Adropion vexatum, Pilato & Sabella & D’Urso & Lisi, 2017

Pilato, Giovanni, Sabella, Giorgio, D’Urso, Vera & Lisi, Oscar, 2017, Macrobiotus nebrodensis and Adropion vexatum, two new species of Eutardigrada (Tardigrada, Parachela) from Sicily, Zootaxa 4362 (2), pp. 267-279 : 272-277

Adropion vexatum sp. nov.

Fig. 4

Type locality: Nebrodi Mountains , Cesarò: Pizzo Antenna, 1640 m a.s.l., (37°55'57"N, 14°41'30"E).

Material examined: Holotype (slide No. 5755) and 5 paratypes (slides Nos. 5754, 5756, 5757 and 5782) from a lichen sample on a tree collected by Dr. Rosario Catanzaro (29.04.1986).

Specific diagnosis: Colourless; cuticle smooth; eye spots absent in living specimens; bucco-pharyngeal apparatus of Adropion type; buccal tube narrow; its length is 36.5–39 % of the total length of the bucco-pharyngeal tube; stylet supports inserted on the buccal tube at 63–66 % of the buccal tube length; pharyngeal tube longer than the pharyngeal bulb; pharyngeal bulb with small apophyses and three rod-shaped macroplacoids; microplacoid and septulum absent. The macroplacoid row length is c. 50% of the pharyngeal bulb length. Claws of the Hypsibius type; the main branches with accessory points; lunules and other cuticular thickenings on the legs absent (small dots excluded).

Description of the holotype: Body length 302 µm; colourless; eye spots absent in living specimens; cuticle smooth but with small dots on the legs. Bucco-pharyngeal apparatus of Adropion type ( Fig. 4A ): mouth anteroventral and a steep, almost vertical, front to the head ( Fig. 4B ); bucco-pharyngeal tube (53.9 µm long) without drop-shaped thickening between the rigid buccal tube and the flexible pharyngeal tube; the latter with a spiral thickening. Buccal tube length, 21.0 µm (pbf = 39.0) and 1.8 µm wide (pt = 8.6) without ventral lamina; stylet supports inserted on the buccal tube at 65.5% of its length (pt = 65.5); pharyngeal tube length, 32.9 µm. Pharyngeal bulb elliptic, 30.3 µm by 21.8 µm, with small apophyses and three rod-shaped macroplacoids; microplacoid and septulum absent ( Fig. 4A ). Macroplacoid length: first, 4.0 µm long (pt = 19.0), second, 4.0 µm (pt = 19.0), third, 6.5 µm (pt = 31.0); entire macroplacoid row length, 14.6 µm (pt = 69.5).

Claws of the Hypsibius type ( Fig. 4A,C ); the external claws are longer than the internal and have a longer secondary branch. External claw of legs I, 10.2 µm long (pt = 48.6) (the main branch length is 75.4% of the entire claw length); internal claws of the same pair of legs 7.5 µm long (pt = 35.7); external claws of the second and third pairs of legs 12.7 µm long (pt = 60.5) (their main branch length is 74.0% of the entire claws length); internal claws II and III 9.1 µm long (pt = 43.3); the posterior claws on the hind legs are bent and therefore could not be measured; the anterior claws are 10.0 µm long (pt = 47.6). Main branches of all claws with accessory points; lunules and other cuticular thickenings on the legs, absent (small dots excluded).

Remarks: The paratypes are similar to the holotype in both morphological and quantitative characters; the morphometric characters of the holotype and three paratypes that were correctly orientated for measurements are reported in Table 1 .

Differential diagnosis: There are six species of Adropion described with smooth cuticle, three macroplacoid and lacking microplacoid and septulum: Adropion prorsirostre , Adropion arduifrons ( Thulin, 1928) , Adropion clavatum ( Bartoš, 1935) , Adropion carolae , Adropion montigenum and Adropion modestum .

The new species differs from Adropion carolae in having less elongate pharyngeal bulb ( Figs. 4A and 5A ); macroplacoid row clearly shorter with respect to the buccal tube length (pt = 69.5–79.7 in Adropion vexatum sp. nov., 98.7 in Adropion carolae ), and with respect to the pharyngeal bulb length (48.2–55.6% in the new species, 64–67% in Adropion carolae ); and by having longer claws (pt of the posterior and anterior claws IV about 77 and 44–49 respectively, and in Adropion vexatum sp. nov., c. 55 and 42 respectively in Adropion carolae ).

