Aphelochaeta palmeri Blake 2018, new species

Aphelochaeta palmeri new species

Figures 15–16

Aphelochaeta cincinnata: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717, 719 (in part); Montiel et al. 2005: 197, 2016: Appendix 2 (in part). Not Ehlers 1908.

Material examined. West Antarctic Peninsula: Anvers Island, R / V Hero Sta. 824-38-1, 29 Mar 1982, 64.757° S, 64.144°W, 193 m, holotype, ( USNM 1013884) and 15 paratypes (USNM 1013885); off Anvers Island, R / V Hero Sta. 824-34-1, 26 Mar 1982, 64.788°S, 63.500°W, 305–320 m, 5 paratypes (USNM 1013886); Anvers Island, Ryswyck Point , R / V Hero Sta. 824-32-1, 25 Mar 1982, 64.617°S, 62.833°W, 640–670 m (6, USNM 1490716); Anvers Island, Bismarck Strait, R / V Hero Sta. 824-41-1, 29 Mar 1982, 64.807°S, 64.12°W, 88–112 m (1, USNM 1013940); Gerlache Strait, R / V Hero Sta. 824-25-2, 24 Mar 1982, 64.348°S, 61.592°W, VV grab, 92 m (2, USNM 1490714); Doumer Island, SE of island, R / V Hero Sta. 731-1937, 16 Dec. 1971, 64.8744°S, 63.5503°W, Blake trawl, 96 m (1, USNM 1013935); Wiencke Island, Port Lockroy, USCG Staten Island, Sta. 66- 63, coll. W.L. Schmidt, 1 Mar 1963, 64.8°S, 63.5°W, 62 m, (2, USNM 56073); R / V Hero Sta. 721-970, 07 Dec 1971, 64.8172°S, 63.5467°W, Petersen grab, 102 m (10, USNM 1013921); Bransfield Strait, USNS Eltanin, Cr. 6, Sta. 416, 2 Jan 1963, 63.67°S, 56.22°W, 494–507 m (2, USNM 56007); South of Bransfield Strait, USNS Eltanin, Cr. 6, Sta. 418, 3 Jan 1963, 62.68°S, 57.85°W, 3 Jan 1963, Blake trawl, 311–426 m (1, USNM 56008); Graham Land, Alcock Island, R / V Hero Sta. 721-1034, 16 Dec 1971, 64.2167°S, 61.09°W, Petersen grab, 118 m (1, USNM 1013938); Sta. 721-1035, 16 Dec 1971, 64.2167°S, 61.09°W, 118 m (2, USNM 1013936); Anvers Island, Arthur Harbor, R / V Hero Sta. 721-1070, 28 Jan 1972, 64.795°S, 64.123°W, 100 m (2, USNM 1013922); off Bonaparte Point, R / V Hero Sta. 721-5442, 29 Mar 1972, 64.7811°S, 64.0925°W, Petersen grab, 118 m (1, USNM 1013938); Palmer Station anchorage, USCG Glacier, Sta. Palmer II, 17 Mar 1968, 64.77°S 64.07°W, 40 m (4, USNM 1013930); Brabant Island, Minot Point, R / V Hero Sta. 824-30-1, 25 Mar 1982, 64.236°S, 62.560°W, 90–135 m (2, USNM 1013927).— Greenwich Island, Anchorage Off Yankee Harbor, USCG Staten Island, Sta. 44-63, coll. W.L. Schmidt, 55 m (1, USNM 56071).— South Orkney Islands, S of Coronation, Island, USNS Eltanin Cr. 7, Sta. 496, 20 Feb 1963, 61.17°S, 45.18°W, 234 m (3, USNM 56075).— Drake Passage, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-334, 19 Mar 1998, 61°26.7ʹS. 58°06.6ʹW, MG, 1028 m (4, SMF 24888); Sta. 48-341, 19 Mar 1998, 61°34.5ʹS, 58°07.0ʹW, MG, 429 m, (35, SMF 24889); Sta. 48-345, 20 Mar 1998, 218 m, 61°53.3ʹS, 59°06.9ʹN, MG, 218 m (45, SMF 24890); Sta. 48-356, 20 Mar 1998, 130 m, 62°00.3ʹS, 59°4.9ʹW, MG, 130 m (343, SMF 24891).— South Shetland Islands: King George Island, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-299, 14 Mar 1998, 62°15.8ʹS, 58°42.7ʹW, MG, 207 m, (130, SMF; 24892; 20, JAB); Sta. 48-300, 14 Mar 1998, 62°16.8ʹS, 58°42.1ʹW, MG, 423 m (343, SMF 24893); Sta. 48-325, 17 Mar 1998, 62°21.9ʹS, 58°42.6ʹW, MG, 805 m (217, SMF 24894); Sta. 48-326, 17 Mar 1998, 62°20.1ʹS, 58°38.8ʹW, MG, 606 m (11, SMF 24895); R / V Hero Cr. 721, Sta. 810, 15 Jan 1972, 62.095°S, 58.385°W, 177 m (2, USNM 1013932); Sta. 721-817, 16 Jan 1972, 62.35°S, 58.808°W, 82 m (3, USNM 1490713); USCG Staten Island, Sta. 64-63, coll. W.L. Schmidt, 86 m, (13, USNM 56072); Martel Inlet, R / V Hero Cr. 721, Sta. 811, 15 Jan 1972, 62°05.7ʹS, 058°22.5ʹW, Petersen grab, 208 m (3, USNM 1490715).