Sphaerephesia mamalaensis Magalhães, Bailey, Brock & Barrett, 2011, sp. nov.

Sphaerephesia mamalaensis sp. nov.

Figures 1 (A–E), 2 (A–C), 3 (A–F), 4 and Table 1

Material examined. Holotype: Mamala Bay, south shore of Oahu Island, Hawaii, Barbers Point outfall, 01/25/10, station HB3R4, 21° 16 52.5 N, 158° 0 1 29.1 W, 68.6 m (USNM 1154142). Paratypes: same locality and date as holotype, station HB7R1, 21° 16 53.6 N, 158° 0 1 30.4 W, 71.3 m (2, BMNH 2011.8-9), station HB7R2, 21° 16 53.9 N, 158° 0 1 30.5 W, 71.6 m (2, BPBM R3435), station HB1R3, 21° 16 51.3 N, 157° 59 19.6 W, 64 m (1, USNM 1154143), station HB2R5, 21° 17 0 0.6 N, 158° 0 1 21.3 W, 59.4 m, on stub (2, USNM 1154144).

Non– type material examined. Mamala Bay, south shore of Oahu Island, Hawaii, Barbers Point outfall, 5/94, station HB3R1, 21° 16 52.5 N, 158° 0 1 30.0 W, 68 m (1), 01/94, station HB3R3, 21° 16 52.4 N, 158° 0 1 29.5 W, 68.9 m (1). Sand Island outfall, 1/25/86, station IER3 (1), 01/99, station C5R3, 21° 16 53.4 N, 157° 51 24.4 W, 20.7 m (2), 01/00, station E1R3, 21° 17 10.3 N, 157° 55 33.1 W, 101.8 m (1), 01/02, station E1R1, 21° 17 10.6 N, 157° 55 33.5 W, 102.1 m (1), 08/09, station C5AR1, 21° 16 53.5 N, 157° 51 24.1 W, 20.4 m (1), 8/10, station E5R1, 21° 16 22.7 N, 157° 51 40.9 W, 101.5 m (1 ovigerous female). Waianae outfall, 1/97, station ZWR3 (2). Mamala Bay, ACE project, station 6R1B, 498 m (1), station 6R2B, 498 m (1).

Description. Holotype complete, 1.2 mm long, 0.4 mm wide for 15 chaetigers; paratypes all completes, ranging from 0.8–2.0 mm long, 0.4–0.6 mm wide for 15–19 chaetigers. Additional material examined all completes ranging from 0.6–2.1 mm long, 0.4–0.6 mm wide for 12–19 chaetigers. Body short, grub–like, wider on anterior end, slightly tapering posteriorly, rounded dorsally and flattened ventrally. Preserved specimens white to pale yellow, translucent.

Prostomium broadly truncate anteriorly, without eyes. Median antenna inflated basally, distally blunt, slightly shorter than lateral antenna; paired palps sub–equal in length to lateral antennae, slender; a pair of elongate papillae present between palps and lateral antennae, additional distinct digitiform papillae present on lateral border of peristomial region (Figs 1 A; 2A–B). Peristomial cirri digitiform, posterior to lateral antennae and preceding chaetiger 1 (Fig. 1 A). Proventricle four segments in length, extending from chaetiger 3 to chaetiger 6 (Fig. 1 A).

Dorsal macrotubercles sessile, in four longitudinal rows, with a small button–shaped terminal and sessile papilla (Figs 1 A–B; 2A; 3A–B); rounded on anterior segments, pear–shaped on posteriormost segments (Figs 1 A; 2A, C). Microtubercles absent. Dorsal rounded papillae organized in 4–5 irregular longitudinal rows bounded by two macrotubercle rows (Figs 1 A; 2A; 3A, C). Ventral papillae similar in size and shape to dorsal ones, more abundant on anterior end; papillae organized in 4 transversal rows per segment, each containing 2–10 papillae (Figs 2 A; 4). Dorsal and ventral tegument with heart–shaped texture (Fig. 3 C).

