Terebrasabella hutchingsae, Murray, Anna & Rouse, Greg W., 2007

Murray, Anna & Rouse, Greg W., 2007, Two new species of Terebrasabella (Annelida: Sabellidae: Sabellinae) from Australia, Zootaxa 1434, pp. 51-68 : 53-57

Terebrasabella hutchingsae sp. nov.

Figures 1–4

Material examined. Type material: Holotype, AM W29451, Queensland, Outer Yonge Reef, northeast of Lizard Island, Great Barrier Reef, 14°36’S 145°38’E, from rock and coral rubble covered with pink coralline algae and encrusting sponges, at 9m. Paratypes, AM W29452 (1), AM W29453 (1), AM W29454 (1), AM W29455 (2), all from same locality, depth and habitat as holotype. All type specimens collected 21 January 1977 by P.A. Hutchings and P.B. Weate.

Non-type material: AM W29456 (17), AM W29457 (3), AM W29458 (2), AM W29459 (2), AM W29460 (3 on SEM stub); AM W29461 (1), AM W29462 (2), AM W29463 (1), all from Outer Yonge Reef, Great Barrier Reef, Queensland, 14°36’S 145°38’E, Stns 77 LIZ 51-1, 51-3, 51-4, 9- 10m, rock and coral rubble, collected 21 January 1977 by P.A. Hutchings and P.B. Weate.

Description. Holotype sexually mature, eight thoracic and three abdominal chaetigers. Branchial crown missing. Anterior half of body slender, elongate (damaged by longitudinal split after examination); posterior abdomen slightly expanded, sac-like, with thin body wall. External segmentation indistinct. Total length 3.6 mm, maximum width 0.375 mm. Mucilaginous sheath separated from specimen, retained in separate microvial. Two juveniles lying adjacent to body of female near the 7th thoracic chaetiger.

Description of branchial crown based on paratype AM W29452, which is the only specimen with branchial crown intact ( Figs 1 A–C). All other specimens have branchial crown missing or regenerating. Branchial crown with two pairs of radioles (one of ventral pair broken), ends filamentous, up to eight pinnules. Branchial skeleton present; each radiolar skeleton with two rows of cells, pinnular skeletons with single row of cells. Branchial lobes mid-dorsally fused, with skeleton as a single row of large cells. Radiolar appendages present (sensu Fitzhugh 2003) with dorsal lips elongate, distally tapered, but with no discernable internal extension of branchial skeleton, nor surrounding sheath. Ventral lips absent. Ventral basal flanges present. Palmate membrane, branchial hearts, radiolar flanges, stylodes and radiolar eyespots absent ( Figs 1 B–C). Anterior peristomial collar indistinct; no visible annulation between anterior and posterior peristomial rings. Posterior peristomial ring collar incised mid-dorsally, and with small, subtriangular, distally-rounded ventral lappets ( Fig. 1 B). Indistinct latero-ventral incision present on peristomial ring. Peristomial segment without eyespots, but with internal nephridial ‘glandular patches’ ( Figs 1 B–C).

Chaetiger 1 with capillary notochaetae only, two superior broadly-hooded chaetae and one inferior shorter broadly-hooded chaeta per fascicle ( Figs 2 A-C, 3B-C). Notochaetae of chaetigers 2–5 broadly-hooded chaetae arranged in two rows per fascicle, superior chaetae(2–3) longer than inferior ones (1–2). Chaetigers 6–8 have 2–5 superior broadly-hooded and 1 inferior shorter broadly-hooded capillary notochaeta per fascicle. Neurochaetae of chaetiger 2 are 1–2 large, erect, acicular, long-handled “palmate” uncini (similar to Caobangia spp. Jones 1974) ( Fig 3 D). “Palmate” uncini possess large gap between main fang and semicircle of distal smaller heterodont teeth (with one pair slightly larger than others) and moderately-developed breast below main fang ( Figs 2 G–H, 3D). Fascicles of chaetigers 3–6 with 1–2 long-handled, crested, acicular uncini possessing large main fang surmounted by a crest of small teeth arranged over and between two larger teeth (heterodont, but not “palmate” as there is no large gap between main fang and crest of teeth) ( Figs 2 F, 3E–F, 4E); also 1–2 companion chaetae (sensu Fitzhugh 1989), long-handled with pointed, flattened blade or membrane perpendicular to handle and low distal swelling or breast ( Figs 2 E, 3E–F, 4E). Thoracic chaetigers 7 to 8 with long rows of rasp-shaped avicular uncini ( Fig. 4 C). Uncini with five or more vertical rows of small teeth above distal tooth, prominent breast and handle as long as dentate region ( Figs 2 I, 3A, 3C). Chaetiger 7 with 50–56 uncini in each row; chaetiger 8 with 12 uncini per row. Abdominal neurochaetae 1–3 narrowly-hooded chaetae per fascicle (sensu Fitzhugh 1989) in chaetigers 9–11 ( Figs 2 D, 4D). Abdominal notopodial chaetae acicular “palmate” uncini 1–2 per chaetiger, similar in form to neurochaetae of chaetiger 2 ( Figs 2 H, 4D). Abdomen is extremely fragile and the body wall has ruptured. Faecal groove ascends dorsally from approximately chaetiger 7. A pair of dense cilia bands line faecal groove sides ( Fig. 4 F) (see Fitzhugh & Rouse 1999). Position of the faecal groove posterior to chaetiger 7 indistinct.