— East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 01, 14 May 2000, 64°17.625ʹS, 058°34.678ʹW, 768 m, (22, LACM-AHF Poly 10205); Sta. 02, near Cape Longing, 15 May 2000, 64°18.387ʹS, 058°37.911ʹW, 504 m (12, LACM-AHF Poly 10206); Sta. 27, 23 May 2000, 64°22.934ʹS, 058°36.976ʹW, 684 m (7, LACM-AHF Poly 10207); Sta. 28, 23 May 2000, 64°22.018ʹS, 058°30.942ʹW, 794 m (23, LACM-AHF Poly 10208); Sta. 29, 24 May 2000, 64°21.361ʹS, 058°26.637ʹW, 690 m (8, LACM-AHF Poly 10209); Sta. 30, 24 May 2000, 64°16.875ʹS, 058°26.985ʹW, 843 m (9, MCZ 149890); Sta. 33, 24 May 2000, 64°11.959ʹS, 058°41.857ʹW, 587 m (10, MCZ 149891); Sta. 34, 24 May 2000, 64°10.995ʹS, 058°34.140ʹW, 865 m (18, MCZ 149892); Sta. 35, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m (17, MCZ 149893); Sta. 35A, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m (17, JAB); Sta. 35B, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m (16, JAB).— East Antarctic Peninsula, N of Larsen Ice Shelf A Area, off Lindenberg Island , RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 03, 15 May 2000, 64°53.533ʹS, 059°30.694ʹW, SM grab, 385m (16, MCZ 149894).— East Antarctic Peninsula, former Ice Shelf A, Area, Greenpeace Trough, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 7A, 18 May 2000, 64°43.523ʹS, 060°04.771ʹW, SM grab, 839 m (4, MCZ 149895); Sta. 7B, 18 May 2000, 64°43.523ʹS, 060°04.771ʹW, 839 m (6 JAB); Sta. 16, 19 May 2000, 64°43.897ʹS, 059°55.745ʹW, 713 m (8, MCZ 149896); Sta. 17, 19 May 2000, 64°39.793ʹS, 060°07.662ʹW, 719 m (5, MCZ 149820); Sta. 18, 20 May 2000, 64°39.381ʹS, 059°59.498ʹW, 665 m (28, MCZ 149821); Sta. 19, 20 May 2000, 64°42.778ʹS, 060°20.846ʹW, 879 m (4, MCZ 149822); Sta. 20, 20 May 2000, 64°44.984ʹW, 060°22.345ʹE, 899 m (3, MCZ 149823); Sta. 21, 20 May 2000, 64°45.827ʹS, 060°19.450ʹW, 912 m (1, MCZ 149824); Sta. 22, 20 May 2000, 64°46.632ʹS, 060°21.557ʹW, 868 m (3, MCZ149825); Sta. 23, 21 May 2000, 64°47.144ʹS, 060°21.566ʹW, 901 m (3, MCZ 149826).— East Antarctic Peninsula, former Ice Shelf A Area, border with Larsen B , RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 10, 18 May 2000, 64°57.368ʹS, 060°13.392ʹW, SM grab, 332 m (4, MCZ 149827); Sta. 11, 18 May 2000, 64°56.669ʹS, 060°19.281ʹW, 350 m (8, MCZ 149828); Sta. 12, 19 May 2000, 64°55.101ʹS, 060°24.459ʹW, 317 m (7, MCZ 149829); Sta. 13, 19 May 2000, 64°53.517ʹS, 060°28.836ʹW, 323 m (12, MCZ 149830); Sta. 14, 19 May 2000, 64°51.818ʹS, 060°33.438ʹW, 419 m (11, MCZ 149831).— Weddell Sea, east of former Larsen Ice Shelf A Area, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, Sta. 25, 22 May 2000, 64°43.314ʹS, 059°38.459ʹW, SM grab, 628 m (4, MCZ 149832); Sta. 26, 23 May 2000. 64°39.564ʹS, 059°13.226ʹW, 564 m (4, MCZ 149833).— Weddell Sea, USCG Glacier, Sta. 68-1, 06 Feb 1968, 70.117°S, 39.633°W, 650 m (3, USNM 46805); Sta. 69-4, 26 Feb 1969, 77.092°S, 35.007°W, 743 m (6, USNM 46813); Sta. 69-5, 27 Feb 1969, 77.33°S, 36.6883°W, 1079 m (3, USNM 46801); Sta. 69-8, 02 Mar 1969, 77.603°S, 42.50°W, 585 m (1, USNM 1490718); Sta. 69-11, 05 Mar 1969, 77.15°S, 38.97°W, 851 m (5, USNM 46803); Off Halley Bay, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-146, 10 Feb 1998, 74°39.4ʹS, 27°08.0ʹW, MG, 1021 m (2, SMF 24896).— Ross Sea, USNS Eltanin Cr. 27, Sta. 1890, 06 Feb 1967, 65.00°S, 160.92°E, plankton sampler, 100 m, (1, USNM 1013929); Victoria Land, USNS Eltanin Cr. 32, Sta. 2020, 15 Jan 1968., 74.10°S, 179.18°E, 256 m (1, USNM 1490717); Sta. 2034, 15 Jan 1968, 74.10°S, 179.18°E, 256 m (1, USNM 1013925); McMurdo Sound, SW Tent Island, Deep-Freeze II, USCG Glacier Sta. 9, 29 Dec 1956, 77.718°S, 166.358°E, 421 m, grab on bottom of hard volcanic cinder (1, USNM 1013923); McMurdo Sound, off McMurdo Station, coll. S. Kim & J.A. Blake, scuba, 11 Jan 2000, 77°51.067′S, 66°39.880′E, 20 m, in sand and silt (11, LACM-AHF Poly 10203); same location, 15 Jan 2000, 77°51.067′S, 66°39.880′E, 30 m, in sponge mat (18, LACM-AHF Poly 10204).— East Antarctica, Vincennes Bay, Casey Station, coll. Australian Antarctic Division, O’Brien Bay-5, Sta. S 1P2 R1, 03 Dec 2005, 66.2949°S, 110.5365°E, diver cores, 15–25 m (20, AM); Budd Coast, Wilke’s Station, coll. Virginia Institute of Marine Science, 24 Dec 1961, 66.2657°S, 110.5683°E, trawl, 73 m (1, USNM 1013924).