Parapodia uniramous, similar throughout; acicular lobes broadly rounded, prechaetal lobe conical, elongate, postchaetal lobe absent; ventral cirri conical, similar to prechaetal lobe, as long as the acicular lobes (Figs 1 C–D; 3E). Parapodial papillae rounded, similar to body papillae, 2–3 per parapodial region (Figs 1 C–D; 3E). Composite falcigers throughout; 8–10 composite falcigers per fascicle anteriorly, and 6–8 posteriorly; blades short, 8–10 µm in length, serrated, with falcate unidentate tips; shaft slender with fibrils peeling off (Figs 1 E; 3F).

Pygidium with two ventro–lateral papillae and mid–ventral digitiform anal cirrus (Fig. 2 C).

Remarks. Table 1 summarizes the taxonomic characteristics of the seven species of Sphaerephesia taken from the original descriptions. Sphaerephesia mamalaensis sp. nov., differs from its congeners by the absence of microtubercles (present in S. longisetis and S. fauchaldi), relative length of palps and intermediate antennae (subequals in S. mamalaensis but distinct in S. chilensis and S. fauchaldi), and number of parapodial papillae (2–3 in S. mamalaensis sp. nov., 12 in S. similisetis, 7–8 in S. longisetis, 1 in S. chilensis and S. gesae, 8 in S. fauchaldi, and 1–2? in S. regularis). Composite falcigers have serrated blades only in S. mamalaensis sp. nov., and S. regularis, but the serrations are not easily seen at a magnification of 1000x and the smooth blades described and illustrated for the other species might be serrated if viewed under the SEM.

The diagnosis of the genus is emended to include information about the presence and distribution of microtubercles and body papillae. The presence of microtubercles sensu Fauchald (1974) seems to be rare in Sphaerephesia species and only Sphaerephesia longisetis has true microtubercles between the parapodia. Microtubercles in S. fauchaldi lack the basal collar but have an upper terminal papilla, being distinct from the rounded body papillae (Kudenov, 1987).

Papillae are present on any part of the body but are usually abundant on prostomium and ventral surface of the body (Fauchald, 1974). Prostomial and peristomial papillae are conical to digitiform and some that are elongated have been interpreted as a third pair of antennae (S. chilensis, Table 1; see discussion in Aguado & Rouse, 2006). Body papillae are usually spherical on the dorsal and ventral surface and spherical or digitiform on parapodial region. The arrangement of dorsal and ventral papillae is of specific value and should be investigated in detail when describing or redescribing species of Sphaerephesia. Dorsal papillae are organized in longitudinal rows bounded by rows of macrotubercles in S. longisetis, S. fauchaldi, S. gesae and S. mamalaensis sp. nov., while ventral papillae are organized in transversal rows replicated by segment as shown herein for S. mamalaensis sp. nov., (see Fig. 4) and in S. gesae (Moreira & Parapar, 2011).

Etymology. This species is named after the type locality, Mamala Bay in the south shore of Oahu Island, Hawaii.

Distribution. Off Honolulu, south shore of Oahu, Hawaii, northwestern Pacific Ocean, 20.4 to 498 m.

Biology. Specimens found in medium to fine sand bottoms in the zone of initial dilution of the Barbers Point outfall and at reference stations of the Sand Island, Barbers Point and Waianae outfalls. This species has been commonly found in low abundance in these regions with organic enrichment since the beginning of the monitoring in 1986 and they seem to be resilient to the sewage plume. This sphaerodorid was also collected from almost 500 m depth off the south shore of Oahu during a study of harbor dredge disposal sites. These deeper localities have received dredge spoil sediments from Honolulu and Pearl Harbors over the last few decades and deposits of more than 30 cm thickness cover relict natural sediments and reefs (Hampton et al. 1997).

One female colleted on August 2010 was found with 11 large eggs in the coelom measuring about 70–90 µm in diameter (Fig. 3 D).