Paucibranchia, 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 : 98-103

Paucibranchia sp. 2

Figures 70–73 , Tables 1–2

Marphysa conferta Dean 1996:83 , Table 2 (species list) non Moore, 1911

Material examined. Non-type material: MZUCR 97–02 (1), MZUCR 97–03 (1), sta. GD11 #03 44, Golfo Dulce, Costa Rica, 1995, coll. R. León & J.A. Vargas.

Description. Specimen complete (MZUCR 97–02), gravid female, with 108 chaetigers, L10= 3.4 mm, W10= 0.6 mm, TL= 23 mm. Anterior region with dorsum convex, and flat ventrum, without groove; body depressed from chaetiger 5, widest at chaetiger 7, tapering after chaetiger 50.

Prostomium entire, 0.5 mm long, 0.6 mm wide, lobe frontally rounded, without median sulcus ( Fig. 70A–B ), ventral sulcus shallow ( Fig. 70B ). Prostomial appendages in semicircle, equidistant. Palps reaching second peristomial ring; lateral antennae reaching first chaetiger; median antenna reaching the middle of the first chaetiger. Palpophores and ceratophores ring-shaped, short, slender; palpostyles and ceratostyles tapering, thick, without articulation. Eyes oval, dark, between palps and antennae.

Peristomium wider than prostomium (0.6 mm long, 1.9 mm wide), first ring two times longer than second ring; separation between rings distinct on all sides ( Fig. 70A–B ). Inferior lip with a shallow central depression with a couple of shallow wrinkles ( Fig. 70B ).

Maxillary apparatus with MF= 1+1, 7+8, 5+0, 5+7, 1+1 ( Fig. 71A ). Maxillary carriers 2.5 times shorter than length of MI. MI forceps-like; closing system 10 times shorter than length of MI; ligament between MI and MII rectangular, sclerotized ( Fig. 71A ) . MII wide ; teeth blunt, two distal teeth directed laterally, other teeth recurved; cavity opening oval, 4 times shorter than length of MII ; ligament between MII and MIII, and right MIV, slightly sclerotized ( Fig. 71A–C ) . MIII short, with blunt teeth; with attachment lamella not sclerotized ( Fig. 71A–C ). Left MIV with teeth blunt; with attachment lamella semicircular, sclerotized, wide, situated along length of posterior end of maxilla. Right MIV with small teeth; attachment lamella wide, better developed in the middle, situated 1/2 along length of posterior edge of maxilla ( Fig. 71A–C ). MV rectangular, slightly longer than wide, with a short rounded tooth ( Fig. 71A–C ). Mandibles translucent; with whitish cutting plates, with around 10–11 growth rings.

Branchiae pectinate with up to 8 filaments, in chaetiger 7–21 ( Figs. 70A ; 72B ). Number of branchial filaments per chaetiger in order anterior-posterior: 5, 6, 7, 8, 8, 8, 8, 8, 8, 7, 7, 7, 6, 4. Branchial filaments longer than dorsal cirri.

First two parapodia smallest; most developed in chaetigers 3–23, following one becoming gradually smaller. Notopodial cirri conical, slightly increasing in size from chaetiger 3 (Lcd3: 0.28 mm; Lcd13: 0.29 mm), from chaetiger 28, gradually decreasing in size; in posterior region, almost of similar length as in pre-branchial region ones (Lcd99: 0.25 mm); Hayashi & Yamane’s organ present ( Fig. 72A–E ). Prechaetal lobes as a transverse fold in all chaetigers ( Fig. 72A–E ). Chaetal lobes in chaetigers 1–9, rounded, shorter than postchaetal lobes, with aciculae emerging dorsal to midline; from chaetiger 33, triangular, longer than other lobes, with acicula emerging in midline ( Fig. 72A–E ). Postchaetal lobes well developed, in chaetigers 1–33, wide basally and digitiform ending; thinner, elongated in branchial region; decreasing in size in chaetigers 20–33, following ones inconspicuous ( Fig. 72A–E ). Ventral cirri conical in chaetigers 1–3; in chaetigers 4–25 with oval swollen base and digitiform tip, gradually reducing in size posteriorly; from chaetiger 26, conical ( Fig. 72A–E ).

Aciculae blunt, translucent ( Fig. 72A–E ). First 13 chaetigers with 2 aciculae; from chaetiger 14, with only one acicula.

