Scalibregma australis Blake, 2015, new species

Scalibregma australis new species

Figures 1‒3

Scalibregma inflatum: Hartman 1967: 134, 1978: 181; Blake 1981: 1146; Siciński 1986: Table II, Fig. 5, 2000: 164, 2004: 82; Hartmann-Schröder 1986: 84; Hartmann-Schröder & Rosenfeldt 1989: 73, 1991: 75; Cantone & Sanfilippo 1992; Knox & Cameron 1998: 75, figs 141‒142; Cantone 1994: 41; Cantone et al. 2000: 554; San Martín et al. 2000: 85, 91; Lovell & Trego 2003: 1813; Montiel et al. 2005: 199; Hilbig et al. 2006: 724; Schüller et al. 2009: 63; Barbosa et al. 2010:1155; Parapar et al. 2011a: 728; Pabis & Sobczyk 2015: 115 ‒117. Not Rathke 1843.

Material examined. East Antarctic Peninsula, RVIB Nathaniel B. Palmer Cruise 2000-03, Collector, J.A. Blake.— Prince Gustav Channel, Sta. NBP-01, 768 m, 62 paratypes (LACM-AHF Poly 7001); Sta. NBP- 27, 684 m, 12 paratypes (USNM 1281913); Sta. NBP- 28, 794 m, 4 specimens (JAB); Sta. NBP- 29, 690 m, 11 paratypes (LACM-AHF Poly 7007); Sta. NBP- 30, 843 m, 13 specimens (JAB); Sta. NBP- 33, 587 m, 19 specimens (JAB); Stas. NBP-35, NBP-35A, NBP-35B, 651 m, 3, 6, and 14 specimens, respectively, from three grabs (JAB).— Off Cape Longing, Sta. NBP-02, 504 m, 19 paratypes (LACM-AHF Poly 7002).— Off Lindenberg Island, Sta. NBP-03, 385 m, 12 paratypes (USNM 1281909).— Larsen Ice Shelf Area, Greenpeace Trough, Sta. NBP-04, 668 m, holotype and 17 paratypes (LACM-AHF Poly 7003, 7004); Sta. NBP-05, 798 m, 7 specimens (JAB); Sta. NBP-06, 733 m, 7 paratypes (LACM-AHF Poly 7005); Sta. NBP-07A, 839 m, 8 paratypes (USNM 1281910); Sta. NBP-07B, 839 m, 15 paratypes (MCZ 60891); Sta. NBP- 16, 713 m, 14 paratypes (MCZ 60892); NBP- 17, 719 mm, 7 paratypes (MCZ 60893); Sta. NBP- 18, 665 m, 11 specimens (JAB); Sta. NBP- 19, 879 m, 2 specimens (JAB); Sta. NBP- 20, 899 m, 1 specimen (JAB); NBP-22, 3 specimens (JAB); Sta. NBP- 23, 901 m, 7 specimens (JAB).— Larsen Ice Shelf Area, transect along border with Larsen Ice Shelf B, Sta. NBP- 10, 332 m, 18 paratypes (USNM 1281911); Sta. NBP- 11, 350 m, 3 specimens (JAB); Sta. NBP- 12, 317 m, 27 paratypes ( LACM-AHF Poly 7006); NBP- 13, 323 m, 16 paratypes (USNM 1281912); Sta. NBP-14, 8 specimens (JAB).— Weddell Sea off LIS-A Area, Sta. NBP- 25, 628 m, 9 specimens (JAB).— East Antarctica, Wilkes Land, Vincennes Bay, Casey Station, coll. Australian Antarctic Division, O’Brien Bay, SRE-1, Control R2, 12 Nov 1997, 66.295°S; 110.536°E, diver cores, 12–25 m, 1 specimen (AM).

Description. A large species, body elongate, arenicoliform, expanded in anterior half to variable degree, usually from about setiger 4‒5 continuing to mid-body, then tapering to narrow abdominal region (Fig. 3 C). Body surface covered with numerous annulated rings; most annulations formed of separate elevated pads or blocks (Figs. 1 A–E, 2A). Holotype from Sta. NBP-04 ovigerous female, 32 mm long, 4.5 mm wide across expanded anterior region, with 40 setigerous segments; large paratype from Sta. NBP-01, 21 mm long, 4.5 mm wide anteriorly, for 41 setigers; six smaller paratypes from same sample, 7‒10 mm long, 1.1‒2.1 mm wide for 32‒40 setigers. Numerous smaller specimens including post-larval forms as small as 1 mm long or less with as few as 10 setigers common in samples. Color in alcohol light tan with no yellow-orange caste as in other species; some specimens with distinct dark reddish-colored glands forming a row across dorsum of setigers 4‒5 (Fig. 3 A); similar isolated pigmented glands consisting of numerous twisted tubules on some anterior neuropodia (Fig. 2 B); these glands likely retaining color derived from Rose Bengal stain used in sample processing; similar reddish-colored glands in dorsal and ventral cirri of posterior parapodia (Figs. 2 C–D, 3D–G).

