Phalacrostemma Marenzeller, 1895

Chávez-López, Yessica, 2022, New species of sabellariids (Annelida: Sabellariidae) from the Caribbean Sea and the Gulf of Mexico, European Journal of Taxonomy 831, pp. 109-148 : 118-119

Genus Phalacrostemma Marenzeller, 1895

Type species

Phalacrostemma cidariophilum Marenzeller, 1895 , by monotypy.

Diagnosis

Operculum completely divided into two free lobes. Two rows of opercular paleae. Outer paleae arranged in spiral, with straight, cylindrical blades and ornamented thecae. Few (2–8) inner paleae arranged in one short row near to dorsal junction of inner marginal lobes, with straight, cylindrical, or slightly flattened blades. Two to six pairs of nuchal hooks with limbation. Few tentacular filaments arranged in a single row (simple), absent in some species. Median organ small, conical. Four parathoracic segments ( Kirtley 1994; Capa & Hutchings 2019).

Key to species of Phalacrostemma Marenzeller, 1895 from the Western Atlantic *

1. Outer paleae with distal thecae partially surrounding the blade ( Figs 11D , 12A, E ) ......................... ................................................................... P. dorothyae Kirtley, 1994 . Florida Keys, 349.3 m depth

– Outer paleae with distal thecae completely surrounding the blade ( Fig. 7E ) ................................... 2

2. Outer palea with mid-distal thecae with pectinate margins, extensions of similar size that form a horizontal stroke, like fringe ( Fig. 8D, I ) .......................................................................................... 3

– Outer palea with mid-distal thecae with lacerate margins, elongated extensions of different sizes that form an asymmetrical and irregular stroke ( Fig. 15G ) ..................................................................... 6

3. Outer palea with middle thecae with short extension, irregularly distributed, of different sizes and shapes ( Fig. 8L ) .............................................. P. gwendolynae Kirtley, 1994 . Aruba, 228.7 m depth

– Outer palea with middle thecae with long extensions, of similar size and shape ( Fig. 8C–D, I ) ..... 4

4. Middle thecae of outer palea with inclined extensions, 10–16 times as long as wide ( Fig. 8D ) ........ ................................................ P. paulinae Kirtley, 1994 . Delaware Bay, New Jersey, 2160 m depth

– Middle thecae of outer palea with straight extensions, 6–9 times as long as wide ( Fig. 8I ) ............ 5

5. Inner paleae with horizontal conspicuous thecae, margin of blade serrate ( Fig. 6G ); all opercular papillae of similar size ( Fig. 5C, F ) ......................... P. danieli sp. nov. Grenada Island, 597 m depth

– Inner paleae with horizontal thecae inconspicuous, margin of blade smooth ( Fig. 17E–F ); first pair of opercular papillae twice as large as the others ( Fig. 16B ) .............................................................. ............................................................................. Phalacrostemma sp. The Bahamas, 3000 m depth

6. Middle thecae of outer paleae almost longer than wide, margin forms a horizontal stroke with distal short extensions like denticles ( Fig. 8M–N ) ....................................................................................... ................. P. gloriaae Kirtley, 1994 . Sanibel Island, Florida, Gulf of Mexico, 228.3–235.9 m depth

– Middle thecae of outer paleae three times as wide as long, margin forms a ‘V’ stroke ( Fig. 15F ) .... ........................................... P. perkinsi Kirtley, 1994 . Andros Island, Bahamas, 1362–1364 m depth

Figures

Fig. 11. Phalacrostemma dorothyae Kirtley, 1994 (UMML-22.1184). A. Left opercular lobe. B. Nuchal hooks. C. Outer palea. D. Tip of outer palea. E. Inner paleae. F. Thecae of inner palea. Abbreviations: nh = nuchal hooks; opa = opercular papillae; op = outer paleae; pa = palps. Arrows indicate inner paleae. Scale bars: A = 200 µm; B, E = 100 µm; C–D, F = 10 µm.

Fig. 12. Comparation between opercular paleae of Phalacrostemma dorothyae Kirtley, 1994. A–D. Holotype of P. dorothyae. A. Tip of outer palea. B. Middle region of outer palea. C. Proximal region of outer palea. D. Thecae of inner palea. E–H. P. dorothyae, this work (UMML-22.1184). E. Tip of outer palea. F. Middle region of outer palea. G. Proximal region of outer paleae. H. Thecae of inner palea. A–D, modified from Kirtley (1994).

