The life cycle and ontogeny of Atactorhynchus verecundus Chandler 1935 (Acanthocephala: Neoechinorhynchidae)

Abstract

The adults of Atactorhynchus verecundus from the sheepshead minnow, Cyprinodon variegatus, are redescribed. This species differs from the only other species of Atactorhynchus in that it has a greater number of proboscis hooks. It has 96 hooks arranged in eight spiral rows of twelve hooks each, while A. mugilis has 64 arranged in eight spiral rows of eight hooks each. A study of the embryology and the experimental determination of the life cycle are also made. The embryology of this acanthocephalan most closely resembles that of N. rutile, an eoacanthocephalan, and differs most widely from that of P. minutus, a palaeacanthocephalan. In the present species the acanthor is unarmed, and three egg envelopes are present. The intermediate host is determined to be a limnetic copepod, Cletocamptus deitersi, in which at 25°C the larval development time from ingestion of the egg to infective juvenile is fourteen days. This is the shortest development time ever reported, except that Paulisentis fractus; the latter has a development time of thirteen days and also utilizes a copepod as an intermediate host. Within four to six days a definite pseudocoel is apparent and the embryonal nuclear mass is undergoing differentiation. The greatest differentiation takes place between the eight and eleventh days, by the end of which period all major adult organs are present. At no time is the larval stage encysted within the copepod; hence, the term cystocanth is not correctly applicable to this or any other larval eoacanthocephalan in the intermediate host. Closely confined populations of the host become more heavily infected than those which were not confined. Differences in the feeding behavior of this fish and the other fish present may be responsible for the apparent host specificity reported for A. verecundus. This feeding behavior of C. variegatus appears to preclude a possible paratenic host.