Haltidytes ooeides (Brunson, 1950)

Minowa, Axell K. & Garraffoni, Andre R. S., 2018, Redescription of the dasydytid gastrotrich Haltidytesooeides (Brunson, 1950) based on type material, ZooKeys 785, pp. 41-48 : 42

Haltidytes ooeides (Brunson, 1950) Figs 1, 2

Redescription.

The observed specimen has a compact, bowling pin-shaped body, measuring 88 μm in total body length, 184 μm with spines included. Conical head with convex sides (24 μm wide), pentalobate, dorsally with a middle furrow (Figure 1D). Cephalic ciliature consists of two lateral tufts, one adjacent to mouth and another slightly posterior, and a transverse band interrupted medially in the ventral and dorsal portion on middle head region (Figures 1E, 2C, D). Kephalion, trapezoidal in shape (9 μm length, 13 μm wide) (Figures 1D, 2C), hypostomion, triangular in shape (5 μm length, 8 μm wide) located around the ventral portion of the mouth ring (Figures 1F, 2D). Distinct neck constriction (17 μm wide), much narrower than the head and trunk. Trunk ovoidal in shape (42 μm in maximum width) with a rounded posterior end (Figure 1A).

Cephalic spines or rear spines not observed. On the anterior half of the trunk four paired groups of 2-2-2-1 curved simple spines (ta1-2, tb1-2, tc1-2, td) respectively, inserted directly on the cuticle without scales (Figs 1B, C, 2 A–D). The first group (ta1 at U32; ta2 at U35) inserted ventrolaterally at the neck base strongly bends dorsally at the neck level showing a slightly (almost straight) concave curvature extending all over the trunk (Figure 2B). The other three groups (tb, tc and td) are inserted ventrally at U32, U35, U38, U40, U46, U50, and U60, respectively (Figure 1 B–C, 2 B). Spines tb2 turn dorsally like spines ta. Spines tb1, tc1-2, and td show a slight convex curvature and extend ventrally along the trunk, (Figure 2B). Spines of ta to tc group measure 100, 90, 75, 90, 82, 80 μm respectively. Group td is composed of one pair of very long saltatorial spines, 140 μm in length.

Trunk locomotory ciliation divided into 2-paired ventral tufts at 15U and 93U on the ventral side of at the neck and posterior trunk, respectively (Figure 2C, D). No dorsal sensory bristles were observed.

Mouth ring is terminal (3 μm in diameter). Pharynx (33 μm in length) increases in width uniformly from 9 μm anteriorly to 11 μm at the posterior end) (Figure 1A, D, F).

Remarks.

Usually, the trunk width is given as the maximum trunk widthwhich is at the midgut level. In this case, the type specimen H. ooeides is 42 μm wide. However, Brunson (1950) measured the trunk width posterior to the midgut level (close to the posterior end of the body) and found it to be 36 μm wide.

Differences in spines length between the original description and the present one (Table 1) are due to different measurement methods. We chose to measure each spine length outlining its curvature (100, 90, 75, 90, 82, 80 μm respectively) instead of measuring the distance between the spine base insertion and apex as a straight line, as Brunson (1950) did (86, 86, 67, 82, 82 and 58 μm, respectively).

Additionally, the original description mentions a pair of caudal bristles (Figure 2C) that originate 10 µm from the posterior end of the trunk. After reexamination of the type specimen (Figure 2A, B–D) we conclude that Brunson (1950) may have misinterpreted these structures. In fact, our observations revealed that the caudal bristles described by Brunson (1950) actually are the ta1 spines, due to their similar position relative to the posterior trunk, size and shape (Figure 2A, B).

As previously mentioned, the description of some morphological characters of H. ooeides were misinterpreted by Brunson (1950) and incorrectly replicated by Balsamo et al. (2014) and Minowa and Garraffoni (2017). We address this issue by correcting the taxonomic key Haltidytes in order to correct previous misinterpretations.