Chrysopetalum mexicanum

Description. Based on the holotype: complete with 53 segments. TL = 6.7 mm, AT = 1.2 mm. Body long, tapered posteriorly (Fig. 23 A). Body pale orange to brown. Paleae fan translucent to golden bright, slightly imbricated dorsally. Prostomium visible among the first five segments. Lateral antennae long, inserted on antero-ventral prostomial margin, median antenna slightly shorter than lateral ones. Eyes red-violet, two pairs. Nuchal organ large, round, partially covering prostomium (Fig. 23 B). Palps long, cylindrical, visible in dorsal view. Mouth fold wide, placed between segment 3 and 4. Pharynx eversible, not exposed, stylets slender. Parapodium from segment 27, notochaetae in three main groups (Fig. 23 E). Notochaetae: lateral group inserted below notaciculum, 4 – 5 paleae, slender and narrow, with 2 – 3 internal ribs and 0 – 1 raised rib (Fig. 23 F). Main group, 15 – 18 paleae; lateral-most, slender, curved and asymmetrical, with 5 – 6 (7) internal ribs (Fig. 23 G); midmost, broader and symmetrical, with 5 – 7 internal ribs (Fig. 23 H); midline-most, slender and asymmetrical, with 4 – 5 (6) internal ribs (Fig. 23 I). Median group, 3 – 4 paleae short, curved and asymmetrical; the distal-most with 3 internal ribs and 1 raised rib; the next proximal palea smaller with 3 internal ribs and 1 raised rib, and the proximalmost with 2 internal ribs (Fig. 23 J – K). All paleal groups with margins markedly serrated, and dorsal paleal surface ornamented with tiny tubercles. Neuropodium leaf-shaped, larger than notopodium. Neurochaetae: unit 1, 4 – 5 falcigers, blades straight and long, 7 times longer than wide (Fig. 23 L). Unit 2, 4 – 6 falcigers, blades straight and long, 4 – 5 times longer than wide (Fig. 23 M). Unit 3, 3 falcigers, blades straight and medium-sized, 5 – 6 times longer than wide (Fig. 23 N). Unit 4, 2 – 3 falcigers, blades straight and short, 4 – 5 times longer than wide (Fig. 23 O). Pygidium rounded with two anal cirri (Fig. 23 C). Oocyte size: 40.3 – 64.2 µm (n = 3) (Fig. 23 D). Habitat. Intertidal to subtidal (0.5 – 7 m). Specimens of C. mexicanum n. sp. were collected mostly on rocks and as epibiont of algae, sponges, and as members of the fouling community.

Figs 23, 25, 26 urn: lsid: zoobank. org: act: F 68660 D 1 - DFF 8 - 4 DDF- 86 FB- 296 B 0 C 1 A 532 C

Remarks. Chrysopetalum mexicanum n. sp. belongs to the group of Chrysopetalum with slender paleae, such as C. elegans Bush in Verrill, 1900, C. elegantoides and C. tovarae n. sp. Specimens of C. mexicanum n. sp. possess main paleal group with two different forms of main paleae: mid-most shorter and wider, which resembles those on C. occidentale, whereas the lateral-most long and slender which, resembles those on C. elegantoides and C. tovarae n. sp. However, the differences can also be found in this group of paleae. Main paleae of C. elegantoides are broader than those in C. mexicanum n. sp. (7 times wider than long vs 9 times wider than long); regarding C. tovarae n. sp., the specimens possess main paleae thinner than those in C. mexicanum n. sp. (11 times wider than long vs 9 times wider than long). On the other hand, C. mexicanum n. sp. possesses all paleae groups present tips with an acute distal projection, while C. elegantoides and C. tovarae n. sp. present rounded tips. Finally, C. elegans has all main paleae slender and long, from the lateral-most to midline-most main paleae, whereas C. mexicanum n. sp. has lateral-most and midline-most main paleae long and slender, and the mid-most main paleae short and broad.

Distribution. From La Paz Bay, Baja California Sur to La Tijera, Oaxaca (Fig. 26).

Etymology. The specific epithet indicates where the first specimen was collected, from the Pacific coast of México. The name includes a suffix to match the genus gender (ICZN 1999, Art. 32.2), meaning Mexican.

Type locality: La Manzanilla, Nayarit, México. Type material. Holotype: ECOSUR- 270, on a separated vial, La Manzanilla, Nayarit, México, northern Mexican Pacific, 2 m, November 29, 2004, coll. BY & PSS. Paratypes: ECOSUR- 271, 3 spec., same data as holotype. ECOSUR- 272, La Cruz, Nayarit, México, northern Mexican Pacific, on rock, 0.5 m, November 26, 2004, coll. BY & PSS. Other material examined. Twenty-one specimens. Baja California Sur: ECOSUR- 3069, Marina Palmira, 24 º 10.992´N, 110 º 18.185´W, La Paz Bay, 0.5 m, 1 spec. / 250 cm 2, August 15, 2011, coll. TVG & MAC. Jalisco: ECOSUR- 3210, 2 spec. Andador, San Pedro Melaque, on rocks with algae, 3 m, December 2, 2004, coll. BY & PSS; ECOSUR- 3211, 4 spec. Barra de Navidad, on rocks, 4 m, December 3, 2004, coll. BY & PSS; ECOSUR- 3067, 6 spec. Pajarera Island, on coral, 7 m, June 26, 2013, coll. BY. Michoacán: UMAR-Poly 948, Faro de Bucerías, October 4, 1994, coll. RBZ & SGM. Guerrero: UMAR-Poly 949, Manzanillo Beach, 16 º 50´31 ” N, 99 º 54´37 ” W, on sponge, 1 m, September 21, 2007, coll. SGM et al. Oaxaca: UMAR-Poly 950, UMAR-Poly 951, 3 spec., Estacahuite Bay, 15 º 40´05 ’’ N, 96 º 28´56 ’’ W, on algae and dead coral, 0.5 m, July 3, 2007; UMAR-Poly 952, 3 spec. El Maguey Beach, July 4, 2007. Grand Caribbean region: 1 spec. of Chrysopetalum elegans Quintana Roo: ECO- SUR-PXXX, Aventura Beach, Cancún, 1 m, February 19, 2001, coll. MTH.