Paucibranchia conferta ( Moore, 1911 ) Molina-Acevedo, 2018

Molina-Acevedo, Isabel C., 2018, Morphological revision of the Subgroup 1 Fauchald, 1970 of Marphysa de Quatrefages, 1865 (Eunicidae: Polychaeta), Zootaxa 4480 (1), pp. 1-125 : 36-40

Paucibranchia conferta ( Moore, 1911) n. comb.

Figures 23–25 , Tables 1–2

Marphysa conferta Moore, 1911:252 –254, Pl. XVI, Figs. 29–34 ; Hartman 1944:129; Hartman 1961:83.

Material examined. Type material: Holotype USNM 17328 , sta. 4431, off Brockway Point Santa Rosa Island, 15 Apr 1904, 75 m. Additional material : LACM-AHF POLY 10193 (1), Santa Monica Canyon, Southern California Bight , California, USA, North Pacific , Nov 1958, 54 – 56 m. LACM-AHF POLY POLY 10194 (2), R/V VELERO IV sta. 5712-58, 6 miles from Hyperion Sewage Treatment Plant Smokestack , bearing 270.5°T, El Segundo, Los Angeles County, Southern California Bight , California, USA, North Pacific , 33°55'50'' N 118°33'05'' W, 18 Apr 1958, in sand and gravel, grab, 88 m.

Description. Holotype incomplete, gravid female, with 55 chaetigers, L10= 4.5 mm, W10= 0.8 mm, with TL= 21 mm. Anterior region with convex dorsum, and flat ventrum, without groove; body depressed from chaetiger 6, widest at chaetiger 11, tapering after chaetiger 46.

Prostomium entire, 0.6 mm long, 0.8 mm wide, lobe frontally rounded, without median sulcus ( Fig. 23A–B ), ventral sulcus deep. Prostomial appendages in a semicircle, equidistant. Palps reaching the middle of the first peristomial ring; lateral antennae reaching second peristomial ring; median antenna reaching the middle of the first chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, thick, without articulation but with colored rings. Eyes rounded, brown, between palps and lateral antennae.

Peristomium wider than prostomium (0.8 mm long, 1.2 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides ( Fig. 23A–B ). Inferior lip with a central depression.

Maxillary apparatus with FM= 1+1, 7+6, 7+0, 5+7, 1+1 ( Fig. 23D ). Maxillary carriers 2 times shorter than length of MI. MI forceps-like; closing system 8 times shorter than length of MI; ligament between MI and MII slightly sclerotized ( Fig. 23D ). MII wide; teeth recurved; cavity opening oval, 3 times shorter than length of MII; ligament between MII and MIII, and right MIV, slightly sclerotized ( Fig. 23D ). MIII short; with triangular teeth; with attachment lamella not sclerotized ( Fig. 23D ). Left MIV with a small basal tooth; attachment lamella semicircular, sclerotized, wide, situated 2/3 along length of posterior edge of maxilla. Right MIV with small teeth; attachment lamella wide, better developed in the middle, situated 2/3 along length of posterior edge of maxilla ( Fig. 23D ). MV rectangular, slightly longer than wide, with a short rounded tooth ( Fig. 23D ). Mandibles not examined.

Branchiae pectinate with up to 7 filaments, in chaetigers 8–16 ( Figs. 23C ; 24B ). Number of branchial filaments per chaetiger in order anterior-posterior: 6, 6, 7, 7, 5?, 7, 7, 5, 4. Basal branchial filaments shorter than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 3–24, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (L5: 0.48 mm; Ldc25: 0.52 mm), from chaetiger 28, gradually decreasing in size ( Fig. 24A–E ), in specimen LACM-AHF POLY 10193 (Ldc3 0.31 mm; Ldc120: 0.39 mm) posterior region 1.2 times longer than the pre-branchial region ones. Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 24A–E ). Chaetal lobes in chaetigers 1–18, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 19, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 24A–E ). Postchaetal lobes well developed in chaetigers 1–26, bluntly conical, thinner, elongated in branchial region; decreasing in size in chaetigers 14–26, following ones inconspicuous ( Fig. 24A–E ). Ventral cirri digitiform in chaetigers 1–4; in chaetigers 5–25 with oval swollen base and digitiform tip, gradually reducing in size posteriorly; from chaetiger 26, conical ( Fig. 24A–E ).

