Idanthyrsus bastidai n. sp.

Figures 1A–F; 2A–G

LSID: urn:lsid:zoobank.org:act: 2D4701B1-FC70-4B65-8CCB-456DC980120D

Material examined. Venezuela. Holotype (ECOSUR-250), Cumaná Turpialito, on Millepora, 1.5 m, February 22, 2002, coll. I. Liñero-Arana). Thirty-eight paratypes (ECOSUR-251), Cumaná, Turpialito, same data as for the holotype.

Description. Holotype complete (ECOSUR-250), mature female. Body colorless, 11 mm long, 2 mm wide, with three parathoracic segments, 28 abdominal segments, caudal peduncle 3 mm long (Fig. 1).

Opercular crown and opercular stalk completely divided into two lobes (Fig. 1A–B). Opercular disc oblique, two rows of light amber paleae; outer row with 25 paleae per lobe, inner row with ~18 paleae per lobe. Outer paleae straight, marginal spines long, thin, progressively larger distally; 20–30 pairs of lateral spines. Paleal anterior region with compact thecae with irregular margins. Blade slightly inclined at an angle of 170° (Fig. 2A–B). Inner paleae cylindrical, slightly inclined, tapered; blade with transverse thecae (Fig. 2C); tip smooth, blunt (Fig. 2D).

Opercular peduncle colorless (Fig. 1A–C). Two amber nuchal hooks on the left lobe, one hook on the right (Fig. 1B). Nuchal hooks falcate, with long limbation, tip sharp (Fig. 2H). Tentacles and palps colorless. Median ridge as long as opercular stalk, with marginal brown eyespots. Median organ small, conical, colorless, without eyespots (Fig. 1E). Building organ with small brownish spots.

Thorax without notochaetae. Chaetiger 1 with a pair of neuropodia bearing capillary, pinnate chaetae. Chaetiger 2 with capillary neurochaetae, a pair of lateral small cirri, and branchiae.

Parathorax colorless with three segments, all with paired branchiae (Fig. 1C–D). Notopodia with six lanceolate and seven pectinate chaetae. Neurochaetae lanceolate and capillaries, thinner than notochaetae.

Abdominal segments colorless, with a pair of branchiae decreasing in size towards segment 16. Neuropodia with verticillate chaetae (Fig. 2E). Notopodia with a series of uncini with 6–7 transverse rows of teeth (Fig. 2F). Abdominal segment eight with longer neurochaetae (Fig. 1F). Caudal peduncle cylindrical, colorless (Fig. 1A).

Variation. Body 4–12 mm in total length, 0.8–2 mm wide, 18–33 abdominal segments, caudal peduncle 1–4 mm. Opercular crown made of 10–33 outer paleae per lobe, and 8–19 inner paleae per lobe. Almost all specimens with one pair of hooks (Fig. 2H), except for five bearing an extra hook on one side, including the holotype.

One paratype specimen with fragments of the tube made of coarse sand (Fig. 2G).

Etymology. This species is named after Dr. J. Rolando Bastida Zavala, for being a great mentor and teaching me about the world of polychaetes. The species name is a noun in the genitive case (ICZN 1999, Art. 31.1.2).

Distribution. Turpialito, Cumaná, Venezuela at 1.5 m depth. Associated with Millepora corals.

Remarks. Idanthyrsus bastidai n. sp. closely resembles Idanthyrsus sp. fide Chávez-López (2019) from Guerrero, Mexico. Both species have outer paleae with long, thin, straight spines; however, Idanthyrsus sp. has completely straight outer paleae and blunt nuchal hooks (Chávez-López 2019: Fig. 9C, F) with limbation shorter than that in I. bastidai n. sp. that is characterized by slightly bent outer paleae (Fig. 2A–B) and sharp nuchal hooks (Fig. 2H).

The coloration pattern also differs in both species, while Idanthyrsus sp. has the opercular peduncle and thorax strongly pigmented (Chávez-López 2019), I. bastidai n. sp. lacks apparent pigmentation (Fig. 1A–C).