Paleanotus macrophthalmum (Hartmann-Schröder, 1959)

Figs 4, 12

Chrysopetalum macrophthalmum Hartmann-Schröder, 1959: 94, Fig. 14–18.

Paleanotus macrophthalmum Watson 2015: 708 (n. comb.).

Paleanotus sp. 2 .— Cruz-Gómez et al. 2021: 183, Fig. 6J (key of chrysopetalids from Tropical America).

Type locality: Jiquilisco Estuary, San Juan, El Salvador (Hartmann-Schröder 1959) .

Material examined. Costa Rica: UMAR-Poly-OH-020, cruise pier, Puntarenas, on pier piles, 1.5 m, November 22, 2012, coll. TVG; Four specimens, UMAR-Poly-OH-019, UMAR-Poly-OH-030, UMAR-Poly-OH-031, UMAR-Poly-OH-032, same data as UMAR-Poly-OH-020 .

Description. Based on the best-preserved specimen (UMAR-Poly-OH-020): complete with 37 segments. TL= 1.9 mm, TW= 0.5 mm. Body short, broad, tapered posteriorly (Fig. 4A). Body pale yellow to bright yellow. Paleae fan translucent, slightly imbricated dorsally.

Prostomium not visible, completely retracted among the first anterior segments. Palps short, oval visible in ventral view. Mouth fold wide, placed between segment 3 and 4. Pharynx muscular eversible, not exposed, stylets slender.

Parapodium from segment 10, notochaetae in three main groups (Fig. 4B). Notochaetae: lateral group inserted below notaciculum, 4–5 paleae, slender and symmetrical, with 3–4 internal ribs (Fig. 4C); subunit 1, 1 palea, slender, shorter and symmetrical, with 6 internal ribs (Fig. 4D). Main group, 8–10 paleae, broad, curved and asymmetrical, with 12–16 (17) and 3 finely raised ribs (Fig. 4E). Median group, 3–4 paleae, short, curved and asymmetrical, with 9–12 internal ribs and 2–3 raised ribs (Fig. 4F–G).

Neuropodium conical, slightly short than notopodium. Neurochaetae: unit 1, 1–3 superior spinigers, blades straight and long, 8–9 times longer than wide (Fig. 4H). Unit 2, 4–5 falcigers, blades straight and medium-sized, 4–5 times longer than wide (Fig. 4I). Unit 3, 4–5 falcigers, blades straight and short, 3–4 times longer than wide (Fig. 4J). Unit 4, 2–3 falcigers, blades straight and short, 3–4 times longer than wide (Fig. 4K). Pygidium quadrate, with two anal cirri (Fig. 4L). Oocytes not seen.

Habitat. Intertidal to subtidal (1.5– 4 m). Specimens of this species were collected on pier piles and previously recorded on limey-sandy (Hartmann-Schröder 1959).

Distribution. From San Juan, El Salvador, to Puntarenas, Pacific Coast of Costa Rica (Fig. 12).

Remarks. Hartmann-Schröder (1959) described Paleanotus macrophthalmum (as a member of Chrysopetalum) from El Salvador, including specimens from Costa Rica. Since then, this species was scarcely recorded in the region, mostly included in compilatory checklists (Molina-Lara & Vargas-Zamora 1995, Dean 2004, Rivera & Romero de Rivera 2008). The species should be redescribed, using the holotype and, because the type specimen is in poor conditions (CW Pers. Comm. 2020), topotype specimens should be considered. Recently, Watson (2015) stated that this chrysopetalid was the only tropical species of Paleanotus; however, the conclusion of this study revealed another species (described below) that can be found in the region and inhabits similar substrata.

This species is characterized among tropical Paleanotus species by short, narrow main paleae with fine denticulate internal ribs, rounded brow and serrated margins.