Myrianida gidholmi, Nygren, Arne & Pleijel, Fredrik, 2007

Nygren, Arne & Pleijel, Fredrik, 2007, A new species of Myrianida (Syllidae, Polychaeta) from Belize, Zootaxa 1595, pp. 17-29 : 22-24

Myrianida gidholmi sp. n.

( Figs 1–2 )

Material examined. Holotype. Belize, North side of Carrie Bow Cay (Ellen Cay), 16°48.805’N, 88°04.902’W, 2 m, Halimeda sand, dive, coll. F. Pleijel, 11 Nov 2006 (preserved in formalin, GNM Polychaeta 13.102).

Paratypes. Belize, Twin Cays, 16°49.991’N, 88°06.240’W, 1 m, Halimeda , dive, coll. G. Rouse, 3 Nov 2006 (preserved in alcohol, GNM Polychaeta 13.103); Belize, North side of Carrie Bow Cay (Ellen Cay), 16°48.162’N, 88°04.913’W, 1 m, under jetty, dive, coll. F. Pleijel, 11 Nov 2006 (preserved in alcohol, GNM Polychaeta 13.104).

Diagnosis. Myrianida with characteristic colour markings as red transverse and longitudinal bands.

Description. Length 1.5–1.8 mm for 26–30 stock chaetigers, length including stolons 2.2–3.8 mm; width at level of proventricle, excluding parapodial lobes, 0.20 mm. Live specimens with two red longitudinal bands in atokous part, region posterior to proventricle reddish in between these bands ( Fig. 1 ); stolons with a single, wider, red longitudinal band; red transverse dorsal bands across each segment; all appendages, especially median antenna, dorsal cirri on first chaetiger, and anal cirri, reddish; cirrophores and basal part of cirri in atokous part orange, intestinal region with conspicuous white specks from intestinal granular accumulations, parapodial glands restricted to parapodial lobes; eyes red. Preserved specimens with faint reddish brown transverse bands.

Body shape, excluding parapodial lobes, cylindrical in transection, venter flattened. Body of fairly constant width. Ciliation as one troch per segment.

Prostomium rounded rectangular. Four eyes, with lenses, in trapezoid arrangement, anterior pair larger. Eyes separated; eye spots present. Palps in dorsal view projecting c. 1/3 of prostomial length, fused. Extension of nuchal epaulettes to between end of chaetiger 3 and beginning of chaetiger 4 ( Fig. 1 ).

Prostomium with three antennae; median antenna inserted medially on prostomium, lateral antennae on anterior margin. Tentacular cirri two pairs. Median antenna reaching chaetiger 9–11. Lateral antennae and dorsal tentacular cirri, length 1/2–2/3 of median antenna. Ventral tentacular cirri 1/3–1/2 as long as dorsal pair. First dorsal cirri as long as median antenna, second dorsal cirri as long as dorsal tentacular cirri. Cirri from chaetiger 1–27 with following alternation in direction, with D=cirri pointing down and U=cirri pointing up: U DDU DU DDU followed by eight DU-groups, chaetiger 28-30 with single DDU-group. Dorsal cirri from chaetiger 3 of equal length ( Fig. 1 ), c. 1/2 of body width excluding parapodial lobes. Cirrophores present on tentacular cirri and all dorsal cirri. Cirrophores shorter than parapodial lobes, cirrophores shorter than cirrostyles. Cirrophores and cirrostyles not alternating in length along the body. All appendages cylindrical.

Parapodial lobes rounded. Single acicula in all chaetigers. Chaetal fascicle with 8–12 compounds in anterior chaetigers, 4–8 in median and posterior chaetigers. Compound chaetae with small distal tooth; serration present ( Fig 2 B). Single thin bayonet chaetae, subdistally denticulated ( Fig. 2 C), beginning between chaetiger 10–15.

Pharynx with several sinuations anterior to proventricle. Trepan in chaetiger 1–2, with 9–10 equal teeth, in single ring ( Fig. 2 A). Thin basal ring present; infradental spines present (n=2). Proventricle equal in length to two segments in chaetiger 5–7 with 20–23 rows of muscle cells (n=3). Anal cirri equal in length to 1.5 times body width excluding parapodial lobes.

Reproduction. Schizogamous reproduction by gemmiparity behind chaetiger 26 or 30. Morphology of epitokous stages. No fully developed stolons examined. Distribution and habitat. Only known from the type locality, Belize, in Halimeda sand or among fouling

organisms, 0–2 meters depth.

Etymology. The species is named in honour of Lennart Gidholm.

Figures

FIGURE 1. Myrianida gidholmi sp. n. with a row of developing stolons. The specimen in the figure is 3.8 mm long.

FIGURE 2. Myrianida gidholmi sp. n. – A. Trepan. – B. Compound chaeta, median chaetiger. – C. Bayonet chaeta,