SUPPLEMENTAL DESCRIPTION OF CABALLEROTREMA ANNULATUM (DIESING, 1850) OSTROWSKI DE NÚÑEZ AND SATTMANN, 2002 (DIGENEA: CABALLEROTREMATIDAE) FROM A NEW HOST (ELECTROPHORUS CF. VARII) AND LOCALITY (AMAZON RIVER, COLOMBIA) WITH PHYLOGENETIC ANALYSIS AND EMENDED GENERIC DIAGNOSIS.

Herein, we provide a supplemental description of Caballerotrema annulatum (Diesing, 1850) Ostrowski de Núñez and Sattmann, 2002 (Digenea: Caballerotrematidae Tkach, Kudlai, and Kostadinova, 2016) based on specimens collected from the intestine of an electric eel, Electrophorus cf. varii (Gymnotiformes: Gymnotidae) captured in the Amazon River (Colombia). This caballerotrematid can be differentiated from its congeners by the following combination of morphological features: body surface spines forming contiguous transverse rows, concentric (wrapping dorso-ventrally around body), distributing into posterior body half (vs. restricted to anterior body half in Caballerotrema brasiliensePrudhoe, 1960; indeterminate for Caballerotrema aruanenseThatcher, 1980 and Caballerotrema piscicola [Stunkard, 1960] Kostadinova and Gibson, 2001); head collar lacking projections (vs. having them in C. brasiliense, C. aruanense, and C. piscicola), narrow (head collar more narrow than maximum body width vs. the head collar being obviously wider than the body in C. brasiliense, C. aruanense, and C. piscicola); corner spines clustered (vs. corner spines distributing as 2 separated pairs in C. brasiliense, C. aruanense, and C. piscicola); pharynx approximately at level of the corner spines (vs. pharynx far anterior to corner spines in C. brasiliense, C. aruanense, and C. piscicola); and testes ovoid and nonoverlapping (C. aruanense; vs. sinuous and overlapping in C. brasiliense and C. piscicola). Based on our results, we revise the diagnosis of CaballerotremaPrudhoe, 1960 to include features associated with the shape and distribution of body surface spines, orientation and position of head collar spines, cirrus sac, seminal vesicle, oviduct, Laurer's canal, oötype, vitellarium, and transverse vitelline ducts. We performed Bayesian inference analyses using the partial large subunit ribosomal (28S) DNA gene. Our 28S sequence of C. annulatum was recovered sister to that of Caballerotrema sp. (which is the only other caballerotrematid sequence available in GenBank) from an arapaima, Arapaima gigas (Schinz, 1822) (Osteoglossiformes: Arapaimidae) in the Peruvian Amazon. Our sequence of C. annulatum comprises the only caballerotrematid sequenced tethered to a morphological description and a voucher specimen in a lending museum. The present study is a new host record and new locality record for C. annulatum. The phylogeny comprises the most resolved and taxon-rich evolutionary hypothesis for Echinostomatoidea published to date.

FIRST RECORD OF A PARASITE, DACTYLOGYRUS CF. SKRJABINI (MONOGENOIDEA: DACTYLOGYRIDAE), INFECTING INVASIVE SILVER CARP, HYPOPHTHALMICHTHYS MOLITRIX (VALENCIENNES, 1844) (CYPRINIFORMES: XENOCYPRIDIDAE) IN NORTH AMERICA.

The parasites infecting invasive carps in North America (all Cypriniformes: Xenocyprididae: grass carp, Ctenopharyngodon idella [Valenciennes, 1844]; silver carp, Hypophthalmichthys molitrix [Valenciennes, 1844]; bighead carp, Hypophthalmichthys nobilis [Richardson, 1845]; and black carp, Mylopharyngodon piceus [Richardson, 1846]) are little studied, and no parasite has been reported from silver carp there. We herein surveyed silver carp from Barkley Reservoir and Cheatham Reservoir (Cumberland River, Tennessee; June and December 2021) and the White River (Arkansas; May 2022) and collected numerous monogenoid specimens infecting the pores on the outer face of the gill raker plate. We heat-killed, formalin-fixed, and routinely stained some specimens for morphology and preserved others in 95% ethanol for DNA extraction and sequencing of the large subunit ribosomal DNA (28S). We identified our specimens as Dactylogyrus cf. skrjabini because they had a dorsal anchor deep root that is much longer than the superficial root, an approximately parallel penis and accessory piece, and a relatively large marginal hook pair V. No type specimen of Dactylogyrus skrjabiniAkhmerov, 1954 (type host and locality is silver carp, Amur River, Russia) is publicly available, but we borrowed several vouchers (NSMT-Pl 6393) that infected the gill rakers of silver carp captured in the Watarase River, Japan. The original description of D. skrjabini was highly stylized and diagrammatical, differing from the specimens we studied from North America and Japan by the dorsal anchor having a superficial root and shaft that comprise a strongly C-shaped hook (the superficial root curves toward the dorsal anchor point) (vs. superficial root straight, at ∼45° angle to deep root and directed away from the dorsal anchor point), a single, much reduced transverse bar that is narrow for its entire breadth (vs. dorsal and ventral transverse bars robust and broad, having an irregular outline), an accessory piece that lacks digitiform projections (vs. accessory piece with 4 digitiform projections), and an accessory piece that lacks a half cardioid-shaped process (vs. accessory piece having a half cardioid-shaped process). Our 28S sequences (generated from 4 specimens of D. cf. skrjabini: 2 from Tennessee [763 base pairs (bp)] and 2 from Arkansas [776 bp]) were identical to 1 ascribed to D. skrjabini from Japan. The present study is the first verifiable and credible report of a parasite from silver carp in North America and the first nucleotide information for a parasite from silver carp in North America.