Heterolepidoderma mariae, Garraffoni, André R. S. & Melchior, Marina P., 2015

Garraffoni, André R. S. & Melchior, Marina P., 2015, New species and new records of freshwater Heterolepidoderma (Gastrotricha: Chaetonotidae) from Brazil with an identification key to the genus, Zootaxa 4057 (4), pp. 551-568 : 555-558

Heterolepidoderma mariae sp. nov.

( Figs. 3–6 ; Tab. 2 )

Type material. Holotype. Photographs of one specimen (adult), collected from an urban lagoon on 26/Jun/2015, in floating vegetation with Eichhornia sp. in the city of Paulínia, Brazil, available at the Museum of Zoology, University of Campinas, Brazil, under accession number ZUEC GCH 19. Paratypes. Photographs of five specimens (adults), collected from an urban lagoon on 03/Mar/2015, in floating vegetation with Eichhornia sp. in the city of Paulínia, Brazil, available at the Museum of Zoology, University of Campinas, Brazil, under accession numbers ZUEC GCH 20, 21, 22, 23, 24 and 25.

Additional material. Three specimens were examined alive with a compound microscope and are no longer extant (collected at Broa Dam, city of São Carlos, Brazil); two specimens were prepared for SEM.

Etymology. The specific epithet honors Dr. Maria Balsamo, who has greatly contributed to our understanding of freshwater gastrotrichs. She was also very kind and helpful to the first author (ARSG) when he first started studying this tiny, funny-looking worms 7 years ago.

Autapomorphies. Dorsal body surface covered by keeled scales of three different shapes, on the head a thin line of cilia connecting the two lomgitudinal bands of ventral cilia, interciliary area with elliptical keeled scales with short spines, with pharyngeal field portion naked.

Diagnosis. Small species, 129–151 Μm in total length. Body width 9–11 Μm, 19–25 Μm, 27–31 Μm, 16–17 Μm and 11–14 Μm at head, neck, trunk, base of furca and adhesive tubes, respectively. Three-lobed head with developed cephalion, pleurae and hypostomium. Anterior sensory bristles anchored by papillae and posterior sensory bristles anchored by double-keeled scales. Straight furca with rather thin adhesive tubes pointing slightly outward at distal end. Dorsal body surface covered by keeled scales of three different shapes, distributed into 20– 22 longitudinal rows of 34–38 scales each. Columns converge on the narrow parts of the body. Ventral interciliary area with round keeled scales, pharyngeal field portion naked, and one pair of large keeled scales. Ventral ciliation in two longitudinal bands, connected in the anterior part of the body. Subterminal mouth. Pharynx 35–38 Μm in length, with anterior and posterior swellings.

Description. Description based on holotype. Heterolepidoderma mariae sp. nov. is a small-sized species, 138 Μm in total body length ( Figs 2–4 ). Head is three-lobed, epipleurae more developed than hypopleurae. Cephalion 9 Μm in width. Hypostomium 9.5 Μm in width, well developed without anterior teeth, upper part straight, lower part concave ( Figs. 4 E; 5B; 6A–B). One pair of cephalic ciliary tufts with two different sizes of cilia: 8, 15 Μm, respectively. Ocellar granules absent.

Body width 22 Μm at the head (U10), 20 Μm at the neck (U25), 29 Μm at the trunk (U54) and 13 Μm at the base of the furca (U80). Head slightly delimited from trunk by neck constriction that gradually widens into the trunk, which reaches its greatest width around U45–50. The trunk then tapers into a straight furca, 7 Μm in length, with rather thin adhesive tubes, 13.5 Μm in length, pointing slightly outward at their distal ends. Base of furca covered dorsolaterally, laterally and ventrally with keeled scales. Anterior and posterior sensory bristles present, anterior pair at U26–27 anchored by papillae and posterior pair at U84 anchored by double-keeled scales.

Dorsal body surface covered by 20–22 longitudinal rows of 34–38 keeled scales with visible edges ( Figs. 3 A; 4B; 5A; 6C–F). The median row of dorsal scales is straight, except in the narrowest part of the neck and the rearmost trunk region, where it is replaced by 4 to 6 rows of diagonally arranged scales. Three different dorsal scale shapes: a) head scales small, oval with trilobate keels, 2.3–2.5 Μm in length and 1.4–2.1 Μm in width ( Figs. 3 A; 4B; 5A; 6C); b) trunk scales elongate-oval with slight constriction in the median region, straight posterior end and trilobate keels, 4–6 Μm in length and 1.5–2 Μm in width ( Figs. 3 A; 4B; 5A; 6D–E); c) posterior body scales elongate-oval with fine keels drawing out into simple fine spines, 5 Μm in length and 2 Μm in width ( Figs. 3 A; 6D,F).