Prostomium T-shaped, with lateral processes or horns well developed, pointed laterally, sometimes oriented dorsally or anteriorly (Figs. 1 A–C, 2A, 3A–C); posterior margin of prostomium visible dorsally (Fig. 1 A–B); eyes absent. Nuchal organs not everted on any specimens; ciliated grooves apparent between prostomium and peristomium on some specimens. Peristomium achaetous, not concealing posterior margin of prostomium, consisting of single ring complete dorsally (Figs. 1 A–C), split into three rings ventrally forming the upper lip of the mouth and together with annulated rows from setiger 1 forming the lower lip of the mouth (Figs. 2 A, 3B). Mouth surrounded by broad lateral lips divided anteriorly into a row of small elongate lobes forming upper lip of mouth and posteriorly by 4–5 large paired lobes or blocks forming lower lip of mouth at level of setiger 1 (Fig. 2 A). Juvenile morphology suggests that upper and lower lip morphology entirely derived from peristomium (see below). Proboscis smooth sac when everted.

Dorsally, setiger 1 biannulate and setigers 2‒3 triannulate (Figs. 1 A–B); ventrally, setigers 1–3 triannulate (Fig. 2 A); subsequent anterior setigers of expanded region quadriannulate, narrow posterior segments initially quadriannulate, then becoming pentannulate and quadriannulate in far posterior setigers (Fig. 1 D). Each annulation divided into separated elevated pads or square-shaped blocks, providing complex areolated appearance to body surface. Ventral midline from setiger 2 with group of four large epidermal pads per segment in anterior segments (Figs. 2 A, 3B), merging into a single pad in middle and posterior segments, forming ridge line within mid-ventral groove; mid-ventral groove and ridge line continuing posteriorly (Fig. 3 C).

Arborescent or dendritically branched branchiae present on setigers 2‒5 posterior to notosetae (Figs. 1 A, C, 2A–B, 3B). Parapodia reduced, inconspicuous anteriorly (Figs. 1 C, 2B) becoming larger and more conspicuous in middle and posterior setigers (Figs. 1 D, 2C–D); Dorsal and ventral cirri develop from about setigers 17‒20 or midbody; dorsal cirri initially short, triangular (Figs. 2 C, 3D), becoming slightly longer and narrower by about setiger 30 (Figs. 1 E, 2D, 3F), continuing to posterior end; ventral cirri narrower than dorsal cirri, oval, tapering to rounded tip. Each dorsal and ventral cirrus with darkly pigmented glands; each gland formed of tubules appearing to exit dorsally on dorsal cirri and ventrally on ventral cirri (Figs. 3 D‒G). Interramal papillae small, inconspicuous in anterior setigers, becoming larger in middle and posterior parapodia (Fig. 2 C).

All setigers with noto- and neuropodial fascicles of slender capillaries, with those of anterior fascicles more numerous, arranged into 2‒3 rows, with setae of posterior row longest; capillaries of middle and posterior setigers arranged in 1‒2 rows; all capillaries with numerous short bristles along length, representing emerging fibril endings (Figs. 1 F–G); setiger 1 with additional anterior row of inconspicuous short, slender, pointed aristate spinous setae (Figs. 1 F–G; 2E) with occasional spine having two thin branches (Fig. 2 E); spines numbering 8‒12 on large specimens, fewer on specimens of 10 mm or less in length. Setigers 2 and following with lyrate setae in same anterior position as short spines of setiger 1; each lyrate seta with nearly equal tynes tapering to filamentous tips and with numerous flattened, plate-like bristles on inner margins (Fig. 1 H–I, 2F), details best seen with SEM.

