Collothecacea Remane, 1933

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 : 501-502

Order Collothecacea Remane, 1933 (= Paedotrocha de Beauchamp, 1965)

Collothecacea is a cosmopolitan order of two families ( Atrochidae , Collothecidae ) comprising a total of five genera dominated by the genus Collotheca , which possesses ~50 species ( Jersabek & Leitner 2013). Several characteristics separate this order from other taxa. All species possess uncinate trophi and a contoured anterior end that is elaborated into the infundibulum (L., funnel) ( Hochberg et al. 2019). Prey captured in the infundibulum are moved into a temporary holding chamber called the vestibulum (L., entrance); from there the trophi eventually pull prey into the stomach for digestion. [NB: Edmondson (1959) reverses identification of these the infundibulum and vestibulum (figure 18.102b) and Remane (1929 –1933) alternates use of the names in two places (compare figures 159A and 162C).] The margin of the head end may or may not possess lobes or tentacles with cilia and/or setae. All collothecans are raptorial, ambush predators. Predation has been described in Collotheca by Meksuwan et al. (2013), in Cupelopagis by Bevington et al. (1995) and Preza (2017).

Generally, these rotifers possess elongate bodies, including a long slender foot. In adults of Collotheca and Stephanoceros ( Collothecidae ) the infundibulum is usually edged with cilia or setae; in adults of Acyclus , Atrochus , and Cupelopagis ( Atrochidae ) these are absent. External gelatinous tubes that surround adult females are present in three genera: Acyclus , Collotheca , and Stephanoceros . Unlike the species of Flosculariidae , no collothecaceans form colonies. However, aggregations of densities above 6 individuals mm 2 have been reported (Wallace & Edmondson 1986). These clusters probably do not represent contagious settlement by the larvae as is seen in barnacles. Rather, they may indicate recruitment due to a factor(s) associated with the surface of the preferred plant ( Wallace 1980). As in the sessile Flosculariidae , Collotheca possesses several planktonic species. The monospecific genus Atrochus does not affix permanently to surfaces and is capable of some crawling movement ( Wierzejski 1893).

The etymon for both the order and one family ( Collothecaceae ; Collothecidae ) refers to the gelatinous tube (G., collo, glue + G., theca, case). However, into the early part of this century, collothecids were known as Floscularia (L., flosculus, little flower), which to many observers is a better allusion to their form: a flower-shaped animal situated on a long foot stalk with a funnel-shaped head possessing numerous radiating setae. Nevertheless, for reasons of priority both names were changed by Harring (1913).

Larval collothecids are small (~100–500 μm), often spindle shaped, and with a pair of red eyespots just below a ciliated corona; these are lost in the adults of species that are permanently attached. Organ systems are not well developed and there is often a ciliated cavity at the base of their foot. Only after settlement do they begin metamorphosis to the adult body form and secrete an extracorporeal tube around their body.

Diagnosis. Corona bowl- to funnel-shaped, narrowing at its base, the margin is edged with long setae or short cilia (both often motionless), or cilia and setae lacking. The corona may be elaborated into lobes or tentacles (arms) or lobes absent. Mastax enlarged into a storage chamber (proventriculus). Trophi uncinate. Foot elongate, retractile, but not within the body. Foot ends with attachment disk or peduncle; toes absent. Most species secrete clear gelatinous tubes. Mainly sessile species, but several planktonic and ≥ 1 benthic species. All collothecans are solitary.