Synsyllidia alternata Uchida, 2019

Hiro, Uchida, omi, Lopéz, Eduardo & Sato, Masanori, 2019, New Hesionidae (Annelida) from Japan: Unavailable Names Introduced by Uchida (2004) Revisited, with Reestablishment of their Availability, Species Diversity 24, pp. 69-95 : 70-71

Synsyllidia alternata Uchida , sp. nov.

[New Japanese name: Hoashi-otohime] ( Fig. 1 )

Synsyllidia alternata Uchida, 2004: 33–36 , fig. 3 (unavailable specific name, without explicit fixation of name-bearing types).

Type material. Holotype: (NSMT-Pol H-691), Kii Peninsula, Arita, Kushimoto , Wakayama Prefecture (33°28′41″N, 135°44′2″E), lobster gillnet, 7 February 1979.

Diagnosis. Holotype 1.5 mm long for 10 chaetigers, body colorless. Prostomium lacking median antenna; a pair of lateral antennae; a pair of bi-articulated palps; two pairs of reddish eyes, anterior eyes larger than posterior ones ( Fig. 1A, B ). Proboscis without teeth or jaws; ten large papillae and nine small ones arranged alternately on outer rim ( Fig. 1B, C ). Parapodia sub-biramous ( Fig. 1D–F ). Notopodia bearing long and articulated cirri ( Fig. 1D, E ). Neuropodial lobes proportionately long; bearing compound chaetae with hooked tips and fine serration ( Fig. 1H–J ; from chaetiger 6 single simple chaeta inserted on dorsal margin of parapodium ( Fig. 1G ), with weakly hooked blunt tip ( Fig. 1K ).

Etymology. Named for the alternate arrangement of large and small papillae on proboscis.

Remarks. The detailed description of the holotype was presented in Uchida (2004). Synsyllidia alternata sp. nov. is similar to the species of genus Syllidia , but they possess conspicuous chitinous jaws in their proboscis. Synsyllidia alternata sp. nov. is also similar to Micropodarke dubia ( Hessle 1925) , also from Japan. The two species share having six pairs of tentacular cirri, papillated proboscis without jaws, a pair of lateral antennae without median one, bi-articulated palps, and sub-biramous parapodia ( Hessle 1925; Pleijel and Rouse 2005). The new species, however, has simple conical parapodial cones, whereas in M. dubia pre- and postchaetal neuropodial lobes can be found. Moreover, M. dubia lacks acicular simple neurochaetae. In fact, neuropodial acicular simple chaetae are rare in Hesionidae . Other two species have such kind of chaetae, namely Oxydromus brevis ( Hartmann-Schröder 1959) , from El Salvador (Hartmann- Schröder 1959), and Hesiospina similis ( Hessle 1925) , from western Europe ( Hessle 1925; Parapar et al. 2004), but the first species has only two pairs of tentacular cirri and the second one has eight pairs in turn. Additionally, the identity of the first one has been challenged, and Pleijel (1998) regarded it as nomen dubium. Several species of Microphthalmus also have simple neurochaetae ( Parapar et al. 2004); however, they never have distinct cirrophores in tentacular or dorsal cirri.

Figures

Fig. 1. Synsyllidia alternata gen. et sp. nov., holotype (NSMT-Pol H-691). A, dorsal view of the anterior body.B, enlarged dorsal view of the anterior end, showing the everted proboscis, prostomium, and the following segments. C, ventral view of the anterior end. D, anterior view of right parapodium 9. E, posterior view of the same. F, notopodial cirrophore in the same parapodium, with notoacicula. G, neuropodial acicula and a simple chaeta in the same parapodium. H, superiormost compound falciger. I, median falciger. J, inferiormost two falcigers. K, tip of simple chaeta. Scale bar: 0.5mm for A; 0.2mm for B–D; 0.1mm for E; 0.05mm for F–J; 0.02mm for K.