Eclysippe yonaguniensis, Reuscher, Michael G. & Fiege, Dieter, 2016

Reuscher, Michael G. & Fiege, Dieter, 2016, Ampharetidae (Annelida: Polychaeta) from cold seeps off Pakistan and hydrothermal vents off Taiwan, with the description of three new species, Zootaxa 4139 (2), pp. 197-208 : 201

Eclysippe yonaguniensis sp. nov.

( Figs 3 A–C; 7A)

Specimens examined. Holotype: SMF 24136, Yonaguni Knoll IV Hydrothermal Field, low CO2 seepage site, Okinawa Trough, 24°50.355’N 122°41.736’E, 1324 m, SO 196, Station 65, TV-MUC, 18 March 2008 (cs, broken into 3 pieces during examination).

Description. Length 1.9 mm, width 0.16 mm. Prostomium triangular with conical front, without lobes, incisions, glandular ridges or eyes ( Fig. 3 A). Buccal tentacles smooth, with ventral groove ( Fig. 3 B). Three pairs of smooth cirriform branchiae arranged in one transverse row in segment III, separated by median gap of about twice the branchial width; outermost and second outermost branchiae of right group missing; innermost branchiae short and digitiform, less than half as long as remaining branchiae ( Fig. 3 A); second outermost branchiae of transverse row originating from segment II, outermost branchiae of transverse row originating from segment III, median branchiae originating from segment IV ( Fig. 7 A). Segment II with enlarged chaetae, formed as paleae; three paleae in left group, four in right group ( Fig. 3 B). Notopodia with capillary chaetae from segment III, present in 15 chaetigers; first two pairs of notopodia very small, gradually increasing in size to fourth pair, decreasing again from twelfth pair; notopodia without cirri ( Fig. 3 A). Notochaetae of first two and last four thoracic uncinigers fewer in number, thinner and shorter than those in median thoracic notopodia. Neuropodial tori with uncini from segment VI, present in 12 thoracic uncinigers; tori without cirri. Continuous ventral shields present to thoracic unciniger 8. Segment length gradually increasing between thoracic unciniger 7 and 9; each of thoracic uncinigers 9–12 about as long as first six thoracic uncinigers combined ( Fig. 3 A). Two intermediate uncinigers ( Fig. 3 C). Eight abdominal uncinigers without rudimentary notopodia. Pinnules without dorsal cirrus. Pygidium with terminal anus and two short stout ventrolateral anal cirri. Uncini in thoracic, intermediate and abdominal uncinigers with numerous teeth in two alternating rows over rostral tooth and basal prow.

Remarks. Eclysippe yonaguniensis sp. nov. differs from E. trilobata by the possession of very short branchiae in the innermost position of the transverse row. In E. vanelli the innermost branchiae are unknown because they were missing in Fauvel’s (1936) and Eliason’s (1955) specimens. Eclysippe vanelli and E. trilobata were both described with modified notopodia in the last five thoracic uncinigers. In the new species the last five notopodia are slightly reduced in size, but their shape is not different. Furthermore, both E. trilobata and E. vanelli have much smaller gaps between branchial groups and a higher count of paleae (around 10). Eclysippe vanelli was described with 12 ( Eliason 1955), E. trilobata with 12–14 ( Hilbig 2000) abdominal uncinigers. Because the number of intermediate uncinigers (sensu Imajima et al. 2012), i.e., segments that have neuropodia of the thoracic type but lack notopodia, is constant within a genus, we assume that the first two uncinigers that were included in the counts of abdominal uncinigers of these species are actually intermediate uncinigers. Therefore, the adjusted counts of abdominal uncinigers in E. vanelli , E. trilobata , are assumed to be 10 and 10–12, respectively, whereas Eclysippe yonaguniensis sp. nov. has only 8 abdominal uncinigers.

Distribution. Exclusively known from the Yonaguni Knoll IV Hydrothermal Field in the Okinawa Trough off the northeastern coast of Taiwan.

Figures

FIGURE 3. Eclysippe yonaguniensis sp. nov. Holotype: (A) entire specimen, dorsal view; (B) anterior end, ventral view; (C) thoracic, intermediate, and abdominal uncinigers, ventral view.

FIGURE 7. ID cards: (A) Eclysippe yonaguniensis sp. nov. (B) Glyphanostomum bilabiatum sp. nov. (C) Pavelius makranensis sp. nov.