Aspidiophorus ontarioniensis 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 : 469

Aspidiophorus ontarioniensis Schwank, 1990

( Fig. 4 )

Type locality. Among Lemna spp. and from muddy surfaces in ponds, Galt Creek, Puslinch district, Ontario, Canada.

Type material. Drawing of one specimen. Lectotype, SMNH Type-8550 deposited at the Swedish Museum of Natural History, Stockholm, Sweden.

Other material. 3 specimens that are no longer extant.

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

Diagnosis. Small species, 120–140 µm in total body length. Head rounded with two pairs of sensory ciliary tufts. Hypostomion, epipleuria and ocellar granules absent. Furca straight, 18 µm long, with adhesive tubes 8–9 µm long. Dorsal body surface covered by pedunculate scales with rounded anterior part and indented posterior part distributed in 17–19 columns in the head and neck region and 9 columns in the trunk region. All scales without keels. The last 2–3 lateral scales with endplates elongated into a simple spine up to 20 µm long. A pair of 25 µm long simple parafurcal spines anchored by round to oval scales also present. Ventral interciliary area covered by 25 rows of minute pedunculate scales. Pharynx 30–35 µm long.

Only parthenogenetic individuals were observed.

Description. A small and elegant species, 120–140 µm in total body length. Body tenpin-shaped. Head more or less rounded with two pairs of sensory ciliary tufts; posterior pair with considerably longer cilia (up to 15 µm) than those of the anterior pair. Cephalion very thin and close to the cuticle, 12 µm in width. Hypostomion and epipleuria absent. Hypopleuria small. Ocellar granules absent.

Body width 19 µm at the head (U07), 15 µm at the neck (U21), 24 µm at the trunk (U57) and 14 µm at the base of the furca (U81). Head delimited from trunk by neck constriction. Furca straight, 18 µm in length with adhesive tubes 8–9 µm in length. Proximal part of furca naked, adhesive tubes slightly curved. Anterior and posterior dorsal sensory bristles present, anterior pair anchored at U27 and posterior pair anchored directly on cuticle at U76. Head and neck covered by 17–19 dorsal columns of pedunculate scales distributed in 12–13 rows. Trunk covered by 9 dorsal columns of pedunculate scales distributed in 16–17 rows. The scales are without keels, with a rounded anterior part and indented posterior part. The peduncle is on average 1.5 µm in height. Scales of the dorsal trunk region measure 6–7 µm in length and 2–4 µm in width. The endplates of the last 2–3 lateral scales are elongated into simple spines, up to 20 µm in length. In addition a pair of simple parafurcal spines, 25 µm in length are anchored at U81 by small round to oval scales. The parafurcal spines extend beyond the tips of the furcal branches.

The ventral interciliary area is covered by 25 rows of minute pedunculate scales.

Mouth subterminal. Mouth tube very small, only 3 µm in diameter, and weakly cuticularized. Pharynx 30–35 µm in length with a small bulb at each end. PhIJ at U30.

Only parthenogenetic individuals were observed.

Taxonomic remarks. Because of its very long posterior spines A. ontarioniensis can be morphologically separated from all Aspidiophorus without spines. There are 7 taxa within the genus that possess posterior spines: Aspidiophorus aster Martin, 1981 , Aspidiophorus heterodermus heterodermus Saito, 1937 , Aspidiophorus heterodermus levantinensis Kisielewski, 1999 , Aspidiophorus longichaetus Kisielewski, 1986 , Aspidiophorus pori Kisielewski, 1999 , Aspidiophorus squammulosus ( Roszczak, 1936) and Aspidiophorus tetrachaetus Kisielewski, 1986 . A. ontarioniensis can be separated from A. aster , A. heterodermus heterodermus , A. squammulosus and A. tetrachaetus in that it has a pair of parafurcal spines that extends beyond the furcal branches. Such spines are also present in A. heterodermus levantinensis , A. longichaetus and A. pori . In the case of A. heterodermus levantinensis there is a pair of simple parafurcal spines that extends just beyond the furca much as in A. ontarioniensis . However, A. heterodermus levantinensis also has a median group of spines in the posterior trunk region and does not possess the 2–3 pairs of lateral scales drawn out into spines. A. pori has several posterior spines that extend beyond the furcal branches and also a median group of spines in the posterior trunk region. The above characters of A. ontarioniensis together with the prominent hypostomion furrow separates it from the other species of Aspidiophorus . A. ontarioniensis is morphologically closely related to A. longichaetus . Both species share a pair of parafurcal spines that extend beyond the furcal branches (although they are more than twice as long in A. longichaetus ) and they also share the 2–3 posteriormost lateral scales that are drawn out into simple spines. However,

Figures

FIGURE 4. Schematic drawing of Aspidophorus ontarioniensis. A) Dorsal view. B) Lateral view.