Dendroichthydium silvaticus, Minowa & Kieneke & Campos & Balsamo & Plewka & Guidi & Araújo & Garraffoni, 2025

Dendroichthydium silvaticus comb. nov. ( Varga, 1963)

( Figs 7–9)

Sononomo: Chaetonotus (Chaetonotus) silvaticus ( Varga, 1963) in Kisielewski 1997: 149.

Aspidiophorus silvaticus Varga, 1963: 210 View in CoL .

Emended diagnosis

Elongated, fusiform body measuring 85–250 μm in length. Head oval, without any visible lobes or notches in outline, with strong neck constriction and evenly widening body width towards mid-trunk. Distinctly separated narrow cylindrical furcal base, very long and ventrally and slightly outward-curved adhesive tubes, distally tapering to a blunt end. Wide, anteriorly positioned cephalion. Small elliptical epipleura and slightly smaller rounded posterior hypopleura. Rod-shaped hypostomium close to the mouth. Dorsal and lateral body covered with 40–60, evenly arranged columns of pedunculated scales. Furcal base dorsally covered by four or five alternating columns of five short-spined scales. Ventral interciliary field is covered by several transversal rectangular plates from the pharyngeal region to the furcal base.

Head ciliature consists of scarce cilia organized in four sets of a few cilia each: three lateral tufs adjacent to each cephalic plate and a fourth ventral suboral tuf adjacent to the mouth edge with very short cilia. Te subterminal mouth is oval, with a small buccal cavity. A paired group of granular formations is laterally adjacent to the mouth opening. Ventral locomotory cilia form two longitudinal bands from the mouth ring to the furcal base. Te longest cilia are on the anterior part, and the length of the cilia decreases evenly to become very short in the posterior part of each band. Tere are two short sensory bristles at the cylindrical furcal base and at the base of the adhesive tubes. Te pharynx is 33 μm long, cylindrical, and with slight widening at both ends; the pharyngeal–intestinal junction is at U25; the intestine is cylindrical and wider than the pharynx, and the anus is ventrally situated. A fully mature, oval-shaped egg, sometimes a pair of eggs, fills more than half of the body, with a very thick shell bearing small spikes.

Locality

MichaelPlewka:treemossfromforestsinHatingenOberstueter, North Rhine-Westphalia, Germany, Moos in Wildenloh Edewecht, Germany; Sphagnum moss, Helvete, Norway.

Material examined

Tree specimens (adults) in total, all photomicrographed.

Redescription

Dendroichthodium silvaticus has a slender, fusiform body ( Figs 7–9) 85–250 μm in length. Te head is wide, with a diameter of 22 µm at U10, and gradually narrows towards the neck constriction at U26 (minimum diameter of 16 µm), strongly marked against the widening trunk ( Figs 7–9). Te trunk is stout and elliptical, only slightly wider than the head (widest at U55, at ~40 µm), and gradually tapers towards a sharply separated and highly characteristic narrow cylindrical furcal base (U77). Te adhesive tubes are only slightly set apart and point outwards. Tey are long and ventrally curved, with a well-marked proximal bulb, gradually tapering distally towards a blunt end ( Figs 7A–D, 8A). Te head is anteriorly broad, oval, rounded in front, and from a dorsal view without visible epipleura and hypopleura ( Fig. 8). Te small cephalion (U01–U02) covers the dorsal and anterior part of the head, clearly visible by the absence of the dorsal pedunculated scales, and is ~14 µm in width ( Figs 7B, 8B, C). Tere are small elliptical lateral epipleura (7 µm long) and posterior ventrolateral hypopleura (6 µm long). Te hypostomium is transversal and rod shaped (3 µm in diameter), posteriorly adjacent to the mouth ring (U03). Te subterminal mouth is wide, with a large oral cavity having long and strong, finger-like inner reinforcements, but without cuticular teeth ( Figs 8D, 9D). Ocellar granules are absent. Te pharynx (U06–U29) is cylindrical, narrow (diameter of 40 µm), and long, without visible dilatations ( Figs 7A, 8A, C, 9D). Te pharyngeal–intestinal junction is subtle and slightly posterior to the neck constriction at U26 ( Figs 8A, 9B–E). Te intestine is without separated sections.

Cephalic ciliature consists of three paired ciliary tufs ( Figs 7A, B, 9A). Te anterior tufs emerge dorsolaterally, lateral to the cephalion (U01), with two extremely long tactile rigid bristles pointed anteriorly. Te second tufs emerge ventrolaterally, between the epipleura and hypopleura (U02), and the third tufs are ventral and emerge laterally posterior, adjacent to the hypopleura, with long cilia perpendicularly oriented outwards (U05). Te ventral suboral tuf emerges laterally adjacent to the edges of the mouth with very short sensory cilia. Tere are ventral cephalic locomotory cilia in three paired tufs along the pharyngeal region at U10, U15, and U19 ( Fig. 9A). Ventral locomotory cilia form two longitudinal bands running from the mouth ring area at U35 to the separated furcal base at U77 ( Figs 7D, 9C).

