Phalacrostemma dorothyae , Kirtley 1994

Phalacrostemma dorothyae Kirtley, 1994

Figs 9– 11, 12E–H

Phalacrostemma dorothyae Kirtley, 1994: 153, figs 9.3.1a–c, 9.3.2a–e. Type locality: Pourtales, Florida Keys, 349.3 m depth.

NORTH ATLANTIC – Bahamas • 2 specs; northwest of North Cat Cay; RV Gerda, stn 242; 25°37′ N, 79°22′ W; depth 494 m; on sea urchin spine; 30 Jan. 1964; UMML-22.1183 • 1 spec. (using mid operculum for SEM); same collection data as for preceding; UMML-22.1184 • 1 spec.; same collection data as for preceding; ECOSUR-P3237. – Florida Strait • 6 specs; southeast of Long Key; RV Gerda, stn 456; 24°39′ N, 80°47′ W; depth 132 m; on sea urchin spine; 23 Jan. 1965; UMML-22.1185 • 1 spec.; same collection data as for preceding; ECOSUR-P3238 • 1 spec.; southeast of Long Key; RV Gerda, stn 457; 24°37′ N, 80°46′ W; depth 178 m; on sea urchin spine; 23 Jan. 1965; UMML-22.1186 • 1 spec.; south of Duck Key; RV Gerda, stn 480; 24°31′ N, 80°55′ W; depth 192 m; 26 Jan. 1965; UMML- 22.1187 • 2 specs; south of Saddlebunch Key; RV Gerda, stn 861; 24°00′ N, 81°36′ W; depth 536; on a gastropod shell; 29 Aug. 1967; UMML-22.1200. – East Florida • 7 specs; east of Boynton Beach; RV Gerda, stn 158; 26°31′ N, 79°23′ W; depth 535 m; 25 Jun 1963; UMML-22.1188 • 4 specs; east of Fort Lauderdale; RV Gerda, stn 718; 26°08′ N, 79°19′ W; depth 448 m; 3 Aug. 1965; UMML-22.1189. – South Grand Bahamas • 1 spec.; south of Xanadu Beach; RV Gerda, stn 694; 26°27′ N, 78°42′ W; depth 658 m; on sea urchin spine; 21 Jul 1965; UMML-22.1190.

BODY. Complete specimen (UMML-22.1183), broken in middle part of abdomen, 13 mm long, 1 mm wide, 12 abdominal segments, caudal peduncle 8 mm long (Fig. 9A).

OPERCULUM. Opercular disc truncate (Fig. 9B, E). Opercular crown with some broken or missing paleae (Fig. 9E). Outer paleae arranged spirally, 19 paleae on right lobe, 31 paleae in on. Inner paleae arranged diagonally, three paleae on each lobe (Figs 9E–F, 10A). Outer paleae amber, cylindrical, 1.5 mm long (Fig. 10A). Proximal region with compacts thecae, margins non-expanded (Fig. 10B). Thecae of middle region with margins slightly expanded, denticulate (Figs 10C, 11C). Tip with thecae partially surrounding blade, margins expanded, pectinate (Fig. 11D). Inner paleae amber, cylindrical, with conspicuous, compact thecae, margins non-expanded; tips blunt, smooth (Figs 10D, 11F). Opercular stalk pale brown, 1.5 times as long as wide. Opercular papillae in one row peripheral to outer paleae; 10 papillae on each lobe. Papillae conical, robust, tapered, 2.5–4 times as long as wide (Fig. 9B–C). First papilla appears on inner region of opercular peduncle, at level of nuchal hooks (Fig. 11A–B). Five pairs of amber nuchal hooks, compressed, tip slightly falcate, with short limbation. Limbation not reaching tip curvature, almost three times as long as tip (Figs 10E, 11E). Palps robust, tapered, four times as long as wide (Fig. 10A–E). Pair of broad buccal flaps (Fig. 11D). Tentacular filaments absent. Median organ conical, colorless, without eyespots.

THORAX. First thoracic segment with long, triangular-shaped lateral lobe and capillary neurochaetae. Second segment with two triangular-shaped lateral lobes and paired branchiae, without chaetae (Fig. 9C).

P ARATHORAX. Four segments, all with paired branchiae. Notopodia with five lanceolate chaetae and five capillary chaetae (Fig. 10F). Neurochaetae capillary.

ABDOMEN. Abdominal segments brown, with paired branchiae up to segment 2. Neurochaetae capillary, ornamented with irregular thecal laminal extension. Notopodia with series of uncini with 8–9 rows of teeth (Fig. 10G). Caudal peduncle cylindrical, brownish (Fig. 9A).

Body 6–14 mm long, 1–2 mm wide. Incomplete specimens with 5–18 abdominal segments; complete specimens with 11–12 abdominal segments and caudal peduncle 5–8 mm. Operculum with 15–35 outer paleae per lobe, 1–4 inner paleae per lobe, and 3–6 pairs of nuchal hooks. Outer paleae 1–1.5 mm long. Opercular papillae with 7–13 per lobe.

Phalacrostemma dorothyae was described by Kirtley (1994) from Florida Keys. Its original description is brief and only included the partial description of opercular paleae and nuchal hooks. The revised specimens share the morphology of the outer paleae with P. dorothyae. Both species have elongated, irregular thecae at the tip of the outer paleae that partially cover the blade, only the inner side (Fig. 12A, E); thecae with finely denticulate expanded margins in the middle region (Fig. 12B, F); and proximal compact thecae with irregular margins (Fig. 12C, G). However, my specimens differ from P. dorothyae in the inner paleae; P. dorothyae has inner paleae with “irregular, slightly swollen thecae with distal margins with smoothly rounded distal denticles” (Kirtley 1994: 153) (Fig. 12D), while my specimens have compact thecae with irregular margins in the inner paleae (Fig. 12H).

The nuchal hooks of my specimens are slightly different from those of P. dorothyae. Kirtley’s (1994: fig 9.3.2d) P. dorothyae has nuchal hooks with shorter tips, about three times as long as wide, while in what is herein regarded as P. dorothyae they are six times as long as wide.

Another possible difference between the revised specimen here and P. dorothyae is in the buccal tentacles. According to the key in Kirtley (1994: 149), P. dorothyae is grouped with species having 3–5 simple buccal tentacles, whereas my specimens lack them. Unfortunately, in the description of P. dorothyae, Kirtley (1994) did not mention anything about the number of buccal tentacles.

Phalacrostemma dorothyae and my specimens have similar outer paleae and may even be found in the same geographic area at similar depths (P. dorothyae from the Florida Keys at 200–350 m, holotype; P. dorothyae from Southeast Florida at 130–530 m, this study), and on same substrates (urchin spines). Despite some minor morphological differences above, I have assigned them to the same species.

Southeast of Florida and Grand Bahamas, at 132–536 m depth, on sea urchin spine and gastropod mollusk shells (Fig. 22).