Phalacrostemma perkinsi Kirtley, 1994

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 : 131-135

Phalacrostemma perkinsi Kirtley, 1994

Figs 13–15

Phalacrostemma perkinsi Kirtley, 1994: 163 , fig. 9.8a–c. Type locality: The Bahamas, 1362–1364 m depth.

Material examined

NORTH ATLANTIC – Southeastern Bahamas • 1 spec.; RV Columbus Iselin , stn 47: 23°43′ N, 77°09′ W; depth 3000 m; 24 Feb. 1973; UMML-22.1191 • 1 spec. (using mid operculum for SEM); same collection data as for preceding; UMML-22.1192 • 1 spec.; RV Columbus Iselin , stn 250; 23°52′ N, 76°56′ W; depth 1305 m; 31 Oct. 1974; UMML-22.1193 • 1 spec.; same collection data as for preceding; ECOSUR-P3239 .

Description

BODY. Incomplete specimen (UMML-22.1191), 13 mm long, 3 mm wide, six abdominal segments ( Fig. 13A–F ).

OPERCULUM. Opercular disc truncate ( Fig. 13A–B ). Opercular crown with some broken or missing paleae. Outer paleae arranged spirally, 22 paleae on right lobe, 14 paleae on left. Inner paleae arranged diagonally, two paleae on each lobe. Outer paleae amber, cylindrical, 3–4 mm long ( Figs 14A–E , 15A– D ). Proximal region with compacts thecae, margins non-expanded ( Fig. 14B, D ). Thecae of middle region with margins non-expanded ( Fig. 15E ) to slightly irregularly expanded ( Figs 14C , 15F ). Thecae of mid-distal region elongate with margins irregularly expanded ( Fig. 15G ); tips hirsute ( Figs 14D , 15H ). Inner paleae amber, cylindrical, with thecae inconspicuous; tips lanceolate ( Figs 14E , 15I ). Opercular stalk brown. Opercular papillae in two rows, each row with 11–13 opercular papillae on each lobe ( Fig. 13B ). Papillae conical, tapered, 2–4 times as long as wide ( Figs 13B , 15B ). First papilla appears in dorsal region of opercular peduncle, at level of nuchal hooks. Six pairs of amber nuchal hooks, compressed, tips sharp falcate, with limbation. Limbation not reaching tip curvature, 1.5 times as long as tip ( Figs 14G , 15C ). Palps robust, tapered, three times as long as wide ( Fig. 13D ). Pair of broad buccal flaps ( Fig. 13D ). Tentacular filaments absent. Median organ conical, brownish, without eyespots. Building organ U-shaped, brown.

THORAX. First thoracic segment with three long, triangular-shaped lateral lobes and neurochaetae capillary ( Fig. 13E ). Second segment with two long triangular-shaped lateral lobes and paired branchiae, without chaetae.

PARATHORAX. With four segments, all with paired branchiae. Notopodia with seven lanceolate chaetae and three capillary chaetae ( Fig. 14H ). Neurochaetae capillary.

ABDOMEN. Abdominal segments brown, all with paired branchiae. Neurochaetae capillary, ornamented with irregular thecal laminar extensions. Notopodia with series of uncini with 7–8 rows of teeth ( Fig. 14I ).

Tubes

With foraminiferans ( Fig. 14J ).

Variation

Body incomplete 8–13 mm long, 1.5–3 mm wide, 3–7 abdominal segments. Operculum with 21–30 outer paleae per lobe, 2–4 inner paleae per lobe, and 5–6 pairs of nuchal hooks, commonly five. Outer paleae 2–4 mm long. Opercular papillae with 9–13 per lobe. First thoracic segment with 2–4 triangularshaped lateral lobes.

Remarks

Phalacrostemma perkinsi Kirtley, 1994 (1362–1364 m) was described based on specimens collected by RV Columbus Iselin at station 322 ( Fig. 22 ). In this work, I reviewed specimens from the same expedition and cruise from two stations near the type locality of P. perkinsi ( The Bahamas, 1342– 3000 m depth, Fig. 22 ).

As the description of P. perkinsi is brief, only the morphology of the outer opercular paleae can be compared. Phalacrostemma perkinsi is characterized by outer paleae with numerous short, distal slightly expanded margins, thecae with weakly expanded margins in the middle region, and proximal transversal thecae with unexpanded margins. All these characteristics are shared with my Bahamian specimens; however, the latter have irregularly expanded thecae on the mid-distal region of the outer paleae that are not described or illustrated in P. perkinsi .

Kirtley’s (1994) identification key for Phalacrostemma species groups P. perkinsi with those species having 3–5 tentacular filaments. The specimens reviewed here do not have buccal tentacles, so this feature could be a difference between the specimens identified by Kirtley. Redescription of P. perkinsi based on type material is necessary to confirm the presence of two rows of opercular papillae and the presence of buccal tentacles. Because P. perkinsi was described based on specimens from the same cruise as those reviewed in this work, and they have similar opercular paleae, I have assigned them to the same species.

Distribution

The Bahamas, at 1342 and 3000 m depth ( Fig. 22 ).

Figures

Fig. 13. Phalacrostemma perkinsi Kirtley, 1994 (UMML-22.1191). A. Anterior region, dorsal view. B. Operculum, dorsal view. C. Anterior region, ventral view. D. Operculum, ventral view. E. Anterior region, lateral view. F. Another specimen (UMML-22.1192). Abbreviations: bf = buccal flaps; c1 = cirri 1st thoracic segment; c2 = cirri 2nd thoracic segment; nh = nuchal hooks; op = outer paleae; opa = opercular papillae; pa = palps. Numbers indicate the cirri. Scale bars: A, C = 1 mm; B, D–F = 0.5 mm.

Fig. 14. Phalacrostemma perkinsi Kirtley, 1994 (UMML-22.1191). A. Outer palea. B. Distal region of outer palea. C. Middle region of outer palea. D. Tip of outer palea. E. Inner palea. F. Nuchal hook. G. Detail of nuchal hook.H. Parathoracic notochaetae. I. Uncini. J. Tubes. Abbreviation: Li = limbation. The arrows indicate capillary chaetae. Numbers indicate the rows of teeth. Scale bars: A, E–F, H = 200 µm; B–D = 20 µm; G = 100 µm; I = 10 µm; J = 2 mm.

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. 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.