Te dorsal, lateral, and ventrolateral body is evenly and densely covered with small, one-lobed oval pedunculated scales, clearly visible on the outermost edge of the body ( Fig. 8A). Te upper plate of the scale is very thin, oval (2 µm long), and connected to a rather thick peduncle. Te scales are distributed in 40–60 alternating columns, with 41 scales in the central column ( Fig. 9A). Scales are closely located to one another, without gaps or overlaps between individual scales ( Figs 7B, 8A, B). Te dorsal region of the separated narrow cylindrical furcal base is armoured with four to five alternating columns of five scales each, and laterally covered by a very large and wide smooth scale (without a keel); the ventral area is naked. Te ventral interciliary area is covered by 35 short but wide rectangular plates from the neck constriction (U35) to the trunk posterior rear end at the transition to the furcal base ( Figs 7D, 9C). Two pairs of dorsal sensory bristles are present ( Figs 7B, 8B, 9A). Te first pair is located on the neck (U27) and inserts directly on the cuticle at the head base. Posteriormost dorsal sensory bristles are inserted in the middle of the separated narrow cylindrical furcal base (U77), emerging from small papillae ( Figs 7B, 8A). Te egg-bearing specimens carry either a very large ovum that fills almost the whole trunk region or might have a pair of large eggs on either side of the trunk. At the mid-trunk at about U54, there must be a certain muscle (pair) that enables repetitive constrictions of that area ( Fig. 7C). Observations of living individuals showed this behaviour, with a frequency of contractions every few seconds. It seemed as if the mature egg was gently ‘kneaded’ by those contractions.

Remarks

Initially placed in the genus Aspidiophorus by Varga (1963), owing to its cuticular ornamentation, with the dorsal body covered by small, short-stalked scales, subsequent studies by Kisielewski (1991, 1997) suggested a taxonomic affiliation of this species within the genus Chaetonotus , leading to its formal transfer to Chaetonotus silvaticus , aligned within the subgenus Chaetonotus s.s. ( Kisielewski 1997, Balsamo et al. 2009). Tis reclassification was based on the presence of short-spined scales covering the dorsal part of the furcal base in Brazilian specimens; such spines/spined scales were already illustrated on the original holotype drawings ( Varga 1963) and in subsequent reports (e.g. Tretjakova 1989), but not mentioned explicitly in descriptions (see Kisielewski 1991). Now, we have been able to confirm that the furcal base is also adorned with small spined scales in German and Norwegian specimens (present study). Kisielewski (1991) identified his Brazilian specimens not explicitly as Chaetonotus (C.) silvaticus but as Chaetonotus (C.) aff. Silvaticus , based on the assumed absence of such spines on the furcal base in the European form, and explicitly claimed re-examinations of European specimens. Our current re-investigation of European specimens not only demonstrated the presence of spined scales on the furcal base, but, furthermore, revealed rectangular plates on the entire ventral interciliary field. Tis peculiar cuticular coverage of the ventral surface has not been reported for Chaetonotus (C.) silvaticus so far, neither from specimens of the type locality ( Varga 1963), nor from specimens sampled in different Polish peat bogs ( Kisielewski 1981). However, in the original description of Chaetonotus (C.) silvaticus (i.e. Aspidiophorus silvaticus ), Varga (1963) reports ‘big, very thin and loosely arranged scales’ on the ventral side. We are convinced that this was a misinterpretation of the rectangular plates, atributable to suboptimal microscopic equipment. Likewise, the reported absence of the ventral plates in Polish specimens is also rather weak ( Kisielewski 1981): ‘…they seemed to lack any large scales on the ventral field. It seemed to be bare in all the specimens studied’. Interestingly, even one of the co-authors of the present study did not recognize the presence of these plates when he made the microscopic images 17 years ago. We are convinced that specimens of the earlier records of this morpho-species from the type locality in Hungary and from the Polish peat bogs indeed possessed rectangular ventral plates. Of course, such an assumption also has to be verified by re-examinations of specimens from both localities. Although we have so far no DNA sequence data of D. silvaticus (all effort in 2023 to find fresh specimens in Germany for extracting genomic DNA failed), the overwhelming similarity (synapomorphic concurrence) to D. iborapora makes a relocation of C. silvaticus to the new genus well supported, even without molecular evidence yet.

DNA-based phylogenetic analysis

Te multi-gene phylogenetic analyses under ML and BI algorithms yielded topologies that are congruent with each other, with most of the common clades showing high nodal support ( Fig. 10, 11). Among the families analysed, the family Dasydytidae is shown as paraphyletic with species from Neogosseidae and some Chaetonotus lineages nested within, which, in turn, is nested in non-monophyletic Chaetonotidae . Except for Polomerurus Remane, 1927, Halichaetoderma Križanová & Vďačný, 2023 , Lepidochaetus Kisielewski, 1991 , and Bifidochaetus Kolicka & Kisielewski, 2016 , the majority of Chaetonotidae genera represented by two or more terminals in the analyses are not monophyletic, with members of Aspidiophorus , Chaetonotus , and Ichthodium scatered along the evolutionary tree, with alliances between different genera. Concerning Brazilian D. iborapora , both analyses (ML and BI) strongly indicate (bootstrap> 99 and Bayesian posterior probability = 1) it to be a sister-group of Ichthodium skandicum Kånneby, Todaro & Jondelius, 2009 , within a group containing Bifidochaetus and various members of Aspidiophorus and Chaetonotus , with monophyletic Lepidochaetus as the outermost group.