Description. A moderate- to large-sized species, holotype 18 mm long, 0.5 mm across anterior or thoracic setigers and 0.8 mm across posterior end, with 90 setigers; 20 setigers in expanded anterior or thoracic region, segments then narrowing (Fig. 15A), and expanding again in far posterior region for another 20 setigers (Fig. 15C). Segments of anterior and posterior regions short, crowded (Figs. 15A, 16A), segments of middle 50 segments about as long as wide, but not moniliform, posterior segments again short, but not as short as anterior segments (Fig. 15C). Anterior segments with dorsum broadly rounded, without mid-dorsal groove (Figs. 15A, 16A, C); venter similar but with shallow mid-ventral groove typically first present in anterior segments (Fig. 16D) continuing posteriorly; sometimes groove not apparent until posterior thoracic or anterior abdominal segments. Mid-ventral groove with line of low mounds along mid-line, these mounds continuing posteriorly, but not well developed in some specimens. Posterior expanded region somewhat fusiform (Fig. 15C), greatly expanded dorsally in some specimens; ventrally flattened or with weak groove (Fig. 15C) with mid-ventral line of mounds; small specimens with posterior end narrow, only weakly expanded, flattened ventrally. Weak ventral glandular bands apparent on peristomial annuli; prominent ventral bands of glands across anterior or thoracic segments (Fig. 16D). Color in alcohol: tan to brown; ventral thoracic glands yellow to golden in color, forming pigmented rows across venter (Fig. 16D). A few specimens exhibit some dusky pigment in anteriormost setigers.

