HESIONIDAE (ANNELIDA, POLICHAETA) FROM JAPAN. I. by Hiro ...

36 Kuroshio Biosphere : BULL. BIOL. INST. KUROSHIO Vol. 1, 2004
[Syllidia] inermis (Ehlers, 1912) from the Antarctic Sea closely related to the new
species. Both species have no jaws in proboscises, and no extra lobes (superior and inferior
lobes characterizing the species of Nereimyra) in parapodia. According to the original
description, [S.] inermis has six pairs of tentacular cirri, which are arranged three pairs in
segment I, two pairs in segment II, and a single pair in segment III. However, the
arrangement described by Ehlers (1912) is doubtful. In the new species, six pairs of
cirrophores of tentacular cirri look like the manner (see Fig. 6, B). This is due to the
oblique shift of tentacular cirri on segment II to antero-dorsally. The shift results in the
dorsal tentacular cirrophores of segment II (D2) carrying on the dorsal tentacular cirriphres
of segment I (D1), and ventral tentacular cirrophores of segment II (V2) carrying on the
ventral tentacular cirrophores of segment III (V3). Therefore, six pairs of tentacular cirri
are arranged as if D2-D1-V1 dorsoventrally on segment I, V2-V3 on segment II, and D3
on segment III. [S.] inermis has, however, no acicular simple setae, and has 12 papillae of
a same size on its proboscis.
[Nereimyra] longicirrata Knox & Cameron, 1971 has the parapodia without any
lobes characterizing the species of Nereimyra. The form of proboscis is unknown.
Therefore, the generic status of the species is uncertain. [N.] longicirrata has simple
conical neuropodial cones resembling to the new species. The Australian species, however,
is devoid of acicular simple setae.
Neuropodial acicular simple setae are rare in Hesionidae. Only two hitherto-known
species have those setae: Orseis brevis Hartmann-Schröder, 1959, and Hesiospina similis
(Hessle, 1925). But the former has only two pairs of tentacular cirri, and the latter has
eight pairs of tentacular cirri, instead of six pairs. Many species of Microphthalmus have
simple neurosetae. The new species, however, has distinct cirrophores of tentacular cirri and
dorsal cirri.
The alternate arrangement of large and small proboscial papillae is very curious.
Syllidia armata Quatrefages, 1865 is the only a single known species with the type of
proboscis. S. armata, however, has horny jaws in proboscis.
Syn. Podarke Ehlers, 1864, p. 199.
Irma Grube, 1878, p. 107.
? Parasyllidia Pettibone, 1961, p. 173.
Genus Ophiodromus Sars, 1861
Body rather stout, with rather few segments. With a pair of bi-articulated long palpi,
and three antennae. Proboscis without a pair of chitinous ventral ridges, chitinous jaws, or
marginal papillae, but with fine ciliation. Without facial tubercle. With six pairs of
tentacular cirri. Cirrophores of dorsal tentacular cirri of segment II tend to shift toward
dorsal side of dorsal tentacular cirrophores of segment I. Parapodia biramous or
sub-biramous, with noto-acilula, and with or without notosetae. Neuropodium with one or
two acicula, a more or less indistinct postsetal lobe, and a long presetal lobe. Notosetae, if
present, simple capillary or forked. Forked seta with two arms in different length.
Neurosetae all compound falcigers.