Heterolepidoderma sinus, Kolicka, Małgorzata, Jankowska, Emilia & Kotwicki, Lech, 2015

Kolicka, Małgorzata, Jankowska, Emilia & Kotwicki, Lech, 2015, Baltic Sea Gastrotricha — one new species and one new record of Chaetonotida from Poland, Zootaxa 4027 (4), pp. 487-508 : 489-500

Heterolepidoderma sinus spec. nov.

( Figs. 1–6 ; Table 1 –2)

This new species has been described by the first author (M. Kolicka).

Locality. Southern Baltic Sea, outer Puck Bay, Jastarnia (N54° 41.4 E 18°40.9)

Material. Twelve specimens (11 adult and 1 juvenile), including 7 photographed. The micro-photographs are available in the Natural History Collections at Adam Mickiewicz University in Poznań under access numbers NHC-GHS- 10-1-10 /h (holotype) and NHC-GHS- 10-11-15 /p (paratypes) and in the author's collection.

Etymology. From Latin sinus , ‘ bay,’ referring to the place where the species was found.

Diagnosis. Body length from 102.0 to 128.5 Μm. Stocky body. Head short, five-lobed. Cephalion wide; epipleuria small, weakly marked in the head outline; hypopleuria large, convex and clearly marked. No ocellar granules present. Hypostomium large and rectangular. Pharynx narrow, with anterior and posterior dilatations. The anterior dilatation is stronger than the posterior one. Inside the anterior pharynx dilatation a strong cuticular reinforcement, composed of two thick rods connected at a right angle and a thinner transverse bar. Scales form 35– 39 individual longitudinal rows, 23–27 scales in each. Scales located close one to another. Their edges juxtaposed but do not overlap. Scales have a strong, long keel that continues into a short, vestigial spine. Two types of lamellae are present: triangular small lamellae that emerge from lateral scales and large, long lamellae that emerge from ventral scales located directly at the ciliary bands. Ventral interciliary field is covered from the beginning of the anterior pharynx dilatation with narrow, oval scales with long clear keel and a thin, straight spine. Three pairs of terminal scales of the ventral interciliary field are oval and without a posterior notch and have long keels and straight spines.

Description. Heterolepidoderma sinus spec. nov. is a species with a stocky body, clearly marked neck constriction and a narrow furca base. The head is short, blunt and five-lobed. The cephalion (U1–U3) is wide and short ( Table 1 ), and adheres to the head along its entire length. Epipleuria (U4) are very small and weakly marked in the head outline. Hypopleuria (U4–U10) are large (over five times larger than the epipleuria), strongly convex and clearly marked in the body outline. Epipleuria are located on dorsolateral and lateral body sides. A greater part of hypopleuria are located dorsally, dorsolaterally and laterally, with only a small part of them located ventrolaterally and ventrally. The hypostomium (U6–U9) is large, rectangle-shaped with rounded edges and has no reinforcements. Two pairs of cephalic ciliary tufts, four cilia each, are present. The anterior tufts emerge dorsally between the cephalion and epipleuria on U3. The first cilium in both anterior tufts is the shortest. Two subsequent cilia are longer and similar in length. The fourth cilium is the longest. Posterior tufts emerge ventrolaterally from the notch between the epipleuria and the hypopleuria on U4/5. The first cilium in both posterior tufts is the shortest. The second cilium is much longer than the first one. The third cilium in both tufts is shorter than the second one. The fourth cilium is shorter than the third one but longer than the first one (see Table 1 ). Ocellar granules are not present. The mouth ring is large, located subterminally on U3–U5 and has strong, thick cuticular reinforcements. Short cuticular mouth bristles are present inside the mouth ring. Suboral bristles are present around the mouth ring. The pharynx (U3–U28) is narrow and has anterior and posterior dilatations. The anterior dilation is clearly marked and slightly wider than the posterior one ( Table 1 ). The posterior dilatation is weakly marked. A strong reinforcement is present inside the anterior dilatation at U5–U8, composed of three cuticular rods: two thick, slightly curved rods connected to each other anteriorly at a right angle and a thinner transverse rod that connects the free postero-lateral edges of the two thick rods ( Fig. 6 B). The pharynx connects to a straight intestine (which extends from U29 to U85) through the small and narrow pharyngeal intestinal junction (U28). The intestine has a distinct short anterior separate section different in form of morphology that adheres directly to the posterior end of the pharynx.

