Echinoderes microaperturus, Sørensen & Rho & Min & Kim & Chang, 2012

Sørensen, Martin V., Rho, Hyun Soo, Min, Won-Gi, Kim, Dongsung & Chang, Cheon Young, 2012, An exploration of Echinoderes (Kinorhyncha: Cyclorhagida) in Korean and neighboring waters, with the description of four new species and a redescription of E. tchefouensis Lou, 1934 *, Zootaxa 3368 (1), pp. 161-196 : 175-183

publication ID	https://doi.org/ 10.11646/zootaxa.3368.1.8
persistent identifier	https://treatment.plazi.org/id/03E08792-E202-FFB9-FF36-F92FFDB5FAF0
treatment provided by	Felipe
scientific name	Echinoderes microaperturus
status	sp. nov.

Treatment

Echinoderes microaperturus View in CoL sp. nov.

( Figures 7–10 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 , Tables 5–6)

Diagnosis. Specimens with middorsal spines on segments 4 to 8, not extending beyond the posterior margin of their respective segments; ventrolateral tubules on segment 2; lateroventral tubules on segment 5; lateroventral spines on segments 6 to 9; midlateral tubules on segment 10. Minute glandular cell outlets type 2 subdorsal on segment 2 and laterodorsal on segments 8 and 9. Females with glands with funnel-shaped subcuticular structure ventrolateral on segment 7 and ventromedial on segment 8. Tergal extensions of segment 11 long, spinose. Lateral terminal spines 69–81% of trunk length.

Type material. Holotype adult male collected on 6 June 2008 from station MAP-08 in the Korea Strait, ca. 100 km south of Jeju Island , ( Fig. 1C View FIGURE 1 ), 32 o 21.59’N 126 o 46.32’E, from mud at 113 m depth, mounted in Fluoromount G, deposited at NIBR under accession number INBRIV0000245083 GoogleMaps . Allotype adult female collected on 6 August 2008 from station MAP- 24 in the East China Sea, ca. 325 km southwest of Jeju Island, ( Fig. 1C View FIGURE 1 ), 30 o 19.86’N 125 o 17.06’E, from mud at 74 m depth, mounted in Fluoromount G, deposited at NHMD under accession number ZMUC KIN-539 GoogleMaps . Paratypes: five specimens (two females and three males) from the same locality as holotype GoogleMaps ; two specimens (a female and a male) from same locality as allotype; and GoogleMaps two males collected on 28 September 2006 from station MAP-05 in the East China Sea, ca. 300 km south of Jeju Island, ( Fig. 1C View FIGURE 1 ), 30o31.66’N 125o55.86’E, from mud at 79 m depth; all paratypes mounted in Fluoromount G, deposited at NHMD under accession number ZMUC KIN-540 to KIN-548 GoogleMaps .

Additional material. Mounted for SEM and stored in personal collection of MVS, originated from stations MAP-05 and MAP-08 (mentioned above), as well as stations MAP-07 and MAP-27 (see Fig. 1C View FIGURE 1 and Table 1). Four additional specimens, mounted in Fluoromount G, are stored in the personal collections of HSR and CYC.

Etymology. The species name microaperturus refers to the minute openings of the glandular cell outlets type 2 that make it easy to recognize the species.

Description. Adult specimens consist of a head, a neck and eleven trunk segments ( Figs 7A–B View FIGURE 7 , 10A View FIGURE 10 ). Measurements and dimensions are given in Table 5. A summary of sensory spot, spine, tubule and glandular cell outlet positions is provided in Table 6.

