Laonice sp. 1

Abe, Hirokazu & Sato-Okoshi, Waka, 2021, Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan, ZooKeys 1015, pp. 1-86 : 1

Laonice sp. 1 Fig. 4D

Larval morphology.

Remnants of egg envelope apparent in early trochophore (Fig. 4D ). Two pairs of red eyes located in approximately a straight line, lateralmost pair larger in early larvae. Parapodia weakly differentiated; serrated larval chaetae introverted toward medial line of dorsal side. The body opaque yellowish with abundant yolk internally. Pigmentation absent except in the eyes.

Remarks.

Adult individuals of this species were collected from bottom sediments at 22 m depth in Onagawa Bay in December 2011 using a Smith-McIntyre grab sampler. To date, two Laonice species, L. cirrata (Sars, 1851) and L. japonica (Moore, 1907) have been recorded from Japan. Sikorski (2002) indicated that L. cirrata , a previously presumed widespread species, is probably limited to Norway and adjacent regions. This was supported by a molecular study that suggested previously unrecognized diversity within this species ( Bogantes et al. 2018). Laonice japonica , originally described as Spionides japonicus from Japan and later considered as synonymous with L. cirrata (e.g., Söderström 1920; Berkeley and Berkeley 1936; Okuda 1937; Imajima and Hartman 1964; Foster 1971), was reexamined and considered a valid species by Maciolek (2000) and Sikorski (2011). However, even after that, since L. cirrata has been recorded from Japan (e.g., Imajima 2006, 2009, 2011), the validity of these records is ambiguous and might represent different species. In addition to these two species, unidentified Laonice sp. was also reported from Japan by Imajima (1990c) but it is unclear whether the species is identical to the species reported here. Although the 18S rRNA gene sequences obtained in the present study match (1731/1731 bp, except for gaps) with Laonice cirrata sequences from Russia in DDBJ/EMBL/GenBank (KM998754), because taxonomic knowledge on this genus in Japan is still limited and the 18S rRNA gene is relatively conservative, this species was referred to Laonice sp. The larvae and adults were confirmed to match (18S: 1754/1754, 16S: 500/504 bp) using molecular data (Fig. 3 ).

Larvae of this species were rare in the planktonic community found in Onagawa Bay in September 2011 and October 2012. Although two parallel rows of encircling vesicles of egg envelope, similar to those of Aonides pretrochophore and trochophore stages, were reported in oocytes of Laonice species ( Radashevsky and Lana 2009), this characteristic was not observed in early larval stages with egg envelope in the present study (Fig. 4D ). Blake (2006) described the larval development of Laonice sp. from California; however, the identification of these larvae is doubtful because they seem to lack serrated larval notochaetae introverted toward the medial line of the dorsal side, which are characteristic of Laonice larvae.

Figures

Figure 3. Maximum Likelihood tree inferred from nuclear 18 S and mitochondrial 16 S rRNA gene sequences of spionid polychaetes obtained from Japan in the present and previous studies (shown in Table 1) and from DDBJ / EMBL / GenBank (shown in Table 2). The tree is divided into two parts A, B. The gene sequences obtained in the present study are highlighted by bold and red color and the adult and larval sequences are indicated by solid squares and circles in front of each species name, respectively. SH-aLRT / approximate Bayes support / ultrafast bootstrap support values of ≥ 80 % / ≥ 0.95 / ≥ 95 %, respectively are given beside the respective nodes. Nodes with red circles indicate triple high support values of SH-aLRT ≥ 80, approximate Bayes support ≥ 0.95, and ultrafast bootstrap support ≥ 95. The scale bar represents the number of substitutions per site. Sequences of Laonome sp. and Sabella pavonina Savigny, 1822 obtained from GenBank were used for outgroup rooting.

Figure 4. Light micrographs showing morphologies of living spionid larvae of Aonides, Laonice, Rhynchospio, Scolelepis, and Spiophanes A-C Aonides cf. oxycephala, dorsal view of early planktonic (A), 8 - chaetiger (B), and 18 - chaetiger larvae (C) D Laonice sp. 1, dorsal view of early planktonic larva E Laonice sp. 2, dorsal view of 12 - chaetiger larva F Poecilochaetus sp., dorsal view of 17 - chaetiger larva G, H Rhynchospio aff. asiatica, dorsal view of 6 - chaetiger (G) and 12 - chaetiger larvae (H) I Scolelepis cf. kudenovi, dorsal view of 7 - chaetiger larva J, K Scolelepis sp. 1, dorsal view of 17 - chaetiger (J) and 19 - chaetiger larvae (K) L Scolelepis sp. 2, dorsal view of 20 - chaetiger larva M, N Spiophanes uschakowi, dorsal (M) and lateral view (N) of 18 - chaetiger larvae O, P Spiophanes aff. uschakowi, dorsal view of 16 - chaetiger larva (O) and 27 - chaetiger juvenile (P). Scale bars: 300 μm.