Kijanebalola devestiva Todaro, Perissinotto & Bownes 2013

This description is mainly based on an adult specimen, 267 μm in total length (TL, posterior spines excluded). The body is roughly barrel-shaped with the head weakly separated from the trunk by a slight neck constriction and the posterior trunk region rounded-off, without paired lateral projections but exhibiting medially a group of five spines. Body widths at the head/neck/trunk/caudum are 57/55/90/32 μm, at U09/14/52/97, respectively. The head is provided with a pair of club-like tentacles projecting antero-laterally; they are 26 μm in length and insert ventro-laterally at U07; the hypostomion is absent; a shallow cephalion (10 × 4.5 μm) is appreciable only under SEM (Figure 5C). Under dissecting microscope, the animals appear swimming slowly in a rectilinear direction, with some following loose helicoidal trajectories. When purposely stimulated with a needle, specimens react by escaping aside, but never retracting the head inside the body; by contrast, most of the fixed specimens appear to have the head retracted to some extent (Figure 6A). Cuticular armour. The body is covered by a smooth cuticle, except for a minute patch of keeled scales located on the ventral side of the posterior trunk region, at U93 (Figures 1B, 2E). The scales, arranged in 5–7 columns of 3–5 scales each, are very small (ca 1 μm) and may go undetected under light microscopy (DIC); when observed with a scanning electron microscope, they appear roughly triangular in shape and their keel continues in a proportionally long spiny process (Figure 6C). Five robust terminal spines, 15–24 μm in length, ornate the posterior end of the trunk; they are inserted dorsally to the anus (Figure 6B, D). Ciliation. Locomotory cilia are arranged in tufts and interrupted bands around the head and paired transverse bands along the trunk (Figures 1, 2A–E, 5A, B). Most of the cephalic cilia have a ventral or ventro-lateral distribution; however, a precise organization is difficult to see due to their high density and relatively long span (16-18 μm in length). From anterior to posterior end, it is possible to discern the following groups: a pair of antero-lateral tufts, a median ventral band, a pair of lateral bands extending ventrally and dorsally, followed by a pair of ventro-lateral tufts (Figure 1). The trunk ciliature consists of four pairs of oblique short bands, with first (U32) and fourth (U94) inserted dorso-latero-ventrally, the second (U59) inserted latero-ventrally and the third (U66) latero-dorsally (Figures 1, 2D, E, 5A). Three pairs of sensory bristles (14–16 μm in length) are present on the dorsal side at U12, U22 and U92, respectively (Figures 1A, 4B, C). The bristles of the first two pairs emerge from round pits, while posterior bristles originate directly from the cuticle and are flanked by two anteriorly-converging keels. Presence of additional sensory bristles hidden among the cephalic locomotor ciliation cannot be excluded. Digestive tract: The strong mouth ring is terminal and about 13 μm in diameter; it appears slightly protruding down forward and is reinforced inside by 17–20 thick longitudinal cuticular ridges, which protrude externally and bend on the outer contour (Figure 5). The pharynx is 64 μm in length and shows anterior and posterior bulbs separated by a noticeable constriction; the anterior bulb, deprived of cuticular reinforcement, is roughly spherical (28 × 24 μm), while the posterior one (30 × 40 μm) is more nosecone-shaped (Figures 1, 4A); PhIJ is at U27. The intestine is straight; in the adult it appears impressively filled with green material (Figures 2A, 3A) while in juveniles it is packed with translucent globules (Figure 4A). Peculiarly, the anterior portion of the intestine extends forward encircling a large part of the posterior portion of the pharynx (about half the length of the posterior bulb), resulting in this region much wider than the pharynx itself (36 μm); at the PhIJ and for a short tract the intestine is about as wide as the pharynx (28–30 μm), then it widens again reaching a maximum width of 45 μm at about mid-body (U52); after this point the gut progressively narrows until it joins the 5–6 μm sub-terminal anus at U97 (Figures 1, 6B, C). Nephridial system. There is a pair of conspicuous protonephridia adjacent to the intestine; each protonephridium occupies an area extending from the PhIJ to about mid-body (U27-U53) and includes a clearly visible tubular canal containing two vibrating flagella, corresponding to the proximal canal cell lumen of Kieneke et al. (2008a). This canal is about 25 μm in length and runs almost parallel to the intestine, slightly converging towards the gut with its posterior portion (see Appendix: Figure 2S). Reproductive tract. All the adult specimens were in parthenogenetic phase, with respective eggs at different stages of development. Variability and remarks. The largest adult was about 310 μm in total length (terminal spines excluded) and was carrying a very big egg inside (73 × 107 μm, Figure 3A). Remarkably, the egg shell was ornated with spikes (Figure 3B); this is quite surprising because in freshwater Gastrotricha the shell ornamentation is believed to appear only after the egg has been laid, probably due to osmotic differences between the external vs internal milieu (Hummon 1984). The smallest animal was about 183 μm in total length and had no recognizable female gametes inside. Oocytes became appreciable as such in a 230 μm long specimen (Figure 4A).