Description of Neoechinorhynchus pikensis n. sp. (Acanthocephala: Neoechinorhynchidae) from Catostomus commersoni (Lacépède) in Wisconsin, USA

Introduction

With his description of Neoechinorhynchus robertbaueri Amin, 1985 from Erimyzon sucetta (Lacépède) in Wisconsin, Amin [1] provided a key to the 20 species of Neoechinorhynchus known in North American freshwater fish then. Amin [2] revised the genus Neoechinorhynchus Stiles and Hassall, 1905 and provided keys to 88 species in two subgenera, Neoechinorhynchus Stiles and Hassall, 1905 and Hebesoma Van Cleave, 1928. Of 26 species in 10 families of fish examined from two adjacent river systems in Racine and Kenosha counties, SE Wisconsin (the Root and Pike rivers), 15 species of fishes in 8 families were infected with helminth parasites between 1976 and 1984 [3, 4]. During the same period, we also examined 3,386 fishes in 10 families from two adjacent lakes (Silver and Tichigan lakes) from which we recovered specimens of Neoechinorhynchus cylindratus (Van Cleave, 1913) in 142 and 25 fishes, respectively, along with specimens of 4 other species of Neoechinorhynchus [4]. In the Pike River, 231 individuals of the white sucker Catostomus commersoni (Lacépède) were captured and examined for parasites [3] with additional and more recent collections that were not recorded. Only 1 sucker that was examined in a 1983 class project contained a unique male specimen of Neoechinorhynchus that was considered new then but has not been examined further since. This single whole mounted specimen is being resurrected and described herein. Line drawings and microscope images were generated but this limited sample size of one whole-mount prohibits the production of SEM images, molecular or EDXA (Energy Dispersive x-ray analysis) studies.

