Apistobranchus jasoni Neal & Paterson, 2020

Neal, Lenka, Paterson, Gordon L. J., Blockley, David, Scott, Ben, Sherlock, Emma, Huque, Cate & Glover, Adrian G., 2020, Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration, ZooKeys 938, pp. 1-86 : 1

Apistobranchus jasoni Neal & Paterson sp. nov. Figures 13 , 14 , 15

Materials.

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). Other materials: Sample 15MFC, 454 m, -49.2686572, -59.1133764, coll. 16/04/2012, ind. 1, NHM.2018.24086. Sample 19MFB, 448 m, -49.2870544, -59.1680519, coll. 17/04/2012, ind. 1, NHM.2018.24172. Sample 26MFB 449 m, -49.3048414, -59.1402400, coll. 24/04/2012, ind. 1, NHM.2018.24333. Sample 26MFC, 449 m, -49.3048414, -59.1402400, coll. 24/04/2012, ind. 1, NHM.2018.24343. Sample 28MFA, 452 m, -49.3044189, -59.0852225, coll. 23/04/2012, ind. 1, NHM.2018.24371. Sample 35MFA, 450 m, -49.3221858, -59.0573711, coll. 15/04/2012, ind. 1, NHM.2018.24476. Sample 3MFC, 464 m, -49.2326806, -59.1140206, coll. 16/04/2012, ind. 1, NHM.2018.24593. Sample 40MFA, 450 m, -49.3403947, -59.0845558, coll. 23/04/2012, ind. 1, NHM.2018.24601. Sample 43MFA, 430 m, -49.3588058, -59.1392994, coll. 24/12/2012, ind. 1, NHM.2018.24669. Sample 43MFC, 341 m, -49.3588058, -59.1392994, coll. 24/12/2012, ind. 1, NHM.2018.24688. Sample 45MFC, 434 m, -49.3583828, -59.0842219, coll. 23/04/2012, ind. 1, NHM.2018.24740. Sample 59MFB, 448 m, -49.2545600, -59.0688839, coll. 19/03/2012, ind. 1, NHM.2018.25010. Sample 62MFA, 447 m, -49.2487310, -59.1108340, coll. 18/03/2012, ind. 1, NHM.2018.25084. Sample 64MFC, 447 m, -49.2455380, -59.1060962, coll. 18/03/2012, ind. 1, NHM.2018.25121. Sample 66MFA, 445 m, -49.2583220, -59.1058241, coll. 18/03/2012, ind. 1, NHM.2018.25156. Sample 69MFA, 442 m, Latitude -49.2887900, -59.1005700, coll. 19/03/2012, ind. 1, NHM.2018.25198. Sample 70MFB, 446 m, -49.2985060, -59.1150831, coll. 22/03/2012, ind. 1, NHM.2018.25243. Sample 73MFA, 436 m, -49.3416430, -59.1309949, coll. 22/03/2012, ind. 1, NHM.2018.21484. Sample 75MFC, 438 m, -49.3383880, -59.1262342, coll. 22/03/2012, ind. 1, NHM.2018.21523. Sample 79MFA, 446 m, -49.2488410, -59.1867771, coll. 17/03/2012, ind. 1, NHM.2018.21573. Sample 79MFB, 446 m, -49.2488410, -59.1867771, coll. 17/03/2012, ind. 1, NHM.2018.21578. Sample 7MFB, 455 m, -49.2510775, -59.1686567, coll. 17/04/2012, ind. 1, NHM.2018.21597. Sample 80MFC, 445 m, -49.2518660, -59.1722163, coll. 17/03/2012, ind. 1, NHM.2018.21615. Sample 81MFA, 444 m, -49.2618590, -59.1865357, coll. 16/03/2012, ind. 1, NHM.2018.21622. Sample 82MFA, 443 m, -49.2614970, -59.1672448, coll. 16/03/2012, ind. 1, NHM.2018.21638. Sample 8MFB, 459 m, -49.2508764, -59.1411775, coll. 24/04/2012, ind. 1, NHM.2018.21654. Sample 9MFB, 451 m, -49.2506689, -59.1136986, coll. 16/04/2012, ind. 1, NHM.2018.21695. Sample 10MFC, 460 m, -49.2504547, -59.0862200, coll. 25/04/2012, ind. 2, NHM.2018.11380-11381. Sample 12MFA, 453 m, -49.2500069, -59.0312639, coll. 24/04/2012, ind. 2, NHM.2018.11408-11409. Sample 12MFC, 454 m, -49.2500069, -59.0312639, coll. 24/04/2012, ind. 2, NHM.2018.11420-11421. Sample 13MFB, 