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

Dendroichthydium ibyrapora sp. nov.

( Figs 2–6; Table 2; Supporting Information, Table S3)

Morphological diagnosis

Dendroichthodium iborapora has a slender, fusiform body measuring 130–186 μm in length. Head oval, wide cephalion anteriorly located, large elliptical lateral epipleura and posterior, ventrolateral hypopleura. Hypostomium is reniform, posteriorly to the sub-terminal mouth ring, without internal cuticular teeth. Elongated elliptical trunk, with a sharply separated, narrow cylindrical furcal base, dorsally ornamented with four or five longitudinal columns of elongated scales with short simple spines. Long, laterally curved adhesive tubes, proximally broader and distally tapering to a blunt end. Pharynx narrow, with anterior and posterior dilatation; intestine straight, without differing sections, ending on the ventral anus at furcal base. Cuticular ornamentation is homogeneous, with well-organized, densely arranged small pedunculated one-lobed round to elliptical scales, distributed into 40–80 columns of 56–90 scales each, without gaps or overlaps. Te ventral field is covered with a column of 30 narrow rectangular plates from the pharyngeal region to the furcal base, with plates increasing in width towards mid-trunk, decreasing again towards the furcal base.

Molecular diagnosis

In the 18S rRNA gene, 36 of 1777 bp (2.0%) are diagnostic molecular characters (34: G, 42: C, 61: C, 62: A, 63: A, 76: C, 94: T, 105: T, 108: T, 118: A, 123: A, 141: G, 144: C, 150: G, 154: C, 171: T, 177: C, 277: C, 634: T, 652: C, 658: C, 660: A, 664: T, 687: T, 688: C, 701: T, 734: G, 796: T, 1073: C, 1080: C, 1368: C, 1395: C, 1533: A, 1553: A, 1568: T, 1569: A). In the 28S rRNA gene, 8 of 1292 bp (0.6%) are diagnostic molecular characters (458: A, 459: G, 460: C, 461: G, 464: A, 716: C, 761: C, 1106: G). In the COI mitochondrial DNA gene, 3 of 712 bp (0.4%) are diagnostic molecular characters (42: G, 143: T, 162: G). Te sequences of Dendroichthodium iborapora were compared with the closest sequences in ML and BI analyses: Bifidochaetus arcticus AMUMK 164 KP713403 View Materials , KP713404 View Materials ; Bifidochaetus veronicae HA2857 MN 496207, MN496274 View Materials ; Chaetonotus aff. heideri GA 61 MN496208 View Materials , MN496275 View Materials ; Lepidochaetus tirjakovae VR 1 MW826075 View Materials , MW826065 View Materials ; L. tirjakovae VR 4 MW826076 View Materials , MW826066 View Materials ; L. tirjakovae VR 9 MW826077 View Materials , MW826067 View Materials ; Lepidochaetus zelinkai TK 180 JN185486 View Materials , JN185527 View Materials ; L. zelinkai TK 181 JN185487 View Materials , JN185528 View Materials ; L. zelinkai TK 227 JN185497 View Materials , JN185534 View Materials ; L.zelinkai TK 94 JN185503 View Materials , JN185538 View Materials ; Lepidochaetus brasilense TK 223 JN185495 View Materials , JQ798658 View Materials ; Ichthodium skandicum TK 182 JQ798573 View Materials , JQ798645 View Materials ; I. skandicum TK 96 JQ798606 View Materials , JQ798673 View Materials ; I. skandicum TR 839 MN496211 View Materials , MN496278 View Materials ; and I. skandicum TR 93 MN496225 View Materials , MN496292 View Materials .

Autapomorphies

Very small pedunculated scales on the dorsal, lateral, and ventrolateral body; four rows of small but strongly spined scales on the narrow cylindrical furcal base.

Etymology

From Nheengatu (a Brazilian indigenous language from Tupi language branch, within Tupi–Guarani language family, also know as Modern Tupi), Ibora, meaning ‘tree’, and pora ‘inhabitant’, meaning ‘the tree-dweller’.

Examined material

Photomicrographs and video records from 10 specimens (3 adults and 7 subadults) in total ( Table 2; Supporting Information, Table S 3). Digital image data are available in the Museu de Diversidade Biológica at the University of Campinas under ZUEC-PIC 1087 (holotype) and nine accession numbers (ZUEC-PIC-1088–ZUEC-PIC-1096; paratypes), with additional video records under ZUEC-VID 1329–1335 at htps://www.ib.unicamp.br/museu_zoologia/ and in the authors’ collection. Afer observation, the physical specimens were preserved in ethanol, and four were used for DNA analysis (GenBank accession numbers PP694049–PP694056 and PP697535–PP697538) .

Type locality

Hoophila moss on a tree at Serra do Japi Biological Reserve , Jundiaí City, São Paulo State, Brazil, 23°14 ʹ 00.3″S, 46°58 ʹ 45.4″W GoogleMaps .