......conitnued on the next page ......conitnued on the next page The head is wide, and separated from the trunk with a clear neck constriction ( Figs. 1 , 3–5). The neck transitions into the trunk, which gradually widens to the largest trunk diameter at approximate two-thirds of the length of the trunk (ca. U63). The trunk then gradually narrows up to a clearly marked furca base at U85. Furcal branches are set wide apart (at a distance equal to the width of the trunk at its widest point) ( Figs. 1 , 3). The furcal indentation is parabolic, and the ends of adhesive tubes point outwards ( Figs. 3, 6 A). Furcal appendages are relatively short and conical. Adhesive tubes are long and thin with slightly curved terminal segments and do not taper at the ends. The ends of the adhesive tubes are slightly rounded.

The entire body, except for the ventral interciliary field, is covered with one-lobed scales with a strong, high keel that extends along the entire length of the scale and transitions into a short vestigial spine. The vestigial spines slightly and gradually lengthen from the beginning of the head to the widest part of the trunk. Scales form 35–39 longitudinal alternating rows of 23–27 scales per row. The scales on the head and neck are positioned diagonally in the form of rounded arches that converge at the midline of the head. A median row of scales is absent on the posterior head and on the neck regions, instead of one, there are two median longitudinal rows of scales which are positioned relative to each other alternately ( Fig. 1 ). Subsequently, the longitudinal rows of scales on the trunk run parallel to the central row. On the posterior trunk region, before the furca base, the rows form straight arches that gradually converge on the central row of scales. Scales are located close one to another. Their edges meet but do not overlap. Scales differ morphologically in particular body regions. The scales on the head and neck are shaped like narrow, elongated triangles with rounded edges, and they gradually change their shape towards the trunk, transitioning into strong, narrow trapeziums with rounded edges. A single large scale shaped like a rounded triangle is located dorsally, in the central row of scales on the furca base (on U86–U88) ( Figs. 1 , 6 A). The tip of the single triangular scale points towards the inner furcal indentation. Two pairs of scales completely different from other scales are located on the dorsal and dorsolateral sides of the furcal branches ( Fig. 6 A). The first pair is located dorsolaterally on furcal appendages at U86–U88. The scales in the first pair are large and spineless, shaped like circles and have a strong keel that runs along their entire length. The second pair of scales is located dorsally on the inner side of furcal appendages (intrafurcal scales) on U88–U90. These scales are spineless, shaped like long, narrow rectangles with rounded edges and have a strong keel that runs along their entire length ( Figs. 1 C, 4C). Scales with small, triangular lamellae are located in three paired longitudinal rows on both body sides along its entire length ( Figs. 1–5 ). Lamellae of a different type emerge ventrally from longitudinal rows of scales located closest to the ciliary bands. Each of these longitudinal rows consists of 33–35 scales with lamellae. The lamellae are large and long and have rounded edges. They reach beyond the body outline.

Scales differ in size through the body (see Table 1 , Figs. 1–3 ). The largest scales are located in the central longitudinal row on the trunk. The scales slightly and gradually become smaller from the dorsal side, through the dorsolateral, lateral, ventrolateral and ventral sides, up to the scales near ciliary bands. Furthermore, the scales become smaller from the head to the neck. The scales then become larger from the beginning of the trunk up to its widest point. Scales located beyond the widest point of the trunk become slightly smaller up to the furca base. Scales in the last longitudinal rows adjoining the ciliary bands are positioned diagonally, at an angle of approximately 30° towards the longitudinal body axis. The large lamellae originate from these scales (“hydrofoil scales”).

Locomotor ventral cilia form longitudinal bands that extend from U5 to U85 and two separate, oval patches located immediately beyond the hypostomium on U10–U11 ( Figs. 1 , 4 C). The longitudinal rows of cilia on the head and neck are wider than on the trunk. The ventral interciliary field is covered from about the beginning of the posterior pharynx dilatation (from U18) with narrow, oval scales with clear keels and straight spines. Scales on the ventral interciliary field gradually become larger from the beginning of the body to the widest part of the trunk. Beyond this point they slightly and gradually become smaller up to the furca base ( Fig. 1 C). This species has three pairs of terminal scales of the ventral interciliary field ( Fig. 1 ). The first scales are centrally located at U82–U86. These scales are large and shaped like elongated ovals with a strong large keel that runs along their entire length. They have long, straight spines that pass the contour of the furcal indentation. The second pair of scales is located laterally in relation to the first pair at U84–U86. Scales of the second pair are similar in shape to the scales of the first pair but are smaller and have perceptibly shorter spines that pass the contour of the furcal indentation. The third pair is located at U87–U89 laterally in relation to the first and second pairs, next to the inner edges of the ciliary bands. The scales in the third pair are shaped like narrow, elongated ovals and have strong, long keel that extend along their entire length and a short, straight spine.

