Anisonyches eleutherensis, Bartels & Fontoura & Nelson, 2018

Bartels, Paul J., Fontoura, Paulo & Nelson, Diane R., 2018, Marine tardigrades of the Bahamas with the description of two new species and updated keys to the species of Anisonyches and Archechiniscus, Zootaxa 4420 (1), pp. 43-70 : 60-64

Anisonyches eleutherensis sp. nov.

Table 3, Figs. 9–11

Material examined: A single female, slide B: 14-15-1, collected at site 10. The holotype is deposited in the collection of tardigrades of the Department of Biology , Faculty of Sciences, University of Porto, Portugal.

Specific diagnosis: Anisonyches with ovoid-shaped primary clava and papilla on the fourth pair of legs. Sensory organs on the first three pairs of legs absent. Claws with narrowly divergent basal spurs directed downward, a long curved distal point, medial claws longer than outer claws, and all claws bearing an apical accessory point.

Description of the holotype: Female, with the characteristic worm-like body 193 µm long and 57 µm wide (at the level of the third pair of legs) ( Figs. 9 and 10 ). Conical head with terminal mouth. Cuticle smooth without evident punctations. Large black round eyes located anteriorly to the lateral cirri.

Cephalic cirri with a swollen transparent pedunculate base (scapus), resulting in a clearly visible inner filament, and a short flagellum ( Fig. 11 ). Median cephalic cirrus very short and very difficult to see (about 2.5 µm long). Internal cephalic cirri in a dorsal position, 7.4 µm long (3.4 and 4.0 µm for the basal peduncle and the flagellum, respectively); ventral external cephalic cirri 5.0 µm long (basal peduncle = 2.6 µm + flagellum = 2.4 µm). Lateral cirrus A (10.5 µm long) bears an accordion-shaped basal peduncle (5.1 µm) and a terminal spike (5.4 µm). The terminal spike of the lateral cirrus has a cylindrical base tapering to a thin apical point. Primary clava ovoid, 3.6 µm, with thickened cuticle, a van der Land’s body at the base and a distal circular pore. Perceptible lensshaped secondary clava 16.0 µm in diameter ( Figs. 10 and 11 ).

Long cirrus E (15.2 µm long) also bearing an accordion-like pedunculate base (about 6.9 µm) and distal flagellum (8.3 µm) ( Fig. 11A ). Ovoid papilla (3.7 µm), with a terminal circular pore, present at the base of legs IV. Sensory organs on legs I to III not evident.

Buccal cavity with two thickened rings (probably teeth) ( Fig. 11B ) followed by a long buccal tube (35.9 µm) ( Fig. 11A ). The first portion (about 7 µm long) of the thin-walled buccal tube is very narrow (0.6 µm wide). A long wider portion (1.3 µm wide) follows with thicker walls in the anterior-medial part. The pharyngeal bulb is small (15.2 x 12.8 µm), with three placoids of about 6 µm and apophyses 2.4 µm long which exit the buccal tube at approximately right angles ( Fig. 10 ). However, details of the pharynx need confirmation because in our specimen it is detached from the buccal tube ( Fig. 11A ). Stylets, 43.8 µm long, with sheaths (20.4 µm), terminated by a conspicuous T-shaped furca. Branches of the furca (4 µm each) with round apexes. Stylet supports absent.

Stubby legs with claws. Four claws on legs I to III and three claws on legs IV as typical of the genus. The medial claws (two on legs I–III, of about 7.4 µm, and the one on leg IV, about 8.4 µm) are larger than the outermost claws (about 6.7 on legs I–III, and 7.6 on leg IV) and the smaller innermost claws (6.1 on legs I–III, and 7.5 on legs IV) ( Fig. 11C ). All claws with basal membranes, connecting each claw to the leg, and a light-refracting portion on its base. All claws with an apical accessory point and a pair of thin basal spurs directed downwards ( A. mauritanius - type claws, Chang & Rho (1998b)). The claws are strongly curved apically (the long terminal portion is bent at about 90° relatively to the basal portion).

Rosette-like gonopore, surrounded by six small membranes, 12.8 µm distant from the anus. Anus a fissure surrounded by pursed lines between legs IV. Large oblong seminal receptacles (9.9 x 5.0 µm), lateral to the gonopore, with seminal ducts inserted posteriorly. The entire length of the ducts was not discernible.

Measurements of the holotype and type material of the other Anisonyches species are compared in Table 3.

Larvae and males were not found.

Etymology: This species was found only in Eleuthera, thus the specific epithet.

Differential diagnosis: Only three species of the genus Anisonyches have been described previously: A. diakidius Pollock, 1975 , the type species from the Bahamas, A. mauritanius Grimaldi de Zio et al., 1987 and A. deliquus Chang & Rho, 1998 . The new species has intermediate characteristics between A. diakidius on one hand, and A. mauritanius and A. deliquus on the other.

