Echinoderes cernunnos, 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 : 169-175

publication ID	https://doi.org/ 10.11646/zootaxa.3368.1.8
persistent identifier	https://treatment.plazi.org/id/03E08792-E204-FFA1-FF36-FDB2FEA1F9D8
treatment provided by	Felipe
scientific name	Echinoderes cernunnos
status	sp. nov.

Treatment

Echinoderes cernunnos View in CoL sp. nov.

( Figures 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 , Tables 3–4)

Diagnosis. Segments 1 and 2 consisting of closed rings; segments 3 to 10 of one tergal and two sternal plates, and segment 11 consisting of two tergal and two sternal plates. Specimens with middorsal spines on segment 4–8, gradually increasing in length towards the more posterior segments; lateroventral tubule on segment 5; lateroventral spines on segments 6–9; very short, laterodorsal, distally fringed elements (tubules?) on segment 10. Glandular cell outlets type 2 present in subdorsal, laterodorsal, sublateral and ventrolateral positions on segment 2, midlateral positions on segments 5 and 7, and in sublateral position of segment 8. Tergal extension of segment 11 extremely elongated, forming strong, horn-like extensions.

Type material. Holotype: adult female, collected on 6 October 2008, at station MAP-27, in the Korea Strait between Tsushima Island and the Korean mainland ( Fig. 1B View FIGURE 1 ), 34 o 16.41’N 128 o 40.40’E, from mud with tiny shells at 96 m depth, mounted in Fluoromount G, deposited at NIBR under accession number INBRIV0000245082. No allotype designated GoogleMaps . Paratypes: two females, collected on 6 June 2008 from station MAP-08 in the East China Sea, ca. 100 km south of Jeju Island, ( Fig. 1B View FIGURE 1 ), 32 o 21.59’N 126 o 46.32’E, from mud at 113 m depth, mounted in Fluoromount G (one in lateral position), deposited at NHMD GoogleMaps under accession number ZMUC KIN-536 and KIN- 537 .

Additional material. One female from the same locality as the holotype, mounted for SEM and stored in the personal collection of MVS GoogleMaps .

Etymology. The species is named after Cernunnos—The Horned God—from Celtic mythology, inspired by the species’ diagnostic long, horn-like tergal extensions.

Description. Adult specimens consist of a head, a neck and eleven trunk segments ( Figs 4A–B View FIGURE 4 , 6A View FIGURE 6 ). Trunk cuticle appears relatively thin and flexible. Measurements and dimensions are given in Table 3. A summary of sensory spot, spine, tubule and glandular cell outlet positions is provided in Table 4.

The head consists of a retractable mouth cone and an introvert. Inner oral styles are clearly present, but their exact arrangement could not be examined. Outer armature with nine outer oral styles composed of two subunits. Bases of outer oral styles with a single fringe, flanked by a pair of off-set spikes ( Fig. 6B View FIGURE 6 ). The arrangement of scalids on the introvert ( Fig. 6C View FIGURE 6 ) is identical with the one found in E. microaperturus sp. nov. (see Fig. 8 View FIGURE 8 and description below) and several other species described herein. Leaf-like scalids (see definition under description of the following species) are present as single ones in sections 1, 5, 6 and 7, and pairs in sections 3 and 9. A distinct band of longitudinal ridges that extend into fringe tips stretches around the introvert at the level between Rings 05 and 06 ( Fig. 6C View FIGURE 6 ).

The neck consists of 16 placids, all measuring 12 µm in length and 7 µm in width at bases ( Figs 4A–B View FIGURE 4 , 5A–B View FIGURE 5 ), except midventral placid that measures 11 µm in width ( Figs 4B View FIGURE 4 , 5B View FIGURE 5 ). Placids number 2 and 16 (counting clockwise from midventral placid) with broad trichoscalid plate and attached trichoscalid ( Fig. 5B View FIGURE 5 ). Smaller trichoscalid plates with trichoscalids on placids number 6, 8, 10, and 12 ( Figs 4A View FIGURE 4 , 5A View FIGURE 5 ).

Segment 1 consists of one complete cuticular ring ( Figs 4A–B View FIGURE 4 , 5A–B View FIGURE 5 ). Pairs of subdorsal ( Fig. 5A View FIGURE 5 ), laterodorsal ( Fig. 6D View FIGURE 6 ) and ventromedial ( Fig. 4B View FIGURE 4 ) sensory spots present. Sensory spots are small and rounded, with numerous papillae. Only few cuticular hairs present; hairs emerge through rounded perforation sites, and are scattered around the segment ( Fig. 6D View FIGURE 6 ). Posterior margin with pectinate fringe; fringe appears serrated on its dorsal side, whereas the ventral fringe tips extend into filiform tips.

