Microfilaria mynah n.sp.
(Text-figure 2, Figs. 3–6)

This parasite is described from the heart-blood of one of four examples of the mynah Acridotheres tristis tristis (Linnaeus), shot in the lower reaches of the Wainimbuka River, Viti Levu, on 15th June, 1949, The host bird has become well established in Fiji, having originally been introduced from India. Microfilaria Cob-bold is used here in the sense of a collective name for young larval Filarioidea occurring in the blood of vertebrates. The infection was a moderately heavy one, a total of eight larvae being present in the three smears taken from the parasitized bird. No adult nematodes were encountered.

Microfilaria mynah is a very long, sheathed filarial larva, bluntly truncated anteriorly and tapering to a fine point posteriorly. The nuclear column stains light blue with Giemsa, appearing as a more or less homogeneous mass. Individual somatic cells are only occasionally distinguishable, towards the anterior extremity (Fig. 5). Cuticular annulations are readily apparent. Among the non-staining page 9

Text-figure 2

Fig. 1: Erythrocytes of Canis familiaris Linnaeus. Fig. 2: Dirofilaria immitis (Leidy, 1856), from C. familiaris. Figs. 3, 5, 6: Microfilaria mynah n.sp., from Acridotheres tristis tristis (Linnaeus). Fig. 4: Erythrocytes of A. tristis tristis.

page 10portions of the body the nerve ring and the excretory and anal pores may always be distinguished. The excretory and genital cells (Fig. 3) can seldom be clearly seen. The average and range of the various dimensions of the examples studied are as follows, the distance figures given in every case expressing the percentage of the total body length:—

Plimmer (1913) was the first to record microfilariae from the blood of Acridotheres tristis, the host having died in the Gardens of the Zoological Society of London. Beyond stating that the embryos of his parasite were long and thin, he published no further description. Mello (1936) described Microfilarium acridotheris from the same host in India. M. acridotheris is of much shorter length than M. mynah (90.0μ–120.0μ, as compared with 265.5μ–359.9μ). This fact is not necessarily of taxonomic significance, for the length of individual species of embryo filariae in the blood of birds often varies greatly. Thus Coles (1914) found the microfilariae in the blood of English blackbirds and thrushes to vary from 140μ to 400μ in length. However, M. acridotheris differs from M. mynah in that its anterior extremity is enlarged comparatively to the breadth of the body, whereas in the latter species the width of the body in this area remains uniform. Also, the posterior extremity, which tapers to a fine point in M. mynah, is either obtusely pointed or abruptly truncated in M. acridotheris.

The microfilaria of Acridotheres tristis tristis in Fiji cannot be identified with any of the avian species already described, the published accounts of many of which are in any case very incomplete, and differs from M. acridotheris Mello as outlined above. It is hence designated Microfilaria mynah n.sp., having the features set out in this account.

The type slide of Microfilaria mynah has been deposited in the collection of the Dominion Museum, Wellington (catalogue number Z200), while two paratypes are in the author's private collection (catalogue numbers NF1–2).