Atrochidae Bartoš, 1959

Davies, Natalie, Lafleur, Alexandre, Hochberg, Rick, Walsh, Elizabeth J. & Wallace, Robert L., 2024, Key to sessile gnesiotrochan rotifers: Families, monospecific species in Flosculariidae, species of Atrochidae, Conochilidae, and Limnias, Zootaxa 5397 (4), pp. 497-520 : 503-505

Atrochidae Bartoš, 1959

This small, enigmatic family comprises three monospecific genera ( Acyclus , Atrochus , Cupelopagis ). Only Acyclus possesses a gelatinous tube. Except for Cupelopagis , relatively little is known about the biology of these forms. All possess an infundibulum that is often relatively large and gaping. All possess interesting modes of feeding. Acyclus lives within colonies of Sinantherina socialis (Linnaeus, 1758) and occasionally Lacinularia flosculosa ( Flosculariidae ), on whose ova and larvae it feeds. Lacking an attaching foot, Atrochus crawls slowly over the bottom and feeds on algae. Although sessile Cupelopagis is capable of tracking and orientating toward its animal and protistan prey by detecting vibrations in the water ( Bevington et al. 1995). Atrochidae was separated from the family Collothecidae because of the atypical anterior end ( Koste 1978). However, Koste suggests that the Atrochidae is an artificial grouping; its assignment is retained here as a matter of convenience and to emphasize the uncertain relationship of the three genera to the remaining Collothecacea .

The etymon of the family (G., a, without + G., trochus, wheel) emphasizes the lack of a ciliated corona, which is present in most Rotifera.

Diagnosis. Infundibulum variously shaped: large asymmetric bowl, or small with a dorsal hood-like lobe, or fringed with short, hollow, finger-like projections, but always lacking setae and cilia as adults. Vestibulum absent. Larvae resemble other Collothecacea : ciliated anterior end providing locomotion. Foot elongate and tapering, or a short thick stalk, or absent. Oviparous or ovoviviparous. Adults sessile with or without gelatinous tube or capable of limited locomotion (crawling).

Dichotomous key to species of family Atrochidae

1 Infundibulum large, bowl-shaped, as wide as body width; body a slightly flattened spheroid; mouth (infundibulum) positioned parallel to substratum; sessile by a short, flexible centrally positioned, ventral foot; gelatinous tube absent; body size ≤1000 µm; ovoviviparous. ( Fig. 4A )...................................................... Cupelopagis vorax (Leidy, 1857) [The morphology of this species is review by several workers including Cori (1925), Hünerhoff (1931), Koste (1973), and Vasisht & Dawar (1968, 1969). Bevington et al. (1995) and Preze (2017) report studies on feeding.

1’ Infundibulum and body not as above; gelatinous tube present or absent; sessile or mobile; foot not a short stalk........... 2

2(1) Infundibulum with long, prehensile dorsal lobe; transparent gelatinous tube; foot relatively short; sessile, often in colonies of Sinantherina and occasionally Lacinularia ( Flosculariidae ). Adult ≤1500 µm; oviparous. ( Fig. 4B )................................................................................................. Acyclus inquietus Leidy, 1882 [ Acyclus feeds on the ova and young of the colonial rotifers it inhabits. Hochberg et al. (2010) reported on the behavior, metamorphosis, and muscular anatomy of this species. An undescribed congener, reported from Thailand ( Meksuwan et al. 2013), should be explored further.]

2’ Infundibulum lacking long dorsal lobe, possessing finger-like projections (horny processes) on dorsal side; body elongate oval; tube absent; foot short and hemispherical in shape; 1200–1500 µm; mobile (crawling), lying on surfaces; ovoviviparous. ( Fig. 4C ).................................................................. Atrochus tentaculatus Wierzejski, 1893 [Additional work needs to be done on this enigmatic species; consult Koste et al. (1984) and Wierzejski (1893).]

Figures

FIGURE 4. Three species in family Atrochidae. A. Cupelopagis vorax (Leidy, 1857), side view; insert dorsal view. B. Two individuals of Acyclus inquietus Leidy, 1882 removed from a colony of S. socialis. C. Atrochus tentaculatus Wierzejski, 1893. (C. After Wierzejski, 1893). Symbols: B = body; F = foot; I = infundibulum; G = gelatinous matrix; S = substratum. Bars ~1000 µm.