Echinoderes horni, Higgins, 1983

Anguas-Escalante, Abril, Herranz, María, Martínez-Arce, Arely, De Jesús-Navarrete, Alberto & Sørensen, Martin V., 2023, New Echinoderes (Kinorhyncha: Cyclorhagida) from Mexico: Molecular barcoding demonstrate species delimitation between highly similar morphospecies, Zoologischer Anzeiger (Zool. Anz.) 302, pp. 146-165 : 159-161

3.3. Redescription E. horni Higgins, 1983

Fig. 9A–B , 10–12 , Tables 6–8. 3.3.1. Emended diagnosis

Middorsal spines and glandular cell outlets type 2 absent. Acicular spines present in lateroventral positions on segments 6 to 9. Tubes present on segments 2 and 5 in lateroventral positions, on segment 8 in lateral accessory positions, and in laterodorsal positions on segment 10. Females with minute laterodorsal tubes and lateral terminal accessory spines on segment 11. Males with well-developed laterodorsal tubes on segment 10, and three pairs of penile spines on segment 11.

3.3.2. Material examined

Type material and new collected specimens were analysed and measured with light microscope. Female holotype ( USNM 69966 ) and male paratype ( USNM 69971 ) were loaned from Smithsonian Institution, United states National Museum , and compared with images of nine additional paratypes ( USNM 69967 , USNM 69968 a to 69968h) from a previous loan. In addition, six specimens from Xcalak Quintana Roo (two males and four females), and two specimens from Xahuayxol, Quintana Roo (two females) were mounted in 100% glycerine at glass slides with cover slips, and deposited at the Natural History Museum of Denmark under catalogue number NHMD-1176464 to 1176468 (St. T1 XC), NHMD-1176471 ( St. T1 XA), and NHMD-1176469 to 1176470 (St. Xahuayxol) . Additional material includes two specimens mounted for SEM collected on St. X 3 LE, which have been stored in the personal reference collection of MVS. However , the specimens were so dirty that they contributed with very little information .

DNA sequences ( COI) were obtained from five specimens and deposited in GenBank ( NCBI) under accession number OP617666 to OP617670, and their cuticle was deposited as hologenophores at the Natural History Museum of Denmark, under catalogue number NHMD-1176472 to 1176473, and NHMD-1176486 to 1176488 ( Table 6) .

3.3.3. Redescription

The species appearance ( Fig. 10A–B , 11A, H) generally follows the original description provided by Higgins (1983). However, due to the changes in terminology and reinterpretation of cuticular structures after more than 30 years, additional and updated information is provided in the following. For complete overview of measures and dimensions, see Table 7. Distribution of cuticular structures, i.e., sensory spots, glandular cell outlets, spines, and tubes, is summarized in Table 8, and NCBI accession numbers for COI sequences are listed in Table 6.

Segments 1 and 2 consist of closed cuticular rings. Pectinate fringe of posterior segment margin on segment 1 crenate. Pectinate fringe of posterior segment margin on segment 2 with short uniform fringe tips along dorsal, lateral, and ventral sides; on remaining segments fringe tips progressively longer and wider except on segment 10 and 11. Segment 3 and remaining segments consisting of one tergal and two sternal plates with pachycyclus of the anterior segment margin of medium thickness, interrupted at the tergosternal junctions and middorsally. Segment 11 with pachycyclus only interrupted at tergosternal junctions.

Glandular cell outlets type 2 absent on all segments. Glandular cell outlets type 1 are also reported by Higgins (1983), but referred to as cuticular spots. Glandular cell outlets type 1 are located in following positions: middorsal on segments 1 to 3, and segments 5, 7, and 10 (two longitudinally arranged); paradorsal on segments 4, 6, 8, and 9; lateroventral on segment 1; ventromedial on segments 2 to segment 9, and paraventral on segment 10 ( Fig. 10A–B , 11B, D, E, I-K, M, 12A-B).

The original description does not provide any information about sensory spot distribution, and they are indeed difficult to observe with LM. Following information on sensory spot distribution was to some extent generated with SEM, but mainly through CLSM ( Fig. 12A–C ): subdorsal positions on segments 1, 3, and 5 to segment 10 (sensory spots on segments 5 to 10 alternatingly vary between being closer to the paradorsal or laterodorsal positions, but they always stay within the subdorsal area); laterodorsal positions on segment 1, 2 (as twin pair) and 9; midlateral positions on segments 5 to 7; sublateral positions on segment 3; ventrolateral positions on segment 9 and 10; and ventromedial positions on segment 1 to 2, and 5 to 7. It should be noted that the reported sensory spot pattern might be incomplete.

Tube and spine distributions follow Higgins (1983): lateroventral tubes on segments 2 and 5; lateroventral spines on segments 6 to 9; lateral accessory tubes on segment 8; lateral terminal spines, and lateral terminal accessory spines in females ( Fig. 10A–D , 11 B-D, F, J, L, N). Males with three penile spines: dorsal and ventral penile spines thin and flexible, whereas median one is short, thicker, and rigid ( Fig. 10C–D , 11G). Not mentioned in the original description: sexually dimorphic laterodorsal tubes on segment 10, well-developed in males, strongly reduced in females.

Covering of cuticular hairs as described by Higgins (1983), but regular hairs in paraventral positions on segments 3 to 6 have been replaced by two transverse rows: anterior row with extremely short, stiff hairs, and posterior row with four, strong bristle-like hairs ( Figs. 10B and 11B). 3.3.4. Barcoding

Cytochrome c oxidase subunit 1 of 618 bp was sequenced from five specimens of E. horni , and cuticles from the extracted specimens were mounted as hologenophores ( Fig. 9A–B ). The sequenced barcodes showed a similarity between 99.191% and 99.838% ( Table 6).

Figures

Fig. 9. Light micrographs of cuticles from paratypes and hologenophores mounted after DNA extraction and COI sequencing. (A–B) Echinoderes horni, NHMD- 1176472, GenBank Acc. No. OP617666. (C–D) Echinoderes wilberti sp. nov., NHMD- 1176460, GenBank Acc. No. OP617672. (A) Dorsal overview. (B) Segments 1 to 6, dorsal view. (C) Dorsal overview. (D) Segments 1 to 6, dorsal view. Arrows indicate subdorsal tubes on segment 2.

Fig. 10. Line art illustrations of Echinoderes horni Higgins, 1983. (A) Female, dorsal view. (B) Female, ventral view. (C) Segments 10 to 11 in male, dorsal view. (D) Segments 10 to 11 in male, ventral view. Abbreviations: lat, lateral accessory tube; ldss, laterodorsal sensory spot; ldt, laterodorsal tube; ltas, lateral terminal accessory spine; lts, lateral terminal spine; lvgco1, lateroventral glandular cell outlet type 1; lvs, lateroventral spine; lvt, lateroventral tube; mdgco1, middorsal glandular cell outlet type 1; mlss, midlateral sensory spot; pdgco1, paradorsal glandular cell outlet type 1; pe, penile spines; pvb, paraventral bristles; sdss, subdorsal sensory spot; vlss, ventrolateral sensory spot; vmgco1, ventromedial glandular cell outlet type 1; vmss, ventromedial sensory spot.

Fig. 12. Confocal laser micrographs of Echinoderes horni (NHMD-1176472) showing focal overview sections, from most dorsal in (A) and a deeper focus through (B) to (C). Sensory spots are indicated by full circles, and glandular cell outlets type 1 by dashed circles.