Aciculae blunt, with reddish basal end, distally translucent ( Fig. 24A–E ). First 15 chaetigers with 2 aciculae; from chaetiger 16, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 12. Two types of pectinate chaetae, in anterior chaetigers isodonts narrow with long and slender teeth, with 1–2 pectinate, with up to 8–9 teeth, with transverse distal edge ( Fig. 25C ); in median-posterior chaetigers isodonts narrow with short and slender teeth, 2–3 pectinate, with 10–11 teeth, with transverse distal edge ( Fig. 25D ). Compound falcigers present in all chaetigers; in anterior region with one-sized blade (49 µm, Fig. 25A ); all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in media-posterior chaetigers with all blades of similar size, slightly shorter than blades of anterior chaetigers (43.3 µm, Fig. 25B ), with triangular teeth, distal shorter than proximal, distal tooth directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 28, with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally ( Fig. 25E ).

Pygidium with two pairs of anal cirri; dorsal pair as long as last chaetigers; ventral pair short, as long as pygidium edge.

Variation. Material examined varied in the following features: L10= 2.3–4.5 mm, W10= 0.7–1 mm. Palps reaching first peristomial ring or middle of the first peristomial ring. Lateral antennae reaching second peristomial ring or first chaetiger. Median antenna reaching first chaetiger or middle of the first chaetiger. The maxillary formula varies as follows: MII 7+7–6, MIV 4–5+7. The proportion of maxillary apparatus varies as follows: maxillary carriers with respect to the MI varies 1.4–2 times; closing system with respect to the MI varies 7–8 times; cavity opening with respect to MII varies 2.5–3 times. Branchiae from chaetigers 7–8 to 13–16. Maximum number of branchial filaments varied from 6 to 8. Well developed postchaetal lobe in first 23–26 chaetigers. Start of subacicular hooks in chaetigers 15–28.

Distribution. Southern California, USA.

Remarks. This species has been recorded from Southern California to Natividad Island, Mexico ( Hartman 1944, 1961; Fauchald 1970), and Golfo Dulce, Costa Rica ( Dean 1996). However, the only specimen reviewed by Fauchald (1970) from Natividad Island (NI) differs from P. conferta n. comb. in several features. The specimen from NI (L10: 3.5 mm, W10: 0.9 mm) has translucent aciculae, compound falcigers with blades of two sizes in anterior chaetigers (longer 63 µm, smaller 46.2 µm), branchiae in chaetigers 9–22, and subacicular hook from chaetiger 26. Whereas, P. conferta n. comb. (L10: 3.4 mm, W10: 1 mm) has aciculae with a dark basal-middle region and distally translucent, compound falcigers with all blades of similar size (49 µm), branchiae in chaetigers 7–16, and subacicular hooks from chaetiger 18. It is possible that the specimen reviewed by Fauchald (1970) correspond to Paucibranchia sp. 2 or to another undescribed species. It is necessary to examine material available from NI to confirm this last hypothesis.

On the other hand, the specimens from Golfo Dulce, Costa Rica belong to a new species morphologically similar to P. conferta n. comb. (see Remarks section for Paucibranchia sp. 2).

Paucibranchia conferta n. comb. resembles P. adenensis n. comb., P. gemmata n. comb., and P. patriciae n. sp. by having a bidentate and translucent subacicular hooks, and falcigers present in all chaetigers. However, P. conferta n. comb. differs from P. adenensis n. comb. by the color of aciculae, which is reddish basally and translucent distally in the former and translucent in the latter; also, P. conferta n. comb. has compound falcigers with blades of similar size in anterior chaetigers, whereas in P. adenensis n. comb. falcigers have blades of two sizes. Concerning P. gemmata n. comb., this species lacks eyes, the dorsal cirri are two times longer in postbranchial chaetigers, and falcigers have blades of three sizes in anterior region; whereas P. conferta n. comb. has eyes, dorsal cirri are of similar size in pre- and postbranchial regions, and falcigers from anterior chaetigers have blades of the same size. The comparison with P. patriciae n. sp. is provided in the Remarks section on the latter species. The comparison with other Paucibranchia n. gen. species with only compound falcigers present is provided in Table 2.