Segment 2 consists of one complete cuticular ring. Pairs of conspicuous glandular cell outlets type 2 present in subdorsal, laterodorsal, sublateral and ventrolateral positions ( Figs 4A–B View FIGURE 4 , 5A–B View FIGURE 5 , 6D View FIGURE 6 ). Sensory spots present as an unpaired one in middorsal position, two pairs in laterodorsal position on each side of the gco2 ( Fig. 6D View FIGURE 6 ), and one pair in ventromedial positions; sensory spots on this and following eight segments are minute, consisting of a few papillae forming a circle around a central pore. An unpaired middorsal pore field (i.e., glandular cell outlet type 1 (gco1)) is present in middorsal position ( Fig. 5A View FIGURE 5 ). Cuticular hairs on this and the following segments emerge through slit-like perforation sites; hairs on dorsal and lateral sides are scattered in a median belt that is limited posteriorly by the IJ-line; no hairs present on ventral side. A secondary pectinate fringe was not observed on this or any of the following segments. Posterior segment margin with regular pectinate fringe on dorsal and ventral sides, whereas the fringes on the lateral sides are composed of well-spaced long and narrow fringe tips, with much shorter tips in between.

Segment 3 and following seven segments, down to segment 10, consist of one tergal and two sternal plates ( Fig. 4B View FIGURE 4 ). On all segments with this composition, pachycycli are well-developed along anterior margins of the sternal plates, and along anterior 1/3 of tergosternal and midsternal junctions. Segment with sensory spots in subdorsal and midlateral positions, and unpaired middorsal and paired ventromedial pore fields (gco1). Cuticular hairs scattered in a median belt around the tergal plate and onto the ventrolateral areas of the sternal plates; no cuticular hairs in ventromedial and paraventral areas. Posterior segment margin as lateral margin on preceding segment.

Segment 4 with middorsal spine ( Fig. 4A View FIGURE 4 ). One pair of sensory spots present in subdorsal position. Pore fields (gco1) in ventromedial positions ( Fig. 4B View FIGURE 4 ). Cuticular hairs and pectinate fringe as on preceding segment.

Segment 5 with middorsal spine and lateroventral tubules (length = 13 µm, estimated with SEM) ( Figs 4A–B View FIGURE 4 ). Paired paradorsal pore fields (gco1) present, anterior to the attachment point of the middorsal spine ( Figs 4A View FIGURE 4 , 5C View FIGURE 5 ); one additional pair present in ventromedial position. One pair of conspicuous glandular cell outlets type 2 present in midlateral positions ( Figs 4B View FIGURE 4 , 5C View FIGURE 5 ). Sensory spots present in subdorsal and ventromedial positions; subdorsal sensory spots with short, tube-shaped subcuticular structure ( Fig. 5D View FIGURE 5 ). Cuticular hairs and pectinate fringe as on preceding segment.

Segment 6 with middorsal spine and lateroventral spines ( Figs 4A–B View FIGURE 4 , 5C View FIGURE 5 , 6E View FIGURE 6 ). Paired pore fields (gco1) present slightly anterior to attachment point of the middorsal spine ( Fig. 5C View FIGURE 5 ); one additional pair present in paraventral position. Sensory spots present in paradorsal, subdorsal, midlateral ( Fig. 5C View FIGURE 5 ) and ventromedial positions; paradorsal ones are very close to the subdorsal area, and do not readily appear as perispinal sensory spots; subdorsal sensory spots with tube-shaped subcuticular structure ( Fig. 5D View FIGURE 5 ); ventromedial ones located slightly closer to the midsternal line than those on the preceding segment. Cuticular hairs and pectinate fringe as on preceding segment.

Segment 7 with middorsal spine and lateroventral spines. Paired pore fields (gco1) present slightly anterior to attachment point of the middorsal spine ( Figs 4A View FIGURE 4 , 5C View FIGURE 5 ); one additional pair present in paraventral position. One pair of conspicuous glandular cell outlets type 2 present in midlateral positions ( Figs 4B View FIGURE 4 , 5C View FIGURE 5 , 6E View FIGURE 6 ). Sensory spots present in paradorsal (as on preceding segment), subdorsal and ventromedial positions; subdorsal sensory spots with tubeshaped subcuticular structure; ventromedial ones located slightly more lateral than those on the preceding segment. Cuticular hairs and pectinate fringe as on preceding segment.

Segment 8 with middorsal spine and lateroventral spines. Paired pore fields (gco1) present slightly anterior to attachment point of the middorsal spine; one additional pair present in paraventral position. One pair of conspicuous glandular cell outlets type 2 present in sublateral positions ( Fig. 4B View FIGURE 4 ). Sensory spots present in paradorsal (as on preceding segment) and subdorsal positions; subdorsal sensory spots with tube-shaped subcuticular structure. Cuticular hairs and pectinate fringe as on preceding segment.

