Heterolepidoderma macrops Kisielewski, 1981

Križanová, Františka Rataj & Vďačný, Peter, 2024, A Heterolepidoderma and Halichaetoderma gen. nov. (Gastrotricha: Chaetonotidae) riddle: integrative taxonomy and phylogeny of six new freshwater species from Central Europe, Zoological Journal of the Linnean Society 200 (2), pp. 283-335 : 312

Heterolepidoderma macrops Kisielewski, 1981

( Figs 19A–H , 20A–F ; Supporting Information, Table S12)

Material examined: Adult (hologenophore, CU-FNS-22-06-20), Kuchajda Lake, municipal recreation area, Nové Mesto, Bratislava, Podunajská rovina plain, Slovakia, 4810ʹ15.7ʹʹN, 1708ʹ30.6ʹʹE. The voucher specimen is shown in Figure 20A–F and its photomicrographs are available at the Department of Zoology, Comenius University in Bratislava at https://fns.uniba. sk/en/gastrotricha/.

Description of a Slovak population: Habitus. Heterolepidoderma macrops is about 120 µm long and has a slender tenpin-shaped body, with a clearly defined head region, a narrowing neck, and a bulbous trunk ( Fig. 19A ). The body width is 17.9 µm at U10, 15.5 µm at U25, and 21.5 µm at U62. Dorsal sensory bristles arise from a bulbous papilla in three pairs at U3, U23, and U80 ( Figs 19A, D , 20C ). The furcal indentation is narrowly helmet-like in shape. The furca branches are set apart and bear well-developed adhesive tubes, which are 10.7 µm long ( Figs 19A , 20F ).

Head

The head is slightly five-lobed.The cephalion is well developed with a free posterior (dorsal) edge ( Fig. 20A, B ). The epipleurae and hypopleurae are only indistinctly marked in the head outline. Two pairs of cephalic ciliary tufts emerge laterally between the cephalion and the epipleurae edge (c. U4), as well as between the epi- and the hypopleurae edge (c. U7) ( Figs 19A , 20E ). Ocellar granules are situated between the epi- and the hypopleurae edge at U7 and they are about 1.2 µm across. The mouth ring is oval, approximately 6.9 μm in the largest diameter, and located ventroterminally at U1– U4. There are strong but short, rod-like reinforcements lining the walls of the mouth ring. Two cuticular teeth are clearly visible and placed right and left of the centre of the mouth opening ( Figs 19C , 20E ). The hypostomium (c. U4–U7) carries a very broadly tongue-shaped plate with a reinforcement bar ( Fig. 19C ).

Internal morphology

The pharynx extends from c. U3 to U27, is 35 μm long and 5.9– 8.6 μm wide. It has two weakly marked anterior and posterior dilatations. The posterior dilatations are wider than the anterior ones. The pharynx smoothly continues through the pharyngealintestinal junction to the differentiated anterior section (U28– U31) of the intestine, which extends from U32 to U85 ( Fig. 20A ). Paired adhesive glands (c. U85–U90) are placed slightly laterally, right behind the terminal part of the intestine, forming a short dichotomy at the furca base.

Scales

Almost the entire body is covered by overlapping scales that adhere to the basal cuticle layer along most or all of their perimeter. All scales are keeled. Scales are distributed in 24 longitudinal dorsal alternating columns, with usually 31 scales in the central column. Their size slightly increases in a posterior direction. Central dorsal longitudinal rows of scales begin at the level of the posterior edge of the cephalion (c. U3), while dorsolateral and lateral rows start at c. U5–U9 at the posterior edge of the epipleurae/hypopleurae. They run almost along the whole body length (till U88), forming a characteristic suture-like pattern in the dorsal trunk region ( Figs 19A , 20A, E, F ). Three main types of dorsal body scales were recognized. (i) Head, neck, and trunk scales represent the most abundant type. They are very narrowly oblong and slightly increase in size in a posterior direction (head 3.9–4.6 × 1.2–1.3 µm, neck 4.1–4.2 × 1.0–1.3 µm, trunk 4.4– 5.0 × 1.2–1.4 µm) ( Figs 19B, E , 20C–E ). (ii) Upper-furcal scales are oblong, roughly hexagonal with all edges rounded. They form two horizontal rows (c. U87–U89) that extend from each lateral body side towards the furcal indentation forming a concave pattern ( Fig. 19F ). (iii) A pair of relatively large (5.11 × 3.30 µm) and oval scales is situated dorsolaterally at the transition between the furca base and the furca appendages ( Figs 19A, H , 20F ). In addition, three pairs of oblong, posteriorly truncated, keeled scales cover the ventral and ventrolateral sides of the furca appendages ( Fig. 19G ).

Ventral ciliary bands and ventral interciliary field

Ventral ciliary bands commence almost right behind the hypostomium. The anterior region of ventral ciliary bands is only slightly bifurcated (U7–U9) by contrast to He. kolickae ( Fig. 20E ). Ciliary bands extend till U88. The ventral interciliary field is almost naked but one pair of oblong scales, which are located on the ventral side of the furca base.

Distribution: Heterolepidoderma macrops has been recorded in Poland ( Kisielewski 1981), France ( Grilli et al. 2008), Sweden ( Kånneby 2011, Kånneby et al. 2012), Germany, and also possibly in Russia, United States, and Japan (Schwank 1990).

Figures

Figure 19. Heterolepidoderma macrops. A, dorsal overview showing the keel pattern. The body is about 120 µm long and has a slender tenpinshaped silhouette, with a clearly defined head region, a narrowing neck, and a bulbous trunk.The furcal indentation is narrowly helmet-like in shape.The furca branches bear well-developed adhesive tubes.B, head dorsal scales are keeled and oblong.C, mouth and under-mouth region.D, sensory bristle arises from a bulbous papilla. E, trunk dorsal scales are keeled and oblong.F, upper-furcal scales are keeled, oblong, and roughly hexagonal with all edges rounded.G, furca appendage ventral scales are keeled and oblong with a truncated posterior end.H, furca base dorsal scales are relatively large and oval.ceph, cephalion; ct, cuticular teeth; hs, hypostomium; rr, rod-like reinforcements.Scale bar = 50 µm.

Figure 20. Heterolepidoderma macrops. A, lateral overview showing the internal morphology.The pharynx extends from c. U3 to U27, is 35 μm long and 5.9–8.6 μm wide, and smoothly continues through the pharyngeal-intestinal junction to the differentiated anterior section (U28–U31) of the intestine, which extends from U32 to U85. B, detail of the head region showing the cephalion with a free posterior edge. The mouth ring is oval, approximately 6.9 μm in the largest diameter, and located ventroterminally at U1–U4. C, sensory bristle arises from a bulbous papilla.D, trunk dorsal scales are keeled and narrowly oblong. E, ventrolateral view of the anterior body region.Note the mouth ring and the hypopleurae. F, dorsolateral view of the posterior body region.Arrowhead denotes the relatively large and oval scale at the transition between the furca base and the furca appendages.at, adhesive tube; ceph, cephalion; hyp, hypopleura; m, mouth; s, sensory bristles; sc, sensory cilia.Scale bars = 5 µm (C, D), 10 µm (B), 15 µm (E, F), 25 µm (A).