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During surveys of the meroplankton in the South. China Sea, I found a pilidium from the “auriculatum” group, which appeared to be a new form. A description.

ISSN 10630740, Russian Journal of Marine Biology, 2011, Vol. 37, No. 1, pp. 73–75. © Pleiades Publishing, Ltd., 2011. Original Russian Text © A.V. Chernyshev, 2011, published in Biologiya Morya.

BRIEF NOTES

A New Form of Larvae of the Pilidium auriculatum Group (Nemertea) from the Coastal Waters of Vietnam A. V. Chernyshev Institute of Marine Biology, Far East Branch, Russian Academy of Sciences, Vladivostok, 690041 Russia; Far East State University, Vladivostok, 690600 Russia email: tshe[email protected] Received May 20, 2010

Abstract—A new form of pilidium ex. gr. auriculatum from the coastal waters of Vietnam (Van Phong Bay) is described. One distinguishing feature of this form is the presence of a short unpaired strand connecting the juvenile larva to the posterior wall of the helmet. Keywords: nemerteans, pilidia. DOI: 10.1134/S1063074011010068

idium. The lateral lobe is narrow, curved, and directed downwards; the anterior and the posterior lobes do not protrude. The helmet consists of large pentagonal– septagonal cells, reaching to 90 µm in diameter. In live pilidia, the ciliary band in front of the lateral lobes and on the lower end of the lobes is pigmented light yellow. The apical organ is 40 µm in diameter, not pigmented, its tuft about 160 µm long. Any retractor muscle that is connected with the apical organ has not been yet detected. The juvenile larva is connected with a thick and short (43 µm) strand to the posterior wall of the helmet (Fig. 1c). The helmet wall is thickened in the site of the connection; nuclei in the thickening form two adjacent groups (Fig. 1f). The anterior–posterior axis of the pilidium and the anteriorposterior axis of the juvenile form an angle of approximately 15°. The juvenile larva is about 320 µm long; its posterior part was drawn and curled up to form, very probably, the caudal cirrus. The anterior end bears an accumulation of lightyellow pigment. The proboscis of the juvenile was partly turned inside out upon fixation.

Pilidia from the “auriculatum” group were described as early as 1858 [6]. Since then, they have been found in various coastal areas of Europe, North America, and at the Pacific coasts of Asia and Austra lia [1, 3–5, 7]. Dawydoff [4] has described three forms (“species”) of pilidia of this group, viz., p. galeatum, p. appendiculatum, and p. longivertex, from the coastal waters of Vietnam. There is no doubt that pilidium auriculatum are actually larvae of nemerteans of the family Hubrechtellidae [2, 3]. During surveys of the meroplankton in the South China Sea, I found a pilidium from the “auriculatum” group, which appeared to be a new form. A description of this form is presented here. The pilidium was stud ied in vivo and fixed in 4% formaldehyde with prelim inary magnesium chloride anesthesia. DAPI staining was used to reveal the distribution of nuclei with the use of fluorescent microscopy: 2 µl of DAPI stock solution were added to 100 ml of phosphate buffer; the pilidium was placed for 1 min into a droplet of the solution obtained, then washed in the phosphate buffer and examined under a Leica MZ75 microscope.

Comparison. The pilidium described is undoubt edly similar in its form to typical pilidium auriculatum; however, it differs from them by having a higher hel met and the presence of one short and thick strand (the typical pilidia have two long and thin strands, which connects the juvenile specimen with the poste rior part of the helmet.

Pilidium ex gr. auriculatum (Fig. 1a–1f) Material. Single specimen. Collected on June 3, 2007 in the South China Sea, Van Phong Bay, 12°36'N, 109°18'E, subsurface catch. Description. The pilidium is at a late stage of devel opment. The larva is 430 µm long and 495 µm high; the lateral lobes are 167 µm long, the maximum width of 90 µm. The anterior and posterior surfaces of the helmet are convex; the anterior surface of the live pil idium is more convex than the posterior one. The anterior lobe is wider than the posterior part of the pil

Comments. The description of pilidium auriculatum notes two distinctly separate strands of muscle fibers that connect the embryo with thickenings on the pos terior wall of the helmet [3]. I have observed similar pairs of strands in pilidium auriculatum from the Sea of Japan; the sites of their connections stand widely apart, with accumulations of cells there; their nuclei 73

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CHERNYSHEV

(c)

(а) (b)

(d)

(e)

(f)

(g)

Fig. 1. Pilidium ex gr. auriculatum from the South China Sea (a–f) and from the Sea of Japan (g). a, b, general side view; c, con necting strand; d, general front view; e, general rear view; f, g, arrangement of nuclei in the site of connection of strands (shown with arrows, DAPI staining). Scales: 100 µm in a, b, d, e, and c; 50 µm in g and f.

are distinctly conspicuous upon DAPI staining (Fig. 1g). The presence of muscular elements in these formations has not been confirmed yet (in contrast to the apical retractor muscle in other pilidia). According to the private unpublished data of Schwarz [8], phal loidine staining does not reveal actincontaining ele ments in the pair of strands in pilidium auriculatum. Only one similar strand was detected in the new form; as the DAPI staining showed, the strand has a twin pattern. The strand was probably formed through the conjugation of paired strands to a single one. The pres ence of a pair or a single strand and the absence of the apical retractor muscle are a specific feature of the pil idia from the group auriculatum, and probably are a synapomorphic trait of the family Hubrechtellidae.

ACKNOWLEDGMENTS This work was supported by the Russian Founda tion for Basic Research (project no. 090498540) and by APN (project no. ARCP201018NMY). REFERENCES 1. Chernyshev, A.V., The Larvae of Unarmed Nemerteans in Peter the Great Bay (Sea of Japan), Russian Journal of Marine Biology, 2001, vol. 27, no. 1, pp. 58–61. 2. Chernyshev, A.V., New Species of the Genus Hubrech tella (Nemertea, Anopla) from the Sea of Japan and Validation of the Family Hubrechtellidae, Russian Journal of Marine Biology, 2003, vol. 29, no. 5, pp. 333– 336.

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A NEW FORM OF LARVAE 3. Cantell, C.E., Morphology, Development and Biology of the Pilidium Larvae (Nemertini) from the Swedish West Coast, Zool. Bidr. Uppsala, 1969, Bd. 38, S. 61– 111. 4. Dawydoff, C., Les Formes Larvaires de Polyclades et de Némertes du Plancton Indochinois, Bull. Biol. France Belg., 1940, vol. 74, pp. 443–496. 5. Lacalli, T.C., Diversity of Form and Behaviour among Nemertean Pilidium Larvae, Acta Zool., 2005, vol. 86, pp. 267–276.

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6. Leuckart, R. and Pagenstecher, A., Untersuchungen über niedere Seethiere, Arch. Anat. Phys., 1858, S. 569–588. 7. Norenburg, J.L. and Stricker, S.A., Phylum Nemertea, Atlas of Marine Invertebrate Larvae, San Diego: Acad. Press, 2002, pp. 163–177. 8. Schwartz, M.L., Untying a Gordian Knot of Worms: Systematics and Taxonomy of the Pilidiophora (Phy lum Nemertea): Ph.D. Thesis, George Washington Univ. Washington, USA, 2009, 425 p.

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