Heterolepidoderma joermungandri Kånneby, 2011

Kolicka, Małgorzata, Kisielewski, Jacek, Kotwicki, Lech, Zawierucha, Krzysztof & Grzelak, Katarzyna, 2014, Checklist of Gastrotricha of the Polish Baltic Sea with the first reports of Heterolepidoderma joermungandri Kånneby, 2011, and Turbanella hyalina Schultze, 1853, Zootaxa 3869 (2), pp. 101-130 : 110-119

Heterolepidoderma joermungandri Kånneby, 2011

( Figs 4–10 ; Table 4 )

Localities: Sites 20, 25

Material: 9 specimens (6 adults and 3 juveniles), 8 photographed. The micro-photographs are available at the Natural History Collections at Adam Mickiewicz University in Poznań and in the collection of the first author.

Short description: Heterolepidoderma joermungandri Kånneby, 2011 , is a small-sized species. The body is stocky with a slightly marked neck constriction. The five-lobed head has a semicircular shape with a developed cephalion (U1–U2) and two pairs of pleuria (U3–U6). The cephalion and hypopleuria are well visible in the body outline, while the epipleuria are barely visible. The hypopleuria are approximately two times longer than the epipleuria. Two pairs of cephalic ciliary tufts are present. The first pair (four cilia per tuft) is located between the cephalion and the epipleuria (at U2); the second pair of ciliary tufts (five cilia per tuft) arises between the epipleuria and hypopleuria (at U4). In each ciliary tuft one cilium is considerably longer than the rest. Ocellar granules are absent. The mouth ring is situated subterminally at U2–U3 and possesses leaf-like reinforcements. The hypostomium is kidney-shaped and located at U4. There are weak transverse cuticular bars near the anterior hypostomium edges. The head is slightly delimited from the trunk by a neck constriction that gradually widens into the trunk. The trunk’s greatest width is found approximately two-thirds down the length of the body (ca. U68), then tapers into the furca (U88). The furcal branches are unparallel with thin, slightly tapering, adhesive tubes pointing somewhat outward at their distal ends.

The head, neck, and trunk on the dorsal, dorsolateral, lateral, ventrolateral, and ventral sides are covered with scales with pronounced keels and visible edges. The scales are arranged in 36–40 longitudinal alternating rows, with 23–24 scales in each row. The longitudinal rows of scales begin directly after the cephalion and pleuria. The median longitudinal row of dorsal scales is straight, except in the neck constriction, where it is replaced by two longitudinal rows of diagonally arranged scales, while the longitudinal rows on either side of the median converge toward the narrower parts of the body. A pair of large rounded keeled scales is present just at the base of the furcal branches at U87. Just posterior to these scales, an additional pair of keeled scales is situated on the inner edge of each furcal branch. The head and neck scales have a rounded rhomboidal shape and prominent keels. In the trunk, the dorsal, dorsolateral and lateral scales are hemi-elliptical in shape with prominent keels. Two pairs of sensory bristles are present: the anterior pair anchored by papillae (at U23) and the posterior pair anchored by doublekeeled scales (at U85).

On the ventral surface, the longitudinal ciliary bands start directly after the hypostomium (from U4). The pharynx section (from U4 to U24) of the interciliary field is naked, without any scales. The intestinal section of interciliary field (from U25 to U87) is covered with one-lobed keeled scales arranged alternately, close and next to one another. These scales have the shape of elongated, narrow ovals ( Figs. 4 C, 8C, 9E). The sizes of interciliary field scales increase from the beginning to the end of intestinal section. Only the keels are clearly visible, and they are situated in alternating longitudinal rows of 9–10 scales. The ventral terminal scales of the interciliary field are arranged in two pairs and consist of scales that are significantly longer than the other interciliary scales. They are of an oval, elongated shape and are situated at U87. The ventral terminal scales possess keels and straight spines extending beyond the furcal indentation.

The pharynx has a well-developed anterior dilatation and a posterior dilatation that is wider than the anterior dilatation. Cuticular reinforcements are present in the anterior dilatation. These reinforcements are composed of two weakly developed merged rods. The pharynx is connected via the pharyngeal intestinal junction to the straight intestine without a separate enzymatic section.