The head consists of a retractable mouth cone and an introvert ( Figs 8 View FIGURE 8 , 10B–C View FIGURE 10 ). Inner armature in mouth cone could not be examined. Outer armature with nine outer oral styles composed of two subunits. Bases of outer oral styles with ornamented double rows of fringes; inner fringe rows with several, rather short fringe tips; outer fringe rows with 6 to 8 much longer and more slender fringe tips ( Fig. 10C View FIGURE 10 ). Introvert with 10 spinoscalids in ring 1, followed by 10, 20 and 10 scalids, respectively, in rings 02 to 04. Ring 05 with 10 scalids, arranged as two scalids in each uneven numbered section; and ring 06 with 15 scalids, arranged as one scalid in each uneven numbered section and two scalids in each even numbered one. Hence, described section-wise, uneven numbered sections have seven regular scalids, whereas even numbered ones have six ( Figs 8 View FIGURE 8 , 10B View FIGURE 10 ). Additional scalids are present in ring 07. These resemble an intermediate between regular scalids and trichoscalids. Their bases are broad with fringed lateral edges, which give the bases a leaf-like appearance, hence, these scalids will be referred to as leaflike scalids. Leaf-like scalids do not follow a strict pentaradial distribution, but are present as one scalid in sections 1 ( Fig. 9B View FIGURE 9 ), 5, 6 and 7, and two scalids in sections 3 and 9 ( Figs 8 View FIGURE 8 , 10B View FIGURE 10 ).

The neck consists of 16 placids ( Fig. 8 View FIGURE 8 ), all measuring 13 µm in length and 7 µm in width at bases ( Figs 7A View FIGURE 7 , 9A View FIGURE 9 ), except midventral placid that measures 12 µm in width ( Figs 7B View FIGURE 7 , 9B View FIGURE 9 ). Placids in positions corresponding to introvert sections 2 and 10 with broad trichoscalid plate with attached trichoscalid ( Figs 7B View FIGURE 7 , 8 View FIGURE 8 , 9B View FIGURE 9 ). Smaller trichoscalid plates with trichoscalids associated with placids in positions corresponding to introvert sections 2, 5, 7 and 8 ( Figs 7A View FIGURE 7 , 8 View FIGURE 8 , 9A View FIGURE 9 ).

Segment 1 consists of one complete cuticular ring. Pairs of subdorsal, laterodorsal, midlateral and ventromedial sensory spots present ( Figs 7A–B View FIGURE 7 , 9A–B View FIGURE 9 ). Sensory spots on this, and all following segments, are generally small (ca. 1 µm in diameter) and rounded. Pore fields were not observed. Cuticular hairs on this and following segments emerge through slit-like perforation sites (unless other is mentioned). Hairs are scattered on all sides of the segment, from anterior margin to IJ-line. Posterior margin with short, but well-developed pectinate fringe; fringe tips become progressively longer on each segment towards segment 8 and 9.

Segment 2 consists of one complete cuticular ring with pair of ventrolateral tubules ( Figs 7B View FIGURE 7 , 9B View FIGURE 9 ). Pairs of laterodorsal and ventromedial sensory spots present. A pair of small (opening ca. 0.8 µm) glandular cell outlets type 2 present in the subdorsal position ( Figs 7A View FIGURE 7 , 9A View FIGURE 9 ). Cuticular hairs scattered over tergal plate and in ventrolateral positions of sternal plates. Narrow, elongate clusters of filiform cuticular projections are present in the paraventral positions.

Segment 3 and following eight segments consist of one tergal and two sternal plates. All segments with this composition have well-developed pachycycli along anterior segment margins, and along anterior 1/3 of tergosternal and midsternal junctions. Paired sensory spots located in subdorsal position ( Fig. 7A View FIGURE 7 ). Cuticular hairs are scattered all over the tergal plate, except in a small hairless laterodorsal patches on the anterior part of the segment. Cuticular hairs and filiform extensions on sternal plates as on preceding segment.

Segment 4 with short middorsal spine and ventromedial sensory spots ( Fig. 7A–B View FIGURE 7 ). Cuticular hairs and filiform extensions as on preceding segment.

Segment 5 with short middorsal spine and lateroventral tubules ( Fig. 7A–B View FIGURE 7 ). Length of lateroventral tubes could not be measured exactly with LM, but from SEM observations they are estimated to be about same length as lateroventral spines on segment 6, hence, ca. 15 to 20 µm. Pairs of subdorsal and laterodorsal sensory spots present. Cuticular hairs and filiform extensions as on preceding segment.

