Acoetes melanonota (Grube 1876)

Acoetes melanonota (Grube, 1876)

Panthalis melanonotus Grube, 1876:71; 1878:48, pl. 4: fig. 1a,b.—Willey 1905:254, pl. 1: figs. 21–27.—Hoagland, 1920:606. [Not sensu Mohammad, 1973:24; (= Acoetes mohammadi, new species).]

Panthalis melanotus [sic].—Ehlers, 1918:235.

Polyodontes melanonotus.—Fauvel, 1919:339, pl. 15: figs. 1–3, pl. 17: figs. 70–75; 1932:37, fig. 6a–c; 1953:72, fig. 33c-g.—Monro, 1934:359.—Day. 1951:19; 1962:634; 1967:96, fig. 1.17.g–h.—Uschakov and Wu, 1959:16, 37, pl. 10A,B; 1965:175, fig. 12A–C; 1979:35, fig. 12A–C—Gibbs, 1971:127.—Strelzov, 1972:287, figs. 5, 6 [part]. [Not sensu Monro, 1931:8 (= Polyodontes atromarginatus Horst); 1937:264 (= Polyodontes sp.).]

Polyodontes gracilis Pflugfelder, 1932a:288, fig. 8A–C; 1934:351, figs. 7–9.—Gallardo, 1967 [1968]:49, pl. 3: figs. 6–7, pl. 4: figs. 1–4.

Panthalis panamensis.—Treadwell, 1936:265. [Not Panthalis panamensis Chamberlin, 1919.]

Polyodontes melanotonus [sic].—Thomassin, 1970:52.

MATERIAL EXAMINED.—PHILIPPINES. Tartara Island, off Western Samar, 37 m, Albatross sta D5209, 14 Apr 1908, 1 specimen (USNM 18973, identified by Hoagland, 1920).

CHINA. Amoy, T.Y. Chen, collector, 1 specimen (BMNH 1932.3.2.9, identified by Monro, 1934) and 1 specimen (USNM 21983, as Panthalis panamensis by Treadwell, 1936).

SOUTH VIETNAM. Sta 317, 323, 4 Jan, 4 Apr 1960, 14 m, mud and sandy mud, 2 specimens (AHF, as Polyodontes gracilis by Gallardo, 1967 [1968]).

THAILAND. Ang Hin, Cholburi Province, 13°20′N, 100°55′E, 5–10 m, G.M. Moore, 11 Mar 1959, 6 specimens, in muddy mucous tubes (USNM 71500). Entrance to Trat Bay, Gulf of Thailand, 11°58′N, 102°44′E, 5 m, George Vanderbilt Foundation sta 26, 29 Oct 1957, R.R. Rofen, 1 specimen, in muddy mucous tube (USNM 71499).

INDONESIA. Aru Islands, Pulu-Bambu, 12 m, mud, Dr. Merton, 11 Apr 1908, 2 specimens (ZMH P-E 193, identified by Ehlers, 1918).

SOLOMON ISLANDS. Marovo Lagoon, New Georgia, 11 m, mud, sta ML 194, 2 Nov 1965, P. Gibbs, 1 specimen (BMNH 1970.163, identified by Gibbs, 1971).

MADAGASCAR. Tulear, sta 6 and 28, B. Thomassin, 2 specimens (MNHNP, as Polyodontes melanotonus [sic] by Thomassin, 1970).

TYPES.—Type material of Panthalis melanonotus Grube from the Philippine Islands and Polyodontes gracilis Pflugfelder from the East Coast of Sumatra not located.

DESCRIPTION.—Largest complete figured specimen from Thailand (USNM 71500) with 108 segments, 75 mm long, 6 mm wide with setae. First pair of elytra cordiform, larger than following few pairs, covering prostomium; following elytra oval, leaving small area of middorsum uncovered. Elytra rather thick, gelatinous, anterior few pairs with irregular flecks of black pigment, with lateral pouch on more posterior elytra (Figure 52B–D).

Prostomium bilobed, rounded, with globular ommatophores with slender neck; median antenna with ceratophore in middle of prostomium, extending posteriorly as indistinct triangular ridge, with style extending to tips of ommatophores; lateral antennae attached ventrally on ommatophores, with only tips visible dorsally; pair of small posterior eyespots lateral to ceratophore of median antenna; ventral palps stout, long, tapered, with longitudinal rows of short papillae on distal half, with irregular flecks of black pigment or pigment in bands. Tentacular segment distinct dorsally; tentaculophores lateral to prostomium, each with 2 acicula, 2 bundles of capillary setae, and pair of tentacular cirri, longer and stouter than median antenna (Figure 52A,E; Strelzov, 1972, fig. 5A).

Second segment with first pair of elytrophores and long ventral buccal cirri, similar to tentacular cirri; biramous parapodia larger than following few parapodia; conical notopodium with bundle of long capillary notosetae; large triangular neuropodium with numerous slender neurosetae, wider basally, finely spinous, tapering to capillary tips (Figure 52F–H; Strelzov, 1972, figs. 5B, 6C). Distal border of muscular pharynx with 13–15 pairs of papillae, middorsal one much pharynx with 13–15 pairs of papillae, middorsal one much larger and longer than others; 2 pairs of hooked jaws each with 4–7 lateral teeth.

Third segment with first pair of dorsal cirri, with short cirrophores and subulate styles extending beyond neurosetae; notopodium with bundle of long notosetae; neuropodium with rounded presetal acicular lobe, truncate postsetal lobe and distinct anteroventral bract enclosing numerous lower neurosetae, curved, with larger spines basally and close-set spinous rows distally; middle row of neurosetae short, stout, acicular, aristate; upper neurosetae long, slender, lanceolate, finely spinous; ventral cirri tapered, almost as long as dorsal cirri (Figure 52I–L). Parapodia of segments 4 to 8 similar (Figures 52M, 53A,B).

Beginning with segment 9, notopodium wide, flattened, truncate, on anterodorsal half of larger neuropodium, with notoaciculum, spinning glands and row of short notosetae; neuropodium, lower and middle groups of neurosetae similar to more anterior parapodia; upper group of neurosetae of 2 types: (a) longer, tapering abruptly to long slender spinous tip, with subdistal long spines and short spinous rows basally; and (b) shorter, more slender, with widely spaced spines, nearly hidden by notopodium (Figure 53C–F; Strelzov, 1972, figs. 5D, 6A,G,J). Parapodia of more posterior segments with aristate neurosetae with subdistal rows of spines on one side; dorsal cirri with wider cirrophores and triangular styles; single wide digitiform branchia near cirrophores and elytrophores on some parapodia (Figure 53G–L; Willey, 1905, pl. 1: figs. 22–27; Pflugfelder, 1932a, fig. 8a–c). Additional thin-walled, low, branchial areas medial to ventral cirri. Pygidium with terminal anus and pair of anal cirri.

TUBES.—Rather soft, flabby, muddy mucous tubes, not compact

DISTRIBUTION.—Philippine Islands, Solomon Islands, Yellow Sea, South China Sea, Gulf of Thailand, Indonesia, Indian Ocean, Madagascar. Low water to 421 meters.