Malacoceros indicus Fauvel 1928

Malacoceros indicus (Fauvel, 1928)

(Figs. 6–7)

Scolelepis indica Fauvel, 1928: 93, fig. 2g –m. Fauvel, 1930: 35, fig. 7g –m. Fauvel, 1953: 313 –314, fig. 165g –m. Monro, 1931: 25. Berkeley and Berkeley, 1941: 21. Reish, 1961: 277.

Malacoceros indicus: Pettibone, 1963: 99. Day, 1967: 477, fig. 18.5.p–u. Blake and Kudenov, 1978: 185. Blake, 1983: 219, Blake, 1996: 105 –107 [synonymy], fig. 4.4; Ben-Eliahu et al., 1984: 96. Dauer and Ewing, 1991: 395 –400, fig. 1. Imajima, 1991: 6 –9, figs. 2a–g, 3a–j.

Malacoceros (Malacoceros) indicus: Foster, 1971a: 50 –53, figs. 93–99. Foster, 1971b: 1455 –1457, figs, 1–6.

Spio punctata: Hartman, 1961: 89 –90, pl. 11, figs.1–3. Hartman, 1969: 175, figs. 1–3. Fide Blake, 1996.

Material examined. Philippines, Diniwid Beach, Boracay, 11°60´N, 121°54´E, sandy beach, 13 Apr 1999 (one posterior end in alcohol, USNM 1096797; one anterior end on SEM stub, USNM 1096798); Boracay, White Beach, 11°59´’N, 121°55´E, sandy beach, 14 Apr 1999 (three complete specimens in alcohol, USNM 1096799; one complete specimen on SEM stub, USNM 1096800; four anterior ends in alcohol, ZRC 2006.0221; one anterior end on SEM stub, USNM 1096801).

Description. Largest complete specimen with 184 setigers, 30.7-mm long and 1.0 mm-wide at setiger 16 (maximal width); an incomplete specimen of 140 setigers reached a length of 44.0-mm and 1.9-mm wide at setiger 16. Body broad, dorsally flattened anteriorly tapering in middle setigers, subcylindrical in cross section. Palp present on one individual, extending posteriorly for approximately 16 setigers; median groove on ventral side of palp lined by frontal cilia. Color in alcohol opaque off white, no pigmentation present.

Prostomium T-shaped with short frontal horns, rounded on distal margin (Figs. 6 A, B, 7A, B); posteriorly short caruncle, extending to middle of setiger one (Figs. 6 A, 7B); occipital tentacle absent; with 2–4 pairs of round eyes in two irregular clusters (Fig. 6 A). Proboscis partially everted with two bulbous lobes below lateral

Branchiae from setiger 1 continuing to posteriormost setigers, branchiae elongate, slender, tapering to a blunt tip, fused basally with notopodial postsetal lamellae, branchiae slightly longer than notopodial lamellae of setiger 1 (Fig. 6 C), increasing in length posteriorly (Figs. 6 D–F, 7A, B, F), by setiger 10 twice as long as notopodial lamellae and slightly overlapping at midline, heavily ciliated on inner and outer margin, joined to corresponding branchiae on opposite side by band of cilia across dorsum, second band of cilia present on each setiger posterior to band joining branchiae (Fig. 7 B).

Notopodial postsetal lamellae elongate, triangular, tapering to blunt tip on anterior setigers, gradually becoming shorter in posterior setigers; notopodial presetal lamellae low, lobe surrounding base of notosetae (Fig. 7 A, C, E–G). Neuropodial postsetal lamellae of anteriormost setigers small conical, base of lamellae broadening posteriorly, small, nipple-like projection at tip of lamellae (Fig. 7 A, C, E). Lateral organs between notopodial and neuropodial postsetal lamellae present from setiger 1 to posteriormost setigers (Fig. 7 C).

Notosetae thin, capillaries in two rows, anterior row slightly shorter than posterior row, anterior setigers with approximately 16–24 setae in each row, gradually decreasing in number in posterior setigers. Neurosetae on anterior setigers in two rows, similar in morphology to notosetae but shorter in length, plus ventral fascicle of 3–4 sabre setae (Fig. 7 C–D); 1–2 neuropodial hooded hooks from setigers 28–62, with up to seven hooks in more posterior setigers, accompanied by dorsal fascicle of 3–4 fine capillary setae and ventral fascicle of sabre setae (Fig. 7 E); hooded hooks with three small teeth above main fang (Fig. 6 G). Notosetae and neurosetae (including sabre setae) with minute spinelets (see Fig. 7 D).

Pygidium with two dorsal cirri and two slightly longer ventral cirri, cirri conical, tapering to blunt rounded tip; anus terminal (Figs. 6 H, 7G).

Remarks. The genus Malacoceros is composed of 8 recognized species, including one recently described from hydrothermal vent chimney walls (Hourdez et al. 2006). Malacoceros indicus is a widely distributed species and the Philippine specimens closely match previous descriptions. However, the neuropodial hooded hooks of the Philippine specimens exhibited three secondary teeth while those examined by Blake (1996) from California had two secondary teeth and those examined by Imajima (1991) from Japan had four secondary teeth. As indicated by Foster (1971a, b) and Blake (1996), the morphology of the hooded hooks is variable within this species. The Philippine specimens do not exhibit large rounded lobes in an interparapodial position as found in specimens from California; however, these structures may represent interparapodial pouches that differ in size depending on maturity of the specimens (Blake 1996). This is the first time lateral organs have been found between notopodial and neuropodial postsetal lamellae of M. indicus, but this is not surprising since no previous taxonomic investigations utilized SEM for examination of this species. Recently, Purschke & Hausen (2007) investigated the ultrastructure of lateral organs in members of seven families of polychaetes including the Spionidae and Malacoceros fuliginosus (Claparède, 1886). Dauer & Ewing (1991) studied the palp ciliation patterns of M. indicus with SEM from specimens collected in Australia and found that they exhibited a single group of functional frontal cilia and based on behavioral observations they showed the worms were indiscriminate surface deposit-feeders. Malacoceros indicus apparently shed their palps readily when disturbed (i.e., they are deciduous) since all Philippine specimens except one were lacking these structures. Based on light microscopic examination, this specimen exhibited a single group of frontal cilia as found for specimens from Australia; in addition, one worm was also found to possess sand grains in the gut [mean size = 299.6 ± 75.4 µm (n=12)] within the size range of those found in Australian specimens (Dauer & Ewing 1991).

Distribution. Sandy beaches in Boracay of the Aklan province in the Philippines; shallow subtidal (<5 m); Caribbean; Chile; India; New Caledonia; southwest Africa; Australia (Queensland); Japan; USA (southern California, Massachusetts to Georgia).