Anisonyches eleutherensis sp. nov. shares with A. diakidius the presence of the primary clava and papilla on legs IV and the absence of sensory organs on the other three pair of legs (sensory organs on legs I–III are also absent in A. deliquus ). The mauritanius - type claws characterized by the presence of larger medial claws relative to the outer and innermost claws on legs I–III, smaller outermost claws on legs IV and spiniform basal spurs, narrowly divergent from one another and directed downward are shared by the new species, A. mauritanius and A. deliquus . The unique characters considered of important taxonomic value in the single specimen of A. eleutherensis sp. nov. are some other attributes of claw morphology. In the new species, all the claws without exception, have distal accessory points. In contrast, in A. deliquus only the two medial claws on legs I–III and the innermost two claws on leg IV have accessory points. Our examination of the holotype of A. diakidius revealed widely divergent, horizontally directed basal spurs ( diakidius - type claws), and as Chang & Rho (1998b) speculated accessory points on the medial claws only, at least on legs I-III and probably on inner claws of legs IV but these claws were not clear enough to be certain. The A. diakidius specimens we examined from Bimini, Bahamas collected by Renaud- Debyser also had diakidius - type claws with very small accessory points on medial claws of legs I-III and the inner claws of leg IV. The specimen from Guadeloupe was badly damaged, but did have diakidius - type claws. The absence of accessory points on A. mauritanius is probable based on the expertise of the author, the detailed description of the claw morphology, and the illustrations shown in the original description. Anisonyches eleutherensis sp. nov. also differs from A. diakidius by having mauritanius - type claws rather than diakidius - type claws, and in having the claws more strongly curved apically. In addition, our new species can be distinguished from all three other species in the genus by the presence of relatively longer lateral cirri A and E, both bearing accordion-like pedunculate bases.

= Observations of Chang & Rho (1998b) from specimens from the Philippines.

Specimens from the Philippines attributed to A. diakidius by Chang & Rho (1998b) had widely divergent basal spurs and small accessory points on the medial claws, however, they differed from Pollock’s original description in other ways. In the specimens from the Philippines, conspicuous secondary clavae are present associated with large head swellings, the outermost claws are similar in length to the medial claws on legs I–III, and eye spots are posterior to cirrus A. The A. diakidius holotype did not have large swellings associated with the secondary clavae, but artifacts around the leading edge of the head did not allow a clear view of this structure. Also, as noted by Chang & Rho (1998b) the eyes are quite anterior to lateral cirrus A in the holotype. Thus, we believe the specimens from the Philippines warrant further study, and they could represent a new species similar to A. diakidius .

The following key of the genus Anisonyches is presented:

1 Adult specimens with conspicuous primary clavae, and papillae on the fourth pair of legs............................ 2

1’ Primary clavae and papillae on the fourth pair of legs absent................................................... 3

2 Basal spurs on claws widely divergent from each other, directed horizontally. Claws on legs I–III progressively larger from inner to outermost, all claws of legs IV similar in length. Medial claws on legs I–III and the inner two claws on leg IV with accessory points. Claws slightly curved apically.................................................... A. diakidius

2’ Basal spurs on claws narrowly divergent from another and directed downward. Larger medial claws relative to the outer and innermost claws on legs I–III, smaller outermost claws on legs IV. All claws with accessory points and strongly bent apically.................................................................................. A. eleutherensis sp. nov.

3 Sensory organs on legs I–III present............................................................ A. mauritanius

3’ Sensory organs on legs I–III absent............................................................... A. deliquus

Figures

FIGURE 9. Anisonyches eleutherensis sp. nov. holotype habitus photo (DIC), ventral view. Scale bar = 20 µm.

FIGURE 10. Anisonyches eleutherensis sp. nov. holotype habitus drawing; an = anus, bt = buccal tube, cA = cirrus A, cE = cirrus E, e = eye, ec = external cirrus, go = gonopore, ic = internal cirrus, mc = median cirrus, pc = primary clava, ph = pharynx, pl = placoids, p4 = sensory structure leg IV, sc = secondary clava, st = stylet, sr = seminal receptacle. Scale bar = 20 µm.

FIGURE 11. Anisonyches eleutherensis sp. nov. holotype. A. Head (DIC). B. Buccal cavity with thickened rings (arrows) (DIC). C. Claws from leg III (PhC). ap = accessory points, bs = basal spurs, bt = buccal tube, cA = cirrus A, e = eye, ec= external cirrus, ic = internal cirrus, mc =median cirrus, mo = mouth, pc = primary clava, sc = secondary clava, st = stylet. Scale bars = 10 µm.