Taxonomic remarks: The specimens found in the Baltic Sea correspond well with the morphological features from the original description ( Kånneby 2011). However, adult individuals are noticeably larger than the Swedish specimens (121.2–124.9 Μm vs. 94–105 Μm), which could have been caused by specific living conditions (e.g., lower temperature fluctuations in a large basin, a different structure of the habitat, feeding conditions, or adaptation to brackish water). The sizes of the identified juvenile specimens (94.5–106.9 Μm) corresponded to the values given in the original description. Additionally, the number of scales in a single longitudinal row and the total number of longitudinal rows of scales was higher (23–24 scales vs. 22–23 scales and 36–40 scales vs. 34–38 scales, respectively).

This species was originally described from a freshwater habitat; thus, new records of H. joermungandri are based solely on morphological traits. However, if molecular data reveal great and discontinuous genetic variance between different populations of this taxon, the current opinion that the species is widely distributed may be refuted in favor of a species complex hypothesis.

Differential diagnosis: H. joermungandri most closely resembles H. macrops Kisielewski, 1981 , H. jureiense Kisielewski, 1991 , H. dimentmani Kisielewski, 1999 , and H. caudosquamatum Grilli, Kristensen & Balsamo, 2009 , but differs from:

H. macrops in terms of: body shape (the head of H. macrops is more rectangular, has clearly visible epipleuria and hypopleuria, and has more pronounced neck constriction and H. macrops has less marked furca base), body length ( H. macrops measures 127–148 Μm), and the type, shape, position, and number of scales (the scales have uniform shape on the whole body and lower keel, run nonparallel, i.e., they converge in the neck and trunk areas in H. macrops and are distributed in 45–52 longitudinal rows).

smallest and the largest structure found among all specimens measured, SD – standard deviation.

…… continued on the next page H. jureiense in terms of: body shape (the head of H. jureiense has three lobes with one pair of laterally protruding pleuria and a single pair of cephalic cilia, and it reaches the greatest width in the posterior section from ca. U75 to U85), the type and number of scales (the scale edges are barely visible, the scales have lower keel, and the first ventral row of the cuticular formations located near to the locomotory ciliary bands consists of delicate lamellae; scales are distributed in 35 longitudinal rows of 19–24 scales each in H. jureiense ), shape and type of posteriormost interciliary field scale (only one pair of terminal, spineless scales is in the ventral interciliary field in H. jureiense ), and the structure of the pharynx (the anterior pharynx dilatation is wider than the posterior dilatation in H. jureiense ).

H. dimentmani in terms of: body shape (the head of H. dimentmani has five clearly visible lobes with overlapping, protruding epipleuria and hypopleuria of equal sizes, and has the head much wider than the neck; the furcal branches run nonparallel and the tips of the adhesive tubes are located widely apart in H. dimentmani ), body length ( H. dimentmani measures 78–87 Μm), and the type, shape, position, and number of scales (the scale edges are unclear, the scales have lower keel and are distributed in 28 longitudinal rows in H. dimentmani ), the structure of the pharynx (the anterior dilatation is wider than the posterior dilatation in H. dimentmani ), and the structure of the cuticular reinforcement of the pharynx (the cuticular reinforcement of the pharynx comprises two pairs of strong, cuticular rods and two cuticular granules located near the bars in H. dimentmani ).

H. caudosquamatum in terms of: head shape (the head of H. caudosquamatum is shorter and more rectangular, has clearly visible epipleuria and hypopleuria), body length ( H. caudosquamatum measures 114–118 Μm), shape of hypostomium (trapezoidal shaped hypostomium is in H. caudosquamatum ), the type, shape, position, and number of scales (scales with spiny process (with short spines) are in H. caudosquamatum ; H. caudosquamatum has ventral longitudinal rows of scales with smaller scales with a lamellar expansion (hydrofoils scales); H. caudosquamatum has one unpaired, large, subrectrangular, smooth plate that lies at the furca indentation and has two small keeled scales located on the dorsal base of each furcal branch; the scales are distributed in 27–29 longitudinal rows with 25–27 scales in each row in H. caudosquamatum ), and shape and type of posteriormost interciliary field scale (narrow scales with keels, without spines are in H. caudosquamatum ).