Segments 6, 7 and 8 with short middorsal spine and lateroventral spines ( Fig. 7A–B View FIGURE 7 ). Pairs of paradorsal and laterodorsal sensory spots present. Cuticular hairs and filiform extensions as on segment 5. Segment 7 furthermore with pair of minute (0.8 µm), ventromedial sensory spots, and segment 8 with pair of small (opening ca. 0.8 µm) glandular cell outlets type 2 in the laterodorsal position ( Figs 7A View FIGURE 7 , 9C View FIGURE 9 , 10D View FIGURE 10 ). Females with paired glands with funnel-shaped subcuticular structure in ventrolateral positions of segment 7 ( Fig. 9D View FIGURE 9 ) and ventromedial positions of segment 8 ( Fig. 9E View FIGURE 9 ). Cuticular hairs and filiform extensions as on preceding segment.

Segment 9 without middorsal spine, but with spines in the lateroventral position. Pairs of paradorsal, subdorsal, laterodorsal and ventrolateral sensory spots present ( Fig. 7A–B View FIGURE 7 ). A pair of small (opening ca. 0.8 µm) glandular cell outlets type 2 is present in the laterodorsal position ( Figs 7A View FIGURE 7 , 9C View FIGURE 9 , 10D View FIGURE 10 ), and minute (ca. 3 µm in diameter), rounded sieve plates in lateral accessory position. Cuticular hairs and filiform extensions as on preceding segment.

Segment 10 without acicular spines, but with pair of midlateral tubules that emerge from deep incisions in the posterior segment margin ( Figs 7A View FIGURE 7 , 9C View FIGURE 9 , 10E–G View FIGURE 10 ). Sensory spots present in the subdorsal positions only. Two middorsal glandular cell outlets type 1 (pore fields) are present on the anterior part of the segment; anteriormost outlet may be covered by pectinate fringe of preceding segment ( Fig. 9C View FIGURE 9 ). Cuticular hairs and filiform extensions as on preceding segment. Pectinate fringe of posterior segment margin much shorter than on preceding segments.

Segment 11 with lateral terminal spines. Females furthermore with lateral terminal accessory spines ( Figs 7C–D View FIGURE 7 , 9F View FIGURE 9 , 10E, G View FIGURE 10 ), and males with three pairs of penile spines that emerge from the intersegmental joint with the preceding segment ( Figs 7A–B View FIGURE 7 , 10F, H View FIGURE 10 ). The dorsal- and ventralmost penile spines are long and flexible, whereas the median one is shorter and stouter. A pair of sensory spots is present in the subdorsal position. Cuticular hairs are not present, but a cluster of cuticular filiform extensions covers the mid- to subdorsal positions of the posterior part of the tergal plate ( Figs 7A View FIGURE 7 , 10E–F View FIGURE 10 ). Similar extensions form a transverse band on the sternal plates ( Figs 7B View FIGURE 7 , 10G–H View FIGURE 10 ). A thin pectinate fringe is present along the posterior margins of the sternal plates, and along the attachment site of the lateral terminal spines. Tergal plate terminates into spinous extensions ( Figs 7A–C View FIGURE 7 , 9F View FIGURE 9 , 10E–H View FIGURE 10 ), whereas sternal plates terminate along an oblique margin that never extends beyond the tergal plate ( Figs 7B–D View FIGURE 7 , 10H View FIGURE 10 ).

Notes on diagnostic features. Echinoderes microaperturus sp. nov. is most easily recognized by the pattern of its rather short acicular spines, combined with the presence of long, spinous tergal extensions of segment 11, the small glandular cell outlets type 2 in subdorsal position on segment 2 and in laterodorsal positions on segments 8 and 9.