The interciliary area is covered by 5–6 longitudinal rows of 14 elliptical keeled scales with short spines (1– 1.5Μm), in each longitudinal row, with pharyngeal field portion naked. The last posterior row (including ventral terminal scales) consists of four larger keeled scales, with two different sizes (approximately 2,5 and 5 Μm in length). Ventral ciliation appears as two longitudinal bands that merge on the head, forming a transverse band of cilia ( Figs. 3 B; 4C–D; 5B; 6A,B).

Mouth subterminal, 4–6.4 Μm in diameter; pharynx 35–38 Μm in length with anterior and posterior swellings. Anterior region of pharynx without cuticular rods.

Some specimens were in parthenogenetic phase, with the egg (60–67 Μm in length) positioned laterally in the trunk region.

Remarks. The genus Heterolepidoderma includes 22 species that inhabit inland water. Among them, only Heterolepidoderma mariae sp. nov., H. majus , H. brevitubulatum Kisielewski, 1981 and H. jureiense have a clearly three-lobed head. H. jureiense can be excluded from further comparison as it is the only species with ventrolateral lamellae among these four species. Heterolepidoderma brevitubulatum has adhesive tubes extremely short and slightly bifurcate, whereas in H. mariae sp. nov. and H. majus , the adhesive tubes are at least 4 times longer and not bifurcate. Heterolepidoderma mariae sp. nov. can be distinguished from H. majus because it has a dorsal body surface covered by keeled scales with three different shapes, as well as a transverse band of cilia on the head connecting the two bands of longitudinal ventral cilia, whereas H. majus has only one type of keeled scales on its dorsal surface, and its two ventral bands of cilia separate.

Figures

FIGURE 2. Photos of some sampling sites for the present study. A) Biribiri State Park, Diamantina, State of Minas Gerais. B) Sempre-Vivas Federal Park, Diamantina, State of Minas Gerais. C – D) urban lagoon, Paulínia, State of São Paulo.

FIGURE 3. Schematic drawings of Heterolepidoderma mariae sp. nov. A) Dorsal view. B) Ventral view. The scales are not in scale. Scale bars: 25 Μm.

FIGURE 4. Heterolepidoderma mariae sp. nov. holotype. DIC photomicrographs: A) Habitus. B) Dorsal view of distribution and shape of scales. C) Ventral view showing the paired keeled scales at the base of the furca. D) Ventral view showing the interciliary scales. E) Ventral view showing the connection between the parallel rows of cilia. Scale bars: 22 Μm.

FIGURE 5. Heterolepidoderma mariae sp. nov. paratype. DIC photomicrographs: A) Dorsal view of distribution and shape of scales. B) Ventral view of distribution and shape of scales and cilia. White arrow indicates hypostomium. Scale bars: 22 Μm.

FIGURE 6. Heterolepidoderma mariae sp. nov. SEM photomicrographs: A) Ventrolateral view of anterior end of the trunk. B) Ventrolateral view of anterior end of the trunk. White arrow indicates the connection between the parallel rows of cilia. C) Close-up of dorsal region of anterior end of the trunk, showing the keeled scales. D) Dorsal view of distribution and shape of scales. E) Close-up of dorsal region of the trunk, showing the keeled scales. F) Close-up of dorsal region of posterior end, showing the keeled scales. Scale bars: A, B, 5 Μm; C, 4 Μm; D, 10 Μm; E, F, 2 Μm.

Tables

TABLE 2. Morphometrical features of Heterolepidoderma mariae sp. nov. X = mean; N = number of specimens measured.

Features	Range	X	N
Body length	129–151 µm	138.4	5
Length of adhesive tubes	11–14 µm	12.6	5
Pharynx length	35–38 µm	36.8	5
Diameter of mouth ring	4 –6.4 µm	5.2	5
Cephalion length	9–11 µm	9.8	4
Cephalion width	22–23 µm	22.3	3
Total number of longitudinal rows of scales	19–22	21	3
Number of scales in a single longitudinal row	27–30	28.5	4
Length of neck scales	2–3.5 µm	2.8	6
Length of trunk scales	4–6 µm	5.1	6