Distribution: Previously recorded only in freshwater habitat from the Sphagnum spp. rock pool in small island Skarvesäter, Sweden ( Fig. 2 ).

Figures

FIGURE 2. Baltic Sea with points marking stations where Heterolepidoderma joermungandri Kånneby, 2011 was found. 1 — locus typicus, island Skarvesäter; 2 — Puck Bay.

FIGURE 4. Heterolepidoderma joermungandri Kånneby, 2011. Adult specimen—habitus.

FIGURE 5. Heterolepidoderma joermungandri Kånneby, 2011. Adult specimen. A—Dorsal view, B—View of internal morphology, C—Ventral view.

FIGURE 6. Heterolepidoderma joermungandri Kånneby, 2011. Specimen with mature egg—habitus. A—Dorsal view, B—View of internal morphology.

FIGURE 7. Heterolepidoderma joermungandri Kånneby, 2011. Specimen with mature egg. A—Dorsal view, B—View of internal morphology, C—Ventral view.

FIGURE 8. Heterolepidoderma joermungandri Kånneby, 2011. Juvenile specimen—habitus. A—Dorsal view, B—View of internal morphology.

FIGURE 9. Heterolepidoderma joermungandri Kånneby, 2011. Juvenile specimen. A—Dorsal view, B—View of internal morphology, C—Ventral view.

FIGURE 10. Heterolepidoderma joermungandri Kånneby, 2011. A—Dorsal view of scales in head region, B—Dorsal view of scales in posterior trunk region and in furcal base, C—Pharynx with cuticular reinforcements, D—Dorsal view of scales in trunk region, E—Ventral view of scales of interciliary field.

Tables

TABLE 4. Morphometric parameters for Heterolepidoderma joermungandri Kånneby, 2011; N – number of specimens or structures analysed, Range – the

Character	N	Ranges on adults specimens	SD	N	Ranges on juvenile specimens SD
Body length	5	121.2–124.9	1.63	3	94.5–106.9 6.64
Pharynx length	5	32.1–32.6	0.21	3	30.8–31.5 0.36
Width of anterior pharynx thickening (a)	5	9.5–10.0	0.21	3	9.1–10.8 0.87
Width of pharynx narrowing that follows anterior thickening (n) Width of pharynx at its middle length (m)	5 5	6.8–7.0 7.4–8.0	0.07 0.25	3 3	6.6–7.3 0.87 7.5–8.0 0.25
Width of posterior pharynx thickening (p)	5	10.9–11.4	0.22	3	10.6–11.7 0.55
Length of cephalic bristles (anterior tuft)	5	(4.1–5.0)–(17.7–19.1)	0.42; 0.54	3	(4.0–4.8)–(16.8–19.1) 0.44; 1.17
Length of cephalic bristles (posterior tuft)	5	(5.6–7.1)–(18.9–20.3)	0.64; 0.58	3	(4.7–6.4)–(18.9–20.9) 0.85; 1.10
Hypostomium length	5	3.6–4.6	0.40	3	3.3–3.7 0.21
Cephalion length	5	6.0–6.4	3.8	3	5,8–6,4 0.31
Cephalion width	5	13.5–14.4	0.34	3	13.1–13.9 0.44
Diameter of mouth ring	5	5.3–5.7	0.15	3	5.1–5.4 0.15
Furca length	5	16.7–17.8	0.50	3	16.0–16.9 0.45
Length of adhesive tube	5	10.2–11.4	0.54	3	10.1–10.9 0.44
Head scale length	5	(1.8–2.3)–(4.1–4.8)	0.19; 0.34	3	(1.8–2.2)–(4.0–4.5) 0.51; 0.29
Head scale width	5	(1.0–1.4)–(1.8–2.3)	0.16; 1.47	3	(1.1–1.4)–(1.7–2.2) 0.15–0.25
Neck scale length	5	(3.2–3.5)–(4.7–5.6)	0.12; 0.39	3	(3.2–3.7)–(4.2–5.3) 0.25; 0.55
Neck scale width	5	(1.0–1.2)–(1.5–2.0)	0.08; 0.18	3	(1.0–1.3)–(1.4–1.7) 0.15; 0.15