Description

Description based on adult holotype and two adult paratypes. Dendroichthodium iborapora has a slender, fusiform body ( Figs 2–4) 162–186 μm in length, measured from the anterior end to the posterior end. Te head is 29–43 µm wide, and the neck constriction is short and strongly marked, with a minimum diameter of 20–31 µm at the level of the pharyngeal–intestinal junction at U28 ( Figs 3A, 4A). Te trunk is elongated and elliptical, only slightly wider (with 41–65.9 µm, widest at U51) than the head, and gradually tapers towards a sharply separated and very characteristic narrow cylindrical, furcal base (U73). Te adhesive tubes are 28–39 μm long and curved slightly ventrally and significantly outwards, with a well-marked proximal swelling, and gradually taper distally. Both adhesive tubes insert close to each other directly from the furcal base ( Figs 3B, C, 4A).

Te head is broad oval, rounded in front, without visible lobes dorsally ( Figs 2, 3A). Te cephalion (U01–U02) is short and wide, close-fiting, inserted anteriorly on the head, visible on the dorsal head surface as a thin crescent, ~13 µm wide ( Figs 2A, 3A, 4A, 5A, B), clearly recognizable by the absence of the pedunculated scales ( Fig. 3C). Te large elliptical pleura are located laterally and ventrolaterally to the head, giving the impression of a five-lobed head ventrally ( Figs 3, 4B, 5A, B). Lateral epipleura are located posteriorly adjacent to the mouth ring (U03), followed posteriorly by ventrolateral hypopleura ( Figs 3, 4B, 5A, B). Te hypostomium at U05 is reniform, with a wider posterior edge with anterior reinforcements, giving a slight double-edged aspect ( Fig. 4B). Te sub-terminal mouth ring is ~10 µm wide and has long, finger-like reinforcements, without internal cuticular teeth ( Fig. 4B). Ocellar granules are absent. Te pharynx (U03–U28) is 34–45 µm long and cylindrical (11–14.9 μm wide), with slight dilatations at the anterior and posterior ends, with the posterior dilatation being slightly wider than the anterior one ( Figs 3A, 4A). Te pharyngeal–intestinal junction is at U28 ( Fig. 3A). Te intestine is straight and with an almost constant width of ~25 µm (U28–U72), probably with a ventral anus. Tree pairs of cephalic ciliary tufs are present ( Fig. 3). Te anterior tufs emerge dorsolaterally to the cephalion (U02), with numerous short cilia ~6 µm in length and one straight (≤22 µm in length) and a rigid bristle pointed anteriorly. One pair of suboral tufs of short cilia emerges laterally, adjacent to the edges of the mouth ring at the same position (U02), like the anterior tufs. Te third pair of cephalic ciliary tufs emerges ventrolaterally, between the epipleura and the hypopleura at about U05 ( Fig. 3B–D). Te cilia of those tufs are more than twice as long (~12 µm) as those of the aforementioned tufs. Ventral locomotory cilia are arranged in two segmented ventral longitudinal bands, a tuf posterior to the hypopleura at U25 with very elongate cilia arranged in an arc-shaped manner ( Figs 2, 3B) with nearly straight, ~22-µm-long cilia protruding almost perpendicular to the longitudinal axis of the body ( Fig. 4A, B), followed by the paired longitudinal bands, starting at U31 and running to U71 ( Fig. 4A, D).

Te dorsal, dorsolateral, lateral, and ventrolateral body surfaces are evenly and densely covered with pedunculated scales ( Fig. 5B), clearly visible on the outermost edges of the body ( Figs 2–5). Te lower plate is small, oval, with the peduncle inserted at its centre ( Fig. 5). Te upper plate of the scale is droplet shaped, with the wide edge facing anteriorly and with the peduncle inserting at the anterior edge ( Fig. 5). Te scales are distributed in 40–50 alternating columns, with 86–90 scales in the central column. Each scale is located close to its neighbours, without any gap, or overlaps with other scales ( Fig. 4C, D). Owing to the alternating arrangement of columns, the dorsal scales appear well organized in several diagonal rows that resemble the pineapple segment patern ( Figs 3, 4C, 5). Te scales show morphological homogeneity throughout the whole body, except for the dorsal side of the separated, narrow cylindrical furcal base ( Fig. 3A, C), which is armoured with four longitudinal alternating columns of four to five elongated and short-spined scales each ( Fig. 3A). Te entire lateral sides of the cylindrical furcal base are covered by a pair of 18-µm-long, keeled and deltoid-shaped scales ( Fig. 4E). Te ventral interciliary area is covered with ≤47 short and wide rectangular plates, starting posteriorly, adjacent to the hypostomium (U05), gradually increasing in width to the mid-trunk, then only slightly decreasing in width again towards the posterior end until the sudden narrower last plate (U70) close to the abrupt transition to the cylindrical furcal base ( Fig. 4D). Te pedunculated scales decrease in size from the dorsal to ventral body side, to the ventral scales located nearest to the ciliary bands, and they contour the ciliary bands from the mouth ring to the rear end ( Fig. 4D).