Figures

FIGURE 23. Paucibranchia conferta (Moore, 1911) n. comb., holotype USNM 17328 A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Anterior end with branchiae, dorsal view; D. Maxillary apparatus, dorsal view. Scale bars: A, C, 1.1 mm; B, 2.3 mm; D, 0.8 mm.

FIGURE 24. Paucibranchia conferta (Moore, 1911) n. comb. A. Parapodium 3; B. Parapodium 5; C. Parapodium 11; D. Parapodium 25; E. Parapodium 120. All in anterior view. A, E from non-type LACM-AHF POLY 10193; B, C, D, from holotype USNM 17328. Scale bars: A, 0.17 mm; B, C, D, E, 0.20 mm.

FIGURE 25. Paucibranchia conferta (Moore, 1911) n. comb., non-type LACM-AHF POLY 10193. A. Compound falciger, long blade, chaetiger 3; B. Compound falciger, short blade, chaetiger 120; C. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; D. Isodonts pectinate narrow with long and slender teeth, chaetiger 120; E. Subacicular hook, chaetiger 28. Scale bars: A, 17.5 µm; B, 31 µm; C, 11.2 µm; D, 7 µm; E, 10.5 µm.

FIGURE 29. Paucibranchia disjuncta (Hartman, 1961) n. comb. A. Compound spinigers, chaetiger 55; B. Compound falciger, chaetiger 115; C. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; D. Isodonts pectinate narrow with long and slender teeth, chaetiger 6; E. Isodonts pectinate narrow with short and slender teeth, chaetiger 65; F. Subacicular hook bidentante, chaetiger 55; G. Subacicular unidentate with hood, chaetiger 47. A, D, E, G, from non-type LACM-AHF POLY 10195; B from holotype LACM-AHF POLY 724; C from non-type LACM-AHF POLY 10196; F from non-type LACM-AHF POLY6948. Scale bars: A, B, 20 µm; C, 14 µm; D, E, G, 10 µm; F, 20 µm.

FIGURE 30. Length-dependent variation of some morphological features in Paucibranchia disjuncta (Hartman, 1961) n. comb. A. Maximum number of branchial filaments (n= 39); B. First chaetiger with branchia (n=39); C. Last chaetiger with branchia (n=39); D. Last chaetiger with well developed postchaetal lobe (DPL) (n=36); E. Last chaetiger with ventral cirri with swollen base (VCSB) (n=37); F. First chaetiger with falciger (n=29); G. Start of subacicular hook (n=39).

FIGURE 31. Paucibranchia fallax (Marion & Bobretzky, 1875) n. comb., non-type MNHN-A39. A. Body with branchiae, lateral view; B. Anterior end, dorsal view; C. Anterior end with branchiae, ventral view. Scale bars: A, 3.3 mm; B, C, 0.8 mm.

FIGURE 32. Paucibranchia fallax (Marion & Bobretzky, 1875) n. comb., non-type MNHN-A39. A. Maxillary apparatus, dorsal view; B. Mandibles. Scale bars: A, B, 0.3 mm.

FIGURE 33. Paucibranchia fallax (Marion & Bobretzky, 1875) n. comb., non-type MNHN-A39. A. Parapodium 3; B. Parapodium 18; C. Parapodium 36; D. Parapodium 70; E. Parapodium 106. All in anterior view. Scale bars: A, C, E, 0.19 mm; B, 0.23; D, 0.14.

FIGURE 34. Paucibranchia fallax (Marion & Bobretzky, 1875) n. comb., non-type MNHN-A39. A. Subacicular hook, chaetiger 36; B. Compound falciger with short blade, chaetiger 70; C. Falciger with long blade, chaetiger 3; D. Compound spiniger, chaetiger 3; E. Isodonts pectinate narrow with long and slender teeth, chaetiger 18; F. Isodonts pectinate narrow with short and slender teeth, chaetiger 36. Scale bars: A, C, 20 µm; B, 27 µm; D, 10 µm; E, 7 µm; F, 10 µm.