The spine pattern, i.e., middorsal spines on segments 4 to 8, ventrolateral tubules on segment 2, lateroventral spines/tubules on segments 5 to 9, and laterodorsal/midlateral tubules on segment 10, is among the most common ones within the genus and has previously been reported from 19 species (see Thormar & Sørensen 2010). However, Echinoderes microaperturus sp. nov. can quite easily be distinguished from 11 of the 19 species by its rather short middorsal spines that hardly extend beyond the posterior margin of the segments to which they are attached. Oppositely, the middorsal spines (at least those on the more posterior segments) in the 11 species always extend well beyond their segments. Of the remaining eight species, four also differ significantly from E. microaperturus sp. nov.: Echinoderes brevicaudatus ( Higgins, 1966) and E. cavernus Sørensen, Jørgensen & Boesgaard, 2000 are easily recognized by their conspicuously short and stout lateral terminal spines (see Higgins 1966; Sørensen et al. 2000), E. imperforatus Higgins, 1983 is unique in its complete lack of perforation sites (see Higgins 1983), and E. truncatus Higgins, 1983 in its very prominent perforation sites and almost truncate tergal and sternal extensions of segment 11 (see Higgins 1983).

The four species that most easily can be confused with E. microaperturus sp. nov. include E. ehlersi Zelinka 1913 , E. aureus , E. sensibilis and E. lanceolatus . All four species are known from Asia, and especially the three latter have distributions that quite likely could be overlapping with E. microaperturus sp. nov.

The safest way to distinguish E. microaperturus sp. nov. is by its presence of subdorsal glandular cell outlets type 2 (gco2) on segment 2. The presence of gco2 has not been reported from any of the four species (see Zelinka 1913; Higgins & Rao 1979; Adrianov et al. 2002 a, 2002b; Chang & Song 2002), but since this character has tended to be ignored in older contributions, its absence needs further confirmation. For E. sensibilis , though, it seems fair to rely on information from the description. The species’ description is based on examinations with both LM and SEM, specimens examined with SEM appear very clean so that all details would have been recognizable, and the description addresses so many other cuticular details that it seems unlikely that the authors would have decided not to mention the eventual presence of gco2.

For E. ehlersi the situation is a bit fuzzier. The species is described from Zanzibar in West Africa by Zelinka (1913), and Higgins & Rao (1979) subsequently found it in the Andaman Islands, and address different details of its morphology. Neither Zelinka (1913) nor Higgins & Rao (1979) mention any kind of cuticular structures in the positions where E. microaperturus sp. nov. has gco2. However, the senior author recently received a few kinorhynchs from the Andaman Islands, and the specimens could readily be identified as E. ehlersi . A closer examination with SEM revealed though, that the specimens have tiny laterodorsal gco2 on segments 8 and 9 (M. V. Sørensen, pers. obs.). The structures were so small that they could be overlooked with LM. This leaves us with the question whether E. ehlersi also has laterodorsal gco2 on segments 8 and 9, which consequently would bring it very close to E. microaperturus sp. nov., or if the examined specimens belonged to another, yet undescribed species. In any case, subdorsal gco2 were not present on segment 2, which thus makes it possible to distinguish E. microaperturus sp. nov. from its Andaman relatives.

As for E. aureus and E. lanceolatus , the situation is even more complex. Preliminary studies by the authors of the present contribution clearly indicate that E. lanceolatus should be considered a junior synonym of E. aureus , but at the same time, that some of the paratypic specimens of E. lanceolatus are not conspecific with its holotype, and should hence be considered a new, yet undescribed species. These problems will be addressed more specifically in an upcoming contribution, but from the ongoing examinations it is clear that neither E. aureus nor the new species possess subdorsal gco2 on segment 2, as found in E. microaperturus sp. nov.

Another indicative character regards the relative length of the lateral terminal spines. In E. microaperturus sp. nov. the lengths of the lateral terminal spines equal to 69–81% of the trunk length, whereas this ratio is only 46–67% in E. ehlersi , that otherwise is the one with the longest lateral terminal spines. For the remaining three species, the ratios are even lower, namely 46% for E. sensibilis , and 33–43% for E. aureus . Other differential traits include the tergal extensions that are rather short in E. ehlersi and E. sensibilis .

In their description of E. aureus, Adrianov et al. (2002a) mention the presence of prominent subcuticular markings in a paraventral position on segment 1. We have, admittedly, had problems identifying such a structure on any of the specimens of E. aureus that we have examined. However, another diagnostic structure, namely the partial midventral fissure on segment 2 is most often very conspicuous, and makes it easy to distinguish between E. aureus and E. microaperturus sp. nov.