The species has two pairs of dorsal sensory bristles. The first pair is located dorsolaterally on the neck (U26) and emerges from small, round papillae. The second pair emerges from scales with two rounded keels, located on the posterior part of the trunk (U82). These scales are shaped like rounded triangles and do not have a posterior notch.

Remarks. The main character which allowed classify the new species as a member of genus Heterolepidoderma Remane, 1927 is body covering by elongated and keeled scales without posterior notches (e.g. Remane 1927; Schwank 1990; Kisielewski 1997; Todaro et Hummon 2008).

The presence of scales with lamellae is not a typical trait of species of Heterolepidoderma (see more below), but instead is standard for another genus traditionally placed within the Chaetonotidae , i.e., Halichaetonotus Remane, 1936 . Scales with lamellae in other genera are found less frequently.

Among all known taxa, H. sinus spec. nov. is the only species that has two types of lamellae: lateral and ventral ( Fig. 2 ). Prior to this study, there were no described species that possessed scales with lamellae located laterally on the body. However, several species of Heterolepidoderma are known to possess scales with lamellae located ventrally. So far hydrofoil scales have been found in such taxa as: H. foliatum Renaud-Mornant, 1967 , H. contectum Schrom, 1972 , H. axi Mock, 1979 , H. jureiense Kisielewski, 1991 , H. lamellatum Balsamo et Fregni, 1995 and H. caudosquamatum Grilli, Kristensen et Balsamo, 2009 .

The presence of the cuticular reinforcement rods ( Fig. 6 B) inside the anterior pharynx dilatation is a trait often encountered in species Halichaetonotus , marine representatives of Heterolepidoderma and Aspidiophorus and some Chaetonotus . The cuticular reinforcement is also, albeit rarely, present in freshwater taxa, e.g.: Aspidiophorus squamulosus (Roszczak, 1936) ; Chaetonotus (Chaetonotus) eximius Kolicka, Kisielewski, Nesteruk et Zawierucha, 2013 ; Chaetonotus (Hystricochetonotus) furcatus Kisielewski, 1991 ; Chaetonotus (Chaetonotus) intermedius Kisielewski, 1991 Chaetonotus (Chaetonotus) pawlowskii Kisielewski, 1984 ; Heterolepidoderma dimentmani Kisielewski, 1999 ; H. jureiense Kisielewski, 1991 ; and H. joermungandri Kånneby, 2011 . Various taxa differ greatly from H. sinus spec. nov. in terms of the structure and shape of cuticular reinforcements of the pharynx ( Fig. 6 B).

H. sinus spec. nov. has a stronger, more clearly marked anterior pharynx dilatation than posterior one. This trait is common among numerous marine species, e.g. Aspidiophorus ornatus Schrom, 1972 ; Chaetonotus (Chaetonotus) apechochaetus, Hummon, Balsamo et Todaro, 1992 , Chaetonotus (Chaetonotus) tempestivus Mock, 1979 , Halichaetonotus etrolomus Hummon, Balsamo et Todaro, 1992 , Halichaetonotus thalassopais Hummon, Balsamo et Todaro, 1992 , Heterolepidoderma arenosum Kisielewski, 1988 , Heterolepidoderma contectum Schrom, 1972 , Heterolepidoderma clipeatum Schrom, 1972 , Heterolepidoderma foliatum Renaud-Mornant, 1967 and Lepidodermella limogenum Schrom, 1972 . This trait is also present in freshwater species that are considered as evolutionarily young and that likely underwent specialisation in marine waters to later colonise freshwater environments, e.g. H. dimentmani Kisielewski, 1999 (see Kisielewski 1999) and H. jureiense Kisielewski, 1991 , which was found in Brazilian mangrove (see Kisielewski 1991).

