Measurement. BL = 15 mm; BW = 5 mm.

Body: Entire body surface rough and granular, covered with small hair-like setae (Fig. 2A, B and Fig. 3A, B).

Figure 2.  

Pseudidothea armata sp. n. male holotype (MNA 10749). A dorsal view; B lateral view; C P1. Scale refers to 0.5 mm length. D A2; E A1; F P2; G P3; H P4; I P5; J P6; K Dactylus of P6; L P7. Scale refers to 1 mm length for D-L.

Figure 3.  

Pseudidothea armata sp. n. male holotype (MNA 10749). A stack photo of lateral view; B stack photo of dorsal view; C stack photo of P1, scale bar represents 0.5 mm; D stack photo of A1, scale bar represents 1 mm; E stack photo of pleotelson. Scale bar represents 1 mm length.

CEPHALOTHORAX. Head with two frontomedial lobes with many small tubercle-like protrusions. Cephalothorax with two large and stout spines, frontally directed (Fig. 2A, B and Fig. 3A, B, Suppl. materials 1, 2), covered with tubercles and with diffused short hair-like setae (not illustrated in drawings, but visible in Fig. 3). Two lateral eyes of medium size, slightly more subtriangular than oval (Fig. 2A B and Fig. 3A, B, Suppl. material 1).

ANTENNA 1. First Antenna (A1) consisting of three peduncular and two flagellar articles. First peduncular article broadest, almost surpassing in width the length of the second peducular article, with one mediolateral simple bristle; second peduncular article long, nearly 1.5 times the first, the third almost a third of the second, rounded distally. First flagellar article short, ring-like, barely distinguishable; last flagellar article as long as the length of all the other articles of the A1. Distoventrally on this article, six pairs of aesthetascs, another single aesthetasc present in the tip of the A1 together with two simple setae (Fig. 2E and Fig. 3D).

ANTENNA 2. Second Antenna (A2) half as long as body, consisting of five peduncular and three flagellar articles. First peduncular article very small, second about double in length of the first; third peduncular article 3 times longer than second, with a two ventral rows of long simple setae, each group with one long and one short seta. Fourth and fifth peduncular articles longest, nearly subequal in length, with similar setae pattern of the third article. Last peduncular article with a distolateral small feather-like seta. First flagellar article about twice as long as second and third flagellar articles together, bearing short bristles and one longer apical simple seta. Second article smaller and narrower than first, with many simple short bristles. Last flagellar article smallest, claw-like. The whole antenna covered with lots of short and small hairs (Fig. 2D).

PEREONITES. Pereonite 1 fused with cephalothorax, but separated by a ridge. Pereonite 2 only slightly shorther than pereonite 3; pereonite 4 longest. Pereonite 5 slightly shorter than pereonite 2, pereonite 6 and 7 smallest and shortest. Pereonite 1 with one pair of large dorsal spine-like tubercles, anteriorly directed. Pereonites 2-4 with two pairs of tubercles (one spine-like dorsal pair and one shield-like lateral pair). Dorsal pair of tubercles in pereonites 2-4 are large and high, apically flattened, covered with few hair-like small setae and small tubercle-like protrusions; in pereonites 5-7, these are smaller, more slender, apically acute, but with blunt tip and more laterally flattened. Lateral pairs of tubercles are large in pereonites 2-4, smaller in pereonites 5-7. Evident elevations separated by deep grooves characterise the surface of pereonites 2-4, between the dorsal and lateral tubercles. Elevations are also present on pereonites 5-7. However, these are more shallow, barely visible and uniformly covering the surface between the dorsal and lateral tubercles (Fig. 2A, B and Fig. 3A, B).

PLEOTELSON. All pleonites fused to pleotelson, frontolaterally of pleotelson two stout and slightly rounded protrusions, caudally directed (Fig. 2A, B and Fig. 3E). Pleotelson frontally broadest, narrowing caudally. Tip of telson acuminating, but with blunt tip, slightly rounded, slightly bent dorsally; subapical telsonic spines absent, but two pairs of rounded large tubercles in two rows in the pleotelson, dorsally; the pleotelson lacks spines, but is covered entirely by medium-sized rounded protrusions, slightly smaller laterally (Fig. 2A, B and Fig. 3E).

PEREOPODS. P1 shorther than P2-7. Basis and propodus longest; basis with few distoventral and distolateral simple setae; a row of small protuberances on the lateral outer-directed side of the article. Carpus trapezoidal, ischium, merus and carpus densely covered with sensory spines, especially on ventral and lateral surfaces. Subchelate propodus broad, oval, dactylus shorter than propodus, with two short smooth claws (the ventral one shorter) and a small spine in between (Fig. 4C). Ventral surface of propodus forming slightly concave “spoon”, medial surface with few short simple bristles (Fig. 2C, Fig. 3C and Fig. 4D). P2-4 similar, one strong spine dorsolaterally on basis of P2-P4, distodorsal margins of ischium, carpus and propodus without strong spines, but with rough cuticular surface; merus of P2-4 presents an evident protrusion on the dorsal surface of the distal part; important protrusion is also present dorsomedially on ischium of P2 and P4. Setation in P2-4 is similar, but most prominent in P2. Merus, carpus and propodus with groups of setae arranged in two ventral rows, each group consisting of one long seta and one short seta (Fig. 4A and B). Small hairs present in all pereopods (Fig. 2F, G, H and Fig. 4A, B). P5-7 slightly shorter, but subequal in length to P2-4. P5 with two long setae on basis, P6 and 7 without long setae. Basis of P5-7 presenting one stout rounded spine dorsolaterally, in addition to smaller spines; stout spines are also present on carpus and merus (Fig. 2I, J, L and K). In P5-7, basis longest, ischium and propodus elongated compared to other articles; dactylus presenting a terminal claw with one simple seta in the terminal part. On propodus of P5-7, some feather-like bristles; all pereopods covered with small hairs (Fig. 2I, J and L).

