Euchone sp. 1

Euchone Malmgren, 1866

Euchone sp. 1

Voucher specimens. INFLEX: station 2MFB.

Diagnosis. Small bodied, slender species; voucher specimen with body complete, but branchial crown missing; 6.5 mm long (body) and 0.5 mm wide, with 8 thoracic and 19 abdominal chaetigers with 7 of these associated with pre-pygidial depression; colour in alcohol pale yellow.

Collar well developed; of similar height all around, only slightly higher ventrally than dorsally; with mid-dorsal margins overlapping; anterior margin entire ventrally with a shallow midventral notch. Glandular ridge present on chaetiger 2, very narrow.

Collar chaetae narrowly limbate arranged in single longitudinal somewhat oblique row; superior and inferior notochaetae of limbate, 3-4 per fascicle. Thoracic neuropodial uncini acicular, about 3 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 narrow pre-pygidial depression occupying 7 chaetigers, with high raised membranous lateral flanges connected anteriorly by a rounded membrane, flanges lower posteriorly. Pygidium well-developed, triangular lobe. Tube not observed.

Mehtyl green staining pattern: refer to plate accompanying this description.

Remarks. A commonly reported species Euchone pallida described by Ehlers (1908) from Kerguelen Island also lacks broad mucronate notochaetae. Ehlers (1908) based his description on relatively small holotype, 22mm long for body plus 14mm for branchial crown and 3 mm wide, for 8 thoracic and 32 abdominal segments, with 12 of those forming the pre-pygidial (anal) depression. Licciano et al. (2007) provided re-description of E. pallida and added valuable information on internal structure of the crown and methyl green pattern based on medium-sized specimens. However specimens of different sizes were considered to belong to E. pallida by different authors (i.e. Hartman, 1978) with considerable variation not just in size, but also number of abdominal segments and the number forming the anal depression. It is possible that different species were lumped under this name as number of abdominal segments is considered of taxonomic character in Sabellidae. In Falkland Island material, specimens with differing number of abdominal segments (19 and 27 respectively, also differing in number of both thoracic and abdominal uncini per ramus) and with different methyl green pattern (see comparative image) are here considered to be different species. Neither of these two species is likely to belong to E. pallida of Ehlers, 1897 as these are much smaller in body size (6.5 and 9.5 mm as oppose to 22 mm) as it is often typical for deep-water fauna (specimens collected from ~1000m), possess fewer abdominal segments and differ in staining pattern. Licciano et al. (2009) provided description of methyl green staining pattern as: a homogeneous dark coloration of thorax and abdomen with distinct intra-segmental furrow, except for presence of thin glandular ridge on chaetiger two, without stain on the collar as apparent from their Figure 1B. Euchone sp. 1 may correspond to what Hartmans (1978) recorded of as juvenile of E. pallida (see comparative table below). These small bodied specimens likely represent a new species (see comparative table for Euchone species recorded so far from Southern Ocean and Magellan region), but complete specimens with branchial crowns will be necessary to fully diagnose these species.

Comparison of Euchone pallida records by different authors and Euchone sp. 1 and 2 from Falkland Islands.