Macvicaria mekistomorphe, Aken'Ova & Cribb & Bray, 2008

Aken'Ova, Thelma, Cribb, Thomas & Bray, Rodney, 2008, Eight new species of Macvicaria Gibson and Bray, 1982 (Digenea: Opecoelidae) from temperate marine fishes of Australia, ZooKeys 1, pp. 23-58 : 32-34

Macvicaria mekistomorphe n. sp.

Type-host: Sillago maculata Quoy & Gaimard (Sillaginidae) .

Type-locality: Off Tangalooma, Moreton Bay, S. E. Queensland. 27°14’S, 153°19’E.

Site: Intestine.

Material studied: 4 from Off Tangalooma, December 1993.

Type-material: Holotype: QM G 230376, paratypes: QM G 230377 - 230378, BMNH 2008.7 .5.39.

urn:lsid:zoobank.org:act:5D0A5349-4643-4587-B3FB-04CD482451D0

Description ( Figs 7-9 )

Based on 4 gravid, whole-mount specimens from Sillago maculata . Measurements are of 4 gravid, unflattened whole-mount worms.

Body elongate oval; width recorded from area of gonads although greatest in region of the ventral sucker, 1440-1904 (1724) × 287-382 (346); width to length ratio 1:4.7-5.2 (5.0). Tegument with irregularly dispersed papillate structures. Oral sucker ventrally subterminal, sub-spherical, 109-154 (130) × 122-160(141). Ventral sucker larger than oral sucker, transversely oval, borne on slight eminence, in anterior third of body, 160-218 (189) × 192-237 (211); sucker width ratio 1:1.4- 1.6 (1.5). Forebody relatively short, 371-467 (414) long, 24.5-25.8 (24.9)% bodylength. Prepharynx, indistinct, short, may be entirely dorsal or posterior to oral sucker. Pharynx well developed, sub-spherical, 77-102 (90) × 83-128 (107); pharynx to oral sucker width ratio 1:1.2-1.5 (1.3). Oesophagus short, thick walled. Intestinal bifurcation 55-104 (81) anterior to ventral sucker. Caeca terminate blindly close to posterior extremity.

Testes 2, entire, usually separate, occasionally contiguous (n=1), tandem, in posterior half of body, anterior 134-173 (154) × 128-154 (141); posterior 154-192 (170) × 125-173 (142). Post-testicular area 339-512 (426) long, 21.0-26.9 (24.5)% bodylength. Cirrus-sac well developed, claviform, extends from point sinistral to oesophagus, overlapping ventral sucker dorsally usually to point just anterior to or level with its posterior margin, occasionally to ventral sucker aperture (n=1), 272-305 (294) × 71-78 (75). Internal seminal vesicle tubular; anterior portion narrower than posterior, loops once, occupies most of broad posterior portion of cirrus-sac. Pars prostatica distinct, narrow, surrounded by gland cells. Ejaculatory duct well developed, surrounded by numerous gland cells. Genital atrium distinct, small. Genital pore antero-sinistral to caecal bifurcation, may be level with posterior margin of pharynx, or on outer margin

of left caecum and more or less level with posterior limit of oesophagus, 220-298 (251) from anterior end, 13-16 (15)% of body-length.

Ovary entire, sub-spherical, anterior to and usually separated from anterior testis, occasionally contiguous with anterior testis (n=1), 90-134 (111) × 77-128 (101). Mehlis’ gland feebly developed, anterior to ovary. Canalicular seminal receptacle large, saccular, elongate, oval, usually overlaps ovary dorsally, occasionally displaced entirely sinistral to ovary (n=1), may extend posteriorly to overlap anterior margin of anterior testis or terminate close to posterior margin of ovary. Laurer’s canal present. Uterus coils intercaecally between anterior margin of ovary and posterior margin of ventral sucker, usually overlapping caeca dorsally and leading to genital pore without coiling. Eggs oval, operculate, 58-70 (63) × 26-29 (26). Metraterm indistinct. Vitelline follicles extend from 294-378 (336) from anterior extremity, 15.4-22.2 (19.7)% of body-length, to 38-67 (54) from posterior extremity; follicles feebly developed, particularly in forebody; fields mostly separate in hindbody, more or less confluent in posttesticular area dorsally and ventrally; follicles lie lateral to caeca mostly, with anterior limit at about level of intestinal bifurcation.

Excretory pore ventrally subterminal to terminal. Excretory vesicle I-shaped, anterior limit dorsal to posterior half of ovary, leads to pore through narrow duct.

Etymology: The species name (Gr. mekistos, longest; Gr. morphe, shape) is derived from the fact that this species is the most elongate worm in its group.

Comments: All the four specimens on which the description of Macvicaria mekistomorphe n. sp. was based were covered in irregularly dispersed papillate structures of unknown origin. Some of the structures appeared to contain nuclei, suggesting infection by a unicellular organism, whereas others appeared anucleate, suggesting the occurrence of tegumental papillae which may have been caused by fixation. Aside from the papillate structures, the vitelline follicles in all four specimens of this worm appeared to be poorly developed. It is not certain if the nature of the tegument is in any way related to that of the vitellarium or if the two conditions arose independently. None of the other Sillago species examined were infected by this worm, so it was not possible to determine whether or not the two features were characteristic of M. mekistomorphe n. sp. or if they were induced by the particular fish from which they were collected.

Macvicaria mekistomorphe fits into the concept of Group B as defined above. It can be distinguished from all the other species of Macvicaria in the group by its distinctly more elongate form, with a width to length ratio of 1:4.7-5.2 (5.0). The next most elongate species, M. ophthalmolyci , has a width to length ratio of 1:3.3-5.0 (4.1), but it can be distinguished from this and all other species in the group by its short forebody and large ventral sucker. The new species can be distinguished further from the other species by its usually separate testes and the ovary which is usually separated from and is more or less medially anterior to the anterior testis. The seminal vesicle in the new species is also distinctive as it forms a single loop medially. In the last feature, M. mekistomorphe resembles M. taksengi , which is less elongate, has a width to length ratio of 1:3.1, and has larger eggs (67-80 × 32-53).

Figures

Figs 7-9. Macvicaria mekistomorphe n. sp. ex Sillago maculata. 7. Whole-mount ventral view. 8. Terminal genitalia. 9. Dorsal distribution of vitelline follicles. Scale bars: 7, 9, 250 µm; 8, 100 µm.