Pygidium of largest specimens with anal opening surrounded by about 12 elongate lobes (Fig. 1 D), pygidium inflated in smaller specimens with fewer poorly defined lobes poorly defined (Fig. 2 G); pygidium with five long, thin anal cirri, two dorsal, two ventral and one mid-ventral (Fig. 2 G); these cirri fragile, missing on most specimens. Ecology. Sediment particle size distributions analyzed from the same grabs as the biology samples from vertical subcores taken to a depth of 12 cm were reported by Gilbert & Domack (2003). A core closest to the Antarctic Peninsula in the LIS-A area (Sta. NBP-05) was dominated by silt and clay, but exhibited higher concentrations of coarse sand and gravel of up to 30% near the surface; adjacent cores taken further offshore (Stas. NBP-06 and -07) had a more uniform particle size distribution of fine silt with depth. Out of 16 subcores analyzed from the LIS-A area, ten showed the maximum amount of gravel to occur in the upper 2.5 cm; of the remaining six subcores, four showed a decrease of coarse particles at the surface and two had subsurface maxima. Of nine subcores collected from the Prince Gustav Channel, seven had a sand-gravel maximum at the surface. Of the 26 subcores collected and analyzed for particle size, 65% had a sand-gravel maximum near the surface overlying fine silt and clay.

With respect to diversity, the dominance of silt + clay overlain with coarse sediments provides a variable sedimentary habitat to support an interesting mix of benthic invertebrates (Blake & Maciolek unpublished data). Out of 32 successful grab samples (21 from the LIS-A area; 11 from the Prince Gustav Channel), a total of 270 species of benthic invertebrates were identified, 128 of which were polychaetes. Of the total invertebrate fauna, Scalibregma australis n. sp. was the fifth most abundant species identified, with a total of 419 specimens. Two cirratulid polychaetes, Tharyx homosetosus (Hartmann-Schröder & Rosenfeldt, 1989) (891 specimens) and Chaetozone sp. 1 (828 specimens), a bivalve, Yoldiella cf. vallettei (Lamy, 1906) (704 specimens) and a scaphopod, Siphonodentalium sp. (688 specimens) were the four most abundant species.

Elsewhere in Antarctica, high benthic biomass (1.3 g / 0.1 m 2) and high density (37.3 ± 20.6 ind/ 0.1 m 2) for S. inflatum was reported by Pabis & Sobczyk (2015) from a glacial fjord on King George Island, South Shetland Islands having strong currents, away from glacial influence, and with poorly sorted sandy sediments.

Typically, scalibregmatid polychaetes do not occur in high densities in benthic communities. Therefore, the dominance of Scalibregma australis n. sp. in sediments along the east Antarctic Peninsula is unusual and reminiscent of similar high densities of S. inflatum in continental slope sediments (600‒1500 m) off Cape Hatteras, NC (Blake 1993; Blake & Hilbig 1994). Live phytoplankton cells were recovered at 14 cm depth in the sediments from the Cape Hatteras sediments, suggesting rapid subduction (Cahoon et al. 1994) and possibly caching by deposit feeders such as S. inflatum. Blair et al. (1996) documented rapid in situ uptake of 13C-labeled Chlorella sp. by S. inflatum and rapid subduction of labeled material from the same area. Similar efforts to understand organic content of sediments along the east Antarctic Peninsula have not been undertaken. R.E. Ruff (personal communication) also provided evidence of high densities of S. californicum in one sample from the NE Pacific in the San Juan Archipelago from 24 m in silt and clay (376 specimens, 14 June 2012) and another from Bellingham Bay, 26 m in silt and clay (683 specimens, 0 8 Apr 2014). Most scalibregmatids are believed to be burrowing subsurface deposit feeders (Jumars et al. 2015).

Available data on the reproduction and post-larval development of S. australis n. sp. is presented in a separate section (below).

Remarks. Scalibregma australis n. sp. from Antarctica is compared with five previously known species, all from the northern hemisphere (Table 2). All of the six known species have a T-shaped prostomium with laterally or anteriorly directed fronta l horns, short spinous setae anterior to capillaries in setigers 1 or 2, lyrate setae from Scalibregma Scalibregma hanseni Scalibregma inflatum Scalibregma celticum Scalibregma californicum stenocerum

Species/Morphology Bakken, Oug & Scalibregma australis n. sp. (Ashworth, 1902) Mackie, 1991 Blake, 2000 (Bertelsen & Weston, Kongsrud, 2014 1980)

