Echinoderes lapitaorum Sørensen 2023, sp. nov.
Creators: name: Sørensen, Martin V.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Kinorhyncha
Cyclorhagida
Echinorhagata
Echinoderidae
Echinoderes
Echinoderes lapitaorum

description: 3.1. Echinoderes lapitaorum sp. nov.
urn:lsid:zoobank.org:act: 804EAB16-F7EE-472A-A6DC-F62B8D982
407.
3.1.1. Diagnosis
Echinoderes with lateroventral tubes on segment 5, lateral accessory tubes on segment 8, and sexually dimorphic laterodorsal tubes on segment 10; spines only present on terminal segment. Large, nephridial area divided into anterior, elongate sieve plate and posterior oval area with central pore field, present in sublateral positions on segment 9. Glandular cell outlets type 2 minute, but with conspicuously fringed margins, present in middorsal positions on segments 8 and 9, paradorsal positions on segments 4 and 6, subdorsal positions on segment 2, laterodorsal positions on segments 2, 4, 6, and 8, sublateral positions on segments 3, 7 and 8, and ventrolateral positions on segment 2; additional pair is present on segment 5 but its exact position may shift between laterodorsal and sublateral. Females with strongly reduced lateral terminal accessory spines, and minute laterodorsal tubes on segment 10. Males with well-developed laterodorsal tubes on segment 10, and three pairs of slender, tubular penile spines on segment 11; dorsal penile spines with conspicuously offset tips.
3.1.2. Etymology
The species name, lapitaorum, is the genitive declension of the Lapita – the indigenous people of New Caledonia.
3.1.3. Material examined
Holotypic male, collected by Dr O. Holovachov on Nov. 21, 2017 from shallow, muddy mangrove soil in Baie de Tar´e, New Caledonia (position: 22 o 15.530 ′ S, 167 o 00.771 ′ E); mounted in Fluoromount G between two cover slips attached to a plastic H-S slide, and deposited at National Museum of Natural History (NMNH), Paris, under catalogue number MNHM-655Ma.
Paratypes, one adult male and two juveniles, same collection data as holotype. The juvenile paratypes are mounted in Fluoromount G on glass slides, and deposited in MNHM under catalogue numbers MNHM-656 Ma to 657 Ma. Paratypic adult male is mounted as holotype and deposited in NHMD under catalogue number NHMD-1175697.
Additional material includes one adult female with same collection data as holotype, mounted for SEM and stored in the author’ s personal reference collection.
3.1.4. Description
Adults with head, neck and eleven trunk segments (Fig. 1A and B; 2A; 3 A-C). The trunk is stout, nearly parallel sided along most segments, and heart-shaped in cross-section. Segment 10 is retractable, and can be almost fully retracted into segment 9. For complete overview of measures and dimensions, see Table 1. Distribution of cuticular structures, i. e., sensory spots, glandular cell outlets, spines and tubes, is summarised in Table 2. Since both adult types mounted for LM were mounted on their lateral sides (Fig. 2A), and the SEM specimen was balancing on the middorsal portions of its segments 1 to 4 (Fig. 3), there is a risk that mid- or paradorsal structures on the four anterior segments could have been overlooked.
The head was fully retracted in all available specimens, and information about mouth cone or introvert morphology is therefore not available. The neck has 16 placids, measuring 16 μm in length. The midventral placid is broadest, measuring 14 μm in width at its base (measure from SEM), whereas all other are narrower, measuring 10 μm in width at their bases. The trichoscalid plates are droplet-shaped, without any conspicuous difference between the four dorsal and the two ventromedial ones.
Segment 1 consists of a complete cuticular ring (Fig. 1A and B; 2B; 3 B-C; 4A-C). Sensory spots are located in subdorsal, laterodorsal and ventromedial positions; subdorsal and laterodorsal ones are located near the anterior segment margin; ventromedial ones are located centrally on segment; sensory spots on this segment are large and circular (Fig. 4A, C). Glandular cell outlets type 1 observed in lateroventral positions only. The segment is densely covered with non-bracteate cuticular hairs, except for a hairless zone near the anterior margin; this hairless zone extends more posteriorly in the ventromedial areas, towards the ventromedial sensory spots (Fig. 4C); bracteate hairs not present on this or any other segment. The posterior segment margin is straight along the dorsal and lateral sides, but with a broad, convex extension ventrally; fringe tips alternate between long and flexible acicular tips, and much shorter, rigid but still acicular ones.
Segment 2 consists of a complete cuticular ring (Fig. 1A and B; 2B; 3 B-C; 4A-C). Pachycyclus of the anterior segment margin is of medium thickness and uninterrupted. Very minute glandular cell outlets type 2 with fringed margins are located in subdorsal, laterodorsal, ventrolateral positions (Fig. 4 D-F); in the following these outlets will be referred to as ’fringed glandular cell outlets type 2’. Sensory spots are present as a laterodorsal twin-pair and one ventromedial pair; sensory spots on this and all following segments are large and droplet-shaped (Fig. 4 A-C, E-F). On this and all following segments, the fringed glandular cell outlets type 2 are located more anterior on the segments, thus outlets are sometimes covered by the fringe of the preceding segment, while sensory spots usually are visible. One pair of glandular cell outlets type 1 present in ventromedial positions. Cuticular hairs are densely covering the entire segment. The posterior segment margin is nearly straight, but forms a distinct ventral extension between the ventromedial positions; pectinate fringe as on preceding along the dorsal, lateral and ventrolateral to ventromedial margins, whereas the fringe tips on the ventral extension are shorter, uniform and acutely triangular.
