Euchone undulocincta Hartmann-Schröder & Rosenfeldt, 1989  

Euchone Malmgren, 1866

Euchone undulocincta Hartmann-Schröder & Rosenfeldt, 1989

Voucher specimens. Sea Lion: station 79MFB.

Diagnosis. Medium sized, robust species; voucher is a complete specimen with branchial crown; 15mm long for body and 7mm long for crown, 1.5mm wide; with eight thoracic and 23 abdominal chaetigers with 7 of these associated with pre-pygidial depression; colour in alcohol pinkish.

Branchial crown with 8 pairs of radioles and 2 pairs of nonvascularized ventral radiolar appendages. Collar well developed, higher ventrally than dorsally, with mid-dorsal margins overlapping, anterior margin entire ventrally with a deep midventral notch. Glandular ridge present on chaetiger 2.

Collar chaetae narrowly-limbate arranged in single longitudinal, somewhat oblique row; notochaetae of two types, superior notochaetae broadly-limbate, inferior notochaetae mucronate (about 8 per fascicle). Thoracic neuropodia uncini aciculae, about 15 per fascicle. Companion chaetae absent. Abdominal chaetae on short, slightly elevated neuropodia, with elongate narrowly limbate chaetae. Notopodia of anterior abdominal chaetigers with quadrate avicular uncini with five rows of similar-sized teeth over main fang, covering half its length, well developed breast and very short handle.

Abdomen with a broad pre-pygidial depression occupying 7 chaetigers, with high raised membranous lateral flanges connected anteriorly by a rounded membrane, flanges lower posteriorly. Pygidium small, bluntly rounded, triangular lobe. Tube not observed.

Remarks. There are two known species of Euchone with two types of notochaetae from the area. Hartman (1978) described E. heterosetosa from South Georgia, 2900m. Nearly a decade later Hartmann-Schröder and Rosenfeldt (1989) described similar species as E. undulocincta from much shallower depths of 133m off Joiville Island without providing comparison of the two species. These species clearly differ in size (see comparative table of Euchone species know from the area) and Falkland Island specimens are consistent with E. undulocincta, although description by Hartmann-Schröder and Rosenfeldt (1989) is rather brief and comparison with holotype is needed for confirmation. Hartmann-Schröder and Rosenfeldt (1989), for example, mentioned that the species is unique in possessing the ridge on chaetiger 2, this however is a generic-level character possessed by several sabellid genera.

Comparison of Euchone species known from the geographical area.