Prostomium pear-shaped, about as long as wide, narrowing anteriorly to rounded lobe on anterior margin (Fig. 15 A–B); eyespots absent; nuchal organs circular openings at posterior lateral margin of prostomium. Peristomium elongate, with three obvious annular rings surmounted by distinct dorsal crest extending to anterior margin of setiger 1; proboscis everted in some specimens, soft, smooth, without lobes (Figs. 15B, 16A). Dorsal tentacles arising medially on posterior margin of peristomium (Fig. 15 A–B, 16A–B); in large specimens, last peristomial ring enlarged, extending posteriorly over dorsum forming a wedge between setigers 1–2 and carrying dorsal tentacles posteriorly between those segments (Fig. 16C). First pair of branchiae arising lateral and in close proximity to dorsal tentacles and appearing to arise from the very posterior edge of the peristomium (Figs. 15 A–B, 16A–B), but in some specimens first branchiae appear to arise from a notch between peristomium and setiger 1 or actually on setiger 1; subsequent branchiae from setiger 1, in more lateral position, dorsal to notosetae (Figs. 15B, 16 A–B), continuing on each segment for about 30 setigers, thereafter becoming fewer, thinner, and irregularly distributed.

Parapodia weakly developed, producing low parapodial shoulders in anterior segments; capillary setae arising from low setal tori. Notosetae usually longer, thicker than neurosetae; setal fascicles with 7–12 setae anteriorly, reduced to 5–7 in middle and posterior segments. All capillaries with smooth blades visible with light microscopy. Notosetae of middle body segments usually elongated, suggesting possible natatory function, these setae longest on gravid specimens. Expanded posterior end fusiform, narrowing to pygidial segment bearing lobe ventral to anal opening (Fig. 15C).

Variability. Due to the large number of specimens available for study, considerable variability has been observed, some of which is likely due to having specimens at all growth stages and affected by different modes of preservation.

Three peristomial rings typically prominent, but in smaller specimens not as distinct; some specimens with evidence of an additional narrow ring anteriorly. Mid-dorsal crest on peristomium usually prominent but may be too low in smaller specimens to discern without staining. Peristomium typically ends at anterior margin of setiger 1, but in large specimens may extend posteriorly to level of setiger 1; thus carrying dorsal tentacles posteriorly and medial to level of setiger 1 or rarely 2. First pair of branchiae always lateral to dorsal tentacles, but actual placement on posterior edge of peristomium not always clear and on some specimens branchiae appear to arise on leading edge of setiger 1 or in groove between first setiger and peristomium.

Mid-ventral segments of anterior or thoracic region typically broadly rounded across each segment and may become interrupted by development of a shallow groove that continues posteriorly. This groove varies from a narrow depression that may widen in post-thoracic segments and continue posteriorly to the expanded posterior end where it forms either a flat or shallow-grooved venter. In the anterior segments, the groove appears as a channel between two lateral mounds.

Expanded posterior end varies from a weakly fusiform-shaped expansion of the posterior segments to a larger, more inflated structure. In all instances, however, lateral and dorsal sides rounded with venter being either flattened or having a shallow groove, usually with a row of segmental mounds along midline. Some specimens from Casey Station of East Antarctica with a shallow dorsal groove on the expanded posterior end.

