Chaetonotus (Chaetonotus) ontariensis Schwank, 1990

Schwank, Peter & Kånneby, Tobias, 2014, Contribution to the freshwater gastrotrich fauna of wetland areas of southwestern Ontario (Canada) with redescriptions of seven species and a check-list for North America, Zootaxa 3811 (4), pp. 463-490 : 477-479

Chaetonotus (Chaetonotus) ontariensis Schwank, 1990

( Fig. 8 )

Type locality. In wet mosses, Galt Creek, Puslinch district, Ontario, Canada.

Type material. Drawing of one specimen. Lectotype, SMNH Type-8554 deposited at the Swedish Museum of Natural History, Stockholm, Sweden.

Other material. 2 specimens that are no longer extant.

Etymology. Species name derived from the province of Ontario in Canada.

Diagnosis. Small species, 120–130 µm in total body length. Head weakly five-lobed with two pairs of sensory ciliary tufts. Head as wide as trunk. Furca straight, 10–15 µm in length with thin adhesive tubes. Seven columns of dorsal scales in head/neck region and 5 columns of dorsal scales in trunk region. Scales are bluntly arrowheadshaped with deep posterior incision and thick strongly curved spines. Both scales and spines increase in size from anterior to posterior. Pharynx 26–27 µm.

Description. A typical species of Chaetonotus , 120–130 µm in total body length. Head weakly five-lobed with two pairs of short sensory ciliary tufts. Head plates weakly cuticularized, cephalion 9 µm in diameter. Dorsal sensory bristles not observed.

Body width 21 µm at the head (U07), 16–17 µm at the neck (U18), 21 µm at the trunk (U53) and 9–10 µm at the base of the furca (U88). Head as wide as trunk but well delimited by a neck constriction. Furca straight, 10–15 µm in length, and somewhat separated from the trunk by weak constriction. Adhesive tubes are thin and account for 5–8 µm of the total furca length. Proximal parts of furcal branches naked. In the head/neck region there are 7 columns of dorsal scales and in the dorsal trunk region only 5 columns of scales. Dorsal scales are distributed in 18 rows and increase in size from anterior to posterior end. The arrowhead-shaped scales are deeply incised distally, without keels. Their edges are slightly rounded. Spines increase in length from 2–3 µm at the head to 10 µm in the trunk region.

The ventral surface could not be observed.

Mouth subterminal, 4–5 µm in diameter. Pharynx, 26–27 µm in length, widens towards the PhIJ at U25.

Taxonomic remarks. Based on its short, simple spines and arrowhead-shaped scales, C. (C.) ontariensis is closely related to a group of species comprising among others Chaetonotus (C.) brevispinosus Zelinka, 1889 and Chaetonotus (C.) polyspinosus Greuter, 1917 . The low number of scales indicates a relationship with C. (C.) brevispinosus but this species has a higher number of dorsal columns and thinner trunk spines. C. (C.) oculatus Schwank, 1990 has a pair of ocellar granules, longer sensory ciliary tufts and a higher total number of dorsal scales. Species within the series polyspinosus and multispinosus (see Schwank 1990) have many more dorsal spines. Chaetonotus (C.) vulgaris Brunson, 1950 is similar but apparently this species has no scales that anchor the spines.

Figures

FIGURE 8. Schematic drawing of Chaetonotus (Chaetonotus) ontariensis. A) Dorsal view. B) Spined scale of the trunk region.