Phalacrostemma sp.

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 : 135-138

Phalacrostemma sp.

Figs 16–17

Material examined

NORTH ATLANTIC – Southeastern Bahamas • 1 incomplete spec.; RV Columbus Iselin , stn 47; 23°43′ N, 77°09′ W; depth 3000 m; 24 Feb. 1973; UMML-22.1194 .

Description

BODY. Incomplete specimen (UMML-22.1194), 10 mm long, 2.5 mm wide, five abdominal segments ( Fig. 16 ).

OPERCULUM. Opercular disc truncate. Outer paleae arranged spirally, 37 paleae on each lobe. Inner paleae arranged diagonally, two paleae on right lobe, one palea on left. Outer paleae amber, cylindrical, 3 mm long ( Fig. 17A ). Proximal region with compact thecae, margins non-expanded ( Fig. 17B ). Thecae of middle region compact with non-expanded margins to thecae with margins irregular slightly expanded ( Fig. 17C ); tips hirsute ( Fig. 17D ). Inner paleae amber, cylindrical, with thecae inconspicuous; tip blunt, slightly inclined ( Fig. 17E–F ). Opercular stalk brown, 1.6 times as wide as long ( Fig. 16 ). Opercular papillae in one row peripheral to outer paleae; 10–11 papillae on each lobe. Papillae conical, small, and tapered, 2–3 times as long as wide ( Fig. 16E–F ). First papilla twice as large as others, appears on dorsal region of opercular peduncle, at level of nuchal hooks ( Fig. 16A– B ). Four pairs of amber nuchal hooks, compressed, tip falcate, with short limbation. Limbation not reaching tip curvature, three times as long as tip ( Fig. 17G ). Palps robust, tapered, twice as long as wide ( Fig. 16D ). Pair of broad buccal flaps ( Fig. 16C–D ). Tentacular filaments absent. Median organ conical, brown, without eyespots.

THORAX. First thoracic segment with 3–4 long, triangular-shaped lateral lobes ( Fig. 16D–F ), and capillary neurochaetae. Second segment with two triangular-shaped lateral lobes and paired branchiae, without chaetae ( Fig. 16B, F ).

PARATHORAX. With four segments, all with paired branchiae ( Fig. 16E ). Notopodia with seven lanceolate chaetae and seven capillary chaetae ( Fig. 17H ). Neuropodia with capillary chaetae.

ABDOMEN. Abdominal segments brownish. Neurochaetae capillary, ornamented with irregular thecal laminar extensions ( Fig. 17I ). Notopodia with series of uncini with 10 rows of teeth ( Fig. 17J ).

Remarks

Phalacrostemma sp. has outer paleae that resemble those of P. danieli sp. nov., with compact proximal thecae, median thecae with denticulate margins, and hirsute tip. However, these species differ in the morphology of the inner paleae and opercular papillae.

Phalacrostemma danieli sp. nov. has inner paleae with conspicuous thecae ( Fig. 6G ) and crenulate margins ( Figs 6F , 7G ), whereas Phalacrostemma sp. has inconspicuous thecae and smooth margins ( Fig. 17E–F ). The opercular papillae are as long as the nuchal hooks in P. danieli sp. nov. ( Fig. 5C ), while Phalacrostemma sp. has short papillae, ½ as long as the nuchal hooks ( Fig. 16B, E–F ). Also, the first papilla is different, P. danieli sp. nov. has a thin, conical papilla ( Fig. 5F ), while Phalacrostemma sp. has a wide, triangular papilla ( Fig. 16B ).

In addition to morphological differences, the species have been found in different habitats. Phalacrostemma sp. has been found in the Bahamas at 3000 m depth, while P. danieli sp. nov. was collected in the Lesser Antilles at 547 m depth.

Distribution

Only in The Bahamas, at 3000 m depth ( Fig. 22 ).

Figures

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.

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. 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. 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. 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. 22. Localities for studied specimens. A. Caribbean Sea and the Gulf of Mexico. B. South Florida. C. Southeastern Bahamas. The crosses indicate type localities of species previously recorded in the tropical Western Atlantic.