Ichthydium

Kolicka, Małgorzata, Kisielewski, Jacek, Nesteruk, Teresa & Zawierucha, Krzysztof, 2013, Gastrotricha from the Poznań Palm House — one new subgenus and three new species of freshwater Chaetonotida (Gastrotricha), Zootaxa 3717 (2), pp. 231-279 : 270-271

Ichthydium sp. ( Table 16)

Locality: Site 1, session II.

Material: 1 sample, 1 adult specimen, photographed.

Short description: This species has a long and slender body with parallel edges. The three–lobed head has a wide cephalion and large hypopleuria, but no epipleuria. The hypostomium is elliptical in shape. On the head there are two pairs of cephalic ciliary tufts. The mouth ring is situated ventrally. The pharynx has slight dilatations at the ends. The furca is massive and thick, with very short adhesive tubes. The branches of the furca are parallel and do not part outwards. On the furca base there is a posterior pair of dorsal sensory bristles. The posterior sensory bristles are anchored at small papillae, situated near the furca base. The body surface is not covered with cuticular structures visible in the light microscope. On the ventral side there are two longitudinal ciliary bands with very long cila. Ocellar granules absent.

Differential diagnosis: From all known Ichthydium species, this species resembles only the species Ichthydium rostrum Roszczak, 1969 .

I. rostrum Roszczak, 1969 (80–100 Μm in length) is a smaller species with a similar body shape and comparable proportions. However, in Ichthydium sp. the body is more slender and the head outline is three–lobed, not single–lobed as in I. rostrum . Moreover, the pharynx is definitely shorter (18–24 Μm) than in the I. sp. (47.7 Μm), and posterior sensory bristles are absent. Both species have very short adhesive tubes when compared to the body length, but the adhesive tubes in I. rostrum are arranged outwards, unlike in the discussed species.

Character Specimen Body length 158.4 Pharynx length 47.7 Width of anterior pharynx thickening (a) 5.9

Width of pharynx narrowing that follows anterior thickening (n) 3.9

Width of pharynx at its middle length (m) 6.0

Width of posterior pharynx thickening (p) 7.1

Length of cephalic cilia 15.8–20.0 Hypostomium length 3.7

Cephalion length 6.8

Cephalion width 10.7 Diameter of mouth ring 4.1

Furca length 11.9 Length of adhesive tube 2.9

Posterior sensory bristles length 8.8

Number of cephalic cilia in one tuft 3 (anterior); 5 (posterior) Number of separated cephalic tufts 4

Pharynx formula a 12.4 Pharynx formula n 8.2

Pharynx formula m 12.6 Pharynx formula p 14.9