Remarks

As of 1985 and 1999, there are 20 species of Neoechinorhynchus that are known from North American freshwater fishes [1, 5] and a few others described since. Amin [6] listed 114 species in two subgenera and species without subgeneric assignment worldwide. Neoechinorhynchus pikensis n. sp. is unique among other species of Neoechinorhynchus in having a combination of the following characters, among others (1) a dark chitin-like proboscis- neck complex in combination with (2) body wall with similar thickness dorso-ventrally, (3) short obovoid roots of apical hooks, (4) lemnisci relatively long and equal, not reaching anterior testis, (5) large syncytial cement gland with 10 giant nuclei, and (6) prominent and thick cement reservoir branching in 2 long cement ducts surrounding Saefftigen’s pouch and feeding into the bursa. We ran this male specimen Worldwide Acanthocephalans except North America: A few species were found to have one or two of the above noted combination of characters characteristic of N. pikensis n. sp. For instance, Neoechinorhynchus (Neoechinorhynchus) arminiacus Mikailov, 1975 from freshwater fish in Armenia has similar organization of lemnisci and testes but it is a much larger worm with proboscis longer than wide and shorter anterior hooks. Neoechinorhynchus (Neoechinorhynchus) prochilodorum Nickol and Thatcher 1971 also has a similar organization of lemnisci and testes but it has a much smaller proboscis with relatively smaller apical hooks and round testes, constricted cement gland, crested dorsal body wall, and is found in Prochilodus reticulatus Valenciennes in Colombia. Neoechinorhynchus (Neoechinorhynchus) saurogobi Yu Yi and Wu, 1989 also has similar equal lemnisci distant from anterior testis and contiguous male reproductive structures but the lemnisci and the more elongate proboscis are markedly smaller with barely different hook sizes in all circles. It is found in Saurogobio dabryi Bleeker in the Yangtze River, China. Neoechinorhynchus (Neoechinorhynchus) roseus Salgado Maldonado, 1978 from the flatfish Achirus mazatlanus (Steindachner) in Mexico has short equal lemnisci distant from anterior testis and compact contiguous reproductive structures; it has, however, a much smaller proboscis with very small apical hooks. Two short equal lemnisci and a very distant compact contiguous reproductive system secluded at the posterior-most end of the trunk characterize Neoechinorhynchus (Neoechinorhynchus) wuyiensis Wang, 1981 from Crossostoma davidi Sauvage in China; it has no hypodermal giant nuclei, a longer than wide proboscis with very small apical hooks and small receptacle, testes and cement gland. Also, Neoechinorhynchus (Neoechinorhynchus) villoldoi Vizcaino, 1992 from Corydoras paleatus (Jenyns) in Argentina has a comparable body plan to N. pikensis except that it has a proboscis longer than wide with very small apical hooks equal to middle hooks in length (all hooks rooted), among other differences. As with N. villoldoi, Neoechinorhynchus (Neoechinorhynchus) rigidus Van Cleave, 1928 from Schizothorax spp. in India (Kashmir) and Afghanistan has a comparable body plan to N. pikensis except that it has 10 dorsal and 4 ventral hypodermal giant nuclei, a proboscis longer than wide with smaller apical and larger and nearly equal middle and posterior hooks (all rooted), almost equal lemnisci reaching anterior testis. Neoechinorhynchus (Neoechinorhynchus) chilkaensis Podder, 1937 from Mugil cephalus Linn. in India bore similarities to N. pikensis including longer, nearly equal lemnisci not reaching anterior testis but has 5-8 dorsal and 3-5 ventral hypodermal giant nuclei, globular proboscis with shorter apical hooks and its contiguous reproductive structures are distantly confined to posterior trunk extremity. The body of Neoechinorhynchus golvani Salgado Maldonado, 1978 from many fish species in Mexican streams has a similar plan to that of N. pikensis but it is a very small acanthocephalan with correspondingly much smaller trunk, globular proboscis, hooks (middle and posterior hooks equal), receptacle, testes and cement gland. Similarly, the larger Neoechinorhynchus coiliae Yamaguti, 1939, a marine acanthocephalan from Coilia mystus (Linn.) in Japan has a similar plan with its equal lemnisci not reaching anterior testis, but it’s much smaller rectangular proboscis has very small apical hooks equal in length to the middle hooks (all hooks are rooted). The larger specimens of Neoechinorhynchus oreini Fotedar, 1968 from Oreinu_s (=_Schizothorax) sinuatus Heckel in Kashmir is most similar to N. pikensis in body form and organization of lemnisci and contiguous reproductive system. It (N. oreini), however, has a proboscis longer than wide with smaller apical hooks of similar size to middle hooks and with very small roots, and 5-7 and 2 giant hypodermal nuclei dorsally and ventrally, respectively. The cement gland is smaller and the lemnisci are nearly subequal not reaching anterior testis. Neoechinorhynchus zacconis Yamaguti, 1935 from Zacco platypus Temminck and Schlegel in Japan is a very small acanthocephalan with equal lemnisci and contiguous reproductive system that has correspondingly very small proboscis, hooks, receptacle, lemnisci, testes, and cement gland; the lemnisci overlap anterior testis and the testes overlap each other. The larger Neoechinorhynchus karachiensis Bilqees, 1972 from Mugil sp. (=M. spegieleri?) off the Karachi coast in Pakistan is a marine worm with a similar body organization to N. pikensis but differs in having a globular proboscis with very small apical hooks, the equal lemnisci overlap anterior testis, and the testes and cement glands are larger. The larger marine acanthocephalan Neoechinorhynchus nigeriensis Farooqi, 1981 from Galeoides decadactylus (Bloch) in Nigeria is similar to the marine N. coiliae from Japan except that the equal lemnisci are distant from anterior testis, the testes and cement glands are larger, and the apical hooks are much smaller with all hooks rooted. A comparable plan in another marine acanthocephalan from Australia very similar to that of N. nigeriensis is exhibited by Neoechinorhynchus aldrichettae Edmonds, 1971 from Aldrichetta forsteri (Valenciennes) in Australia except for its very long equal lemnisci being distant from anterior testis, globular proboscis with smaller apical hooks, contiguous testes and cement glands displaced to posterior trunk, and 8 giant hypodermal nuclei, 6 ventral and 2 dorsal. Neoechinorhynchus ningalooensis Pichelin and Cribb 2001 from Scarrus spp., another marine acanthocephalan from Australia, is practically identical to N. aldrichettae except for having much shorter and equal lemnisci, larger testes, and 5 giant hypodermal nuclei (4 + 1). Neoechinorhynchus elongatus Tripathi, 1959 from Mugil spp. in India is similar to the latter two species of Neoechinorhynchus from Australia in the general plan except that the nearly equal lemnisci do reach anterior testis, the proboscis is slightly longer than wide, and the anterior hooks and cement gland are small. Like N. pikensis, Neoechinorhynchus afghanus Moravec and Amin (1978) from Labeo dero (Hamilton) in Afghanistan is a small worm that has a proboscis longer than wide with very small apical hooks (all hooks rooted), receptacle, and lemnisci, round testes contiguous with the rest of the reproductive system, and two giant hypodermal nuclei, one dorsal and one ventral.