Methyl Green stain. Strong staining reaction limited mainly to body segments; prostomium and peristomium staining weakly; speckles visible after differentiation on posterior half of peristomium, or not staining at all; tip of prostomium sometimes staining dark or not all, when stained most evident on ventral side. When stained, prominent transverse bands produced on venter and dorsum (Fig. 16 D–E). Dorsally, glands staining on anterior medial margin of parapodial shoulders; glands on posterior margin of each segment producing transverse dorsal band (Fig. 16E). Ventrally, stain produces transverse bands on posterior margin and furrows between segments. Ventral golden areas of venter not staining with MG but appearing broad and dark in photographs and contrasting with MG stained area (Fig. 16D).

Etymology. This species is named after Nathaniel B. Palmer, American whaler, who is reputed to be among the first to sight the Antarctic continent.

Remarks. Aphelochaeta palmeri n. sp. is the most common and widely distributed shallow-water species of the genus in Antarctica. It is distinguished from other Antarctic congeners by the pear-shaped prostomium, the elongate peristomium formed of three prominent annuli, the expanded thoracic and posterior regions, and the presence of yellow to golden glandular bands on the venter of the thorax. It is likely that most of the A. cincinnata identifications by authors of benthic surveys refer to this species.

A diffuse speckled MG staining pattern occurs on the posterior half of the peristomium but may not be evident in many specimens; the stain is strong on the dorsal and ventral posterior margins of individual anterior body segments producing prominent transverse bands; glands on the leading edge of anterior parapodia also stain prominently. In larger specimens, the segmentally stained bands may continue along the entire body including the posterior end.

On the largest specimens, the posterior peristomial ring is enlarged medially on the dorsum and forms a wedge that extends posteriorly and carries the dorsal tentacles to a position between setigers 1 and 2. It appears as if contraction during preservation where the peristomium is compressed anterior to posteriorly also assists in shifting the dorsal tentacles back over the dorsum. Initially these specimens with the dorsal tentacles shifted posteriorly were thought to represent a separate species, but after examination of hundreds of specimens are now believed to represent a single, variable species. In addition, the size and shape of the posterior end is variable, ranging from a thickened narrow shape to one that is greatly inflated. However, in all instances, the ventral surface of the posterior end is distinctly flattened or weakly grooved; at the same time, lateral and dorsal sides are rounded, sometimes with a weak dorsal groove.

Aphelochaeta palmeri n. sp. is distinguished with difficulty from other Antarctic congeners such A. aubreyi n. sp., A. dearborni n. sp., and A. spectabilis n. sp. All four species have a pre-setiger region that is about 1.5 times as long as wide, incised with lateral grooves that produce 2–3 annular rings, and a dorsal crest that is variously developed. Aphelochaeta dearborni n. sp. has a narrow posterior region whereas A. palmeri n. sp. and A. spectabilis n. sp. have one that is enlarged and fusiform; the posterior end of A. aubreyi n. sp. is narrow but inflated dorsally. Aphelochaeta aubreyi n. sp. has rounded to moniliform middle body segments, whereas the other species have narrower segments that are not rounded. Aphelochaeta spectabilis n. sp. is the only one of these four to have a strong, distinctive MG pattern in the pre-setiger region. Aphelochaeta dearborni n. sp. and A. palmeri n. sp. have a lightly speckled pattern on part of the peristomium, or no staining pattern. Aphelochaeta aubreyi n. sp. has no obvious MG pattern except in intersegmental grooves on the venter. Black pigment spots or lines are present on the posterior lateral peristomial margins of A. aubreyi n. sp. and on the lower of the lip of the mouth on A. dearborni n. sp. Similar black pigment is absent in A. palmeri n. sp. and A. spectabilis n. sp. although some dusky pigment may be present on the peristomium and anterior segments of A. palmeri n. sp. These characters and others are discussed separately for each of these four species and, together with other species in Table 1, in the Discussion section of this paper (see below).

Habitat & biology. Surficial sediments in the Prince Gustav Channel and vicinity of the former Larsen Ice Shelf A where Aphelochaeta palmeri n. sp. was dominant contained 20–40% sand at the time of the May 2000 survey (Gilbert & Domack 2003).

Some specimens had ova in the coelom, up to 165 µm in diameter. Gut with sand and silt particles.

Distribution. Widespread in Antarctic seas, Antarctic Peninsula to the Ross Sea, in shelf and slope depths, 20–1100 m.