Echinoderes australis, Sánchez & García-Cobo & Shimabukuro & Zeppilli & Nomaki & González-Casarrubios, 2024

Echinoderes australis View in CoL sp. nov.

urn:lsid:zoobank.org:pub:60C568A3-C443-428D-878F-89BAACBE6E31

( Figs. 2–5 View Fig View Fig View Fig View Fig , Tables 1 and 2).

3.1.1. Synonymy Echinoderes sp. 2 (in Grzelak et al., 2021).

3.1.2. Material examined

Type material: Holotype, adult female, collected in 2019/12/19 at South Orkney Trench, Southern Ocean : Station A 6200; Coordinates 60 ◦ 51′ 1.200″S, 41 ◦ 2′ 13.800″ W; at 6.271 m depth; mounted in DMHF, deposited at NHMD under catalogue number: NHMD-1784619 GoogleMaps . Paratypes, 2 adult males and 1 adult female, same collecting data as holotype; mounted in DMHF, deposited at NHMD under catalogue numbers: NHMD-1784620 to NHMD-1784622. An additional male paratype, collected in 2019/12/19 at South Orkney Trench, Southern Ocean : Station A 5200; Coordinates 60 ◦ 52′ 30.000″ S, 41 ◦ 36′ 2.400″ W; at 5.251 m depth; mounted in DMHF, deposited at NHMD under catalogue number: NHMD-1784623 GoogleMaps .

Non-type material: 2 adult females, same collecting data as holotype, mounted for SEM examination, deposited at the meiofaunal laboratory of the UCM GoogleMaps . 1 adult female (broken), same collecting data as holotype, mounted in DMHF GoogleMaps , deposited at the meiofaunal laboratory of the UCM.

3.1.3. Diagnosis

Echinoderes with middorsal acicular spines on segments 4-8 and lateroventral ones on segments 6-9, both increasing in length on posterior segments. Very long middorsal spine of segment 8 and lateroventral spines of segment 9, with whip-like appearance. Paired large tubes in lateroventral position on segments 5, in lateral accessory position on segment 8, and in laterodorsal position on segment 10. Conspicuous middorsal papillary flaps on segments 8-9.

3.1.4. Etymology

The species name, australis , derives from the Latin term “auster” (south) plus the suffix “-alis” (relation or belonging), referring to the area where the species was found, in the Southern Ocean.

3.1.5. Description

All dimensions and measurements are summarized in Table 1, and distribution of cuticular structures in Table 2.

None of the examined specimens had the head everted, hence no details on mouth cone and introvert can be provided.

Neck with 16 placids ( Fig. 2 A–B View Fig , 3 A–B View Fig , 5 A–B View Fig ). Midventral placid broadest (15-17 μm in width, 16-19 μm in length). Remaining placids similar in size and narrower than the midventral one (7-9 μm in width and 17-19 μm in length). Four dorsal and two ventral trichoscalid plates are present ( Fig. 2A and B View Fig ), each carrying a thick and feathery trichoscalid.

Trunk with 11 segments, with segments 1 and 2 as closed cuticular rings and the remaining segments formed by one tergal and two sternal plates ( Fig. 2 A and B View Fig ). Sternal plates reach their maximum width at segment 8, progressively tapering towards the last trunk segments, giving a slender appearance to the body. Cuticular hairs long, filiform, bracteate ( Fig. 5 C View Fig ), arranged in several wavy, transverse rows that extend from the paradorsal regions to the sternal plates ( Fig. 2 A and B View Fig ), except on segment 10 (devoid of hairs in middorsal and subdorsal regions) and 11 (almost completely devoid of hairs) ( Fig. 2 A–D View Fig ). Hairs well-spaced through the surface of each segment, uniformly distributed, except in middorsal, laterodorsal and ventromedial regions, forming hairless longitudinal bands ( Fig. 2 A and B View Fig ). Segments 1 to 5 with up to three dorsal rows of hairs, segments 6 to 10 with up to five dorsal rows of hairs; ventral side with three rows of hairs. Hairs of each anterior row surpass the insertion of the following one, and with those of the last row reaching the pectinate fringe of the segment. Sensory spots small, with a round to oval shape, composed of a single pore surrounded by few, short micropapillae ( Fig. 5 F View Fig ). Sensory spots of segment 1 larger, formed by a higher number of short micropapillae. Posterior segment margin straight, forming well-developed primary pectinate fringes with elongated, strongly serrated tips alternating in size ( Fig. 5 B–C, E View Fig ). Primary pectinate fringes of segments 7 to 10 reduce in size towards the middorsal region ( Fig. 2 A–C View Fig ). Secondary pectinate fringe well-developed, with short and thin serrated tips. Type 1 glandular cell outlets are located at the anterior dorsal region of the segments, except the posterior outlets of segment 1, 10 and 11 that are located towards the middle region of the plate ( Fig. 2 A–D View Fig ).

Segment 1 without spines or tubes. Two type 1 glandular cell outlets in middorsal position, longitudinally aligned, and one pair in lateroventral position ( Fig. 2 A–B View Fig , 3 A–B View Fig ). Paired sensory spots in subdorsal and laterodorsal positions ( Figs. 3 A View Fig and 5 B View Fig ). Pectinate fringe less developed than on following segments ( Fig. 5 B View Fig ).

