Echinoderes remanei (Blake, 1930)

Grzelak, Katarzyna, Yamasaki, Hiroshi, Mincks, Sarah, Phillips, Anna J. & Sørensen, Martin V., 2023, Revision of an Arctic kinorhynch species: Echinoderes svetlanae and E. tubilak are junior synonyms of E. remanei, Zoologischer Anzeiger 302, pp. 75-89 : 85-86

4.1. Comparison of E. remanei , E. tubilak and E. svetlanae

E. remanei was originally described by Blake in 1930, and redescribed in 1964 by Higgins ( Blake 1930; Higgins 1964). Although the redescription provided some more accurate information about the species, important taxonomic characters were still overlooked or interpreted incorrectly. This led to the species being characterized by having middorsal spines on segment 4 to 8 and lateral spines on segment 5 to 9, in addition to the spines on segment 11 ( Higgins 1964). Therefore, when Higgins and Kristensen (1988) described E. tubilak several years later, the only morphological difference reported between E. remanei and a E. tubilak was the presence of ‘round to oval cuticular scars’ on segment 2 ( Higgins & Kristensen 1988). The authors highlighted the similarity between the two species, both regarding the presence of a prominent pectinate fringe on the ventral side of segment 1 and in the differences in the length of the lateral terminal spines between males and females. At present, we know that structures reported as “oval cuticular scars” in the earlier descriptions usually referred to glandular cell outlets type 2 - a diagnostic trait that was not known at that time (see discussion in Neuhaus & Blasche 2006; Sørensen et al., 2012; Grzelak & Sørensen 2018). The occurrence of glands in E. tubilak was also illustrated in the line art illustrations (see Figs 65–66, 68, 72 in Higgins & Kristensen 1988), but only on the dorsal side of segments 2 and 4. The additional pairs in sublateral and ventrolateral positions on segment 2 were overlooked, as well as the pairs of gland openings on segment 5 and 8, which was subsequently reported by Grzelak & Sørensen (2018). Presence of glandular cell outlets type 2 on segment 10 was not confirmed until this study, as there was previously no material available for SEM (visualising glandular cell outlets type 2 on segment 10 using LM only is very challenging). In the case of E. remanei , the presence of glands or cuticular scars has never been mentioned before, but the material deposited in the NMNH shows their presence, which is in agreement with the observation of the E. tubilak type material and additional specimens analysed in the present study. Echinoderes svetlanae that was described by Adrianov in 1999 represents a similar situation. According to the original description, the species was characterized by the presence of middorsal spines on segment 4 to 8, lateroventral spines on segment 6 to 9, and the absence of lateral tubes/spines on segment 5 ( Adrianov & Malakhov 1999). Again, thorough examination of the museum materials revealed a number of traits that were not reported previously, including the number and distribution pattern of glandular cell outlets type 2 matching that observed in E. tubilak , and even the presence of lateroventral tubes on segment 5. This character, however, due to the condition of E. svetlanae specimens was poorly visible, thus it is not really surprising that it was overlooked in previous studies ( Adrianov & Malakhov 1999; Grzelak & Sørensen 2018).

In addition to overlapping morphological characters in the three species, the specimens of E. remanei , E. tubilak , and E. svetlanae share distinct morphometric traits. When specimens of E. remanei from Maine were compared with specimens of E. tubilak from localities in Greenland, Alaska and Japan and with specimens of E. svetlanae from the White Sea, it became evident that most of the spine dimensions are highly comparable across the analysed populations ( Fig. 8 ). The only exceptions were specimens from southern Alaska, of which middorsal spines on segment 8 were significantly shorter than those of specimens from Greenland; and lateroventral spines on segments 6 to 8 were slightly shorter than those from Greenland and Maine, likely due to the smaller body size of southern Alaskan specimens compared to Greenlandic individuals ( Fig. 7 ). Nevertheless, a very clear pattern of the middorsal spine always being shorter on segment 8 in comparison to the middorsal spine on segment 7 was observed for all individuals ( Fig. 8A ). Differences in lateral terminal spines length between the sexes were also very prominent for all populations ( Fig. 9 ), with no significant differences in spines length among males from different locations, and significant differences in spines length of females being detected only between specimens from southern Alaska and Maine.

All of our results provide strong arguments for considering the studied specimens of E. remanei , E. tubilak and E. svetlanae as conspecific, and they should now be regarded as E. remanei .

Figures

Fig. 8. Box plot showing middorsal (A) and lateroventral (B) spines length of Echinoderes remanei collected in different regions.

Fig. 7. Box plot showing total body length of Echinoderes remanei collected in different regions.

Fig. 9. Box plot showing lateral terminal spines length for males and females of Echinoderes remanei collected in different regions.