In North America: See Hoffman [5] and Arai [7] for additional host and distributional records in the US and Canada, respectively. Neoechinorhynchus (Neoechinorhynchus) tumidus Van Cleave and Bangham, 1949 has comparable proboscis, lemnisci and testes plan but its longer lemnisci are nearly subequal and may reach posterior testis, proboscis is globular with middle and posterior hooks not much smaller than anterior hooks, and with markedly larger testes and cement gland; it is found in whitefish, smelt and cisco (lake herring). Neoechinorhynchus (Neoechinorhynchus) strigosus Van Cleave, 1919 which is also found in C. commersoni, among other species of fish including buffalo fish, bears some similarities to N. pikensis such as equal lemnisci that however, reach anterior testis, similar organization of testes that are, however, not contiguous with cement gland, and with a globular smaller proboscis without much difference in size of anterior compared to other hooks. Neoechinorhynchus (Neoechinorhynchus) salmonis Ching, 1984 shares some features with N. pikensis such as the lemnisci that do not reach anterior testis and the organization of the reproductive system with contiguous testes and cement gland and cement reservoir and duct. The roots of the apical hooks are similar. While N. salmonis was originally described from salmonid fishes in British Columbia, we have subsequently found it in the Pike River, Kenosha County, Wisconsin in green sunfish, Lepomis cyanellus Raf.; see Amin (1975, 1986). It does differ from N. pikensis in having slightly subequal lemnisci, much smaller apical hooks, larger testes, ovoid cement gland overlapping posterior testis and a smaller cement reservoir overlapping cement gland. Neoechinorhynchus (Neoechinorhynchus) crassus Van Cleave, 1919 also from the intestine of C. commersoni similarly has almost equal lemnisci and comparable contiguous reproductive structures but the proboscis is longer than wide with much longer hooks in second and third circles and the lemnisci are much longer reaching posterior testis. The circumpolar Neoechinorhynchus (Neoechinorhynchus) rutili (Müller, 1780) Stiles and Hassall, 1905 is a Holarctic acanthocephalan which also infects C. commersoni, among other species of fish, has similar but slightly subequal lemnisci not reaching the anterior testis and all reproductive structures are contiguous; the proboscis is, however, globular with considerably smaller apical hooks, the testes are larger and the cement gland and reservoir are smaller than in N. pikensis. Neoechinorhynchus saginatus Van Cleave and Bangham, 1949 from Semotilus atromaculatus (Mitchill) in Wisconsin is very similar to N. rutili except that the proboscis is more globular with middle and posterior hooks being about equal in length. One of the more recently described species of the genus in North America is Neoechinorhynchus bullocki Doolin and Reyda, 2018 from C. commersoni in New York which is readily distinguishable from N. pikensis by having markedly unequal lemnisci distant from anterior testis, dorsal body wall being much thicker than ventral, much smaller anterior hooks, and smaller cement gland. The most prevalent species of Neoechinorhynchus in North America is probably N. cylindratus (Van Cleave, 1913) Van Cleave, 1919 which has been commonly collected in southeast Wisconsin, ex., 4,158 specimens from 142 of 807 examined fish of 12 species from Silver Lake alone between 1976 and 1984 [4]; other examples from elsewhere in Wisconsin [8] but not in the Pike River. Compared to N. pikensis, N. cylindratus is a larger worm with unequal lemnisci not reaching anterior testis and subspherical proboscis with markedly smaller apical hooks, among other differences.

Discussion

Distinguishing characteristics of N. pikensis n. sp. include the shape and size of the dark chitin-like proboscis-neck complex, body wall with similar thickness dorso-ventrally, long apical hooks with short obovoid roots, much smaller middle and rootless posterior hooks, lemnisci relatively long and equal, not reaching anterior testis, large syncytial cement gland with 10 giant nuclei, contiguous reproductive organs in posterior two thirds of trunk, and prominent and thick cement reservoir branching in 2 long cement ducts surrounding Saefftigen’s pouch reaching bursa. The combination of these characters, and a few more such as the number of giant hypodermal nuclei (5 + 1), size of male reproductive organs, shape of proboscis and hook roots could not be found in any species of the many worldwide acanthocephalans of the genus Neoechinorhynchus, including those known in North America.

We have demonstrated the validity of Neoechinorhynchus pikensis n. sp. by comparing some of its major diagnostic features with those of other species of Neoechinorhychus worldwide. Neoechinorhynchus pikensis appears to be a rare species found only once in one individual of C. commersoni in the Pike River from which we have previously examined hundreds of individuals. The scarcity of N. pikensis may be interpreted as a spillover from a larger population in southwest Lake Michigan in which the Pike River flows not too far from our usual collecting sites in the Pike River. The white sucker populates Lake Michigan, especially its SW region, and it is commonly infected there with Acanthocephalus dirus (Van Cleave, 1931) Van Cleave and Townsend, 1936 [9] which has been collected in large numbers and described from C. commersoni in the Pike River, its type locality [10].

We could only provide line drawings and microscope images but no SEM, molecular or metal analysis could be made as we have only one whole mounted male specimen to work with.

Acknowledgements

This project was supported by an institutional grant from the Parasitology Center, Inc. (PCI), Scottsdale, Arizona. We are extremely fortunate to have had the technical skills and the talents of Dr. Nataliya Yu. Rubtsova of PCI who put together the images in such an artistic way.