Raygibsonia, Sundberg & Chernyshev & Kajihara & Kånneby & Strand, 2009

Sundberg, Per, Chernyshev, Alexey. V., Kajihara, Hiroshi, Kånneby, Tobias & Strand, Malin, 2009, Character-matrix based descriptions of two new nemertean (Nemertea) species, Zoological Journal of the Linnean Society 157 (2), pp. 264-294 : 268-271

RAYGIBSONIA GEN. NOV.

Diagnosis: The genus is diagnosed by the following morphological characters: presence of large cerebral organs lying alongside/close to anterior part of the brain and opening laterally in the cerebral region, the ciliated cerebral canals opening from pores rather than from cephalic furrows; cephalic glands encircling the foregut in the brain region; four groups of anterior eyes and isolated pair of posterior eyes.

Etymology: The new genus is named in honour of Professor emeritus Ray Gibson as a tribute to his accomplishments and significance in nemertean taxonomy.

Type species: Raygibsonia bergi .

Systematic discussion: The phylogenetic analysis based on the 18S rRNA gene shows that the type species belongs in the taxon Hoplonemertea with 100% support ( Fig. 1 ). A more detailed analysis of a selected number of hoplonemerteans based on the COI gene analysis ( Fig. 2 ) places R. bergi in the same clade as Zygonemertes virescens . However, we have chosen not to place the new species in the taxon Zygonemertes for two reasons. First, the taxon sampling was limited in this analysis, and with only one Zygonemertes species available the result can only be indicative. Second, Chernyshev (2005) placed the three genera Zygonemertes , Quequenia , and Pheroneonemertes in the same taxon based on the synapomorphy ‘postcerebral eyes along longitudinal nerve cords’. This character is absent in Raygibsonia , and although this does not per se contradict a close relationship, we interpret this as an indication of two different taxa. Raygibsonia bergi furthermore differs from all species of ‘Zygonemertidae’-group by the absence of postcerebral eyes and the lack of sickleshaped bodies.

RAYGIBSONIA BERGI GEN. ET SP. NOV.

( FIGS 3 , 4 ; TABLE 4)

Hoplonemertean sp. 3 Strand & Sundberg (2005).

Holotype: Sexually immature, series of transverse sections ( GNHM Nemertini 84). Mud , 20 m depth, south of Flatholmen (58°14′48″N, 11°22′54″E according to the WGS 84 ), 18.xi.2002. 18S rDNA sequence of the species has been deposited with GenBank (accession number AY 928351) together with sequences of the mtDNA COI gene (accession number EU489489).

Paratype: Sexually immature, series of transverse sections ( GNHM Nemertini 85) from mud with boulders, fauna dominated by Mycale lingua , 92–106 m depth, Väderöarna (58°19′16″N, 10°57′52″E), 25.iv.2006 .

Further material: Amongst shell gravel, 30 m depth, Humlesäcksrännan (58°16′08″N, 11°24′85″E), 10.v.2006.

External characters ( Fig. 3 ): The largest specimen was about 15 mm long and 1–1.5 mm wide. The body is of more or less uniform width slightly narrowing close to the rounded posterior tip. The primary body colour is light brown, the head is pinkish red with the cerebral ganglia visible as a red lobe in front of the cephalic furrows. Lateral margins translucent to whitish. The head, which is somewhat wider than the body, possesses a lower lip-like projection and two groups of eyes and a single pair of distinct eyes on each side. The foremost group is situated on the lower lip-like projection and a bit further back, above the lower lip-like projection, the second group. Each group contains two to five eyes, probably depending on age. The single pair of posterior eyes lies in front of the cerebral ganglion and is visible from the ventral side of the body. The head is demarcated from the rest of the body by a pair of dorsal cephalic furrows. Moreover, another pair of cephalic furrows are present ventrally, they arch their way from the terminal proboscis pore to the lateral margins on each side of the head. The body possesses a brown middorsal longitudinal band that ends close to the posterior tip. Under higher magnification this band is composed of densely packed pigment spots. Dorsolaterally on each side of the body surface, faint and sometimes abruptly ending longitudinal bands of sparsely packed pigment spots are present ( Fig. 3 ).

Internal characters: Figure 4 , Table 4, and Appendix. Systematic discussion: As for the genus.

Etymology: The species is named in honour of Dr Gunnar Berg (1937–2006) for his contribution to nemertean taxonomy and systematics.

Figures

Figure 1. Phylogeny of a selected number of nemertean taxa to show the position of the two new species described here (in bold). Majority rule consensus tree from a Bayesian analysis based on 18S rDNA sequences. Numbers above branches refer to a posteriori probabilities (only values> 95% reported). Three phoronid species were used as outgroup: Phoronis vancouverensis, Phoronis australis, Phoronis hippocrepia.

Figure 2. Phylogeny of a selected number of hoplonemertean taxa to show the position of the new hoplonemertean species described here (in bold). Majority rule consensus tree from a Bayesian analysis based on COI mtDNA sequences. Numbers above branches refer to a posteriori probabilities (only values> 95% reported). Outgroup species is Reptant nemertean sp500 (from Thollesson & Norenburg, 2003).

Figure 3. Raygibsonia bergi gen. et sp. nov. Drawing by Helena Samuelsson, The Encyclopedia of the Swedish Flora and Fauna.

Figure 4. A–F, Raygibsonia bergi gen. et sp. nov. A, section through anterior-most part of body showing cephalic glands, cerebral organs, oesophagus, and the poorly developed precerebral septum. B, section through cephalic region showing cephalic blood supply, stomach, and cerebral ganglia. Note the vascular plug (arrowhead). C, section through pyloric region showing the connection between pylorus and intestine. Note the myofibrillae in the lateral nerve cord (arrowhead) and the nerves of the proboscis (arrow). D, section through proboscis armature region of body showing the stylet apparatus. Note the accessory stylet (arrow) and the peripheral neural sheath (arrowhead) that connect the proboscis nerves. E, section through gonad region of body showing immature gonads (probably sac-like). Note the accessory lateral nerve (arrowhead). F, section through stomach region of body, showing distribution of gland cells. Abbreviations: AP, accessory stylet pouch; AN, accessory lateral nerve; CB, cerebral ganglion; CC, cerebral canal; CF, cephalic furrow; CG, cephalic glands; CL, dorsal lobules of cephalic glands; CM, circular muscle layer; CO, cerebral organ; D, dermis; DC, dorsal commissure; DG, dorsal ganglion; E, epidermis; ECF, cephalic gland encircling the foregut; G, gonad; I, intestine; IC, intestinal caecum; LD, lateral diverticula; LM, longitudinal muscle layer; LN, lateral nerve cord; LV, lateral blood vessel; MDV, mid-dorsal vessel; OE, oesophagus; P, proboscis; PE, proboscis epithelium; PN, proboscis nerve; PS, precerebral septum; PY, pylorus; R, rhynchocoel; RM, retractor muscle; S, stomach; SB, stylet basis; VG, ventral ganglion.