Pseudopolydora cf. kempi (Southern, 1921)

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

Pseudopolydora cf. kempi (Southern, 1921) Fig. 9C

Larval morphology.

Overall body shape fusiform, head region enlarged due to broad prostomium and expanded lateral lips of vestibule. Prostomium gently notched anteriorly. Three pairs of black eyes present in more or less a straight line, most lateral pairs double-eyes. Mid-dorsal melanophore on first chaetiger usually absent (Fig. 9C ), small non-ramified melanophore present in some individuals. Dorsal pigment consists of four rows of lateral and central pairs of pigment spots. Lateral and central pigments usually begin from chaetigers II and III, respectively. There pigment spots undergo expansion and contraction. Ventral pigment begins on chaetiger III, consists of paired bars on posterior border of each chaetiger. Anterior and posterior margin of prostomium have considerable brown pigment. Black pigment spots occur on sides of peristomium. Pygidium has black central spot. Gastrotrochs on chaetigers V and VII in 13-chaetiger larvae.

Remarks.

Adult individuals of this species were collected from muddy sediment in Gamo Lagoon in January, May, and December 2011, and April 2013. Adult morphology agrees with the description of P. cf. kempi by Abe et al. (2016). Therefore, these individuals were referred to P. cf. kempi . The 16S rRNA gene sequence obtained in the present study showed a 99.7% (305/306 bp) similarity with that of P. kempi japonica Imajima & Hartman, 1964 from Russia (MG460897) reported by Radashevsky et al. (2020b), indicating these two are same species. It will need to be clarified whether P. kempi (type locality India) and subspecies P. kempi japonica (type locality Japan) are the same species. The larvae and adults were confirmed to 100% match using molecular data (Fig. 2 ).

Planktonic larvae of this species larger than 12-chaetiger stages were collected from Gamo Lagoon in August 2012. The larval morphology of this species observed in the present study agrees with the descriptions of P. kempi by Blake and Woodwick (1975) and of P. cf. kempi by Kondoh et al. (2017). These species have adelphophagic and lecithotrophic larval development, in which larvae feed on nurse eggs in brood capsules, hatch at a very late stage, and have a short pelagic life ( Blake and Woodwick 1975; Kondoh et al. 2017). Reproduction and larval development of these species under the name of P. kempi and P. kempi japonica were also described by Srikrishnadhas and Ramamoorthi (1977), Myohara (1979), and Radashevsky (1985). However, the larvae of species in these descriptions resemble those of Pseudopolydora cf. reticulata Radashevsky & Hsieh, 2000 described by Kondoh et al. (2017) and of the present study in having planktotrophic development without nurse eggs and distinct dorsal melanophores including a middorsal melanophore on the first chaetiger. The taxonomy of P. kempi is unclear because its original description is quite brief, and the current location of type specimen is unknown (Radashevsky and Hsieh 2000). Therefore, studies resolving the taxonomy of P. kempi are necessary.

Figures

Figure 2. Maximum Likelihood tree inferred from nuclear 18 S and mitochondrial 16 S rRNA gene sequences of spionids obtained from Japan in the present and previous studies (provided in Table 1). The gene sequences of adult and larval spionid polychaetes 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 DDBJ / EMBL / GenBank were used for outgroup rooting.

Figure 9. Light micrographs showing the morphologies of living spionid larvae of genera Pseudopolydora and Spio A, B Pseudopolydora aff. achaeta, dorsal view of 12 - chaetiger (A) and 25 - chetiger larvae (B) C Pseudopolydora cf. kempi, dorsolateral view of 12 - chetiger larva D Pseudopolydora paucibranchiata, dorsal view of 13 - chaetiger larva E, F Pseudopolydora cf. reticulata, dorsal view of 17 - chaetiger (E) and 16 - chaetiger larvae (F) G, H Pseudopolydora tsubaki, dorsal view of 5 - chaetiger (G) and 11 - chaetiger larvae (H) I Pseudopolydora sp., dorsal view of 7 - chaetiger larva J, K Spio sp. 1, dorsal view of 8 - chaetiger (J) and lateral view of 12 - chaetiger larvae (K) L-N Spio sp. 2, dorsal view of 10 - chaetiger (L) and 17 - chaetiger larvae (M), and 17 - chaetiger metamorphosing larvae (N). Scale bars: 300 μm.