A scanning electron microscopy study of early development in vitro of Contracaecum multipapillatum s.l. (Nematoda: Anisakidae) from a brown pelican (Pelecanus occidentalis) from the Gulf of California, Mexico

Abstract

Eggs obtained from the uteri of female nematodes, genetically identified as Contracaecum multipapillatum s.l., found in a brown pelican (Pelecanus occidentalis) from Bahía de La Paz, Gulf of California, Mexico, were used to study the early developmental stages of this anisakid by scanning electron microscopy (SEM). Egg dimensions were approximately 54 × 45 μm measured by SEM. Observation of the eggs revealed an outer surface of fibrous appearance. The newly hatched larvae were ensheathed and highly motile. Observation with SEM showed that the sheaths of the larvae were striated and revealed an excretory pore and a cleft near the anterior end of the sheath, presumably to facilitate the opening of the sheath for the emergence of the larva. The hatched larvae were placed in nutritive culture medium, where they grew within their sheath, some exsheathing completely 2 weeks later. The surface patterns of the sheath and the cuticle of the exsheathed larvae were clearly different. Although they did not moult during culture, SEM revealed a morphology typical of third-stage larvae of Contracaecum from fish, as previously observed by optical microscopy. Thus, we suggest that newly hatched larvae from eggs of C. multipapillatum are third larval stage but with sheath of the second larval stage, as occuring in other anisakids.

A scanning electron microscopy study of Anisakis physeteris molecularly identified: from third stage larvae from fish to fourth stage larvae obtained in vitro

“…The observation that these sense organs are covered by the cuticle in L3 poses the question as to whether they are functional or not and whether their development in L3 is only preparation for L4. However, the observation of undifferentiated papilla-like structures on the labial protuberances of recently hatched L3 of other anisakids (McClelland and Ronald 1974; Molina-Fernández et al 2017) suggests that these structures may have some function in L3. Jones (1994) proposed that at least the amphids of L3 of A. simplex (s.l.)…”

“…Occasionally, the cuticular annuli are subdivided (Fig. 5 b), probably as part of the growth process of the cuticle (Molina-Fernández et al 2017 ). Vertical bands can also be observed in them (Figs.…”