Paucibranchia fallax ( Marion & Bobretzky, 1875 ) 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 : 48-52

Paucibranchia fallax ( Marion & Bobretzky, 1875) n. comb.

Figures 31–34 , Tables 1, 3

Marphysa fallax Marion & Bobretzky in Marion, 1874:399 nomen nudum

Marphysa fallax Marion & Bobretzky, 1875:13 –15, Fig. 1A–E ; Fauvel 1923:410 –411, Fig. 162O–U (partim); Fauvel 1936:49.

Material examined. Non-type material: MNHN-A39 (1), Napoles, Mediterranean Sea, 1935, Collection P. Fauvel . MNHN-A132 (2), sta. LVII, North Morocco, Atlantic Ocean , 8°24'46"W 33°24' N, 24 Jun 1924, 25 m, Collection P. Fauvel . USNM 1122621 (1), Leghorn , Vada, Tuscany, Italy, Mediterranean Sea, 10 Oct 2001, 15m. USNM 1122624 (1) , USNM 1122625 (1), USNM 1122626 (1), Sardinia coast, Italy, Mediterranean Sea , summer 2001 . ZMB 7597 (1), Rovinj , Croatia, Mediterranean Sea, coll. S. Heider . ZMB 1852 (3), Cres Island , Croatia, Adriatic Sea, coll. Grube, S. de Petris.

Description. Complete specimen (MNHN-A39), with 121 chaetigers, L10= 3.3 mm, W10= 1.1 mm, TL= 22 mm. Anterior region of body with convex dorsum and flat ventrum, without groove; body depressed from chaetiger 10, widest at chaetiger 40, tapering after chaetiger 64.

Prostomium slightly bilobed, 0.6 mm long, 0.6 mm wide, frontally rounded, without median sulcus ( Fig. 31B ), ventral sulcus deep ( Fig. 31C ). Prostomial appendages in a semicircle, median antenna isolated by a gap. Palps reaching second peristomial ring; lateral antennae reaching the middle of second peristomial ring; median antenna reaching first chaetiger. Palpophores and ceratophores ring-shaped, short, thick; palpostyles and ceratostyles tapering, thick, without articulation. Eyes rounded, brown, between palps and lateral antennae.

Peristomium wider than prostomium (0.6 mm long, 1 mm wide), first ring two times longer than second ring, separation between rings distinct on all sides ( Fig. 31A–C ). Inferior lip with a slight central depression, with a couple of shallow wrinkles ( Fig. 31C ).

Maxillary apparatus with MF= 1+1, 7+7, 7+0, 4+10, 1+1 ( Fig. 32A ). Maxillary carriers 2.2 times shorter than length of MI. MI forceps-like; closing system 6.5 times shorter than length of MI; ligament between MI and MII sclerotized ( Fig. 32A ). MII wide; teeth recurved; cavity opening oval 2.5 times shorter than length of MII; ligament between MII and MIII, and right MIV, sclerotized ( Fig. 32A ). MIII short; with blunt teeth; with rectangular attachment lamella, longer than wide, sclerotized, situated only in center of posterior edge of maxilla ( Fig. 32A ). Left MIV with larger three distal teeth; attachment lamella semicircle, wide, situated 2/3 along length of posterior edge of maxilla. Right MIV with larger distal teeth; attachment lamella semicircle, better developed in the middle, situated 2/3 along length of posterior edge ( Fig. 32A ). MV rectangular, longer than wide, with a short rounded tooth ( Fig. 32A ). Mandibles dark; cutting plates whitish, with 8 growth rings ( Fig. 32B ).

Branchiae pectinate with up to two filaments, in chaetigers 16–48 ( Figs. 31A ; 33C ). One filament along chaetigers 16–19; two filaments along chaetigers 20–34; one filament along chaetigers 35–48. Branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 4–47, following ones becoming gradually smaller. Notopodial cirri conical, increasing in size from chaetiger 4 (Ldc4: 0.37 mm; Lcd18: 0.47 mm), from chaetiger 29, gradually decreasing in size, in posterior region almost the same size to the pre-branchial region ones (Ldc186: 0.39 mm) ( Fig. 33A–E ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 33A–E ). Chaetal lobes in chaetigers 1–24, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 25, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 33A–E ). Postchaetal lobes best developed in chaetigers 1–28, bluntly conical; decreasing in size in chaetiger 11–28, following ones inconspicuous ( Fig. 33A–E ). Ventral cirri digitiform in chaetigers 1–6; in chaetigers 7–26 with oval swollen base and digitiform tip; from chaeriger 27, digitiform, gradually reducing in size posteriorly ( Fig. 33A–E ).

