Phragmatopoma balbinae n. sp.

Figures 8 A–I, 12D–F

LSID: urn:lsid:zoobank.org:act: 3D6F8225-7966-4CD3-B5E6-DDCF7B79B7C2

Type material. Holotype: ECOSUR0229, La Condesa, Acapulco, 16°51’23”N, 99°52’08”W, Guerrero, Mexico, southern Mexican Pacific; November 27, 1999, S.I. Salazar-Vallejo coll.); Paratypes: ECOSUR0230, five spec. from La Condesa, Acapulco, same as holotype.

Additional material: One specimen. Guerrero: ECOSUR-P3097, (Acapulco, 16°51’27”N, 99°52’17.1”W, on bivalve mollusk Striostrea prismatica (Gray, 1825), 5–15 m, May 25, 2000, coll. A. Medina-López).

Description. Color pattern of preserved specimens. Body light brown (Fig. 8A). Outer paleae with amber blade and dark amber handle; median plume translucent (Fig. 8D). Middle paleae cherry with handle amber (Fig. 8E). Inner paleae amber (Fig. 8F). Opercular papillae dark brown (Fig. 8C). Median ridge with brown eyespots (Fig. 8C). Tentacles light brown (Fig. 8 B–C). Building organ and thorax light brown with brown spot in all surfaces (Fig. 8 B–C). Parathoracic chaetae translucent (Fig. 8 G–H). Third parathoracic segment with abundant brown spots, in ventral region. Abdominal neuropodia with a series of brown spots, abundant in distal segments. Abdominal neurochaetae and uncini translucent (Fig. 8I). Caudal peduncle light brown with brown lateral spots (Fig. 8A).

Body. Complete specimen of 9 mm total length; parathoracic region 0.7 mm wide; 25 abdominal segments; caudal peduncle 1 mm long (Fig. 8A).

Operculum. Opercular crown and opercular stalk completely fused. Opercular crown conical and oval, protruding in lateral view (Fig. 8 A–C). Three rows of paleae, only two visible: 58 outer paleae, 23 middle and inner paleae. Outer paleae geniculate with a pair of heterodont teeth, one straight and the other slightly curved; flat blade 1/3 longer than wide, serrated margin, without transversal thecae visible; median plume short, almost 2/3 as long as blade, rounded, twice longer than wide, filamentous with thin filaments, 1/3 as long as plume (Fig. 8D). Middle paleae strongly geniculate with elevated peak, rough surface without visible transversal thecae; sub-quadrangular nape, decurrent, serrated surface, wider than peak, almost 2/7 as long as peak; chin slightly longer than wide, margin serrated; sharp tip markedly falcate, with smooth margin (Fig. 8E). Inner paleae strongly geniculate, serrated, elevated peak, five times longer than wide, and transversal thecae present; nape smooth; tip with filaments (Fig. 8F). Papillae small and oval. Oral tentacle unbranched. Median ridge long, 2/3 as long as opercular stalk, with marginal eyespots (Fig. 8C). Median organ absent. Building organ with ‘U’ shape.

Thorax. Chaetiger 1 with a pair of neuropodial capillary chaetae (Fig. 8A). Chaetiger 2 with a pair of lateral cirrus, neuropodia with capillary chaetae and a pair of branchiae.

Parathorax. Three parathoracic segments. Chaetigers with a pair of branchiae. Notopodia with lanceolate chaetae interspersed with capillary of similar length (Fig. 8H). Neuropodia with lanceolate chaetae; neurochaetae thinner than notochaetae.

Abdomen. Segments with a pair of branchiae decreasing in size towards posterior segments; absent in the last nine chaetigers. Neurochaetae verticillate of different length. Notopodia with a series of uncini with six pairs of teeth (Fig. 8I).

Caudal region. Caudal peduncle elastic and smooth (Fig. 8A).

Tube. Tubes with fine sand. Bryozoans and serpulids incrusted; syllids associated (Fig. 12 D–F).

Variation. The number of paleae varied from 45–60 in outer paleae, and 18–22 in middle paleae (n= 3 spec.).

Habitat. Phragmatopoma balbinae n. sp. has been found on the oyster S. prismatica, in the sublittoral zone (5–15 m).

Distribution. Only known from La Condesa, Acapulco, Guerrero, Mexico (Fig. 13).

Etymology. This new species is named after the author’s mother, Balbina López Gutiérrez.

Remarks. Of all described species of Phragmatopoma, P. balbinae n. sp. is similar to P. peruensis only in body size, according to Hartman (1944); to P. attenuata by its conic opercular crown; and to P. digitata by morphology of outer paleae. However, P. attenuata has outer paleae with filamentous median plume, with thin and long filaments, almost longer than the blade (Fig. 2C), in contrast with P. balbinae n. sp. that has outer paleae with filamentous median plume, with thin and short filaments, 1/3 as long as blade (Fig. 8D). Also, the middle paleae with straight nape and peak, and curved tip in P. attenuata (Fig. 2J) is different from decurrent nape, elevated peak and very falcate tip of P. balbinae n. sp. (Fig. 8E).

Phragmatopoma balbinae n. sp. and P. digitata are similar in its outer paleae, but the blade in P. balbinae n. sp. is 1/3 longer than wide, with a median plume long (2/3 as long as blade) (Fig. 8D), while in P. digitata the blade is twice longer than wide and the length of its median plume is barely ½ of the total length of the blade (Fig. 5 E–F). Additionally, P. balbinae n. sp. specimens are small, only 9 mm long and the mean size of P. digitata is 10.8 mm.