T‒shaped, lateral T‒shaped, lateral processed pointed T‒shaped, lateral T‒shaped, lateral T‒shaped, lateral

processes pointed T‒shaped, lateral anterolaterally; narrow posterior to

Prostomium processes pointed laterally processes pointed processes pointed

laterally or processes anterior/lateral projections, then becoming wide and or anterolaterally anterolaterally anterolaterally

anterolaterally inflated Posterolaterally

Pair of dark brown to located, V-shaped

Absent Absent Absent Absent black subdermal eyes with points directed

anteriorly

Does not conceal

A single ring dorsally; posterior margin of Two dorsal rings, partial One dorsal ring encompassing approximately 3 rings Dorsally expanded, hood‒ prostomium, 2 rings Achaetous and covering of posterior prostomium; three rings ventrally

Peristomium ventrally, merging with like, covering eyes and merge dorsally and apodous prostomium; ventrally forming anterior and posterior lips of

the upper lips of the posterior prostomium encompass mouth narrow mouth mouth ventrally

Branched, originating

Present, eversible, Present, eversible, on at posterolateral Ciliated; present laterally on both sides

Nuchal Organs dorsolateral on either lateral side of prostomium??

margins of of prostomium side of the prostomium immediately behind eyes prostomium

Upper lip a large Upper lip with distinct Surrounded by broad Upper lip with a row of narrow pads; biannulate and tessellate longitudinal median fold, lateral lips; small rounded Broad anterior and dorsal

Mouth? lower lip with two rows of 5‒6 large

pad, lower lip narrow, lower lip large with upper lip; lower lip with lips pads; small lobes laterally single row of pads radiating wrinkles 4‒5 short lobes

Proboscis Smooth sac Smooth sac Smooth sac Smooth sac Folded, undulating rim Smooth sac Setigers 1‒4

Setigers 1‒3 triannulate, Setiger 1 triannulate, Anterior most segments triannulate or Setigers 1‒4 triannulate, Transverse quadriannulate;

Annulation quadriannulate or quadriannulate or quadriannulate, posterior segments

pentannulate after annulation subsequent with 5‒6 pentannulate after pentannulate after pentannulate annulations

From setiger 2 From setiger 2 (broad

(hexagonal or Narrow ventral From setiger 2, four raised pads in rectangular to trapezoidal From setiger 2, deep

pentagonal on 2 groove depicted in Present, 1 pad per mid-ventral groove, continuing along

Ventral Midline/ Groove and biannulate on 2, then groove containing large

(possibly 3‒4) drawing, but not segment body; groove deep in narrow posterior rectangular and biannulate epidermal pads

rectangular or biannulate described segments after)

after)

Branchiae Present, setigers 2‒5 Present, setigers 2‒5 Present, setigers 2‒5 Present, setigers 3‒5 Present, setigers 3‒5 Present, setigers 2‒5 Initially small and Initially small and Bulbous, low and Short, inflated, Short triangular at first, rounded, then becoming rounded, then becoming rounded at first, then becoming more Short, triangular at first, then elongate,

Dorsal/Ventral Cirri becoming lanceolate in triangular, then triangular, then becoming becoming larger and elongate in posterior fingerlike posterior segments becoming lanceolate lanceolate triangular segments

Dorsal and ventral

Glands on dorsal and ventral Black spots on dorsal and cirri retain reddish

Present Present Present, yellowish color Present, dark reddish ventral cirri brown pigment in

alcohol

1 setiger rare aristate, around margin 2 dorsal, 2; between some ventral spots apparent when,

from

rounded and

most

1 setiger, setiger 2 equal multilobate /

aperture thin anal cirri, 1 ‒ ventral mid dorsally spots ‒ 3 4 and 5 4 on ‒ isolated, some 2. ‒ 3 These with Bengal Rose Small Present bifurcate From Nearly Crenulate anal Five long ventral, Band of setigers specimens on setigers stained

setiger

about

, 2

1 ‒ blunt

tipped dorsal dorsal and yellow

from setigers curved setiger 3 equal lobes 10 cirri

5

3 5 with ‒transverse; bands with cirri

Present15 Present, short From Nearly About to Up Setigers yellow pigment ventral glands

rounded and, and posterior 2 ‒, setigers 1 3 setiger specimens, located

Small middle parapodia Present From Unequal? 3 ‒ 0 on examined ventrally and ventrolateral?

