Hypocreadium patellare Yamaguti, 1938 Atypical

Bray, Rodney A., Cribb, Thomas H. & Justine, Jean-Lou, 2009, New observations on the genus Hypocreadium Ozaki, 1936 (Digenea: Lepocreadiidae) in the Indo-West Pacific region, including the description of one new species, Zootaxa 2110, pp. 22-40 : 32

Hypocreadium patellare Yamaguti, 1938 Atypical form B

( Figure 8 )

Host: Pseudobalistes fuscus (Bloch & Schneider, 1801) , Balistidae , yellow-spotted triggerfish.

Site: Intestine.

Locality: Lizard Island (14°40’S, 145°28’E, June 2005).

Prevalence: 1 of 1.

Voucher specimens: QM G 230538 – 230540, BMNH 2009.2.12.22–23.

Description: Measurements in Table 3 . Body wider than long, virtually circular and with a distinct anterior notch. No tegumental spines seen. Pre-oral lobe short, distinct. Oral sucker oval, aperture subterminal. Ventral sucker slightly irregularly oval, just pre-equatorial. Prepharynx usually not evident. Pharynx oval. Oesophagus distinct. Intestinal bifurcation in mid-forebody. Caeca narrow, arcuate around gonads, converge posteriorly, may be slightly flexed anteriorly or not, end blindly fairly near midline.

Testes 2, irregularly oval, symmetrical, in anterior hindbody, well separated. External seminal vesicle saccular, at level of ventral sucker. Cirrus-sac large, claviform, reaching from point dextro-lateral to ventral sucker diagonally across posterior forebody, reaches left caecum; surrounded by scattered gland-cells. Internal seminal vesicle oval. Pars prostatica bipartite, folded, lined with large anuclear cell-like bodies. Ejaculatory duct muscular, long, folded, lined with pavement [or carpet] of cobble-stone like small bosses. Genital atrium large, often dilated with eggs. Genital pore sinistral at level of intestinal bifurcation.

Ovary more or less oval, intertesticular or almost completely post-testicular, closest to but usually separated from sinistral testis and separated from dextral testis. Seminal receptacle large, saccular, between sinistral testis and ventral sucker. Laurer’s canal opens dorsally to ovary, sinistral testis or between. Mehlis’ gland anterior to ovary. Uterus usually passes between ovary and dextral testis into post-ovarian region, then anteriorly, narrowing dorsally to ventral sucker, then widens to form metraterm. Eggs tanned, operculate. Metraterm passes anteriorly, with thick muscular wall and distinct sheath of gland-cells, often dilated with eggs. Vitellarium follicular, follicles numerous, surround gonads, well separated from body-margins, contiguous and reaching to midway between caecal termination and posterior extremity posteriorly, separated and reaching to about pharyngeal level anteriorly, lateral and median to caeca, only occasional follicles encroaching over testes ventrally or dorsally.

Excretory pore dorsal to uterus, post-testicular. Vesicle division not seen, arms narrow, reach to level of oesophagus.

Remarks: In Bray & Cribb (1996) this form keys to Hypocreadium balistes . According to the original description by Nagaty (1942) and the illustration of what is considered the same species by Parukhin (1970) from Abalistes stellatus and Rhinecanthus sp. from the Red Sea and Aden Bay, H. balistes lacks an anterior notch, a consistent character according to our observations. The genital pore is consistently at the level of the intestinal bifurcation in this form, as opposed to ‘anterior to the intestinal caeca’ ( Nagaty, 1942) in H. balistes or at the level of the anterior oesophagus or pharynx in H. patellare according to Bray & Cribb (1996). As noted above, this may not be a useful character in differentiating H. patellare , and it is certainly inconsistent in some of the forms we have encountered (see Atypical A), but it is notably consistent here. The uterus always reaches into the post-ovarian region, the ovary is usually intertesticular and a distinct anterior notch is always present. Hypocreadium toombo , from the same host species off New Caledonia, differs in having anteriorly confluent vitelline fields, consistently and markedly anteriorly flexed caecal terminations and the width is always less than the length (width 89–97% of body-length) ( Bray & Justine 2006). Considering the genital pore position at the bifurcal level found by Machida & Kuramochi (1999) in H. patellare in the type-host, we feel that we cannot distinguish this form from this species, although Yamaguti (1938) described a more anterior genital pore in his original description and we did not find this condition in our ‘Typical’ H. patellare specimens. This condition is found, but not consistently, in our ‘Atypical form A’. Similarly the post-ovarian extent of the uterus, while consistent in this (‘Atypical B’) form and in the ‘Typical form’, is also found, but inconsistently, in ‘Atypical form A’. Are these morphological distinctions host induced or genetic? Molecular studies are necessary to answer these questions.

Figures

FIGURES 7 – 8. 7. Hypocreadium patellare Yamaguti, 1938, Atypical form A, ex Rhinecanthus verrucosus, Palau, ventral view, uterus in bold-outline. 8. Hypocreadium patellare Yamaguti, 1938, Atypical form B, ex Pseudobalistes fuscus, Lizard Island, ventral view, uterus in bold-outline. Scale-bars: 7, 8, 500 μm.