440 m, -49.2690658, -59.1683544, coll. 17/03/2012, ind. 2, NHM.2018.11426-11427. Sample 15MFA, 455 m, -49.2686572, -59.1133764, coll. 16/04/2012, ind. 2, NHM.2018.11440-11441. Sample 15MFB, 454 m, -49.2686572, -59.1133764, coll. 16/04/2012, ind. 2, NHM.2018.11454-11455. Sample 16MFA, 459 m, -49.2684428, -59.0858878, coll. 25/04/2012, ind. 2, NHM.2018.11472-11473. Sample 24MFC, 453 m, -49.2859825, -59.0305592, coll. 25/04/2012, ind. 2, NHM.2018.11656-11657. Sample 29MFA, 453 m, -49.3041981, -59.0577142, coll. 15/04/2012, ind. 2, NHM.2018.11758-11759. Sample 35MFC, 450 m, -49.3221858, -59.0573711, coll. 15/04/2012, ind. 2, NHM.2018.11822-11823. Sample 3MFB, 464 m, -49.2326806, -59.1140206, coll. 16/04/2012, ind. 2, NHM.2018.11928-11929. Sample 44MFA, 432 m, -49.3585975, -59.1117606, coll. 14/04/2012, ind. 2, NHM.2018.12038-12039. Sample 46MFA, 434 m, -49.3581611, -59.0566836, coll. 14/04/2012, ind. 2, NHM.2018.12066-12067. Sample 47MFC, 444 m, -49.3769958, -59.1665347, coll. 25/03/2012, ind. 2, NHM.2018.12088-12089. Sample 67MFB, 442 m, -49.2889470, -59.1102897, coll. 19/03/2012, ind. 2, NHM.2018.12394-12395. Sample 6MFC, 458 m, -49.2320192, -59.0316156, coll. 25/04/2012, ind. 2, NHM.2018.12440-12441. Sample 71MFC, 449 m, -49.2983550, -59.0956094, coll. 22/03/2012, ind. 2, NHM.2018.12470-12471. Sample 7MFC, 455 m, -49.2510775, -59.1686567, coll. 17/04/2012, ind. 2, NHM.2018.12600-12601. Sample 81MFB, 444 m, -49.2618590, -59.1865357, coll. 16/03/2012, ind. 2, NHM.2018.12622-12623. Sample 90MFB, 440 m, -49.3626660, -59.1204879, coll. 25/03/2012, ind. 2, NHM.2018.12676-12677. Sample 10MFB, 460 m, -49.2504547, -59.0862200, coll. 25/04/2012, ind. 3, NHM.2018.12723-12725. Sample 11MFA, 460 m, -49.2502342, -59.0587417, coll. 15/04/2012, ind. 3, NHM.2018.12741-12743. Sample 16MFB, 459 m, -49.2684428, -59.0858878, coll. 25/04/2012, ind. 3, NHM.2018.12780-12782. Sample 18MFA, 460 m, -49.2679947, -59.0309117, coll. 24/04/2012, ind. 3, NHM.2018.12816-12818. Sample 18MFC, 460 m, -49.2679947, -59.0309117, coll. 24/04/2012, ind. 3, NHM.2018.12822-12824. Sample 25MFA, 447 m, -49.3050428, -59.1677492, coll. 16/04/2012, ind. 3, NHM.2018.12939-12941. Sample 27MFA, 440 m, -49.3046333, -59.1127311, coll. 19/03/2012, ind. 3, NHM.2018.12978-12980. Sample 29MFC, 452 m, -49.3041981, -59.0577142, coll. 15/04/2012, ind. 3, NHM.2018.13035-13037. Sample 49MFA, 448 m, -49.3765856, -59.1114364, coll. 25/03/2012, ind. 3, NHM.2018.13329-13331. Sample 5MFB, 457 m, -49.2322461, -59.0590836, coll. 16/04/2012, ind. 3 NHM.2018.13494-13496. Sample 5MFC, 457 m, -49.2322461, -59.0590836, coll. 16/04/2012, ind. 3, NHM.2018.13503-13505.Sample 11MFB, 455 m, -49.2502342, -59.0587417, coll. 15/04/2012, ind. 4, NHM.2018.13972-13975. Sample 17MFB, 450 m, -49.2679625, -59.0563564, coll. 15/04/2012, ind. 4, NHM.2018.14012-14015. Sample 31MFB, 442 m, -49.3230311, -59.1674461, coll. 15/04/2012, ind. 5, NHM.2018.15034-15038. Sample 6MFB, 458 m, -49.2320192, -59.0316156, coll. 25/04/2012, ind. 5, NHM.2018.15409-15413. Sample 8MFC, 459 m, -49.2508764, -59.1411775, coll. 24/04/2012, ind. 6, NHM.2018.16193-16198.