Dendroichthodium iborapora possesses three pairs of dorsal sensory bristles ( Figs 3B, 4A, C). Te first pair is located on the anterior head region (U05), the second pair on the dorsal neck (U24), and the posteriormost dorsal pair of sensory bristles is inserted at the furcal base (U77), emerging from thin, elongated papillae ( Fig. 4A). Te egg-bearing specimens (N = 3) have a very large oval egg, filling more than half of the body. Neither X-organ-like structures nor packets of presumptive sperm were observed. At the mid-trunk, there is a set of muscles (see next section) that allow the animal to constrict the middle of the body, giving the impression of having two eggs ( Figs 2A, 3A).

Muscular architecture: Te muscular architecture observed in somatic and splanchnic regions consisted of longitudinal, circular, and helicoidal muscles ( Fig. 6). In the splanchnic region, ≤40 complete circular muscles occur along the whole length of the pharynx ( Fig. 6A, C). Complete circular muscles are not present in the intestinal region. Helicoidal muscles are very thin and extend from the mouth ring up to the first one-third of the gut, wrapping all somatic and splanchnic longitudinal muscles in the pharyngeal region ( Fig. 6C).

Longitudinal muscles are present in dorsal, ventral, and lateral positions and span the entire body length ( Fig. 6A). Longitudinal muscles insert anteriorly in the head region close to the mouth opening and extend posteriorly into the cylindrical furcal base, where they fuse in a single complex. Dorsally, a pair of longitudinal muscles inserts anteriorly on the mouth ring and extends posteriorly to the furcal base. A pair of thin muscles (Rückenhautmuskel) branches off from the later at U33, forming a dorsal arc, and apparently connects to the original muscles again at U76 ( Fig. 6A, B). Te pair of lateral longitudinal muscles ( Fig. 6A, B) insert slightly laterally in the head region at about U01 and extend into the furcal base, where they insert close to the base of each adhesive tube (U90). One pair of ventral longitudinal muscles ( Fig. 6A) line up from the mouth opening posteriorly along the intestine until the mid of the furcal base. Both ventral longitudinal muscles and dorsal longitudinal muscles, apart from the arch-like branch of dorsal longitudinal muscles, are in a splanchnic position throughout their course through the animal ( Fig. 6A, B). Although the paired lateral longitudinal muscles are also in a splanchnic position in the pharyngeal region, they curve laterally in the intestinal region (trunk) and occupy a rather somatic position there.

Two dorsal to dorsolateral semicircular muscles were observed, one in the mid-intestinal region (U55) and a second pair in the furcal base (U95) ( Fig. 6A, B). Te later could be responsible for the constriction between the rear trunk and the cylindrical furcal base, and the former pair of semi-circular muscles might be related to the constriction at the mid-trunk that was observed in some specimens (see above). Inside the adhesive tubes, also some weak signals of stained actin filaments were recognizable ( Fig. 6B, D), probably cytoskeleton rather than muscles. Additional muscles could not be observed; however, it needs to be mentioned that the animals used in this study showed some paterns of degradation.

Remarks

Te newly described species has a close affinity to Chaetonotus (C.) silvaticus ( Varga, 1963) , which is diagnosed and re-described in the next section. Both species share the following traits: (i) the distinctly separated narrow cylindrical posterior furcal base; (ii) the two long and externally and/or ventrally bent adhesive tubes; (iii) a dense cuticular ornamentation exhibiting a well-organized arrangement of small pedunculated scales; and (iv) followed by a sudden change of armature on the furcal base. Furthermore, both species share an interciliary armature consisting of short and wide rectangular plates, very difficult to see, and overlooked in previous records of C. (C.) silvaticus (see Kisielewski 1991). Te most important difference with respect to C. (C.) silvaticus are the cuticular structures of the body, which are significantly thinner in D. iborapora , with a higher number of columns of scales (60–80 vs. 40–60) and with more scales in each column (56–90 vs. 40). Kisielewski (1991) reports Brazilian members of Chaetonotus (Chaetonotus) aff. silvaticus in ground Sphagnum cushion. Te later species shares the cuticular ornamentation of the caudal furcal base armoured with short spines with D. iborapora , but contrasts it for the short spines covering the whole dorsal cuticle ( Kisielewski 1991, 1997). Also, similarities between the new species and members of the marine Paucitubulatina genus Caudichthodium Schwank, 1990 exist and, furthermore, with the rare Asian limnetic Proichthydiidae Remane, 1927 species Proichthodioides remanei ( Sudzuki, 1971) and the Neotropical limnetic species Proichthodium coronatum Cordero, 1918. Tese and the possible systematic and phylogenetic inferences are addressed in the Discussion section below.