species of Bucephalus. Tentacular ducts are located in the sucker musculature.
12.	Gravid specimens of B. longicornutus (Manter, 1954), were recovered from the intestine of Scorpaena cardinalis Richardson, the scarpee, 35 days after feeding page 39 fish infected with metacercariae of 80 days or more development. In addition to this material, 75 specimens of B. longicornutus were recovered from naturally infected specimens of Kathetostoma giganteum Haast, the monkfish, the definitive host, from Foveaux Strait and Cook Strait. Although a few species of fish, other than K. giganteum, have been examined from Foveaux Strait no other natural hosts of B. longicornutus adults have been found.
13.	The range of variation in egg size, and the relative positions of the internal organs is considerable and is comparable to that exhibited by B. varicus Manter, 1940. It is considered that to define species on the basis of a few specimens is unwise. Egg size, and the relative positions of internal organs is of doubtful value in differentiating between species, and some species of Bucephalus will possibly fall as synonyms when further material is examined and the range of variation for the various species is determined.
14.	Attempts to obtain miracidia from the eggs of experimentally induced adults were not successful. The eggs may not have been viable.

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