,

of

cirri

most

, some., inconspicuous1 setiger 1 setiger row,, short pointed 12 setiger 2 equal Numerous lobes anal, thin long from ventral yellow-orange spots black on and rings ventral and cirri Scalibregma Small from Present ‒ 10 spines From Nearly Five arising lobes Body with annulated dorsal of Species 1 1, 2 ‒ smooth about around anal cirri stained ventral setigers on Six from setiger setigers blunt, 3 setiger of ratio (margin aperture, ventrally filiform patches Bengal on dorsally 5 4 ‒ of,

Adults Small Present. short, From Unequal1.3) Crenulate anal (1

long

Five inserted Solitary with

Rose parapodia

to ‒; 4

and

6 ‒ setigers among 1 setiger, 1bifurcate ca 2 of about margin around cirri anal 2 and) patches to ventral 4 setigers Morphology Small from, Present setiger pointed and numbers equal setiger From Unequal (ratio) 1.2 Crenulate anal aperture filiform Five ventral median ventrolateral pairs glandular Small and dorsal parapodia on 5 of

Comparison Sense Organ with 2 / or short row 1 in st. 2 1 and setae to capillaries Setae Tynes Setae Cirri pigment TABLE Interramal Setiger spinous anterior Lyrate Lyrate Pygidium Anal Body setigers 2 or 3, dendritically branched branchiae on four or five anterior setigers, well-developed dorsal and ventral cirri on middle and posterior setigers, and a ventral groove containing elevated pads running the length of the body.

Scalibregma australis n. sp. is most closely related to S. inflatum and S. californicum Blake, 2000. All three species have lyrate setae from setiger 2; the other three species have them from setiger 3; branchiae are on setigers 2‒5, two other species have them on setigers 3‒5; eyes are absent, two other species have eyes (Table 2).

The main characters that separate S. australis n. sp., S. inflatum, and S. californicum from one another are (1) details of the peristomium, (2) the development of the upper and lower lips that surround the mouth, (3) the shape of the dorsal and ventral cirri along the body, and (4) the structure of the short spinous setae in setiger 1.

Peristomium. The peristomium of S. inflatum consists of a single ring dorsally and approximately four rings ventrally, merging with the upper lips of the mouth (Mackie 1991); in S. californicum the peristomium has two rings dorsally that extend ventrally to merge with the lateral lips of the mouth (Blake 2000); in S. australis n. sp., the single dorsal peristomial ring divides into three ventral rings that merge with the upper lip of the mouth.

Upper and lower lips surrounding mouth. The morphology of the upper and lower lips of the mouth differs considerably among S. inflatum, S. californicum, and S. australis n. sp. In S. inflatum, the upper lip of the mouth consists of a biannulate row of large pads and the lower lip by a narrow single row of pads; in S. californicum, padded rows are not present, instead there is a small rounded upper lip, long lateral lips, and a ventral lip consisting of 4–5 short lobes; in S. australis n. sp., the upper lip has a curved row of numerous narrow pads, small lobes laterally, and two rows of 5‒6 large pads ventrally.

Dorsal and ventral cirri. In S. inflatum, the dorsal and ventral cirri transition from a rounded triangular shape anteriorly to a lanceolate shape posteriorly; in S. californicum, these same cirri transition from a bulbous to a triangular shape along the body; in S. australis n. sp., the cirri are initially short and triangular, becoming elongate and finger-like posteriorly, with the dorsal cirri always larger than the ventral ones.

Short spinous setae on setiger 1. In S. inflatum, these spines are simple pointed or distally bifurcate in approximately equal numbers; in S. californicum, all spines are pointed, never bifurcate; in S. australis n. sp. the spines are mostly simple and aristate, rarely bifurcate.

Additionally, there may be differences in the arrangement of the five anal cirri, but given that these structures are fragile and often missing from preserved specimens, their position and location on mature specimens is not well documented. For S. inflatum, Mackie (1991) indicated that one mid-ventral cirrus and four ventrolateral cirri are present; for S. californicum, Blake (2000) reported that the five cirri arise from a ventral position; in the present study, S. australis n. sp. has a single ventral cirrus, two dorsolateral cirri, and two ventrolateral cirri.

Etymology. Australis is Latin for southern.

Distribution. Widespread on both sides of the Antarctic Peninsula: Weddell Sea, Larsen Ice Shelf area, Prince Gustav Channel; Elephant Island, South Shetland Islands, 45‒1000 m. Bellingshausen Sea, ~ 500 m. Ross Sea: Terra Nova Bay, 320‒670 m; off Daniell Peninsula, north of McMurdo; 567‒ 578 m. East Antarctica, Wilkes Land, O’Brien Bay, 10‒ 25 m.