Terebellides Sars, 1835
Terebellides sp. 2
Voucher. VINSON WEST: station 1MFA and TOROA: station T9FB.
Diagnosis. One complete specimen (1MFA) and one specimen with thorax only (T9FB) ; complete specimen 17mm long and 1mm in width for 18 thoracic and about 25 abdominal chaetigers; body tapering posteriorly; chaetiger 1-10 short, getting progressively longer from chaetiger 11; then segments increasingly shorter and crowded towards pygidium.
Prostomium compact; tentacular membrane surrounding the mouth as an enlarged convoluted lobe, buccal tentacles missing. Expanded oblong to rectangular structure (=“lower lip” sensu Hutchings and Peart 2000) below tentacular membrane. Eyespots absent.
Lateral lappets on chaetigers 1–5, anterior margins separated from body wall; a swollen glandular area particularly pronounced in chaetiger 1; chaetigers 6 and 7 without lateral lappets, but still somewhat laterally thickened. Nephridial papillae or nephridial pores not observed (using light microscopy).
Branchiae arising as a single structure from segments 3–4, consisting of a single mid-dorsal stalked structure made up of at least 3 lobes (lobes are completely missing in voucher 1MFA; 3 lobes can be observed in voucher T9FB); pair of anterior lobes large and fused together for more than half of their length; the third lobe positioned ventrally, much smaller, completely free from the anterior pair.
Eighteen pairs of notopodia (segments 3–20), compact, rectangular; notopodia of segment 3 (=1st pair of notopodia) much smaller than on subsequent segments; notopodia of segments 4-7 (2nd – 5th pair) appear slightly smaller than those on subsequent segments. Notochaetae of 1st pair of notopodia similar in length and thickness to notochaetae of subsequent notopodia but less numerous. All notochaetae simple, narrowly limbate capillaries.
Neuropodia present from chaetiger 6 (segment 8). Thoracic neuropodia as sessile pads; abdominal neuropodia as erect pinnules. Neuropodial uncini in single rows throughout. Uncini similar in both vouchers; number slightly variable:
Voucher T4FB: First thoracic neuropodia (chaetiger 6) with few (mostly broken off), sharply bent, geniculate acicular hooks with acute tips. Second and all subsequent thoracic neuropodia with about 10 uncini per torus; uncini long handled denticulate hooks with main fang large and surmounted by a crest of smaller denticles. Abdominal uncini uknown; abdomen missing.
Voucher 1MFA: First thoracic neuropodia (chaetiger 6) with 10, sharply bent, geniculate acicular hooks with acute, slightly upward turned tips. Second and all subsequent thoracic neuropodia with about uncini per torus; uncini long handled denticulate hooks with main fang large and surmounted by a crest of smaller denticles. About 25 abodminal uncinigers. Abdominal uncinigers with about 35 avicular uncini per torus, each uncinus with 3–4 teeth above main fang surmounted by number of smaller teeth. Pygidium damaged.
Remarks. Currently, only three valid species in genus Terebellides are known from the area T. kerguelensis, T. longicaudatus and T. bisetosa. Recent revisionary work (Parapar and Moreira, 2008) concluded that T. minutus Hessle, 1917 (type locality: Straits of Magellan - Tierra del Fuego) and T. antarcticus Hessle, 1917 (type locality: Graham Land, Southern Ocean) are synonyms of T. kerguelensis (McIntosh, 1885). Terebellides kerguelensis (McIntosh, 1885) was redescribed by Parapar and Moreira (2008) and is characterized by the presence of an anterior branchial extension (5th lobe), lateral lappets in five anterior thoracic chaetigers, segmental organs in chaetigers 1, 4 and 5, and first thoracic acicular neurochaetae sharply bent with pointed tips.
Terebellides longicaudatus is characterized by the presence of wide lateral lappets in chaetigers 1 and 2 (segments 3 and 4), first thoracic notopodium which is greatly reduced and large thoracic uncinigerous tori provided with many (45 to 80) uncini and numerous abdominal chaetigers. Terebellides bisetosa Hartmann-Schröder, 1965 known from Chile can be distinguished by having 2 types of notochaetae. Falkland Islands specimens (1st notopodium smaller, with strongly bent and acutely tipped spines, with about 10 uncini per thorus, lobes on chaetigers 1- 5) are therefore most similar to T. kerguelensis. However the number, size and fusion of branchial lobes cannot be assessed with confidence as these are often damaged in Falkland Island material. Only one specimen had branchial lobes attached and only 3 lobes were observed with unpaired 3rd lobe free and much smaller than anterior pair of branchial lobes. This branchial arrangement is not consistent with T. kerguelensis, but it is not clear if the small lobe/s are missing/regenerating or if this is a true branchial form. Segmental organs in chaetigers 1, 4 and 5 present in T. kerguelensis were not confirmed in Falkland Islands specimens (under light microscopy). It is possible that Falkland specimens represent a new species, but better preserved material will be necessary to establish this. The specimens are assigned here to morphospecies Terebellides sp. 2.