Laubieriopsis petersenae Magalhães, Bailey-Brock & Rizzo, 2014, n. sp.

Laubieriopsis petersenae n. sp.

Figures 1 and 2

Type material. Pacific Ocean—Mamala Bay, south shore of Oahu, Hawaii, USA: Holotype: station 6.1.B, 21°13'19.68"N, 157°57'5.7"W, Jun/1995, sandy mud, 498 m (USNM 1251829). Paratypes: station 6.1.B, 21°13'19.68"N, 157°57'5.7"W, Jun/1995, sandy mud, 498 m (1, USNM 1251830); station 1.3.A, 21°15'8.61"N, 157°56'51.07"W, Jun/1995, muddy sand with coral rubbles, 428 m (2, USNM 1251831); station 11.1.B, 21°13'0.66"N, 157°56'59.82"W, Jun/1995, sandy mud, 507 m (1, BPBM R3645); station 12.2.B, 21°13'50.22"N, 157°57'0.18"W, Jun/1995, muddy sand, 481 m (3, BPBM R3646); station 14.2.B, 21°14'55.14"N, 157°58'14.34"W, Jun/1995, carbonate sand, 426 m (1, BPBM R3647); station 15.2.B, 21°14'53.88"N, 157°58'35.05"W, Jun/1995, carbonate fine sand, 417 m (1, BPBM R3648); station 16.1.B, 21°14'54.12"N, 157°59'31.98"W, Jun/1995, sandy mud, 397 m (4, USNM 1251832 on SEM stub).

Description. Holotype (USNM 1251829) 2.6 mm long, 0.2 mm wide, 15 chaetigers. Paratypes 1.0– 3.1 mm long, 0.2 mm wide, 15 chaetigers (one specimen with 12 chaetigers and another with 14 chaetigers are regarded as juveniles). Additional material 2–2.2 mm long, 0.2 mm wide for 15 chaetigers (Figs 1 A; 2A). Body slender, cylindrical, not widening posteriorly (Figs 1 A; 2A, C). Segmentation indistinct; first four chaetigers shorter than the following ones (Figs. 1 A; 2A). Epithelium smooth, iridescent, with micropapillae present throughout and more abundant on last two chaetigers.

Prostomium partially everted in holotype (retracted in most specimens), small, rounded (Figs. 1 B; 2B) with a pair of lateral nuchal organs (dark spots in light microscope; large ciliated fields in SEM). Peristomium a complete ring, slightly shorter than first chaetiger (Figs. 1 B; 2B).

Parapodia biramous throughout, best developed in chaetigers 1–4. Interramal papillae short-stalked, closer to notopodia. Two epidermal glands per segment throughout but easily seen from chaetiger 5, dorsal to notopodia, short-stalked, smooth, rounded (Fig. 1 A).

Chaetigers 1–4 bear two thick and two thin chaetae in each noto- and neuropodia; chaetae of similar length but thinner ones slightly longer and bidentate in all specimens (Fig. 2 D, E). All chaetae with median rows of spines, being smooth basally and distally (Fig. 2 E). Chaetigers 5–15 have one unidentate acicular and one outer capillary chaeta per ramus (cA/Ac sensu Petersen 2000).

In chaetiger 15, very long unidentate acicular, extending 3/4 or 2/3 beyond pygidium while companion capillaries sometimes absent, probably broken (Fig. 2 C). Some mature specimens with chaetiger 14 bearing slightly elongate chaetae as well on chaetiger 15. Paratype with 14 body segments (BPBM R3646) bearing long aciculae on last three chaetigers (non-type juvenile with 12 segments bearing long aciculae on last 4 chaetigers).

Unpaired genital papilla small, easily overlooked and only seen on five specimens at the right side of chaetiger 6/7 (Fig. 1 A), including holotype.

Pygidium usually retracted and with terminal anus; none to four papillae may be seen on pygidium depending on level of contraction of specimen (Figs 1 A; 2C).

Remarks. This species is unique in the genus by the presence of only 15 chaetigers, unpaired genital papilla and bidentate acicula on thoracic region (first four chaetigers). All mature specimens, including four females with large oocytes, had 15 body segments. Two juveniles with 12 and 14 chaetigers were also found.

The new species is most similar to the L. brevis complex from the Atlantic and L. hartmanae and L. brevis japonica from the Pacific Ocean, but differs on the combination of the characters cited above. Petersen (2000) reported variation among the material identified as L. brevis from the Atlantic Ocean in terms of body length, types of chaetae on thoracic region and presence/absence and position of genital papillae. The Hawaiian material, besides having the lowest number of body segments, unpaired genital papilla and thoracic bidentate chaetae, also differs in body length. The longest specimen in Hawaii was 3.1 mm long while the Atlantic specimens reported in Petersen (2000) had up to 8 mm long.

The Pacific species L. hartmanae seems to be the closest related species to L. petersenae n. sp. but differs in having 16 body segments and paired genital papillae. Petersen (2000) points out the presence of ‘very weak distal irregularities’ on thoracic chaetae but does not consider them as bidentation. Levenstein (1970) described L. hartmanae from abyssal depths (4,065–6,835 m) at Japan Trench and Kurile-Kamchatka Trench off Peru coast. It is most noticeably distinct from L. brevis by the shorter acicular spines on last chaetiger, not surpassing the pygidial limit (Zhadan & Salazar-Vallejo, pers. comm.).

Reproduction. Several mature individuals were found with granular structures between chaetigers 6 and 7 or 6 and 8. Females with oocytes organized in two rows at each side from chaetigers 6 to chaetiger 8 or to posterior end. Number of oocytes varied from two to up to 10, 80–95 µm in diameter.

Etymology. This species is named after the late Dr. Mary Petersen for her great contribution to the study of fauveliopsid polychaetes, including the recognition and description of the genus Laubieriopsis.

Distribution. Only known from dredge disposal sites off Honolulu, near Pearl Harbor (Hawaii, USA).