Proamphiporus kaimeiae, Hookabe & Tsuchida & Fujiwara & Kajihara, 2020

Hookabe, Natsumi, Tsuchida, Shinji, Fujiwara, Yoshihiro & Kajihara, Hiroshi, 2020, A New Species of Bathyal Nemertean, Proamphiporus kaimeiae sp. nov., off Tohoku, Japan, and Molecular Systematics of the Genus (Nemertea: Monostilifera), Species Diversity 25, pp. 183-188 : 185-187

Proamphiporus kaimeiae sp. nov.

[New Japanese name: Kaimei-fukamizo-himomushi] ( Figs 2 , 3 )

Material examined. Holotype: ICHUM 6058 , male, transverse sections of anterior body fragment, 6 slides, 19 July 2019, collected at a depth of 262 m, off Ofunato , Japan.

verse line in front of brain ( Fig. 2B ). Paired cerebral ganglia visible through body wall as orange spots ( Fig. 2B ). No eyes evident.

Internal morphology. Epidermis 20–40 µm in thickness, containing numerous red and yellow staining ciliated cells ( Fig. 3A ). Dermis up to 10–15 µm thick. Outer circular muscle layer of body wall 10–20 µm in thickness. Inner longitudinal muscle layer of body wall 50 µm in maximum thickness. Esophagus with ciliated epithelium. Stomach epithelium with glands and cilia. Intestinal diverticula deeply branched ( Fig. 2B ). Mid-dorsal vessel penetrating rhynchocoel wall behind ventral cerebral commissure, forming single vascular plug ( Fig. 3D ).

Proboscis pore terminal. Rhynchocoel long, more than two-thirds of body length, with thin wall comprised of few muscle layers ( Fig. 3B, D ). Proboscis with outer circular, middle longitudinal, and inner circular muscle layers ( Fig. 3E ); proboscis epithelium with developed papillae containing basophilic glandular cells ( Fig. 3B, D, E ); ten proboscis nerves ( Fig. 3E ). Lateral nerves with neither accessory nerves nor neurocords ( Fig. 3G ). Cerebral organs entirely situated alongside brain region, with forked chamber; chamber bifurcating into an anterior radial and a posterior lateral canal, both ciliated ( Fig. 3B, C ); acidophilic glands developed in posterior region of cerebral organs ( Fig. 3C ). Eyes absent. Testes between intestinal diverticula ( Fig. 3F ). Gonoducts and gonopores not found. Execratory collecting tubules near lateral nerve in pyloric region ( Fig. 3G ).

Etymology. The specific name is after the R/V Kaimei, during a research cruise of which the holotype was sampled.

Type locality and distribution. At present known only from the type locality, off Ofunato , Iwate Prefecture, Tohoku, Japan, at a depth of 262 m .

Remarks. The cerebral organs in Proamphiporus kaimeiae sp. nov. are situated alongside the brain region behind the proboscis insertion, which accords with the generic diagnosis for Proamphiporus ( Chernyshev and Polyakova 2019) . The external appearance of P. kaimeiae sp. nov. is quite similar to that of P. rectangulus ; however, they can be differentiated by a depigmented mid-dorsal stripe on the dorsal body surface in P. rectangulus but absent in P. kaimeiae . Proamphiporus kaimeiae differs from P. crandalli by having brown pigments on the dorsal surface.

Phylogeny and genetic distance. The resulting tree topology differed between ML ( Fig. 4A ) and BI ( Fig. 4B ), which is likely due to the lack of gene markers other than COI in P. rectangulus . In both of the analyses, P. kaimeiae formed a clade along with P. crandalli and P. rectangulus with full support values, corroborating the generic placement of the new species as well as the nominal species Amphiporus rectangulus .

The interspecific genetic distances based on COI partial sequences ( Table 2) were 14.1% in p -distance and 15.8% in K2P between P. kaimeiae and P. crandalli , while 13.3–13.5% in p -distance and 14.9% in K2P between P. kaimeiae and P. rectangulus . These values are comparable with 10.4–10.7% in p -distance and 11.2–11.6% in K2P between P. crandali and P. rectangulus , and the interspecific COI divergences for Hoplonemertea suggested in Sundberg et al. (2016).

Figures

Fig. 2. Proamphiporus kaimeiae sp. nov., holotype, ICHUM 6058, photographs taken in living state. A, Whole body, dorsal view; B, ventral view. Abbreviations: cf, cephalic furrow; co, cerebral organ. Scale bar: 500µm.

Fig. 3. Proamphiporus kaimeiae sp. nov., holotype, ICHUM 6058, photomicrographs of transverse sections. A, Body wall in brain region; B, anterior part of cerebral organs; arrowheads pointing to the radial canal; C, posterior part of cerebral organs; arrowhead pointing to the lateral canal; D, brain; arrowhead pointing to vascular plug; E, proboscis; F, testis; G, excretory collecting tubule (arrowhead). Abbreviations: ag, acidophilic glands; br, brain; de, dermis; dg, dorsal ganglion; ep, epidermis; ln, lateral nerve cord; mlm, middle longitudinal muscle layer of body wall; ocm, outer circular muscle layer of body wall; pb, proboscis; pe, proboscis epithelium; pic, proboscis inner circular muscle layer; poc, proboscis outer circular muscle layer; rh, rhynchocoel; st, stomach; te, testis; vg, ventral ganglion. Scale bars: A = 20µm, B = 75µm, C, G = 50µm, D = 100µm, E, F = 40µm.

Fig. 4. Phylogenetic trees of the genus Proamphiporus based on concatenated 16S rRNA (454 bp), COI (657 bp), 18S rRNA (1773 bp), 28S rRNA (1077 bp), and histone H3 genes (326 bp). A, Phylogenetic tree inferred by maximum likelihood (ML) analysis, showing support values generated by a separate partitioned ML bootstrap analysis with 1000 replicates; B, phylogenetic tree inferred from Bayesian analysis, showing posterior probability of a separate partitioned Bayesian analysis.