Limbate chaetae of two sizes in same chaetiger, larger in anterior region, reduced in number around chaetiger 9. Two types of pectinate chaetae, in anterior chaetigers isodonts narrow with long and slender teeth, with 2–3 pectinate, with up to 6–7 teeth, with transverse distal edge ( Fig. 73A ); in median-posterior chaetigers isodonts narrow with short and slender teeth, with 3–4 pectinate with up to 9–10 teeth, with transverse distal edge ( Fig. 73B ). Compound falcigers present in all chaetigers; in anterior chaetigers with blade of two sizes (longer 52 µm, Fig. 73C ; smaller 38 µm, Fig. 73D ); all with triangular teeth, of similar sizes, distal tooth directed upward, proximal tooth directed laterally; in median-posterior chaetigers with all blades of similar size, slightly shorter than blades of anterior chaetigers (32 µm, Fig. 73E ), with triangular teeth, distal tooth shorter than proximal, directed upward, proximal tooth directed laterally. Subacicular hooks bidentate, translucent, starting in chaetiger 23, with one hook per chaetiger; with triangular teeth, distal tooth smaller than proximal, directed upward; proximal tooth directed laterally ( Fig. 73F ).

Variation. Material examined varied in the following features: L10= 3.4–3.7 mm. The maxillary formula varies as follows: MII 7+7–8, MIII 5, MIV 5–6+7–8. Branchiae from chaetigers 7–8 to 20–21. Well developed postchaetal lobe in first 31–33 chaetigers. End of ventral cirri with swollen base in chaetigers 26–29. Start of subacicular hooks in chaetigers 23–25.

Distribution. Golfo Dulce, Costa Rica (Pacific).

Remarks. These specimens are similar to M. conferta (California) ; however, a closer examination of the Costa Rican material allowed me to distinguish it from this species. Paucibranchia sp. 2 (MZUCR 97–0 2, L10: 3.4 mm) differs from P. conferta n. comb. (holotype, L10: 4.5 mm) because the branchiae are distributed from chaetigers 7 to 20–21, the subacicular hooks begins from chaetigers 23–25, and the aciculae are translucent; whereas, in P. conferta n. comb. the branchiae are distributed from 7 to 16–17, subacicular hooks begin earlier (from chaetigers 15–18), and aciculae are dark.

Also, Paucibranchia sp. 2 resembles P. adenensis n. comb., P. gemmata n. comb., and P. patriciae n. comb. by having translucent aciculae and only compound falcigers. Nevertheless, Paucibranchia sp. 2 (MZUCR 97–0 2, L10: 3.4 mm) differs because branchiae start in chaetigers 7–8 and the hooks start in chaetigers 23–25; whereas in P. adenesis n. comb. (holotype L10: 4 mm) branchiae and subacicular hook start later, in chaetigers 14–17 and 29– 35 respectively. Furthermore, Paucibranchia sp. 2 has eyes, dorsal cirri are of similar length in pre- and postbranchial regions, and the compound falcigers have blades of two sizes in anterior region; whereas in P. gemmata n. comb. lacks eyes, dorsal cirri are two times longer in postbranchial chaetigers, and compound falcigers have three sizes in anterior region. Finally, in Paucibranchia sp. 2 the postchaetal lobes are wide basally with a straight digitiform distal end, and the compound falcigers have blades of two sizes in the anterior region; whereas in P. patriciae n. sp. the postchaetal lobes are oval basally with digitiform distal end tilted dorsally, and compound falciger have all blades of similar size. The comparison with other Paucibranchia n. gen. species having only compound falcigers present is provided in Table 2.

Two specimens were examined, and only one was complete and in regular conditions; formal description of the species requires additional material.

Figures

FIGURE 70. Paucibranchia sp. 2., specimen MZUCR 97–02. A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Anterior end with branchiae, dorsal view. Scale bars: A, 0.85 mm; B, C, 1.4 mm.

FIGURE 71. Paucibranchia sp. 2., specimen MZUCR 97–02. A. Maxillary apparatus, dorsal view; B. Left MII-III-IV-V, dorsal view; C. Right MII-IV, dorsal view. Scale bars: A, 0.2 mm; B, C, 70 µm.

FIGURE 72. Paucibranchia sp. 2., specimen MZUCR 97–02. A. Parapodium 3; B. Parapodium 13; C. Parapodium 41; D. Parapodium 70, dorsal cirri broken; E. Parapodium 99. All in anterior view. A, B, E from specimen MZUCR 97–02; C, D, from specimen MZUCR 97–03. Scale bars: A, E, 0.14 mm; B, 0.26 mm; C, 0.10 mm; D, 0.05 mm.

FIGURE 73. Paucibranchia sp. 2., specimen MZUCR 97-02. A. Isodonts pectinate narrow with long and slender teeth, chaetiger 3; B. Isodonts pectinate narrow with short and slender teeth, chaetiger 99; C. Compound falciger, long blade, chaetiger 3; D. Compound falciger, median blade, chaetiger 3; E. Compound falciger, short blade, chaetiger 99; F. Subacicular hook, chaetiger 41. Scale bars: A, 10.5 µm; B, 5.6 µm; C, 18.8 µm; D, 13.7; E, 22.5 µm; F, 10.5 µm.