Four pairs of posterior ventral shields over chaetigers 8–11. Glandular patches occur ventrally on chaetigers 1–5, 7–8, and 9–11. Anus opens antero-dorsally on pygidium. Pygidial eyespots absent. Holotype simultaneous hermaphrodite; paired sperm ducts in chaetiger 8 that appear to terminate dorsally at faecal groove, anterior to notochaetae. Clusters of large numbers of spermatids occur within these ducts, in chaetiger 8. Oocytes only in chaetiger 9. Two juveniles associated with holotype, closely adpressed to dorsal surface of 7th chaetiger, branchial crowns absent, 0.36 mm and 0.39 mm in length respectively. Both juveniles with five chaetigers, as follows:

Chaetiger 1: 2 capillary notochaetae (1 large and 1 small; edges feathery).

Chaetiger 2: 2 capillary notochaetae (1 large and 1 small) + 1 large erect “palmate” uncinus in neurochaetal position.

Chaetiger 3–5: 2 capillary notochaetae (1 large and 1 small) + 1 small erect “palmate” uncinus in neurochaetal position.

Variations/Remarks. Specimens exhibit different degrees of torsion of the body and there is a large variation in the degree of elongation/contraction longitudinally. All specimens are fragile, with thin body walls that are easily damaged. There is some variation in the number of rasp-shaped uncini per row on chaetiger 7, ranging from 50–56 uncini. The variation in the number of rasp-shaped uncini per row on chaetiger 8 is 11– 15. Some specimens (AM W29453, W29457) have two large palmate uncini per fascicle in the 2nd chaetiger. The presence of “palmate” uncini in chaetiger 2 is a unique feature for T. hutchingsae sp. nov., and are absent from the two other known species of Terebrasabella . The expanded lateral teeth of the acicular uncini is a feature shared with T. heterouncinata . The “palmate” uncini of T. hutchingsae sp. nov., and the rows of avicular uncini in chaetigers 7–8 of all Terebrasabella spp. are remarkable and unlike any other sabellids, except for Caobangia spp. ( Jones 1974). Further investigation is required to properly assess this homology hypothesis, but Fitzhugh (2003) does suggest a sister group relationship with Caobangia for Terebrasabella . The fact the “palmate” uncini of T. hutchingsae sp. nov., have two lateral teeth that are very enlarged shows some similarities to the acicular uncini of chaetigers 3–6 and to those of T. heterouncinata . On some specimens, the faecal groove appears to bifurcate on chaetiger 8, and each groove descends, traversing around the body to the midline on the ventrum.

Distribution. Recorded only from Outer Yonge Reef on the Great Barrier Reef, Queensland, Australia. Etymology. Terebrasabella hutchingsae sp. nov., is named after Dr Pat Hutchings, co-collector of the specimens of this species, and mentor to both of us.

Figures

FIGURE 1. Terebrasabella hutchingsae sp. nov., Paratype AM W 29452. A. Whole specimen, lateral view; th = thorax, abd = abdomen. B. Anterior end, ventral view, dorsal radioles omitted; vbf = ventral basal flange, vla = ventral collar lappet. C. Anterior end, dorsal view, ventral radioles omitted; dl = dorsal lip. Scales: A = 1 mm; B and C = 0.1 mm.

FIGURE 2. Terebrasabella hutchingsae sp. nov., Paratype AM W 29454, chaetae. A and B. Superior thoracic notochaetae from chaetiger 2, showing different views. C. Inferior thoracic notochaeta from chaetiger 6. D. Abdominal neurochaeta from chaetiger 10. E. Companion chaeta from chaetiger 3. F. Thoracic uncinus from chaetiger 3. G. “ Palmate ” neurochaetal uncinus from chaetiger 2. H. Notochaetal abdominal uncinus from chaetiger 10. I. Neurochaetal uncinus from thoracic chaetiger 7. Scales: A – I = 0.01 mm.

FIGURE 3. Terebrasabella hutchingsae sp. nov., S. E. M. photographs. AM W 29460 A. Anterior end, lateral view, radioles missing. B. Anterior end, dorsal view. C. Inferior and superior thoracic notochaetae. D. Large neurochaetal “ palmate ” uncinus from 2 nd chaetiger, shown from above. E. Companion chaeta and 2 neurochaetal uncini from thoracic chaetiger 3. F. Companion chaeta and a neurochaetal uncinus from thoracic chaetiger 5.

FIGURE 4. Terebrasabella hutchingsae sp. nov., S. E. M. photographs. AM W 29460 A. Lateral view of chaetiger 7. B. Thoracic notochaetae from chaetiger 7. C. Part of row of rasp-shaped uncini from (thoracic) chaetiger 7. D. Uncinus and capillary chaetae from abdominal chaetiger. E. Thoracic uncini and companion chaeta from chaetiger 6. F. Faecal groove showing bands of cilia.