Segment 3 (Fig. 1A and B, 2B; 4G), and remaining segments, consist of one tergal and two sternal plates. Pachycyclus of the anterior segment margin of medium thickness, and interrupted only at tergosternal junctions. Fringed glandular cell outlets type 2 present in sublateral positions (Fig. 1B; 2B), and sensory spots in paradorsal and midlateral positions. Glandular cell outlets type 1 present in ventromedial positions. Tergal plate is densely covered with long hairs; sternal plates densely covered with long hairs on their lateral-most halves, and shorter hairs on their ventral-most halves. The posterior segment margin is straight; pectinate fringe consists of long, uniform, acutely triangular tips along the dorsal, lateral and ventrolateral to ventromedial margins, and similar, but conspicuously shorter tips along the ventral margin, between ventromedial positions.
Segment 4 (Fig. 1A and B; 2C; 4 G-H) with fringed glandular cell outlets type 2 present in paradorsal (Fig. 2C; 4G) and laterodorsal (Fig. 2C; 4H) positions, and sensory spots in subdorsal positions. Glandular cell outlets type 1 present in ventromedial positions. Cuticular hair patterns as on preceding segment, but with conspicuous hairless patches (muscle attachment sites) in laterodorsal positions. Pachycycli and pectinate fringe of posterior margin as on preceding segment.
Segment 5 (Fig. 1A and B; 2 C-D; 4H-I) with tubes in lateroventral positions. Fringed glandular cell outlets type 2 present, but may shift between laterodorsal (male paratype (Fig. 2D) and female SEM specimen (Fig. 4H) or sublateral (male holotype (Fig. 2C)) positions. Sensory spots present in subdorsal, midlateral and ventromedial positions. Glandular cell outlets type 1 present in ventromedial positions. Pachycycli, cuticular hair covering and pectinate fringe as on preceding segment.
Segment 6 (Fig. 1A and B; 2 C-D; 4H-J) with fringed glandular cell outlets type 2 present in paradorsal (Fig. 4J) and laterodorsal (Fig. 2D) positions, and sensory spots in subdorsal, midlateral and ventromedial positions. Glandular cell outlets type 1 present in ventromedial positions. Pachycycli, cuticular hair covering and pectinate fringe as on preceding segment.
Segment 7 (Fig. 1A and B; 2F; 4I, L) with fringed glandular cell outlets type 2 present in sublateral positions, and sensory spots in subdorsal, midlateral and ventromedial positions. Glandular cell outlets type 1 present in ventromedial positions. Pachycycli, cuticular hair covering and pectinate fringe as on preceding segment.
Segment 8 (Fig. 1A and B; 2 E-F; 4K-L) with tubes in lateral accessory positions (Fig. 2E; 4 K-L). Fringed glandular cell outlets type 2 present in middorsal, laterodorsal, and sublateral positions (Fig. 2F), and sensory spots in subdorsal positions. Glandular cell outlets type 1 present in ventromedial positions. Pachycycli, cuticular hair covering and pectinate fringe as on preceding segment, but with fringe tips being slightly longer.
Segment 9 (Fig. 1A and B; 2 E-F, I; 4K, M O) with large, nephridial area in sublateral positions; consisting of elongate sieve area (partly covered by fringe of preceding segment) anterior to an oval, smooth area with a central pore field (Fig. 1B; 2 E-F; 4K); sieve area is elongate, and broadest anteriorly; entire nephridial area measures around 30 μm in length, thus corresponding to nearly 50% of the segment length. Fringed glandular cell outlets type 2 present in middorsal position, and sensory spots in subdorsal, laterodorsal, midlateral (Fig. 4N) and ventrolateral positions. Glandular cell outlets type 1 present in ventromedial positions. Pachycycli, cuticular hair covering and pectinate fringe as on preceding segment, but with fringe tips being slightly longer.
Segment 10 (Fig. 1 A-D; 2G-I; 4M O) with sexually dimorphic tubes in laterodorsal positions, attaching near posterior segment margin; male tubes are long and slender (Figs. 1A and 2G, I), whereas female tubes are much shorter and curved (Fig.. 1C and 4M). Fringed glandular cell outlet type 2 absent. Sensory spots present in subdorsal and ventrolateral positions, and glandular cell outlets type 1 in ventromedial positions. Patches with lightly scattered hairs present in middorsal and midlateral areas; sternal plates without hairs. Posterior segment margin wavy, with long fringe tips in laterodorsal areas, but otherwise rather short tips; ventral margins oblique, with short fringe tips. Pachycycli as on preceding segment. The segment is retractable, and can be nearly fully retracted into preceding segment (Fig. 3 A-C, 4M O).
