Conochilidae Harring, 1913

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 : 505-506

Family Conochilidae Harring, 1913

Family Conochilidae was separated into two genera ( Conochilus and Conochiloides ) by Hlava (1904). However, Ruttner-Kolisko (1974) argued that the separation was not warranted and subsumed Conochiloides back into genus Conochilus . While this practice has continued ( Fontaneto & De Smet 2015; Koste 1978), some workers have not followed this change ( Bielańska-Grajner et al. 2015; Pontin 1978; Stemberger 1979). Segers & Wallace (2001) added Conochilopsis to the family; it comprises a single species, originally described as a member of the genus Lacinularia ( Vidrine et al. 1985) . Species secrete a gelatinous matrix that affords protection from the predatory rotifer Asplanchna girodi Guerne, 1888 ( Gilbert 1980). In Conochilus hippocrepis (Schrank, 1803) , colony size increases in diameter (number of individuals) in relation to the size of a sympatric predatory copepod ( Diéguez and Balseiro 1998). The gelatinous matrix is often colonized by bacteria (including cyanobacteria), algae, and protozoans ( Fig. 5 ) ( Balvay & Druart 1995). Occasionally population crashes occur due to parasites invading the perivisceral cavity (blastocoel) ( Ruttner-Kolisko 1977). Colonies tumble (rotate) while swimming.

The etymon for this genus (G., cono, a cone + G., chilus, a lip) was given by Ehrenberg (1834) because the apical field—the fleshy region surrounded by the corona—is inflated by two cone-shaped, lip-like structures located on either side of the mouth ( Fig. 6 ). This structure appears to be depicted in individuals (2 of 7) in figure 3 of Conochiloides (Lacinularia) causeyae by Vidrine et al. (1985).

Diagnosis. Apical field with two inflated, cone-shaped, lip-like structures located centrally or dorsally. Corona circular to horseshoe-shaped, as a double ciliated band (trochus and cingulum) with a prominent ventral gap in the cilia present or not. Body shape conical; illoricate integument with unsegmented foot lacking toes. Paired ventral (lateral) antennae separate or fused to various degrees, within or below coronal field; dorsal antenna absent or minute. Two dorsal eyes beneath corona. U-shaped intestine, anus exiting just above the margin of the gelatinous matrix. Trophi malleoramate: rami symmetrical or slightly to strongly asymmetrical; unci with 3–6 club-shaped (clavate) teeth near fulcrum, (number and form of clavate teeth may be different on each side); numerous, thin accessory teeth beyond clavate ones (distal to fulcrum). Planktonic, either solitary or small to large colonies (5 to>400 or more individuals per colony). Animals clustered within a gelatinous mass produced by glands in foot. Oviparous.

Figures

FIGURE 5. Species of Conochilidae. A. Conochilus hippocrepis (Schrank, 1803); B. Conochilus unicornis Rousselet, 1892; C. Conochilus coenobasis (Skorikov, 1914); D. Conochilus exiguus (Ahlstrom, 1938). This amphoteric female is evidenced by presence of a subitaneous embryo and a smaller male embryo. (The cone-lip is evident in C and D.) The foot in the variation of C. unicornis (C. norvegicus) is much longer (~4x) (see below). E. Examples of reported variation in the fusion of antennae in the Conochilus: consult Edmondson (1959) and Pejler (1956). Bars: 500 µm (A,B); 100 µm (C,D). (E. Redrawn from original art provided by W.T. Edmondson.)

FIGURE 6. Cone-like lips that flank the mouth in Conochilidae. (A) Schematic lateral view. (B) Specimen in vivo. Symbols: cl = cone-lip; m = mastax.