Fig. 7. Phalacrostemma danieli sp. nov., paratype (UMML-22.1181).A. Right opercular lobe.B. Nuchal hooks. C–D. Basal region of outer palea. E. Middle region and tip of outer paleae. F. Middle-distal region of outer palea. G. Inner paleae. Abbreviations: nh = nuchal hooks; op = outer paleae; pa = palps; tip = outer palea tip. Arrows indicate inner paleae. Scale bars: A = 200 µm; B–C = 100 µm; D = 20 µm; E, G = 50 µm; F = 10 µm.

Fig. 8. Comparation between some species of Phalacrostemma Marenzeller, 1895. A. Holotype vial of P. paulinaeKirtley, 1994. B–D. Outer palea of P. paulinae. B. Proximal region. C. Middle region. D. Middistal region.E. Nuchal hook ofP. danieli sp. nov.F. Nuchal hook ofP. tenera (Augener, 1918). G–I. Outer palea of P. danieli sp. nov.G. Proximal region.H. Middle region.I. Mid-distal region.J. Abdominal uncini of P. danieli sp. nov. K. Abdominal uncini of P. tenera. L. Middle region of outer palea of P. gwendolynae Kirtley, 1994. M–N. Middle region of outer palea of P. gloriaae Kirtley, 1994. Abbreviations: Ld = limbo distance; Ta = tip angle; Td = tip distance. Numbers indicate the rows of teeth. A, Photo taken by Sergio Salazar-Vallejo; B–D, L–N, modified from Kirtley (1994); F, K, from Augener (1918).

Fig. 15. Phalacrostemma perkinsi Kirtley, 1994 (UMML-22.1192). A. Left opercular lobe. B. Detail of two rows of opercular papillae. C. Nuchal hooks. D–H. Outer palea. D. Proximal region. E. Proximalmiddle region. F. Middle region. G. Middle-distal region. H. Tip. I. Inner paleae. Abbreviations: nh = nuchal hooks; op = outer paleae; opa = opercular papillae. Arrows indicate inner paleae. Numbers indicate the rows of opercular papillae. Scale bars: A = 0.5 mm; B = 100 µm; C = 200 µm; D–E, H = 20 µm; F–G = 10 µm; I = 50 µm.

Fig. 6. Phalacrostemma danieli sp. nov., holotype (UMML-22.1179).A. Outer palea.B. Proximal region outer palea. C. Middle region of outer palea. D. Middle-distal region of outer palea. E. Tip of outer palea. F. Inner palea. G. Tip of inner palea. H. Nuchal hook. I. Parathoracic notochaetae. J. Abdominal parapodium. K. Uncini. Abbreviation: Li = limbation. Numbers indicate the rows of teeth. Scale bars: A, F, H–I = 100 µm; B–E, G = 20 µm; J = 200 µm; K = 10 µm.

Fig. 5. Phalacrostemma danieli sp. nov., holotype (UMML-22.1179). A. Complete body, dorsal view. B. Complete body, ventral view. C. Anterior region, lateral view. D. Anterior region, ventral view. E. Caudal peduncle. F. Nuchal hooks. Abbreviations: bf = buccal flaps; bo = building organ; ca = caudal peduncle; c1 = cirri 1st thoracic segment; c2 = cirri 2nd thoracic segment; mo = mouth; nh = nuchal hooks; ne = neuropodium; op = outer paleae; opa = opercular papillae; pa = palps. Numbers indicate the cirri. Scale bars: A–B = 1 mm, C–E = 0.5 mm; F = 200 µm.

Fig. 17. Phalacrostemma sp. (UMML-22.1194). A. Complete outer palea. B. Distal region of outer palea. C. Middle region of outer palea. D. Tip of outer palea. E. Inner palea. F. Tip of inner palea. G. Nuchal hook. H. Parathoracic notochaetae. I. Abdominal chaetae. J. Uncini. Abbreviation: Li = limbation. The arrows indicate capillary chaetae. Numbers indicate the rows of teeth. Scale bars: A, I = 200 µm; B = 50 µm; C, E = 100 µm; D, F–H = 20 µm; J = 10 µm.

Fig. 16. Phalacrostemma sp. (UMML-22.1194). A. Complete specimen, dorsal view. B. Anterior region, dorsal view. C. Complete specimen, ventral view. D. Anterior region, ventral view. E. Complete specimen, lateral right view. F. Anterior region, lateral view. Abbreviations: bo = building organ; br = branchia; c1 = cirri 1st thoracic segment; c2 = cirri 2nd thoracic segment; m = mount; mo = median organ; nh = nuchal hooks; op = outer paleae; opa = opercular papillae. Numbers indicate the cirri. Scale bars: A, C, E = 1 mm; B, D, F = 0.5 mm.