Segment 11 with lateral terminal spines (Fig. 1 A-D; 2G-I; 4M O). Males with three pairs of penile spines; all three penile spines are thin, flexible tubes, but the dorsal one is longest, and terminates into an abruptly offset tip (Fig. 2H); females with very short (10 μm from SEM), thin, lateral terminal accessory spines (Fig. 4M and N). Sensory spots present in subdorsal positions. Segment densely covered with short hairs, on dorsal side between laterodorsal positions, and on ventral side between ventromedial positions. Tergal extensions are well-spaced, cone-shaped and pointed; margins of sternal plates curved, not forming any kind of sternal extensions.
3.1.5. Notes on diagnostic characters
The enlarged, elongate sieve plate anterior to a pore field, the lack of acicular spines in dorsal and lateral series on all segments but the terminal, the general stout habitus, and dense hair covering of trunk segments clearly indicate that E. lapitaorum sp. nov. belongs to the E. coulli-group. Among species within this group, E. lapitaorum sp. nov. is most easily recognised by its distribution of glandular cell outlets type 2, as these are distinct characters in both LM and SEM.
The overall distribution pattern of glandular cell outlets type 2 is unique for E. lapitaorum sp. nov., and is in itself the easiest and safest way to identify the species. Especially the presence of middorsal glandular cell outlets type 2 on segments 8 and 9 is unique for the species, as is the combined presence of outlets in paradorsal + laterodorsal positions on segments 4 and 6.
Also the morphology of the glandular cell outlets type 2 deserves some attention. Typically, type 2 outlets appear in SEM as plain oval openings without any external structures besides the reinforced margins of the openings (see, e.g., Neuhaus (2013) Fig. 5.1.22 to 23). However, different variations from this general appearance have been reported from species of the E. coulli- group. In Echinoderes rex Lundbye et al., 2011 the margins of the type 2 outlets are lined with long cuticular fringes that form a tuft around the outlet. Lundbye et al. (2011) referred to these as ‘modified glandular cell outlet type II’. Only a year after the description of E. rex, Yamasaki & Kajihara (2012) reported the presence of modified glandular cell outlets type II from the new species E. ohtsukai Yamasaki & Kajihara, 2012, and these outlets were also documented in the subsequent redescription from Herranz & Leander (2016), who referred to them as ‘fringed tubes’. The modified type 2 outlets, or fringed tubes, were furthermore reported from E. maxwelli (Omer-Cooper, 1957) when Randsø et al. (2019) redescribed the species. Interestingly, the accompanying phylogenetic analyses suggested that these three particular species form a clade that is morphologically supported by the presence of modified type 2 outlets.
Thus, E. lapitaorum sp. nov. is only the fourth E. coulli- group species with this kind of outlets. It is too premature to say if the new species is part of the same clade, and running new phylogenetic analyses to determine this would be beyond the scope of the present contribution. It is noteworthy though, that E. lapitaorum sp. nov. and E. maxwelli share another distinct character trait, namely the retractability of segment 10.
Among species outside the E. coulli- group, minute fringed tubes are known from two species, Echinoderes truncatus Higgins, 1983 and E. orestauri Pardos et al., 2016a (Pardos et al., 2016a; Sørensen et al., 2016). However, a homology between the fringed tubes in these species, and those in species of the E. coulli- group is questionable. Among the latter, the fringed structures are obviously a modification of their glandular cell outlets type 2. This is different in E. truncatus and E. orestauri as they have both glandular cell outlets type 2 with a regular morphology, located in laterodorsal or midlateral positions on segments 8 and 9, as well as fringed tubes appearing as numerous pairs across the tergal plates of segments 2 to 9. Without any clear support for a homology between the fringed structures of E. truncatus and E. orestauri, and those of the E. coulli -group species, it seems for now as the presence of fringed glandular cell outlets type 2 is restricted to the E. coulli -group, and potentially to a subclade within this group.
As indicated above, the terminology for this special kind of glandular cell outlets type 2 is not fully established. In the present contribution I prefer to refer to them as ’fringed glandular cell outlets type 2 ′, and consider this term to be more precise than the two previously used ones. Referring to them as ‘modified’ makes good sense, but is also slightly imprecise, as the name does not explain in which way the outlets are modified. Likewise, the ‘fringed tube’-term might mislead a reader to think that the structures are derived from tubules, rather than glandular cell outlets type 2. Thus, ’fringed glandular cell outlets type 2 ′ appears to be the name that catches most information from the two previously used terms.
description: Published as part of Sørensen, Martin V., 2023, New data on the Echinoderes coulli-group (Kinorhyncha: Cyclorhagida: Echinoderidae): A new species from New Caledonia mangroves, and a redescription of E. bengalensis (Timm, 1958), pp. 90-101 in Zoologischer Anzeiger (Zool. Anz.) (Zool. Anz.) 302 on pages 91-96, DOI: 10.1016/j.jcz.2022.11.009, http://zenodo.org/record/8164187