Segment 9 without middorsal spine, but with lateroventral spines. Paired pore fields (gco1) present in paradorsal and paraventral positions; paraventral pore fields closer to midsternal line than those on preceding segments. Sensory spots present in paradorsal (as on preceding segment), subdorsal, midlateral and ventromedial positions; subcuticular structures associated with subdorsal sensory spots are anteriorly expanded, giving them a funnel-shaped rather than tube-shaped appearance ( Fig. 5E View FIGURE 5 ). Small, rounded sieve plates present in lateral accessory positions. Cuticular hairs as on preceding segment, but almost lacking in mid- and paradorsal areas. Pectinate fringe with uniform, well-developed fringe tips around the segment margin.

Segment 10 without spines. Two unpaired, middorsal pore fields (gco1) ( Fig. 5E View FIGURE 5 ) and paired paraventral ones present; paraventral pore fields closer to midsternal line than those on preceding segments. Sensory spots with funnel-shaped subcuticular structure present in subdorsal positions; a regular pair of sensory spots present in ventrolateral position. A pair of fringed tufts extends slightly beyond the posterior segment margin in the laterodorsal position; the structures could be very short tubules with fringed tips, but this is uncertain (structure marked as “ldt?” on Figs 4A View FIGURE 4 , 6F View FIGURE 6 ). Cuticular hairs scattered in middorsal, laterodorsal and lateroventral/ ventrolateral clusters. Posterior segment margin with pectinate fringe; fringe tips short along dorsal margin, and along the lateral ones; paraventrally the sternal plates and the fringe tips are elongated, almost reaching the margin of segment 11 ( Figs 4B View FIGURE 4 , 6H View FIGURE 6 ).

Segment 11 is composed of two tergal and two sternal plates ( Figs 4A–B View FIGURE 4 , 5G View FIGURE 5 , 6F View FIGURE 6 ). Lateral terminal spines and lateral terminal accessory spines present ( Figs 4A–B View FIGURE 4 , 5F View FIGURE 5 ); the latter is probably a sexually dimorphic female trait, but male specimens were unavailable to confirm this. Sensory spots present in paradorsal position ( Fig. 6F View FIGURE 6 ). Cuticular hairs not present. Tergal extensions extremely elongated and posteriorly projecting ( Figs 4A View FIGURE 4 , 5F–H View FIGURE 5 , 6G–H View FIGURE 6 ), measuring 38 µm and constituting 70% of the total segment length; sternal extensions short and rounded with fringed margins and a few longer filiform extensions ( Figs 4B View FIGURE 4 , 6H View FIGURE 6 ).

Notes on diagnostic features and affinities. Even though Echinoderes cernunnos sp. nov. displays a rather classic spine pattern, with five middorsal spines and lateroventral spines/tubules on segments 5 to 9, the species possesses several unique traits that make it impossible to confuse with any other taxon. Also the lack of ventrolateral tubules is uncommon, and only shared with a minority of its congeners. The most prominent characteristic, however, is its extremely elongated tergal extensions. Their lengths clearly exceed tergal extensions in any other species, inclusive those in E. higginsi Huys & Coomans, 1989 and E. spinifurca Sørensen, Heiner & Ziemer, 2005 that otherwise possess the longest tergal extensions among the species known so far (see Huys & Coomans 1989; Sørensen et al. 2005). As stated above, the tergal extensions of E. cernunnos sp. nov. constitute 70% of the total segment length, whereas the corresponding ratios in E. higginsi and E. spinifurca are about 50% only.

Also the distribution of glandular cell outlets type 2 (gco2) appears to be unique for this species. Our information about the presence and distribution of gco2 is still quite limited, because previous descriptions have tended to neglect this character. However, to our knowledge, no other species displays the specific pattern of gco2 as the one found in E. cernunnos sp. nov.

The third character that attracts special attention and makes E. cernunnos sp. nov. unique among congeners is the middorsal division of segment 11 that splits the tergal plate into two paired plates. No other species of the genus has this segment composition, and it inevitably makes the generic assignation of the species problematic. Among the five genera of Echinoderidae , Cephalorhyncha Adrianov, 1999 in Adrianov & Malakhov, 1999, Fissuroderes Neuhaus & Blasche, 2006 and Meristoderes Herranz et al., 2012 accommodate species with middorsally split tergal plate on segment 11 ( Neuhaus & Blasche, 2006; for Meristoderes Sørensen pers. obs. from yet undescribed species). However, these genera are characterized by species with either fully or at least partly differentiated sternal plates on segment 2 ( Adrianov & Malakhov 1999; Neuhaus & Blasche 2006; Herranz et al. 2012). Segment 2 in E. cernunnos sp. nov. is composed of a closed cuticular ring, which characterizes species of Echinoderes , hence we tentatively assign the species to this genus. The conflicting characters could indicate that a future reassignment could be required, and in any case, this character combination clearly makes E. cernunnos sp. nov. special among all echinoderids.