Figure 4.  

Pseudidothea armata sp. n. male holotype (MNA 10749). A left P2; B right P2; C right P1, dorsal part; D right P1, focus on inner part. Scale refers to 1 mm length.

UROPODS. Ventral surface of uropods covered with many simple hairs. Uropod elongated, both rami of uropods about subequal in length (Fig. 3E).

The new species is characterised by one pair of large blunt anteriorly directed supra-ocular spines on the first pereonite. In dorsal view, these are long, divergent, forming a v-shape, reaching beyond the eyes. Pereonites 2-7 with only two pairs of tubercles: one dorsal pair of spine-like tubercles and one lateral pair of shield-like tubercles. Dorsal tubercles on pereonites 2-4 are large, apically flattened in lateral view, slightly anteriorly directed; on pereonites 5-7, these are smaller, slender, more pointed, but apically blunt and upwards directed. Pleotelson with blunt, strong protrusions.

The species is named armata for its long supra-ocular and the dorso-apical spine-like tubercles, not simple “shielded” tubercles like Pseudidothea scutata, but more like strong blunt “spines”: as a contraposition to P. scutata meaning “that bears shield”, P. armata sp. n. “bears weapons”.

Only known from type locality, the Burdwood Bank (Antarctica), found at 852 m.

Specimen is stored and fixed with 96% ethanol in order to preserve it for further genetic analysis.

Pseudidothea Ohlin, 1901 is clearly distinguishable from other genera by the oval shape of the body and peculiar conformation of pereonites and first pereopod. P. bonnieri was the type species representing the genus, described by Ohlin (1901). Subsequently, it was synonymised with P. miersi (Studer 1884) because of the many similarities with the latter species. The genus is only known from the Southern Hemisphere and it is mostly known from the Antarctic Peninsula in the Southern Ocean. A record of Pseudidothea Ohlin, 1901 was also recorded in the Ross Sea (Fig. 1), although undetermined to species level (Mackay 2018). To date, four species belong to the genus Pseudidothea as referred to above (original names are presented; the type species is marked with an asterisk):

Pseudidothea hoplites - Poore and Bardsley (2004)

*Pseudidothea miersi - Ohlin 1901

Pseudidothea richardsoni - Hurley 1957

Pseudidothea scutata - Stephensen 1947

Pseudidothea armata sp. n.

Within the genus Pseudidothea, P. scutata (Stephensen 1947) is most similar to P. armata sp. n. in shape and spine pattern. The main differences are the large supra-ocular spines and general body armature, that significantly differs from the apically flattened tubercles in P. scutata; similar is also the position of the flattened tubercles dorsally located in every pereonite of P. scutata; however, all of these structures are more like blunt spines in P. armata sp. n. Another difference can be found in the extreme reduction of the elevations present in between lateral flattened tubercles and dorsal spine-like tubercles. Brandt and Wägele (1990) re-described P. scutata and illustrated flattened, irregular elevations on pereonites 5-7, while in P. armata sp. n., these are barely present. The pleotelson of P. scutata and P. armata sp. n. is similar in shape and tubercular pattern; however, it completely lacks pleotelsonic dorsal spines in P. armata, only rounded, short and strong tubercles are present in the latter species.

Supra-ocular spines of P. armata are long, dorsally pointed and anteriorly directed, reaching beyond the eyes in dorsal view. P. scutata presents supraocular tubercles that are shorter, dorsally flattened and do not reach the eyes on dorsal view. In addition, supra-ocular spines in P. armata are divergent, forming a v-shape in dorsal view, while in P. scutata the supra-ocular tubercles are aligned parallel. The body armature in the two species shows a different pattern of tubercles. In P. armata, dorsal tubercles are more similar to blunt spines, apically less flattened than those present in P. scutata. In particular, P. armata's spine-like tubercles on pereonites 5-7 are not apically flattened at all, but slender and pointed with a blunt apex, while in P. armata, pereonites 5-7 have small apically flat tubercles. Pseudidothea scutata presents raised areas in the lateral position, between the dorsal and lateral tubercles; these are marked on pereonites 5-7 and even described as distinct tubercles (Brandt and Wägele 1990, White 1992). Pseudidothea armata presents raised areas as well. However, elevations are more evident on pereonites 2-4, separated by deep grooves, making the surface between the dorsal and lateral tubercles look “wrinkly”, while elevations on pereonites 5-7 are less visible. Basis of P5 in P. armata has two long setae, while there are only simple setae on P5 of P. scutata.

The pleotelson of P. scutata and P. armata is similar in shape and tubercular pattern; however, it completely lacks pleotelsonic dorsal spines in P. armata; only rounded, short and strong tubercles are present in the latter species.

Only known from type locality.