Apistobranchidae Mesnil and Caullery, 1898
Apistobranchus Levinsen, 1883
Apistobranchus jasoni Neal and Paterson, 2020 in Neal et al., 2020
Material. Sample 65MFC, 450 m, -49.2584430, -59.1251589, coll. 19/03/2012, ind. 1, holotype (NHM.2018.12712). Sample 65MFC, 450 m, -49.2584430, -59.1251589, coll. 19/03/2012, ind. 1, paratype (NHM.2018.12713)..
Diagnosis. Holotype (NHM.2018.12712), incomplete specimen, 6 mm long and 1 mm wide for 40 chaetigers. Paratype (SEM specimen on stub, NHM.2018.12713), incomplete specimen, 4 mm long and 0.8 mm wide for 22 chaetigers. Body strongly curved, broad, flattened across thoracic region, tapering posteriorly; abdominal segments longer, cylindrical. Colour in alcohol dark yellow to pale orange.
Prostomium bluntly rounded, wider than long, continuing posteriorly as short caruncle terminating in middle of chaetiger 1; palps missing (not observed); eyes absent; paired nuchal organs prominent, located posterior to the origin of palps. Peristomium greatly reduced to lips surrounding mouth.
Notopodia reduced to erect, branchiae-like lobes with internal acicula, present on chaetigers 2–6, then absent on chaetigers 7–10 and then continuing to end of fragment. Chaetigers 1–6 with basally thick, distally tapering interramal cirrus; neuropodia from 7th chaetiger modified, with dense fascicles of pointed capillary neurochaetae. Neuropodia adorned with various lobes and cirri as follow): chaetigers 1–3 with single, triangular lobe at ventral-most edge of neuropodium; chaetiger 4 with two lobes on raised ridge; chaetigers 5–6 with thin membranous lamella with numerous (> 30) very small papillae; chaetiger 7 with ten large triangular lobes (5–7 in smaller specimens). Neuropodia of chaetigers 8–11 resembling those of chaetigers 5–6; subsequent (abdominal) neuropodia reduced to long, narrow lobes with few long neurochaetae.
Neurochaetae of first seven chaetigers somewhat stout with simple, gently bent blunt tips; arranged in 4–6 palisaded rows. Abdominal neurochaetae few, the main fascicle composed of two types : Type 1. Long capillaries, with frayed (damaged?) tips, fewer than ten per fascicle; Type 2. Short, falcate chaetae, with gently curved, very long thin tips, ca. 6 per fascicle. Additionally, a short, blunt posterior, protruding acicular spine, accompanied by a single short capillary with slender tip, have been observed in abdominal neuropodia. Pygidium not observed.
Methyl Green stain pattern. Stain retained on prostomium and peristomium, chaetigers 1–4 do not retain stain (pale stain at the best), chaetigers 5–10 stain lightly interramally, from chaetiger 12 until end of the fragment with stain strongly concentrating on the posterior edge of the neuropodial lamellae, but no patterns of dorsum or ventral surfaces observed.
Remarks. This species belongs to an Apistobranchus group in which notopodia are missing on chaetigers 1 and 7–10, with neuropodium on chaetiger 4 multilobed (see Blake 1996). The Falkland Islands species is clearly different from Apistobranchus glacierae Hartman, 1978 the only valid species known from the area according to Petti et al. (2007), who clarified the status of A. glacierae and A. gudrunae Hartmann-Schröder & Rosenfeldt, 1988. In A. glacierae the notopodia are absent on chaetigers 1 and 8 only, unlike A. jasoni sp. nov. in which they are absent from chaetigers 1 and 7–10.
It is difficult to distinguish Falkland Islands specimens from A. ornatus Hartman, 1965 redescribed by Blake (1996) from the Pacific, which in turn is difficult to distinguish from A. typicus (NW Atlantic distribution) other than by methyl green stain (see discussion in Blake (1996)). Falkland Island specimens do not stain uniformly as Blake (1996) reported for A. ornatus and no paired ventral line extending from chaetiger 7–8 has been detected. Stain is, however, more pronounced in Falkland Islands specimens then in A. typicus, in which a pale reaction is limited to swollen dorsal glandular areas according to Blake (1996). Further, while the posterior protruding spine has been reported in A. ornatus (Blake & Petti, 2019), to our knowledge there has been no reports of its accompanying capillary as observed in Falklands specimens (Fig. 15b). Additionally, when comparing specimens with similar number of segments, further subtle differences can be detected and these are summarised in Table 1. Overall, the Falkland Island specimens are smaller and more slender than A. typicus and A. ornatus, with fewer rows of neurochaetae and fewer lobes on chaetigers 4. We suggest that there is evidence that Falkland Islands’ specimens represent new species.
Table. 1 Summary of morphological variation in Apistobranchus from FI and Apistobranchus ornatus as reported by Blake (1996)
|
Variation in Apistobranchus from FI
|
Variation in A. ornatus |
|
|
Length (mm) |
4 - 6 |
4 - 9 |
|
Width (mm) |
0.8 - 1 |
1.4 - 3 |
|
Number of chaetigers (fragments) |
22 - 40 |
22 - 41 |
|
No. of palisade rows of neurochaetae |
4 - 6 |
4-10 or more |
|
No. of neurochaetae in abdomen |
<10 |
10-15 |
|
No. of lobes on neuropodium of chaetiger 4 |
2-3 |
2 -7 |
|
No. of lobes on neuropodium of chaetiger 7 |
5 - 10 |
7-10 |
|
Branchiae missing on chaetigers |
7 - (9) 10 |
7(8)-10(11) |
REFERENCES
Blake, J.A. 1996. Family Apistobranchidae Mesnil and Caullery, 1898. pages 71-79. IN: Blake, James A.; Hilbig, Brigitte; and Scott, Paul H. Taxonomic Atlas of the Benthic Fauna of the Santa Maria Basin and Western Santa Barbara Channel. 6 - The Annelida Part 3. Polychaeta: Orbiniidae to Cossuridae. Santa Barbara Museum of Natural History. Santa Barbara
Hartman, O. 1965. Deep-water benthic polychaetous annelids off New England to Bermuda and other North Atlantic areas. Occasional Papers of the Allan Hancock Foundation, 28: 1-378., available online at http://digitallibrary.usc.edu/cdm/ref/collection/p15799coll82/id/20299
Hartman, O. (1978). Polychaeta from the Weddell Sea quadrant, Antarctica. Antarctic Research Series. 26(4): 125-223., available online at http://onlinelibrary.wiley.com/doi/10.1002/9781118664599.ch4/summary
Hartmann-Schröder, G. and Rosenfeldt, Pongchai 1988. Die Polychaeten der Polarstern-Reise ANT III/2 in die Antarktis 1984. Teil 1: Euphrosinidae bis Chaetopteridae. Mitteilungen aus dem Hamburgischen zoologischen Museum und Institut, 85: 25-72.
Levinsen, G. M. R. 1884. Systematisk-geografisk Oversigt over de nordiske Annulata, Gephyrea, Chaetognathi og Balanoglossi. Videnskabelige Meddelelser fra Dansk naturhistorisk Forening i Köbenhavn, 1883: 92-350.
Neal L., Paterson, G.L.J., Blockley, D., Scott, B., Sherlock, E., Huque, C., and Glover, A.G. (2020) Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration. ZooKeys 938: 1–86. https://doi.org/10.3897/zookeys.938.49349
