Figures 18 A–B, 19 A–D, 20 A–B
Mediomastus californiensis Hartman, 1944: 264 –265, pl. 26, figs. 64–65.
Mediomastus californiensis.— Hartman 1947: 408, pl. 46, figs. 3–4. Hartman 1969: 387–388, figs. 1–4. Ewing 1984: 14 – 14 to 14–16, figs. 14 –9, 14– 10 a–c. Warren et al. 1994: 239 –241, figs. 2 b, 7 c–d, 9 a–d, 12, tables 1–2. Blake 2000: 78 –79, fig. 4.12.
Material examined. Oahu Island: Paiko Lagoon, Maunalua Bay, 21 ° 17 ʹ 2.9 ʺ N, 157 ° 43 ʹ 21.9 ʺ W, Jan. 1980, coll. J.H. Bailey-Brock (4); Honolulu Harbor, Naval Undersea Center, coll. R. Brock (7); Honolulu Harbor, 13 Nov.
1997, coll. R.C. DeFelice, 10–12 m, Pier 20 (1, BPBM R 2629; 1, BPBM R 2630), Pier 27 (2, BPBM R 2637), Pier 29 (6, BPBM R 2639), Pier 41, dry dock (2, BPBM R 2648), Sea-Land Pier (10, BPBM R 2663), Snug Harbor (5, BPBM R 2665). Pearl Harbor, abandoned pier, Ford Island, 18 Mar. 1993, coll. R. Brock (15, BPBM R 3605); Sta. 9.1.0, Sept. 1997 (3, BPBM R 3606); Pearl Harbor, Environmental Monitoring and Assessment Program (EMAP), State of Hawaii estuaries and bays, Oct. 2002: Sta. 67, 21° 22 ʹ 22.8 ʺ N, 157 ° 56 ʹ 9.6 ʺ W (17, BPBM R 3607); Sta. 11, Pearl Harbor, 21 ° 22 ʹ 19.2 ʺ N, 157 ° 59 ʹ 9.6 ʺ W (4, BPBM R 3608). North Kaneohe Bay, Dec. 1993 (4). Mamala Bay, Jan. 2001, Sta. 25 (3).
Description. Complete specimens 22–34 mm long, 0.3–0.5 mm wide for 89–134 chaetigers. Body elongate, slender, widest on mid-thoracic chaetigers, tapering from abdomen to pygidium. Color in alcohol pale yellow.
Prostomium short with rounded palpode (Figs 18 A, 19 A). Nuchal organs and eyespots not observed. Proboscis everted with numerous short papillae (Fig. 18 A). Peristomium achaetous, slightly longer than anterior thoracic chaetigers (Figs 18 A, 19 A).
Thorax with 10 chaetigers; chaetigers 1–4 slightly expanded, each with shallow inter-segmental groove and bilimbate capillaries (Fig. 18 A). Thoracic chaetigers 5–10 biannulate, with deep inter-segmental grooves and hooded hooks (Fig. 19 C). Notopodia inserted laterally and neuropodia ventro-laterally (Fig. 18 A). Lateral organs present throughout the thorax, between noto- and neuropodia, closer to notopodia. Genital pores not observed but reported by Hartman (1947) to occur from chaetigers 7–10 and by Blake (2000) to occur from chaetiger 5–10.
Transition between thorax and abdomen marked by constriction and changes in shape of segments (Fig. 18 A); abdominal segments multiannulate with hooded hooks throughout. Abdominal noto- and neuropodia well separated. Posterior abdominal segments with posterior parapodial ridges (Figs 18 B, 19 B). Notopodia anteriorly with 6–8 hooded hooks per fascicle, reducing to 2–3 hooks in far posterior; anterior neuropodia with 9–10 hooks, reducing to 3–4 hooks in far posterior chaetigers. Abdominal hooks similar to thoracics; hoods shorter than on thoracic hooks and not extending beyond main fang (Fig. 19 D). Hooks with multiple teeth, with at least 3 rows of teeth in frontal view, 3–4 in basal row, 4–5 in middle row and 3–4 in superior row (Fig 19 D).
Branchiae absent. Pygidium with mid-ventral caudal cirrus as long as 6–7 posterior end segments in the growing zone (Figs 18 B, 19 B, 20 B); anal aperture placed terminally.
Methyl green staining pattern. Prostomium not stained (Fig. 20 A). Peristomium to chaetiger 8 stained with a solid green (Fig. 20 A); peristomium and chaetigers 1–3 with light bands of speckles on posterior half of segment. Chaetiger 9 with a distinct band of speckles on posterior end of segment; chaetigers 10 and 11 with banding similar to chaetiger 9 but segment densely speckled (Fig. 20 A). Subsequent abdominal segments with posterior segmental bands of green speckles, faded on mid-body, but becoming dark again on posterior-end segments (Fig. 20 B).
Distribution. Widespread in North America, from SE Alaska to southern California (Blake 2000). This is the first recorded occurrence of this species in the northwestern Pacific. This species may have been introduced to Oahu, as it is found mainly at Honolulu and Pearl harbors and not frequently encountered at lower intertidal muddy habitats.
Remarks. Several females with coeloms filled with eggs (45 + μm); anterior 25–30 abdominal segments densely filled with eggs, these segments somewhat enlarged with eggs visible through body wall. The Hawaiian specimens agree well with descriptions of M. californiensis by Hartman (1944, 1947), Warren et al. (1994) and Blake (2000). The MGSP is slightly distinct from those patterns reported in Warren et al. (1994) and Blake (2000). Bands are evident on chaetigers 9–11 in Hawaiian material and absent in chaetiger 10 (Warren et al. 1994). A distinct pattern among specimens is reported in Blake (2000) with chaetigers 5–9 or 9–10 sometimes staining. Mediomastus capensis Day, 1961 also has a distinct band on chaetiger 9, but the staining is restricted to this chaetiger.