Phalacrostemma danieli, Chávez-López, 2022

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 : 119-124

Phalacrostemma danieli sp. nov.

urn:lsid:zoobank.org:act:8255C32E-0216-4353-A681-3A5E42915E88

Figs 5– 7 , 8E, G–J

Diagnosis

Outer paleae with pectinate margins on distal thecae, hirsute tips. Inner paleae cylindrical with conspicuous thecae, slightly expanded margins, and blunt tip. Tentacular filaments absent.

Etymology

This species name is after my brother Daniel Chávez-López. It is a noun in the genitive case ( ICZN 1999, Art. 31.1.2).

Material examined

Holotype LESSER ANTILLES • incomplete spec. (body length 10 mm); southwest of Grenada; RV Pillsbury , stn 478; 11°33′ N, 62°09′ W; depth 597 m; 2 Aug. 1966; UMML-22.1179 .

Paratypes LESSER ANTILLES • 9 specs; same collection data as for holotype; UMML-22.1180 • 1 spec. (using mid-operculum for SEM); same collection data as for holotype; UMML-22.1181 • 1 spec.; same collection data as for holotype; ECOSUR-304 .

Additional material

BAHAMAS – Southeastern Bahamas • 4 specs; RV Columbus Iselin , stn 163; 23°37′ N, 77°13′ W; depth 1342 m; 6 Feb. 1974; UMML-22.1182 • 1 spec.; same collection data as for preceding; ECOSUR-P3236 .

Description

BODY. Holotype incomplete (UMML-22.1179), 10 mm long, 2.5 mm wide, six abdominal segments, caudal peduncle 3.5 mm long ( Fig. 5 ).

OPERCULUM. Opercular disc truncate. Outer paleae arranged spirally, 29–30 paleae on each lobe. Inner paleae arranged diagonally, two paleae on right lobe, one palea on left. Outer paleae amber, cylindrical, 2.5 mm long ( Figs 6A–E , 7C–F ). Proximal region with compact thecae, margins slightly expanded, denticulate ( Figs 6B , 7C–D ). Thecae of middle region with margins expanded, denticulate ( Figs 6C , 7E ). Thecae of mid-distal region with margins expanded, pectinate ( Figs 6D , 7F ); tips hirsute ( Figs 6F , 7E ). Inner paleae amber, cylindrical, with conspicuous thecae, slightly expanded margins; tips blunt, smooth ( Figs 6F–G , 7G ). Opercular stalk brown, slightly wider than long ( Fig. 5A–D ). Opercular papillae in one row peripheral to outer paleae; nine papillae on each lobe. Papillae conical and tapered, 5–6 times as long as wide ( Fig. 5C ). First papilla appears in dorsal region of opercular peduncle, at level of nuchal hooks ( Fig. 5F ). Four pairs of amber nuchal hooks, compressed, tip slightly curved, with long limbation. Limbation exceeds curvature of hook tip, 2.5 times as long as tip ( Figs 6H , 7B ). Palps robust, tapered, twice as long as wide ( Figs 5C–D , 7A ). Pair of broad buccal flaps ( Fig. 5D ). Tentacular filaments absent. Median organ conical, tapered without eyespots.

THORAX. First thoracic segment with two long, triangular-shaped lateral lobes and capillary neurochaetae ( Fig. 5C–D ). Second segment with 2–3 triangular-shaped lateral lobes and paired branchiae, without chaetae ( Fig. 5C ).

PARATHORAX. With four segments, all with paired branchiae. Notopodia with six lanceolate chaetae and six capillary chaetae ( Fig. 6I ). Neurochaetae capillary.

ABDOMEN. Abdominal segments brownish with paired branchiae up to segment 4. Neurochaetae capillary, ornamented with irregular thecal laminar extensions ( Fig. 6J ). Notopodia with series of uncini with 10 rows of teeth ( Fig. 6K ). Caudal peduncle cylindrical, brownish, broken, only posterior region attached to abdomen ( Fig. 5B, E ).

