Limnioides ceratophylli Schrank 1803

Limnias ceratophylli Schrank, 1803

Fig. 1C

Melicerta biloba Ehrenberg, 1832

Limnias socialis Leidy, 1874

Types: None designated

Type locality: Bayern (Germany).

Other material: Specimen Preparation ANSP 793.

Diagnosis. Base of tube straight or slightly curved, clear at base, abruptly changing to stucco-like granular surface to the top; tube may be light to dark brown (opaque), depending on water conditions. Solitary or colonial. Ventral antennae short. Dorsal nodules absent. Dorsal gap in corona less than neck width. Tube length ≤1500 µm. Trophi: unci longest tooth ~14 µm; 3 (4?) pairs of main teeth. Amictic embryos: ca. 257 x 88 µm. Males known; diapausing embryos not described. Considered to have a cosmopolitan distribution.

Measurements: Total length, ≤1500 µm; corona width, 125–183 µm; tube length, ≤800, tube width (at top), =80 µm; amictic egg, 40– 50 x 100–110 µm. See also Koste (1978). Putative male poorly described by Hudson and Gosse (1886: 76).

Geographic range: Apparently cosmopolitan: Africa (Senegal), Australia, Europe (France, Russia, U.K.), North America (Canada, U.S.A., Mexico), South America (Brazil, Ecuador, Panama), Thailand.

Ecology: pH, 6–9.6; bicarbonate, 7.3–396 mg /L, conductivity, 77–663 µS/cm2, temperature, 13–30 °C; colonizes inert materials (glass and stones), submerged logs, algae, aquatic moss (Fontinalis), several vascular hydrophytes, including Ceratophyllum, Elodea, Myriophyllum, Potamogeton, Ranunculus, Utricularia), and an animal (crocodile) (Edmondson 1944; Koste 1978; Magnusson 1985; Meksuwan et al. 2011; Nilsen and Larimore 1973; Sarma et al. 2017; Tiefenbacher 1972; pers. obs.). It sometimes forms moderately sized allorecruitive colonies, but its propensity to form colonies has not been studied. A planktonic population has been reported (see below).

Comments. The etymon of this genus is apparently a reference to the plant substratum on which Schrank (1803) found specimens. See Koste (1978) for additional synonyms. Tiefenbacher (1972) reported that he did not see the periodical production of tube material, as in the way that Limnias melicerta deposits its tube in rings (Wright 1954), and that colony formation occurred at high population levels.

Four curious habitats have been reported for L. ceratophylli: three sessile and one planktonic. (1) Leidy (1874) reported a population attached to stones in an undefined region of the Schuylkill River (Philadelphia, Pennsylvania, U.S.A.) where colonies of up to 50 individuals occurred. (2) Nilsen and Larimore (1973) reported population densities reaching 17 inds/cm2 on submerged, bark-less logs. (3) Magnusson (1985) noted L. ceratophylli to be an epizootic on an Amazonian crocodile. (4) Although L. ceratophylli has always been considered to be sessile, Beach (1960) reported abundant planktonic populations in two lakes out of approximately 25 lotic and lentic habitats examined in the Ocqueoc River system, Presque Isle Co. (Michigan, U.S.A.). Regrettably Beach did not state whether he examine hydrophytes for sessile individuals, but he implied that: L. ceratophylli “… was always present and always free-swimming.” In one lake the mean population level over three summers was ~900 inds/L. Beach suggested that his findings of L. ceratophylli as an “adventitiously planktonic” was not from the animals being dislodged from their sessile attachment by water movements, but rather that local factors of lake morphology and water chemistry accounted for this unusual condition. Unfortunately, no drawings or photomicrographs were provided to substantiate these observations. Without that level of documentation the possibility remains that Beach was mistaken and that the organisms he observed were tintinnids or another small, encapsulated planktonic organism. However, apparently Beach was familiar with tintinnids, such as Codonella sp., which he reported being present in the freshwater system he studied. Thus, while his report may be in error, it cannot simply be dismissed.