Ophiosoma microcephalum Szidat 1928

Ophiosoma microcephalum Szidat, 1928 (Figs. 1–2)

Site of infection: small intestine.

Material deposited: in Helminthological Collection MLP 5508. Prevalence: 2 of 4 (50%).

Intensity of infection: 31 (2–60).

Description

Based on 22 specimens. Body distinctly bipartite, division into fore­ and hindbody accentuated, 1.489–1.905 mm (1.696) in total length. Forebody calyciform without equatorial constriction, 314–435 x 242–348 (378 x 301), clearly separated from hindbody by pronounced constriction. Hindbody 3–4 times longer than forebody, 1.170–1.509 x 0.251–0.420 mm (1.320 x 0.321). Ratio of hindbody length to forebody length 3.1–3.8 (3.5). Tegument smooth. Oral sucker subterminal, 34– 50 x 27–50 (43 x 37), poorly developed and always smaller than ventral sucker, 100–145 x 71 –119 (121 x 100) situated in middle of forebody. Suckers width ratio 2.1– 3.6 (2.8). Holdfast organ lobulate with compact proteolytic gland at base of forebody. Prepharynx absent; pharynx well developed, 44– 53 x 29–34 (49 x 32); oesophagus long, branched off posterior to ventral sucker; intestinal caeca reach into post­testicular region. Ratio of pharynx length to oral sucker length 1.2–1.3 (1.25).

Testes round, tandem, in middle posterior hindbody; anterior testis 117–131 x 83 –119 (126 x 105); posterior testis 95–131 x 98 –155 (112 x 130). Ovary round median and pretesticular, 53–102 x 49 –83 (82 x 65). Laure’s canal not seen. Mehlis’ gland postovarian. Vitellarium follicular, distributed mainly in hindbody; in forebody confined to base of holdfast organ; in hindbody occupying its entire width and reaching the copulatory bursa; vitelline reservoir post­ovarian. Uterus ventral containing 1–25 (16) large eggs, 81– 92 x 45 –63 (87 x 54). Copulatory bursa feebly delimited, with muscular ring (Ringnapf) and genital cone not delimited from body parenchyma, 167–193 x 231–328 (180 x 280). Genital pore terminal. Excretory vesicle and pore not seen.

Remarks

In South America only one species of Ophiosoma Szidat, 1928, O. microcephalum Szidat, 1928, has been reported parasitizing falconiform birds. Szidat (1928) found it parasitizing the roadside hawk, Buteo magnirostris and the hen harrier, Circus cyaneus (Linnaeus) from Brazil. In Argentina, this species was briefly reported by Boero and Led (1971) from the intestine of the chimango, Milvago chimango (Vieillot) from Buenos Aires Province.

Szidat (1928) described O. microcephalum briefly from specimens collected by Natterer, providing no detailed drawings of them; Szidat (1929) redescribed it with new morphological data and a drawing. Dubois (1938a) enlarged this description with new morphometrical data.

The general morphology of the present specimens corresponds to the original description and consequently, they are considered to belong to this species. However, the specimens of B. magnirostris from Argentina appeared to be smaller than those from other localities.

The specimens described by Szidat and Boero and Led differ from those described in the present study by having a larger body size (up to 4 mm) and by the ratio of forebody length to hindbody length (Dubois: 6; Boero and Led, our calculation: 4.2–5). We considered these differences as intraspecific variations.

The present report of O. microcephalum has enabled us to augment the original description with new morphometrical data of parasites recovered from the type host.