The antero-ventral mouth and a steep front to the head of the new species separates it from Adropion clavatum , Adropion modestum and Adropion prorsirostre . Additional characters differentiating these species include: absence of granulation on the caudal portion of the body, pharyngeal tube longer than the pharyngeal bulb, and the third macroplacoid not caudally clavate for Adropion vexatum sp. nov. but present in Adropion clavatum . A less elongate pharyngeal bulb and presence of small apophyses in Adropion vexatum sp. nov., longer pharyngeal bulb and absent apophyses in Adropion modestum , and a shorter placoid row length (near half the pharyngeal bulb length in the new species, 48.2–55.6%, and 73–74% in Adropion modestum ). The pharyngeal tube clearly longer than the pharyngeal bulb ( Figs. 4A and 5B , and Table 1 ) in Adropion vexatum sp. nov., shorter for Adropion prorsirostre ( Figs. 4A and 5B , and Table 1 ), a narrower bucco-pharyngeal tube (the pt index is 8.6–8.9 in the new species 10.6–13.9 in Adropion prorsirostre Figs. 4A, B and 5B ), lower values of the pt index relative to the stylet support insertion point (about 63–66 in Adropion vexatum sp. nov. and about 68.5–71 in Adropion prorsirostre , Table 1 ), and higher values of the pt index relative to the claw lengths ( Table 1 ).

Adropion vexatum sp. nov. differs from Adropion montigenum by having rod-shaped macroplacoids (these are oval granules in Adropion montigenum ); the macroplacoid row length is about half the pharyngeal bulb length (48.2–55.6%) while in Adropion montigenum it is about 34%, and the claw shape differs, the basal common portion and the secondary branch being longer ( Figs. 4C and 5C, D ).

Adropion vexatum sp. nov. is similar, but not identical, to Adropion arduifrons . Unfortunately, the original description of Adropion arduifrons ( Thulin, 1928) , was not very detailed. We have attempted to find the holotype but it seems to be lost, as kindly communicated by Prof. Kristensen (University of Copenhagen, Denmark) and Dr. Ekström (University of Lund, Sweden). It is, therefore, necessary to refer to Thulin’s (1928) original description with additional information from Dastych (1985), and we were also able to examine three specimens (kindly given by Dastych). For these comparisons it was necessary to use indices as defined by Thulin and Dastych, which are ms (the length of a structure as a ratio with respect to the body length), and cph (the percent ratio of a structure with respect to the pharyngeal bulb length). Unfortunately, these ratios of body length and pharyngeal bulb length can be influenced by the compression exerted by the coverslip; though if the comparative difference between two values is very high, it may be considered significant.

The new species differs from Adropion arduifrons (as described by Thulin 1928) in a number of characters: the pharyngeal bulb has a different shape and is shorter with respect to the body length in Adropion vexatum sp. nov., in fact the ms index is 98.4–111.4 in the new species (a paratype of uncertain body length has been excluded), and 126 in Adropion arduifrons ; the pharyngeal bulb also has a clearly different ratio length/width (the index cph of the pharyngeal bulb width is 71.9–73.6 in the new species, 55 in Adropion arduifrons ); the pharyngeal tube is clearly longer than the pharyngeal bulb, whereas Thulin (1928) specified that it is almost as long as the pharyngeal bulb; the claws are slightly longer with respect to both pharyngeal and body length (the cph index value of the posterior claw IV is c. 55 in the new species, and 35.7 in Adropion arduifrons ; the ms index c. 61 in the new species, and 45 in Adropion arduifrons ) ( Table 2 ).

Dastych (1985) considered some specimens collected in Spitsbergen as belonging to the species Diphascon arduifrons , but specified that his specimens differed from Adropion arduifrons in, “having more rounded pharynx, longer placoid row, a little longer mouth tube and pharyngeal one and longer claws in regard to the pharynx length”. The specimens studied by Dastych were 118–170 µm long and he hypothesized that: “All these differences may be result from unlike body dimension of the holotype (284 µm – comp. Thulin l.c.) and compared specimens”. Adropion vexatum sp. nov. differs from Adropion arduifrons as described by Dastych (1985), by having larger body size; more rounded pharyngeal bulb; buccal tube shorter with respect to the pharyngeal bulb (cph index 108.6–124.3 in the new species 147–175 in the specimens studied by Dastych); shorter placoid row with respect to both the pharyngeal bulb length and to the body length ( Table 2 ), and longer claws with respect to both the pharyngeal bulb length and to the body length ( Table 2 ).

In conclusion, a number of characters distinguish our specimens of Adropion vexatum sp. nov. from the descriptions of Adropion arduifrons , provided by both Thulin (1928) and by Dastych (1985), and from all the other species of the genus. We therefore believe Adropion vexatum sp. nov. is a valid new species and addition to the Sicilian fauna.

Etymology: The specific name ( vexatum = vexed) refers to the difficulty to be recognized as new species, and described, as a consequence of the problem regarding comparisons with Adropion arduifrons .

Figures

FIGURE 4. Adropion vexatum sp. nov. A, Bucco-pharyngeal apparatus of the holotype; it is evident that the drop-shaped thickening is not present between buccal and pharyngeal tube. B, paratype (slide No. 5754) showing the steep, almost vertical front of the head. C,Claws of the second pair of legs (holotype).Scale bar = 10 µm.

