Diphascon (Diphascon) faialense, Fontoura, Paulo & Pilato, Giovanni, 2007

Fontoura, Paulo & Pilato, Giovanni, 2007, Diphascon (Diphascon) faialense sp. nov. a new species of Tardigrada (Eutardigrada, Hypsibiidae) from the Azores and a key to the species of the D. pingue group, Zootaxa 1589, pp. 47-55 : 48-53

Diphascon (Diphascon) faialense sp. nov.

Figs. 1–4

Material examined: Archipelago of Azores, Faial Island: holotype and 2 paratypes.

Type repository. The holotype (slide N. 5127) is deposited in the collection of Binda & Pilato (Museo del Dipartimento di Biologia Animale “Marcello La Greca”, Università di Catania); the two paratypes (slides BI 60 and BI 61) in the collection of P. Fontoura (Department of Zoology and Anthropology, Faculty of Sciences, University of Porto).

Specific diagnosis. Cuticle smooth; eye spots absent; stylet supports inserted on the buccal tube at about 58–60 % of its length; buccal tube length is about 37 % of the total length of the bucco-pharyngeal tube; buccal tube width is about 7 % of the buccal tube length; pharyngeal bulb with apophyses, three rod-shaped macroplacoids (second one is the shortest, third one is the longest), microplacoid and septulum (about 11 % of the buccal tube length); placoid row (including septulum) about 65–72 % of the buccal tube length; macroplacoid row about 50–58 % of the buccal tube length; claws, of Hypsibius type, well developed with accessory points on the main branches; lunules and other cuticular thickenings on the legs absent.

Description of the holotype. Body length 207 µm ( Fig. 1 A), colourless, cuticle smooth without pores; dots on legs not visible, eye spots absent. Mouth antero-ventral without peribuccal lamellae or papulae.

As in other species of the subgenus, a sclerified drop-shaped thickening between the rigid buccal tube and the flexible pharyngeal tube is present ( Fig. 1 B). Bucco-pharyngeal tube 50.5 µm long; buccal tube length 18.6 µm long (36.8 % of the total length of the bucco-pharyngeal tube). Internal and external buccal tube width respectively 0.9 µm (ptd = 5) and 1.3 µm (ptd = 7.0). Stylet supports inserted on the buccal tube at 11.2 µm (ptd = 60.2). Pharyngeal bulb oval with small triangular apophyses, three rod-shaped macroplacoids, small granular microplacoid and septulum ( Fig. 1 B). The first macroplacoid is 3.3 µm long (ptd = 17.7); the second 3.1 µm (ptd = 16.7) is the shortest; the longest, 4.3 µm (ptd = 23.1), is the third macroplacoid. Septulum 2.0 µm long (ptd = 10.8). The macroplacoid row is 10.7 µm long (ptd = 57.5). The placoid row length including microplacoid and septulum 13.4 µm (ptd = 72.0).

Claws well developed with slender branches ( Fig. 1 C). Primary branches with accessory points; leg I, outer claw 7.5 µm (ptd = 40.3), inner claw 5.7 µm (ptd = 30.6); legs II and III, outer claw 8.1 µm (ptd = 43.5), inner claw 6.5 µm (ptd = 34.9); leg IV, posterior claw 9.2 µm (ptd = 49.5), anterior claw 6.6 µm (ptd = 35.5). Claw bases on all legs slightly enlarged but not indented; lunules and other cuticular thickenings absent on all pairs of legs.

Eggs not found.

The paratypes are similar to the holotype in both qualitative and metric characters. The measurements of some structures of the studied specimens are in Table 1 .

Etymology: The name faialense refers to the locus typicus: Faial Island; faialense = inhabiting Faial.

Differential diagnosis. Diphascon species of the subgenus Diphascon with three rod-shaped macroplacoids, microplacoid and septulum, smooth cuticle (without any sculpture such as granulation, pores or reticulation), without lunules and other cuticular thickenings on the legs and with claw bases without indentation constitute the so-called Diphascon pingue group. According to Pilato and Binda (1997 /98; 1999) it is a very homogeneous group of species very difficult to separate, some of which were previously identified under the name Diphascon pingue . At present, and including the new species described in this work, ten species are known differing from one another in some quantitative characters and only in some cases also in qualitative characters.

