A new species of the genus Trimusculotrema, parasites of stingrays
[summary of Dyer, W.G. and W.J. Poly. 2002. Trimusculotrema schwartzi n. sp. (Monogenea: Capsalidae) from the skin of the stingray Dasyatis zugei (Elasmobranchii: Dasyatidae) off Hong Kong, China. Systematic Parasitology 51(3): 217-225.]
Trimusculotrema schwartzi n. sp. (Capsalidae) is described from the skin of the stingray, Dasyatis zugei (Elasmobranchii, Rajiformes, Dasyatidae) from Hong Kong, China. Only three other species have been placed in the genus Trimusculotrema: T. micracantha (Euzet and Maillard, 1967), T. leucanthemum (Euzet and Maillard, 1967), and T. uarnaki Whittington and Barton, 1990. Trimusculotrema schwartzi n. sp. may be differentiated from all known species of Trimusculotrema by the length of the anterior hamuli and by the absence of pigment shields over the eyes. Its occurrence on a stingray from China represents a northern extension of the geographic range of Trimusculotrema. [A fifth species, Trimusculotrema heronensis Whittington & Kearn, 2008, has been described recently; Whittington, I. and G.C. Kearn. 2008. Trimusculotrema heronensis sp. nov. (Monogenea, Capsalidae) from the skin of the pink whipray Himantura fai (Elasmobranchii, Dasyatidae) from Heron Island, Queensland, Australia. Acta Parasitologica 53(3): 251-257.]
Trimusculotrema schwartzi may be differentiated from all previously described species of Trimusculotrema in having anterior hamuli that are longer than the accessory sclerites in most cases (Fig. 14) and also differs from other T. spp. by the absence of pigment shields over the eyes (Table I). Trimusculotrema schwartzi differs further from T. leucanthemum by the shape and length of the accessory sclerites, which are 95 µm (48-140) in the former compared to 37 µm (32-42) in the latter and by the shape and length of the anterior hamuli, which are 114 µm (60-205) in the former compared with 30 µm in the latter. Furthermore, the haptor of T. schwartzi has three concentric muscle bands and no ribs at the periphery of the haptor, whereas the haptor of T. leucanthemum possesses only two concentric muscle bands and has radial ribs along the margin of the haptor. Trimusculotrema schwartzi may be further differentiated from T. uarnaki by the shape and length of the anterior hamuli, which are 114 µm (60-205) compared to 46 µm (44-52). The haptoral papillae of T. leucanthemum differ from those of the other three T. spp. in having a scalloped margin (illustrated in Euzet and Maillard, 1967). Trimusculotrema schwartzi also differs from T. micracantha as to the level of the vaginal opening, which is at the level of the oötype in T. schwartzi compared to the posterior level of the left anterior attachment organ in T. micracantha (however, note that this characteristic might have been affected by contraction).
The pair of raised structures at the anterior end of T. schwartzi might serve a sensory function (Fig. 11); similar structures were not observed by us on other T. spp. (the structures were visible with LM on most specimens of T. schwartzi). Thus, the structures might be unique to T. schwartzi. Benedeniella posterocolpa has a large conical papilla on each anterior attachment organ (McMahon, 1963; W. Poly and W. Dyer, pers. observ.) that also might be a unique sensory structure for this species (McMahon, 1963).
|Anterior hamulus length (µm) - accessory sclerite length (µm) vs. total length (µm) of four species of the genus Trimusculotrema: T. schwartzi, n. sp., T. uarnaki, T. micracantha, and T. leucanthemum.|
One feature of the genus Trimusculotrema is the muscular rings (2-3) in the haptor (Whittington and Barton, 1990). Although we have not examined specimens of Entobdella apiocolpos Euzet and Maillard, 1967, three concentric muscle bands were illustrated by Euzet and Maillard (1967, p. 1438) for this species; therefore, the concentric muscle bands may not be a unique character of the genus Trimusculotrema. In T. schwartzi and T. leucanthemum the muscle bands are not continuous through the area between the hamuli. In T. micracantha the muscle bands extend into the area between the hamuli but as smaller groups of fibers and not as cohesive bands. The innermost muscle bands of T. uarnaki extend between the hamuli, sometimes becoming discontinuous, but the outermost band usually does not, except as a few small fibers. Whittington and Barton (1990) illustrated all the muscle bands as continuous. Connections between adjacent muscle bands were observed in T. schwartzi, T. micracantha, and T. uarnaki and were illustrated in the latter by Whittington and Barton (1990).
Trimusculotrema schwartzi is only the third capsalid species with reductions in pigment shields and/or other ocular structures; the other capsalids reported to lack eyespots are Pseudoentobdella pacifica (Guberlet, 1936) Yamaguti, 1963 and Lagenivaginopseudobenedenia tinrowi Timofeeva, 1995 (Guberlet, 1936; Price, 1939; Timofeeva, 1995). All four species of Trimusculotrema occur on stingrays of the genera Dasyatis and Himantura. Trimusculotrema schwartzi was found on the ventral body surface (skin) of Dasyatis zugei; other T. spp. occurred on the skin, except T. leucanthemum, which was found on the gills of D. marmorata. Trimusculotrema schwartzi is the only member of its genus that occurs in Asia and thus far is known only from the Zhujiang estuary.
|Distribution of Trimusculotrema schwartzi n. sp. (solid circle with star = type locality).|
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