FIGURE 5. A, Bucco-pharyngeal apparatus of Adropion carolae. B, Bucco-pharyngeal apparatus of a specimen of Adropion prorsirostrefrom the Thulincollection.C, Claws of the thirdpair oflegs of Adropion montigenum. D, Claws of thehind legs of Adropion montigenum. Scale bar = 10 µm.

Tables

TABLE 1. Morphological measurements for the holotype and three correctly orientated paratypes of Adropion vexatum sp. nov., plus a specimen of Adropion prorsirostre. Measurements given in µm, with pbf and pt index values for relevant structures, and the percent ratio between the main branch and the total length of the external claw.

	Adropion	vexatum sp. nov.			Adropion prorsirostre
No. slide	5757 paratype	5757 paratype	5755 holotype	5754 paratype	1036
Body length Total bucco-pharyngeal tube length Buccal tube length	255 55.6 20.3	About 260? 21.3	302 53.9 21.0	316 56.2 21.7	245 51.7 20.9
pbf ratio Pharyngeal tube length External buccal tube width	36.5 35.3 1.8	?? 1.8	39.0 32.9 1.8	38.6 34.5 1.9	40.4 30.7 2.9
pt pt stylet supports insertion point Pharyngeal bulb length	8.9 65.7 28.4	8.5 63.9 29.0	8.6 65.5 30.3	8.8 63.2 31.1	13.9 70.7 31.2
Pharyngeal bulb width First macroplacoid pt	20.9 3.9 19.2	? 4.5 21.1	21.8 4.0 19.0	22.4 4.3 19.8	24.3 4.5 21.5
Second macroplacoid pt Third macroplacoid	4.1 20.2 6.1	4.5 21.1 6.1	4.0 19.0 6.5	4.7 21.7 7.3	4.5 21.5 7.3
pt Placoid row pt	30.0 14.5 71.4	28.6 15.4 72.3	31.0 14.6 69.5	33.6 17.3 79.7	34.9 16.3 78.0
External claw I pt % Main branch/ total claw length	10.1 49.7 75.2	10.5 49. 3 75.9	10.2 48.6 75.4	10.7 49.3 74.1	8.5 40.7 76.5
Internal claw I pt External claw II	7.3 36.0 12.6	7.3 34.3 12.8	7.5 35.7 12.7	7.3 33.6?	5.7 27.3 8.9
pt % Main branch/ total claw length Internal claw II pt	62.1 74.6 8.8 43.3	60.1 74.1 8.8 41.3	60.5 74.0 9.1 43.3	?? 9.4 43.3	42.6 74.2??
External claw III pt % Main branch/ total claw length	12.0 59.1 73.4	12.7 59.6 74.0	12.7 60.5 74.0	13.0 59.9 72.2	???
Internal claw III pt Posterior claw IV	?? 15.6	9.2 43.2?	9.1 43.3?	8.9 41.0?	6.5 31.1?
pt % Main branch/total claw length Anterior claw IV	76.8 79.3 9.8	???	?? 10.0	?? 9.7	?? 6.6
pt	48.3	?	47.6	44.7	31.6

TABLE 2. Morphologicalmeasurements for three specimens of Adropionvexatum sp. nov. (holotype and paratypes), the holotype of Adropion arduifrons (according to Thulin 1928), and the ranges for the West Spitsbergen Adropion arduifrons (according to Dastych 1985). Measurements are given in µm, with the ms and cph index values for relevant structures.

	Adropion	vexatum sp. nov.		A. arduifrons *	A. arduifrons **
No. slide	5757 paratype	5755 holotype	5754 paratype	holotype
Body length	255	302	316	284	118–170
Pharyngeal bulb length	28.4	30.3	31.1	35.9	16–22
ms	111.4	100.3	98.4	126	129.4–135.6
Pharyngeal bulb width	20.9	21.8	22.4	19.7	10.5–14.0
cph	73.6	71.9	72.0	55	63.1–65.0
External buccal tube width	1.8	1.8	1.9	1.7	1.0–1.2
cph	6.3	5.9	6.1	4.7	5.4–6.3
Pharyngeal tube length	35.3	32.9	34.5	about 35	28–36
cph	124.3	108.6	110.9	99	147–175
Placoid row	14.5	14.6	17.3	19.7	9–14
ms	56.9	48.3	54.7	?	76.3–82.4
cph	51.1	48.2	55.6	55	56.2–66.6
Posterior claw IV	15.6	?	?	12.8	5.0–7.5
ms	61.2	?	?	45.1	42.4–44.1
cph	54.9	?	?	35.7	31.2–34.1

* according to Thulin 1928

** according to Dastych 1985