Aquatic Parasite Observatory

Loxogenes sp. (Stafford, 1905)

    • Species Name: Loxogenes sp. (Stafford, 1905)
    • Synonyms: None
    • Taxonomy: (Stafford, 1905) Animalia, Platyhelminthes, Trematoda, Plagiorchiida, Loxogenes sp.
    • Description: Adult stage as described by Stafford, 1905: The habitat is different, for Loxogenes occurs in thick- walled cysts in the liver or pylorus whereas Pleurogenes occurs free in the cavity of the intestine and Brandesia buried in a Lieberkühn's crypt which is of course open to the lumen of the intestine (Mühling, Zool. Anz. Nr. 549. 1898. p. 23). Disregarding the position of the genital opening L. arcanum most closely resembles P. medians. In shape it is much shorter in proportion to its breadth, surpassing even Piosotocus confusus in that respect, but it is broadest behind instead of in front and emarginate at the posterior end from which the large excretory vessels widely diverge. The oesophagus is very short and the coeca broadly spreading, while in P. medians there is a long oesophagus and the coeca are larger and less divergent. The ovary is irregular (lobed) instead of rounded (compact) and is situated just inwards from the right coecum instead of outwards. The uterus folds back and forward in passing across the body behind the coeca instead of folding right and left while forming a long loop back and forwards on each side of the post-acetabular half of the body. The testes are similar, irregular bodies placed obliquely right and left of the acetabulum, at the ends of the coeca, but the penis-apparatus is smaller in L. arcanum than in P. medians and opens on the surface instead of at the margin. The vittellaria extend from the pharynx to the ends of the coeca all across the body ventral to the intestinal system instead of being on each side of the oesophagus as two dorsally situated distinct groups of follicles. The eggs in preserved specimens of L. arcanum vary about 0,022 x 0,014 (Nickerson says about 23 x 13 μ while in P. medians they are 0,03 x 0,016. Morphologically there is considerable difference between Loxogenes arcanum and Brandesia turgida. The only characters in which they particularly approach each other are the size of the worms and the size and position of their suckers. My largest specimen measures 1,9 x 1,28 (not 3 to 4 as given by Pratt, which is the length of the thick cysts), Nickers on' s 2,5, which is also the greatest length given for Brandesia. The ventral sucker I find by measurement to be rather larger than the oral, although it may look smaller, and is situated a little behind the centre of the animal. In Brandesia the oral is the larger and is placed rather farther back. The peculiar form given by Brandes (Arch. f. Naturg. 1888 Taf. 17 fig. 2) was, I fancy, a phase in a single instance; the more normal form is doubtless given by Looss (Zool. Jahrb. XII. 1899. p. 776). Our specimens differ from the European in being broadest behind, indented at the posterior end, and not particularly thick. I take it that the asymmetry of the intestine in Nickerson's drawing is a mistake; the intestine is essentially the same in both. In L. arcanum the testes are lateral from the ventral sucker, immediately behind the ends of the coeca; in B. turgida they are lateral from the coeca, the right one being opposite the interval between oral sucker and ovary. The ovary in the former worm is to the right of the median line and in front of the testes, but in the latter it is on the median line and almost behind the testes. The penis-sac in the one lies obliquely across the left coecum, far in front of the acetabulum, in the other it lies transversely from the ventral sucker, some distance behind the end of the left coecum. According to Nickerson the male and female genital ducts open separately on the surface or into a common groove or depression, the female in front of the male, both on the ventral surface, near the left side, and rather nearer the oral than the ventral sucker. I must say that my specimens seem to agree with this but that, on account of the presence of vittelline follicles, I am not yet fully satisfied as to the separate openings. In Brandesia the genital pore is marginal. In the American worm the folds of the uterus are, for the most part, behind the ventral sucker, in the European they pass first to the left and then forwards across the region of the coeca and pharynx. In the first the vitellaria extend all the way across the intestinal region, but in the second they are in lateral bunches anterior to the coeca. The egg of L. arcanum measures about 0,022 x 0,014, that of B. turgida 0,038 x 0,013.
    • Life Cycle: "Adult Loxogenoides occur in the lumen of the bile duct, and adult Loxogenes are usually encysted in the intestinal or gastric wall in the region of the pyloris sphincter. Metacercariae of Loxogenes encyst in abdominal muscles of numerous species of dragonfly naiads, which are then eaten by frogs acting as definitive hosts" (Sutherland, 2005).
    • Sources: Sutherland, D. 2005. Parasites of North American Frogs. Amphibian Declines: The conservation status of United States Species. p. 110.
    • APO Parasite Records: (by Life Cycle)

Parasite Images:


  • University of Colorado Boulder