Differential diagnosis. Heterolepidoderma sinus spec. nov. most closely resembles marine H. axi Mock, 1979 , H. foliatum Renaud-Mornant, 1967 and H. contectum Schrom, 1972 , H. clipeatum Schrom, 1972 , brackish H. caudosquamatum Grilli, Kristensen et Balsamo, 2009 and H. jureiense Kisielewski, 1991 as well as freshwater H. lamellatum Balsamo et Fregni, 1995 and H. joermungandri Kånneby, 2011 . However all of this species differ significantly from new described (Table 2).

TABLE 2. Condensed comparison of the most important differential characters between Heterolepidoderma representatives the most similar to Heterolepidoderma sinus spec. nov. NA – data

available; – – not applicable

Character H. sinus spec. H. axi H. foliatum H. conectum H. clipeatum H. caudosquamatum H. jureienense H. lamellatum H. joermungandri

nov.

Body length (µm) 114.23– 110–130 70–80 115 125 114–118 80–112 74.6–92.0 94–105 128.45

Cephalic pleuria Cephalion Cephalion Cephalion Cephalion, Cephalion and Cephalion wide; Cephalion Cephalion Cephalion wide; wide; very narrow; wide; epipeuria, hypostomium epipleuria very small wide; wide; epipleuria very epipleuria epipleuria epipleuria hypopleuria absent; only and weakly marked epipleuria epipleuria and small and weakly very small and absent; and one paire of in the head outline; absent; hypopleuria marked in the head and weakly hypopleuria hypopleuria hypostomium large pleuria hypopleuria large and hypopleuria well marked in outline; marked in the unmarked; large and well absent present well marked; large and well the head hypopleuria large head outline; hypostomim marked; hypostomium present marked; outline; and well marked; hypopleuria present hypostomim hypostomim hypostomium hypostomium large and well absent present present present marked;

hypostomium

present

Furca length (µm) 17.52–19.30 ca. 16 ca.16–17 22 24 16–18 ca.17 8.5–11.3 13–15

Length of 12.15–13.94 10 ca. 13 NA 21 NA 9.5–11 7.5 7–8

adhesive tube

µm)

Lateral lamellae Present Absent Absent Absent Absent Absent Absent Absent Absent

presences

Ventral lamellae Present Present Present Present Present Present Present Present Absent

presences

Distribution and Emerge Present from Emerge From the From the Emerge ventrally Emerge Emerge –

type of ventral ventrally from the neck area ventrally from middle of the middle of the from entire ventrally from ventrally from

lamellae entire to the end of entire trunk and their trunk and their longitudinal rows of entire entire longitudinal trunk and longitudinal edges do not edges do not scales located closest longitudinal longitudinal rows of scales develop from rows of scales reach beyond reach beyond to the ciliary bands; rows of scales rows of scales located spines and located closest the lateral body the lateral body their edges do not located closest located closest closest to the keels; the to the ciliary edges edges reach beyond the to the ciliary to the ciliary ciliary bands; ends of bands; large lateral body edges bands; large bands; short, large and long spines and and long and and long and their edges do and have keels extend have rounded have rounded not reach rounded edges beyond the edges edges beyond the posterior lateral body lamella edge edges

Anterior dilatation Yes Yes Yes Yes Yes No Yes No,both No

stronger than dilatation are

posterior one similar

.......continued on the next page TABLE 2. (Continued)

Character H. sinus spec. H. axi H. foliatum H. conectum H. clipeatum H. caudosquamatum H. jureienense H. lamellatum H. joermungandri

nov.

Presents of Present Present Present Present Present Present Present Present Present

cuticular

reinforcements

on the

pharynx

Number of scales 23–27 23 20 15 20 27–29 19–24 22–27 22–23 single

longitudinal row

number of 35–39 25–27 27–28 NA NA 25–27 35 17–23 21–22

longitudinal

alternating rows

scales

of scales With strong, With a With strong, With keel that With long keel With strong, long Scale edges not With long keel With long keel and long keel that sharply cut long keel that continues into and without keel that continues clearly marked, and without without vestigial continues into posterior continues into a short, vestigial spines into a short, vestigial (only a strong vestigial spines spines a short, edge and a short, vestigial spine spine keel is

vestigial spine without vestigial spine marked), keels

vestigial without

spines vestigial spines

Alignment of Edges Edges Edges Edges overlap Edges overlap Edges juxtaposed but NA Edges Edges juxtaposed

scales juxtaposed overlap juxtaposed but do not overlap juxtaposed but but do not overlap

but do not do not overlap do not overlap overlap

Presence of a Present Present Absent Absent Absent Present Absent Absent Present

single scale of a

different type on

dorsal side of

furca base

Presence of oval Present Present Absent Absent Absent Present Absent Absent Present scales with strong

on the

dorsolateral side

furcal

appendages

.......continued on the next page TABLE 2. (Continued)

Character H. sinus spec. H. axi H. foliatum H. conectum H. clipeatum H. caudosquamatum H. jureienense H. lamellatum H. joermungandri

nov.