Description.

Holotype (NHM.2018.12712), incomplete specimen, 6 mm long and 1 mm wide for 40 chaetigers (Fig. 13a ). Paratype (SEM specimen on stub, NHM.2018.12713), incomplete specimen, 4 mm long and 0.8 mm wide for 22 chaetigers (Fig. 13a ). Body strongly curved, broad, flattened across thoracic region, tapering posteriorly; abdominal segments longer, cylindrical. Colour in alcohol dark yellow to pale orange (Fig. 13a, b ).

Prostomium bluntly rounded, wider than long, continuing posteriorly as short caruncle terminating in middle of chaetiger 1 (Figs 13d ; 14a ); palps missing (notobserved); eyes absent; paired nuchal organs prominent, located posterior to the origin of palps (Fig. 13d ). 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 (Figs 13b ; 14b ) 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 (Fig. 14b ): 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 (Fig. 13e ; arranged in 4-6 palisaded rows (Fig. 13b ). Abdominal neurochaetae few (Fig. 15a-e ), the main fascicle composed of two types (Fig. 15a ): Type 1. Long capillaries, with frayed (damaged?) tips, fewer than ten per fascicle (Fig. 15a, c ); Type 2. Short, falcate chaetae, with gently curved, very long thin tips, ca. 6 per fascicle (Fig. 15a, d, e ). Additionally, a short, blunt posterior, protruding acicular spine, accompanied by a single short capillary with slender tip, have been observed in abdominal neuropodia (Fig. 15a, b ). Pygidium not observed.

Methyl Green stain pattern

(Fig. 13c ). 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.

New 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 notopodiaare 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.

Etymology.

Species name is dedicated to Jason Huque, husband of the sixth author (CH). Co-incidentally, Jason Islands are also an archipelago in the Falkland Islands.

Distribution.

This species is known only from its type locality, North Falklands Basin, at ca. 450 m depth.

Figures

Figure 13. Apistobranchus jasoni sp. nov. a example of juvenile (paratype, NHM. 2018.12713) (left) and adult (holotype, NHM. 2018.12712) (right) specimen in lateral view b transition between regions with (chaetigers 2 - 6 and 10 onwards) and without (chaetigers 7 - 10) acicular branchiae-like lobes (abrl) c specimen with Methyl Green stain pattern d SEM micrographs of anterior region in dorsal view e SEM micrographs of capillary chaetae. Scale bars: 1 mm (a); 500 µm (d); 100 µm (e).

Figure 14. Apistobranchus jasoni sp. nov. Illustrations of holotype (NHM. 2018.12712) a anterior end in dorsal view b anterior end in lateral view and c detail of chaetigers 4 to 10 (numbered). Scale bar: 1 mm.

Figure 15. Chaetae of Apistobranchus jasoni sp. nov. (holotype NHM. 2018.12712) a abdominal chaetiger b detail of neuropodial acicular chaeta and accompanying capillary c, d overview of neuropodial chaetal fascicle with long capillaries with frayed (damaged) tips and short falcate chaetae e detail short falcate neurochaetae. Scale bar: 250 µm (a); 25 µm (b); 100 µm (c-e).