Glyphanostomum Levinsen, 1884  

Subfamily Ampharetinae Malmgren, 1866

Glyphanostomum Levinsen, 1884

Glyphanostomum sp. 1

Voucher. Endeavour: station E6FA

Diagnosis.  Voucher is a complete specimen, body long, slender, fragment 15mm long and 0.6mm wide. Tube strongly annulated as typical for the genus, muddy, soft. Thorax composed of 14 chaetigers, of which 11 uncinigers; abdomen posteriorly incomplete; abdomen with 24 uncinigers. First 5 thoracic chaetigers short, subsequent chaetiger progressively longer. Prostomium simple, spade-shaped lobe at anterior end, with a pair of large, but faint red eye-spots. Buccal tentacles not extended, tips smooth. Three pairs of branchiae, arranged in two groups on chaetiger 1, each group with median branchia anteriorly displaced (its branchiphore not visible in dorsal view) to 2 posteriorly laced lateral branchiae with branchiophores exposed and basally fused; two branchial groups separated by a wide gap; styles of branchiae smooth, thin, cylindrical with median pair longest, the lateral pair shorter, of similar length. Notopodia of first and second chaetiger reduced, with second one dorsally displaced; notopodia without cirri. Notochaetae of 2 groups longer, appearing narrowly bilimbate and shorter, simple capillaries. Thoracic uncini with one vertical row of 7 teeth with the second most basal tooth doubled (formula: 1-2-1-1-1-1-1) in frontal view, appearing as 7 teeth above prow. Abdominal uncini with mana small teeth above the main fang, irregularly arranged in multiple rows. Neuropodia free from body wall ventrally. Pygidium with two fleshy, triangular lobes dorsally and ventrally, with smaller lobes laterally; with 2 lateral, medium length cirri.  

Remarks. Currently they are 6 valid species in genus Glyphanostomum, with G. pallescens (Théel, 1879) (type species of this genus) originally described from Arctic (Kara Sea) now considered a cosmopolitan species with wide geographic and bathymetric range.  According to Holthe (1986) type specimen of G. pallescens  has been lost, which probably fuelled its cosmopolitan status and variable description of specimens identified as G. pallescens by different authors from around the world (see for example Holthe, 1986; Hilbig in Blake et al., 2000; Jirkov, 2001; Reusher et al., 2015). Falkland Island specimens are very similar to G. pallescens in number of abdominal chaetigers, with 24-25 reported by Théel (1879) (but see discussion in Reuscher et al., 2015). The main taxonomic characters (see comparative Table used for Glyphanostomum species) are arrangement of branchiae (Reuscher et. al, 2009), form of thoracic uncini and number of abdominal uncinigers. Combination of these characters in Falkland specimens suggests that these may represent a new species. The branchial arrangement which is grouped in 1+2 fashion (the middle branchia is positioned anteriorly to two other pairs and not visible basally as it should be in oblique or transverse row arrangement) is unique among the known Glyphanostomum species so far. Further thoracic uncini are arranged in a single row, but the second basalmost tooth is doubled (Hilbig in Blake, 2000 imaged a similar arraignment in Pacific specimens of G. pallescens). G. scotiarum described from deep waters of Drake Passage, Weddell Sea and South Orkneys possess 33 abdominal uncinigers. In her description of G. scotiarum  Hartman  (1978) did not comment on the form of thoracic uncini in frontal view or detailed the branchial arrangement, which is considered to be in an oblique row (based on her drawing, branchiae appear basally visible and not grouped as in Falkland specimens). 

Comparison of currently known Glyphanostomum species (as reported in literature) and Falkland Is. specimens.