Presence of dorsal Present Absent Absent Absent Absent Present Absent Absent Present intrafurcal scales

Type of scales of Oval scales NA Rectangular – Onlykeels Only keels visible Only spineless Only spineless Only spineless ventral with long scales with visible keels are keels are keels are visible interciliary field clear keel and long clear keel visible visible a thin, straight and a thin,

spine straight spine

Number of 3 pairs 4 pairs 4 pairs 1 pair 2 pairs 2 pairs 1 pair 1 pair 2 pairs terminal scales of

ventral

interciliary field

Distribution of Two Two Two Two Two Two longitudinal Two Two Two longitudinal ventral locomotor longitudinal longitudinal longitudinal longitudinal longitudinal bands longitudinal longitudinal bands cilia bands and bands bands bands bands bands bands

small patches

near

hypostomium

Figures

FIGURE 1. Heterolepidoderma sinus spec. nov. Schematic drawings. A — Dorsal body view, B — Internal body view, C — Ventral body view. Light grey areas indicate the ciliary bands and patches.

FIGURE 2. Heterolepidoderma sinus spec. nov. Schematic drawing. The cross section of the trunk region.

FIGURE 4. Heterolepidoderma sinus spec. nov. — Holotype. A — Ventral body view, B — Internal body view, C — Ventral body view.

FIGURE 6. Heterolepidoderma sinus spec. nov. A — Dorsal view of posterior body end, B — Pharynx with cuticular reinforcements.

Tables

TABLE 1. Morphometric parameters for Heterolepidoderma sinus spec. nov.; N = 6 — number of specimens or structures analysed, Range—the smallest and the largest structure found among all specimens measured, SD—standard deviation.

Character	Holotype	Ranges on adults specimens	SD	Juvenile specimen
Body length	118.18	114.23–128.45	5.676	101.96
Pharynx length	31.11	30.52–32.20	0.580	31.71
Width of anterior pharynx thickening (a)	10.63	9.64–11.84	0.773	10.54
Width of pharynx narrowing that follows anterior thickening (n)	6.54	6.13–6.54	0.144	6.76
Width of pharynx at its middle length (m)	7.40	6.53–7.40	0.298	7.61
Width of posterior pharynx thickening (p)	9.35	8.54–10.54	0.726	9.28
Length of cephalic cilia (anterior tuft)	5.03–18.94	(4.61–5.99)–(18.03–20.66)	0.560; 0.907	5.12–18.95
Length of cephalic cilia (posterior tuft)	8.49–21.40	(8.49–9.95)–(20.95–22.77)	0.547; 0.755	7.61–19.8
Hypostomium length	5.35	5.28–5.96	0.253	5.22
Hypostomium length	9.58	8.67–9.58	0.336	8.42
Cephalion length	6.44	6.44–6.82	0.167	6.73
Cephalion width	13.61	13.33–13.88	0.225	13.42
Diameter of mouth ring	6.42	6.20–6.50	0.111	6.28
Furca length	19.30	17.52–19.30	0.651	18.95
Length of adhesive tube	13.94	12.15–13.94	0.654	12.69
Head scale length	2.42–4.95	(2.01–2.64)–(4.40–5.93)	0.229; 0.504	2.25–4.41
Head scale width	1.17–1.69	(0.94–1.50)–(1.39–1.93)	0.185; 0.175	1.06–1.51
Neck scale length	2.15–4.42	(1.77–2.42)–(4.31–4.66)	0.217; 0.139	1.98–4.16
Neck scale width	0.88–1.21	(0.78–1.13)–(1.17–1.63)	0.129; 0.167	0.83–1.26
Trunk scale length	2.62–6.23	(2.21–2.74)–(5.87–7.22)	0.157; 0.570	2.34–5.69
Trunk scale width	1.11–1.63	(0.84–1.11)–(1.34–1.84)	0.101; 0.177	1.01–1.47
Length of central, trilangular posterior scales	4.81	4.08–5.00	0.336	4.22
Width of central, trilangular posterior scales	5.57	5.13–6.76	0.604	5.08