Variation

Body incomplete 4–10 mm long, 0.5–2 mm wide, 3–6 abdominal segments. Operculum with 16–30 outer paleae per lobe, 1–3 inner paleae per lobe, generally two pairs, and 3–5 pairs of nuchal hooks. Outer paleae 1–2.5 mm long.

Remarks

Phalacrostemma danieli sp. nov. shares the morphology of the outer paleae with P. paulinae Kirtley, 1994 , and the morphology of the abdominal uncini with P. tenera ( Augener, 1906) .

Phalacrostemma paulinae Kirtley, 1994 was described from the Northwestern Atlantic Ocean ( Kirtley 1994: 38 °41′ N, 70°38′ W), from a single specimen collected by RV Atlantis II , stn 95 at 2160 m depth. Its original description is brief and only included a partial description of the outer palea, so it is necessary to redescribe P. paulinae to know the rest of the characters.

According to Kirtley (1994: 162), the type material of P. paulinae was in the Natural History Museum, Los Angeles (NHM) without a specific catalog number. During his stay at NHM (Feb.–Mar. 2022) Dr Sergio Salazar-Vallejo, along with the polychaete collection manager Leslie H. Harris, searched for the type material of P. paulinae and found the holotype vial with catalog number LACM-AHF POLY 1691 ( Fig. 8A ). Unfortunately, the vial was empty, which means the holotype is missing, and there are no other specimens from nearby localities or the same oceanographic expedition in the museum.

In P. paulinae the outer paleae have the proximal thecae with denticulate and slightly expanded margins ( Fig. 8B ); thecae of the middle region with expanded pectinate margins ( Fig. 8C ), and the mid-distal thecae with expanded elongate and pectinate margins ( Fig. 8D ). The morphology of the outer paleae of P. danieli ( Fig. 8G–I ) resembles that of P. paulinae ; although there are some differences in the denticles of the mid-distal thecae. Phalacrostemma danieli sp. nov. has straight denticles, 5–9 times as long as wide ( Fig. 8I ), whereas P. paulinae has slightly inclined denticles, 10–16 times as long as wide ( Fig. 8D ).

Another difference is the locality and bathymetric range where the species were found. According to Kirtley (1994: 162), P. paulinae was collected in the North Atlantic (38°41′ N, 70°38′ W) at 2160 m depth; however, the vial label contains different coordinates (38°33′ N, 68°32′ W) and depth (3753 m) ( Fig. 8A ), even though both refer to the same station and oceanographic cruise: RV Atlantis , stn Atl. 95. Based on the above, P. paulinae could be distributed from 38°41′ N, 70°38′ W to 38°33′ N, 68°32′ W at 2160 m or 3753 m depth, while P. danieli sp. nov. was collected in the Lesser Antilles (11°33′ N, 62°09′ W) at 597 m depth and the Bahamas (23°37′ N, 77°13′ W) at 1342 m.

Phalacrostemma tenera ( Augener, 1906) was described from Barbados at 365.8 m depth. Phalacrostemma danieli sp. nov. shares the abdominal uncini with a curved dorsal region and 10 rows of teeth ( Fig. 8J ) with P. tenera ( Fig. 8K ). Although these species are distributed at similar depths at relatively close localities, they differ mainly in the shape of the nuchal hooks. Phalacrostemma tenera has a short, slightly falcate tip, at a 57° angle, and a slightly wider limbation than the tip ( Fig. 8F ), whereas P. danieli sp. nov. has a curved tip, at a 45° angle, and a wider tip than the limbation ( Fig. 8E ).

The lack of detail mainly in the morphology of the opercular paleae of P. tenera and P. paulinae prevents the determination of their diagnostic characters and therefore hinders their comparison with the other species of the genus. In addition, the type material of P. tenera ( Kirtley 1994: 165) and P. paulinae (Salazar-Vallejo 2022 pers. com.) is missing. Therefore, topotype material is necessary.

Based on the morphological differences found and considering the area of distribution and bathymetric ranges, I assigned the analyzed specimens to P. danieli sp. nov.

Distribution

Southwest of Grenada Island at 597 m depth ( Fig. 22 ).

Figures

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. 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. 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. 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.