Archigetes sp. 3

Toma, Scholz, s, P, Gerardo & Leon, erez-Ponce de, 2021, Caryophyllidean tapeworms (Cestoda), Nearctic parasites of fish in Mexico, including description of a new species of Isoglaridacris and the first report of Khawia japonensis, an invasive parasite of common carp (Cyprinus carpio), International Journal for Parasitology: Parasites and Wildlife 15, pp. 70-78 : 72-73

3. Archigetes sp. 3 Fig. 1D

Material studied: One specimen from silverside, Chirostoma humboldtianum (Valenciennes) ( Atheriniformes : Atherinidae ), Lago de Zacapu, Michoac´an, collected by Berenit Mendoza-Garfias in November 2008 ( CNHE 6801).

Host: Chirostoma humboldtianum .

Distribution: Mexico (Michoac´an).

Remarks

The specimen from C. humboldtianum is in a better condition compared to that found in Notropis nazas , which was designated as Archigetes (?) sp. 2 (see above). It is placed in Archigetes because it corresponds well to its generic diagnosis provided by Mackiewicz (1994), including the presence of a single gonopore and thick-walled external seminal vesicle ( Fig. 1D ). The tapeworm has oblong body shape, 1.47 mm long and 465 μm wide, i.e., width: length ratio 1: 0.32 (almost double compared to Archigetes sp. 2 ; Fig. 1D ). Scolex is 420 μm wide, without a defined neck. Cirrus-sac is thick-walled, subspherical, 94 μm long and 104 μm wide. Testes relatively few (their precise number not countable reliably), begin posterior to anterior-most vitelline follicles; posteriorly, testes reach just the anterior limit of the uterus, i.e., far anterior to the cirrus-sac ( Fig. 1D ). External seminal vesicle is thick-walled, large, oval, oblique, 81 μm long and 52 μm wide. Single gonopore is situated near the ovarian isthmus. Ovary is dumbbell-shaped, 325 μm wide, with ovarian wings 80–100 μm long, i. e., 5–7% of total body length ( Fig. 1D ). Anterior-most vitelline follicles begin 460 μm from the anterior extremity, i.e., 31% of total body length, 57 μm anterior to anterior-most testes. Vitelline follicles forming one irregular field surrounding testes, i.e., lateral and median, reaching posteriorly as far as to the ovary on one side ( Fig. 1D ). Postovarian vitelline follicles are well-developed. Uterine loops reach anterior to the cirrus-sac ( Fig. 1D ). Intrauterine eggs are relatively few (few dozens), 46–49 μm long and 29–30 μm wide (n = 5; only uncollapsed eggs measured).

In North America, only Archigetes iowensis Calentine, 1962 was reported ( Scholz and Oros, 2017). This species was described from Cyprinus carpio (type host; adult tapeworms) and the oligochaete Limnodrilus hoffmeisteri Clapar`ede ( Naididae ; progenetic plerocercoids) in Iowa (Calentine, 1962). This species differs from all three morphotypes found in Mexico by the exclusively lateral position of vitelline follicles, i.e., two separate non-confluent lateral fields (versus lateral and median, i.e., confluent, circum-medullary in Mexican worms), and by the presence of conspicuous, deep loculi on the scolex (versus shallow or even indistinct in Mexican specimens – Fig. 1C, D, E ).

Three morphotypes of Archigetes found in the present study differ from each other in the body shape (much more elongate in Archigetes (?) sp. 2), anterior extent of the testes (at almost the same level as the anterior-most vitelline follicles in Archigetes sp. 1 versus much more posterior in the other morphotypes), the presence of vitelline follicles lateral to dorsolateral to the ovary (in Archigetes sp. 1 ; absent in the other two morphotypes), and shape and thickness of an external seminal vesicle (widely oval, thick-walled in Archigetes sp. 3 ) ( Fig. 1 ). In fact, morphotypes 2 and 3 are more similar to each other than with Archigetes sp. 1 , including the shape of the scolex with shallow, almost indistinct lateral loculi, but the single specimen of Archigetes (?) sp. 2 is damaged and shape of its body may have been affected by long relaxing before fixation.

The occurrence of three morphotypes of Archigetes , which may represent three new species, indicates that the actual diversity of species of this genus is much higher in North America than previously thought ( Scholz and Oros, 2017). This assumption is supported by the fact that

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Scholz et al. (2021) reported two putative new species of Archigetes from Ictiobus spp. in Mississippi. They differ conspicuously in their morphology from A. iowensis as well as all three morphotypes found in endemic leuciscids and atherinopsids in Mexico.

Archigetes sp. 3 from C. humboldtianum represents the first record of any caryophyllidean tapeworm from atheriniform fish. Caryophyllideans occur mainly in siluriform and cypriniform fishes, with few records from cichlids (Cichliformes) and elephant fishes (Mormyriformes) in Africa ( Scholz et al., 2021). The present finding may represent an accidental infection of a silverside or it results from a host switching of a species of Archigetes from cypriniform to atheriniform fish host.

Figures

Fig. 1. Archigetes sp. 1 from Notropis caliensis, Michoac´an (CNHE 6800) (A, C, F); Archigetes (?) sp. 2 from Notropis nazas, Durango (CNHE 6797) (B, E); Archigetes sp. 3 from Chirostoma sp., Michoac´an (CNHE 6801) (D). A, B – total view, dorsally; C, E – anterior part with scolex; note different position of anterior-most testes and vitelline follicles between C and E; D – total view, ventrally; F – ovarian and uterine region, dorsally. Abbreviations: cs – cirrus-sac; eb – excretory bladder; eg – eggs; esv – external seminal vesicle; lo – loculi; ov – ovary; sr – seminal receptacle; te – testes; vf – vitelline follicles.