Chaetonotus furcatus Kisielewski, 1991

Salgado, Kelly Fernanda Acosta, Minowa, Axell Kou & Garraffoni, André Rinaldo Senna, 2022, New records, neotype designation and DNA sequences of three species of Chaetonotus (Gastrotricha: Chaetonotidae) from Brazil, Zootaxa 5213 (2), pp. 101-129 : 117-122

Chaetonotus furcatus Kisielewski, 1991

(figs. 10–13, table 4)

Additional material examined

Photomicrographs of 1 specimen (adult), collected in an urban lagoon with floating vegetation ( Eichhornia sp. ) in Paulínia, São Paulo, Brazil (July 2017) available at the Museum of Biological Diversity - MDBio - IB/ UNICAMP, under access number ZUEC–PIC 437.

Emended diagnosis of the species

Chaetonotus from maximus group having body 134-199 μm long. Spined tree-lobed scales distributed in 15-18 longitudinal alternating rows, 15-18 in each. Dorsal spines straight, of equal thickness on their whole length, distally furcated, 6-12 μm long on trunk. Ventrolateral spines long, thin and usually lacking furcation. The rearmost lateral spines shorter than those from m id-trunk. Ventral field entirely covered with fine keeled scales having rudimentary spines or lacking spines at all; a pair of large keeled and spined scales occurs at the field end. Pharynx with a pair of cuticular rods.

Description

The description is based on one individual studied alive and documented digitally. The morphometric characteristics are shown in Table 4 .

Habitus

Tenpin-shaped body of 199 μm in length, pentalobed rounded head 16 μm long (U1-U19). Subterminal mouth (8 μm in diameter) (fig. 10 A-C).Two pairs of sensory tufts located lateroventrally. Strong cephalion (37 μm long and 19 μm wide). The epipleuria (U1–U10) smaller than hypopleuria (U11–U19) (fig. 10 A-B). Hypostome not observed. Head 22 μm in width (U18), neck 18 μm in width (U20), with slight constriction of 4 μm long marking neck (U30), trunk 30 μm in width (U49) and at the base of the furca 21 μm in width (U97) (fig. 10 A–C). V-shaped furcal slit, adhesive tubes approximately the same length (11 μm) one fairly distant from the other (24 μm) ( Figs. 11 A-F, 12, 13).

Scales

Body covered by 15 to 18 columns, with 15 to 17 scales per row not overlapping each other. Expanded trilobed scales with a well marked anterior lobe and long, narrow posterolateral lobes; the same shape throughout the body (figs. 10B). Dorsal scales increase in size from the anterior to posterior region: on the head 5 μm (U24), on the trunk 7 μm (U43) and in the posterior region 4 μm (U95). ( Fig. 10B ). One pair of double keeled scales with sensory cilia (15 μm, U94) at the dorsal base of the furca (U93), posteriorly 3 three-lobed scale keeled scales (11 μm, U96) ( Figs. 10D , 13 ). Three dorsolateral scales arranged in longitudinal rows measuring 14 μm (U97) (figs. 11A–F, 12).

Spines

All spines are inserted in trilobed scales departing from a single central point, but varying in appearance along the body. Dorsal spines basally thick, slightly curved and furcated at the apex (8 μm, U22) ( Figs. 10 B , 11 A-F, 12). Lateral spines heavily curved and distal half tapered towards the hair-like end (15 μm, U23)( Figs. 10B , 11F ). Dorsal spines progressively increase in length along the body 8 μm (U24), 10 μm (U43), 12 μm (U95). Lateral spines measuring 14 μm (U23), 15 μm (U52), 8 μm (U92).

Ventral interciliary area

Locomotor ciliary bands not clearly observed. Scales of the interciliary area unilobed with slight tips in the posterior region measuring 8 μm in length, and possessing short spines. One pair of keeled scales located at the base of the furca 11 μm long (U96) (figs. 10D, 13).

Internal Morphology

Pharynx of 26 μm length (U6 - U27), width of the anterior region 8 μm, mean region 9 μm, posterior region 12 μm, presenting clear dilation (fig. 11A). Narrow small pharyngeal intestinal junction with a diameter of 13 μm (U31) (fig. 10B).

Taxonomic comments

Kisielewski (1991) described the species Chaetonotus furcatus from bromeliads in the Juréia Ecological Reserve of the state of São Paulo, Brazil. Then, Kolicka (2016) found them again at The Palm House Botanical Garden in the city of Lódz, Poland, in an artificial environment in non-native plants imported from South America (see discussion for more details).

The presence of only one specimen found by us did not allow a complete comparison to draw conclusions, but the main features described by Kisielewski (1991) for Chaetonotus furcatus are observed in our specimens, such as cephalion and hyplopleura sizes, different patterns of dorsal and lateral spined scales along the body (especially spines that are equally thick along their length and have distal furcation) and ventral scales in the furca base.

The individuals observed in Poland have one specific morphological characteristic that differs slightly from the original description and our specimens. Kolicka (2016) stated that “lateral spines of the last pair on the trunk larger, more heavily curved, tapered towards the end in the lateral plane, distally bifurcated and extending almost to the ends of the adhesive tubes (U98)”, but it was neither mentioned by Kisielewski (1991) nor noted in our specimen.

Due to the lack of differences in the main taxonomic characters, there is no basis for concluding that the present recorded individuals represent distinct species.

Distribution

Brazil: São Paulo ( Kisielewski, 1991) and Paulínia (present study, Fig.14 ).

Figures

FIG. 11. Chaetonotus furcatus, light microscopy photomicrographs (DIC). A–F. Distinct optical focal plans of the posterior body end, dorsal view. Ks: Keeled scale, Lt: Lateral spine, Psc: Posterior sensory cilia, St: Dorsal spined scales. Scale bars: A–F, 20 μm.

FIG. 10. Chaetonotus furcatus, light microscopy photomicrographs (DIC). A. Dorsal view of the anterior region, B. Detail of the spined scales in the anterior dorsal region, C. Detail of the pharynx, lateral view, D. Ventral view of the posterior ventral end. Asc: Anterior scales, Ce: Cephalion, Epi: Epipleura, Hyp: Hypopleura, Ks: Keeled scale, Pha: Pharynx, Si: Spines, St: Dorsal trunk spined scales, Vs: Ventral scales. Scale bars: A–D, 20 μm.

FIG. 13. Chaetonotus furcatus Kisielewski, 1991, schematic illustration. Ventral view of the ventral posterior end, with ventrolateral spined scales and interciliary keeled scales. Scale bar: 20 μm.

FIG. 14. Distribution of three species of Chaetonotus in South America. Green: Chaetonotus dadayi, Blue: C. paucisquamatus, Yellow: C. furcatus.