Aciculae blunt, translucent ( Fig. 33A–E ). First 13 chaetigers with 3 aciculae; in chaetigers 14–19 with 2 aciculae; from chaetigers 20, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 15. Two types of pectinate chaetae, in anterior chaetigers isodonts narrow with long and slender teeth, with 1–2 pectinate, with up to 11–12 teeth, with transverse distal edge ( Fig. 34E ); in median-posterior chaetigers, isodonts narrow with short and slender teeth, with 3–4 pectinate, with up to 12 teeth, with transverse distal edge ( Fig. 34F ). Compound spinigers in chaetigers 1–26, three or four per chaetiger, with all blades of similar size ( Fig. 34D ). Compound falcigers in all chaetigers, more abundant than spinigers; in anterior region (first 22 chaetigers) with all blades of similar size (56 µm, Fig. 34C ); all with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally; in median-posterior chaetigers with all blades of similar size, shorter than blades of anterior chaetigers (38 µm, Fig. 34B ), with triangular teeth, of similar size, distal tooth directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 22, with one per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally ( Fig. 34A ).

Pygidium with two pairs of anal cirri; dorsal pair as long as last 11 chaetigers; ventral pair short, as long as last three chaetigers.

Variation. Material examined varied in the following features: L10= 2.6–4.9 mm, W10= 0.6–1.1 mm. Palps reaching middle of the first peristomial ring or second peristomial ring. Lateral and median antennae reaching second peristomial ring or first chaetiger. The maxillary formula varies as follows: MII 7–8+6–7, MIII 7–8, MIV 3–4+8–10. The proportion of maxillary apparatus varies as follows: maxillary carriers with respect to the MI varies 2–2.5 times; closing system with respect to the MI varies 6–7 times; cavity opening with respect to MII varies 2.5– 4 times. Branchiae from chaetigers 15–16 to 28–48. Maximum number of branchial filaments varied from 1 to 3. Well developed postchaetal lobe in first 14–28 chaetigers. Ventral cirri with swollen base from chaetigers 6–7 to 22–32. Start of subacicular hooks in chaetigers 20–25. Compound spinigers present only in first 19–26 chaetigers.

Distribution. West and central region of Mediterranean Sea, and North-West Morocco.

Remarks. This species is unique within Paucibranchia n. gen. by having the highest number of chaetigers with branchiae (32 chaetigers) and the lowest number of branchial filaments present (2–3 filaments). Although specimens with only 2 branchial filaments appear to have palmate branchiae, in specimens with three filaments the branchiae are pectinate.

The type material is lost; therefore, it would be necessary to find topotypic specimens or near to the locality ( Monaco, France) in order to establish a neotype. The specimens studied here match the descriptions of Marion & Bobretzky (1875) and Fauvel (1923).

The species has been reported from the west-central region of the Mediterranean Sea and north of Morocco (Atlantic Ocean). Likewise, Fauvel (1923) reported a specimen from Dinard, France (English Channel); however, the specimen does not match P. fallax n. comb. but is most similar to M. sanguinea in lack of falcigers, and the branchiae and ventral cirri with swollen bases are distributed along the body. Thus, the distribution of P. fallax n. comb. is doubtful in this region of France.

Paucibranchia fallax n. comb. resembles P. carrerai n. sp., Paucibranchia sp. 1 and P. stragula n. comb. by having a translucent and bidentate form of subacicular hooks, and the presence of compound spinigers and falcigers. However, the P. fallax n. comb. differs from P. carrerai n. sp. and P. stragula n. comb. because it has only one hook per chaetiger; whereas the latter two species have 6 and 14 subacicular hooks per chaetiger, respectively. Further, in P. fallax n. comb. dorsal cirri are almost the same size in pre- and postbranchial regions; whereas in P. carrerai n. sp. dorsal cirri are two times longer in postbranchial region. Also, P. fallax n. comb. has postchaetal lobe bluntly conical in the pre-branchial region; whereas in P. stragula n. comb. postchaetal lobe is digitiform in same region. Finally, P. fallax n. comb. is different from Paucibranchia sp. 1 since postchaetal lobe is bluntly conical in branchial region, branchiae start in chaetiger 16 and finish in chaetiger 48, and have only two filaments (USNM 0 90007, L10: 2.9 mm); whereas in Paucibranchia sp. 1 the postchaetal lobe is wide basally with digitiform end in branchial chaetigers, branchiae are distributed from chaetiger 7 to 16 (ECOSUR-P2937, L10: 3.3 mm) and have up to 6 filaments. The comparison with other Paucibranchia species having compound falcigers and spinigers present is provided in Table 3.

Figures

FIGURE 1. Maxillary apparatus. A. Paucibranchia disjuncta n. comb. (Hartman, 1961), LACM-AHF POLY 6447, dorsal view; B. Marphysa viridis Treadwell, 1917, ECOSUR-P2678, dorsal view; C. Treadwellphysa yucatanensis Molina-Acevedo & Carrera-Parra, 2017, ECOSUR-P2811, dorsal view; D. Left MI-II-III-IV-V of P. disjuncta n. comb., dorsal view; E. Left MI- II-III-IV-V of M. viridis, dorsal view; F. Left MI-II-III-IV-V of T. yucatanensis, dorsal view. Scale bars: A, D, 0.4 mm; B, E, 0.45 mm; C, F, 0.25 mm. Dark and thin lines in D, E and F indicate the different forms in the MI of the apparatus of each species. fa= falcal arch, boe= basal outer edge, bie= basal inner edge, rp= rounded projection in base of MII.

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.