Diphascon (D.) faialense sp. n. differs from D. pingue , from D. mitrense and from D. polare in having the macroplacoid row longer than half of the buccal tube length. It also differs from D. pingue in having the second macroplacoid not longer than the first and in having a more marked difference in length between the third macroplacoid and the first two ( Figs 1 B and 2A); from D. mitrense in having higher percent ratio between the buccal tube length and the bucco-pharyngeal tube length (about 37 % in D. faialense sp. n., about 31–32 in D. mitrense ), wider bucco-pharyngeal tube (ptd = 7–7.2 in D. faialense sp. n., 5.5–6.0 in D. mitrense ), and in having a more marked difference in length between the third macroplacoid and the first two ( Figs 1 B and 2E). The new species also differs from D. polare in having the drop-shaped thickening between buccal tube and pharyngeal tube not forked; stylet supports inserted in a slightly more cephalic position (ptd = 58.0– 60.2 in D. faialense sp. n., 61.1–62.8 in D. polare ); the third macroplacoid clearly longer than the first and the second; and claws shorter and with branches more slender ( Figs 1 C and 2D).

Diphascon faialense sp. n. differs from D. australianum in having shorter placoids but longer septulum ( Figs 1 B, 3C), buccal tube slightly shorter in relation to the body length and, due to this fact, slightly higher values of the ptd index relative to the claws and to the other structures of the same length; claws more slender ( Figs 1 C and 3D).

The new species differs from D. dastychi in having a relatively smaller buccal tube length (buccal tube length is about 37 % of the bucco-pharyngeal tube length in Diphascon faialense sp. n.,> 41 % in D. dastychi ) and clearly shorter claws ( Figs 1 B, C and 4C, D).

Diphascon faialense sp. n. differs from the most similar species by the following features:

- From Diphascon pinguiforme in having wider buccal tube and slightly shorter macroplacoids and septulum ( Table 2 ; Figs 1 B and 3A).

- From D. victoriae in having stylet supports inserted in a slightly more cephalic position; slightly shorter placoid row and macroplacoid row ( Table 2 ; Figs 1 B and 4A) and second macroplacoid slightly shorter than the first ( Table 2 ).

- From D. claxtonae in having slightly shorter bucco-pharyngeal tube; buccal tube slightly longer with respect to the total length of the bucco-pharyngeal tube (% is about 37 in D. faialense sp. nov., 32.1–35.1 in D. claxtonae ); relatively longer septulum ( Table 2 ; Figs 1 B and 4E).

- From D. zaniewi in having wider buccal tube; shorter placoid and macroplacoid row length; second macroplacoid slightly shorter than the first ( Table 2 ).

As mentioned above, the D. pingue group is very homogeneous and some species are very similar to one another; therefore we think it opportune to provide here a dichotomous key to all the species of the group.

Figures

FIGURE 1. Diphascon faialense sp. nov., A, habitus of the holotype (scale bar = 30 µm); B. bucco-pharyngeal apparatus of the holotype (scale bar = 10 µm); C, claws of the third pair of legs of a paratype (scale bar = 10 µm).

FIGURE 2. Bucco-pharyngeal apparatus and claws of the second or third pair of legs of: A – B, Diphascon pingue; C – D, Diphascon polare; E – G, Diphascon mitrense. Scale bars = 10 µm.

FIGURE 3. Bucco-pharyngeal apparatus and claws of the second or third pair of legs of: A – B, Diphascon pinguiforme; C – D, Diphascon australianum. Scale bars = 10 µm.

FIGURE 4. Bucco-pharyngeal apparatus and claws of the first or second or third pair of legs of: A – B, Diphascon victoriae; C – D, Diphascon dastychi; E – F, Diphascon claxtonae. Scale bars = 10 µm.