Segment 2 without spines or tubes. Unpaired middorsal type 1 glandular cell outlet and paired ones in ventromedial positions ( Fig. 2 A–B View Fig , 3 A View Fig ). Paired sensory spots in subdorsal and ventromedial positions ( Fig. 2 A–B View Fig , 5 I View Fig ).

Segment 3 without spines or tubes. Unpaired middorsal type 1 glandular cell outlet and paired ones in ventromedial position ( Fig. 2 A–B View Fig , 3 A–B View Fig ).

Segment 4 with a middorsal acicular spine, reaching the posterior margin of the following segment ( Fig. 3 A–C View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 3 A–D View Fig ).

Segment 5 with a middorsal acicular spine longer than of preceding segment, reaching the posterior margin of the following segment, and one pair of lateroventral tubes ( Fig. 3 C and D View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 3 C and D View Fig ). Paired midlateral sensory spots ( Fig. 3 C–D View Fig , 5 H View Fig ).

Segment 6 with a middorsal acicular spine longer than of preceding

(caption on next page)

segment, reaching medially on segment 8 ( Fig. 3 C View Fig ); and one pair of lateroventral acicular spines, reaching the posterior margin of segment 7 ( Fig. 3 D View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 3 C and D View Fig ). Paired midlateral sensory spots ( Fig. 3 C and D View Fig ).

Segment 7 with a middorsal acicular spine longer than of preceding segment, reaching medially on segment 10 ( Fig. 3 C–E View Fig ); and one pair of lateroventral acicular spines longer than those of the preceding segment, reaching the posterior margin of segment 8 ( Fig. 3 D–F View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 3 C and D View Fig ). Paired sensory spots in ventromedial position ( Figs. 2 B View Fig and 5 F View Fig ). Primary pectinate fringe reduces in size towards the middorsal region ( Fig. 2 A–C View Fig ).

Segment 8 with a whip-like middorsal acicular spine much longer than on preceding segment, exceeding far beyond the posterior margin of segment 11 ( Figs. 3 E View Fig and 4 A View Fig ). One pair of lateroventral acicular spines longer than those of the preceding segment, reaching the medially on segment 10 ( Figs. 3 F View Fig , 4 D View Fig and 5 C View Fig ). One pair of long tubes in lateral accessory position ( Figs. 3 F View Fig , 4 D View Fig and 5 C View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 3 E–F View Fig ). A papillary middorsal flap located at the most posterior margin of the segment ( Figs. 3 E View Fig , 4 C, E View Fig , 5 E, J View Fig ), flanked by a pair of paradorsal sensory spots ( Fig. 2 A View Fig ). Primary pectinate fringe reduces in size towards the middorsal region ( Fig. 2 A–C View Fig , 5 E View Fig ).

Segment 9 with one pair of very long lateroventral acicular spines, exceeding well beyond the posterior margin of segment 11; the distal end is whip-like ( Figs. 3 F View Fig , 4 D View Fig and 5 A View Fig ). Paired paradorsal and ventromedial type 1 glandular cell outlets ( Fig. 2 A–B View Fig , 3 F View Fig ). Longer papillary middorsal flap than on preceding segment ( Figs. 3 E View Fig , 4C, F View Fig , 5 E, K View Fig ), located at the posterior margin of the segment, and flanked by a pair of paradorsal sensory spots ( Fig. 2 A View Fig ). Three additional pairs of sensory spots located in subdorsal, laterodorsal and ventrolateral positions ( Fig. 3 E–F View Fig , 5 E View Fig ). Subdorsal and laterodorsal pairs located in the middle of the segment; ventrolateral pair located near the posterior segment margin. Rounded nephridiopores as sieve plates in sublateral position ( Fig. 3 F View Fig ). Primary pectinate fringe reduces in size towards the middorsal region ( Fig. 2 A–C View Fig ).

Segment 10 with paired, long and slender laterodorsal tubes near posterior segment margin with similar appearance in both sexes ( Fig. 2A–C View Fig , 4 B View Fig , 5 G View Fig ). Two longitudinally arranged middorsal type 1 glandular cell outlets and paired ones in ventromedial position ( Fig. 2 A–D View Fig ). Pairs of sensory spots in subdorsal and ventrolateral positions ( Fig. 2 A–D View Fig , 3 F View Fig ). Subdorsal pair located in the middle of the segment; ventrolateral pair located near the posterior segment margin. Margins of the sternal plates midventral extended ( Fig. 2 B–D View Fig , 3 F View Fig ). Primary pectinate fringe reduces in size towards the middorsal region ( Fig. 2 A–C View Fig ).

Segment 11 with a pair of very long lateral terminal spines ( Fig. 2 A–D View Fig , 3 E View Fig , 4 A–B View Fig , 5 D View Fig ). Females with strong and stout pair of lateral terminal accessory spines ( Fig. 2 A–B View Fig , 3 E View Fig , 4 A View Fig , 5 D View Fig ). Males with three stout pairs of penile spines: the median ones stouter than the other two pairs ( Fig. 4 B View Fig ). Two longitudinally arranged middorsal type 1 glandular cell outlets (2 A and C). Sensory spots in paradorsal and subdorsal positions ( Fig. 2 A–C View Fig ). The paradorsal pair located posteriorly to the subdorsal ones. Pectinate fringe with short tips, except in lateral margins where are a bit longer. Tergal extensions short and triangular ( Fig. 3 E View Fig ) and with hairy mesial areas. The posterior margin of the sternal plates rounded, similar in length to the tergal extensions.