Octineon suecicum Carlgren, 1940

Sanamyan, N. P., Sanamyan, K. E., McDaniel, N. & Bocharova, E. S., 2018, First record of two genera of sea anemones (Cnidaria: Actiniaria), Octineon and Edwardsiella, from the North Pacific Ocean, Invertebrate Zoology 15 (1), pp. 1-18 : 4-11

Octineon suecicum Carlgren, 1940

Table 3 ; Figs. 1–5 .

Octineon suecicum Carlgren, 1940: 59 ; 1942: 65; 1949: 38.

MATERIAL EXAMINED. KBPGI 473 /1, Sakinaw Rock , Sechelt Inlet, British Columbia, Canada, 49°34.047′N, 123°48.151′W, 23 m, granite bedrock, t=12.5°C, 14 September 2015, 12 specimens, collector Neil McDaniel ; KBPGI 474 /2, same locality, 30 m, 24 February 2016, 11 specimens , in formalin.

ADDITIONAL MATERIAL EXAMINED. SMNH 5633 , syntypes of Octineon suecicum Carlgren, 1940 ( Fig. 2B in the present paper) .

DESCRIPTION. The specimens form compact, up to 20 cm diameter, clusters of numerous crowded individuals (more than 130 were counted on one underwater photograph). The pedal disc is broad, irregular in outline, flattened, strongly adhesive. Its diameter in large live specimens is about 10 mm, the largest observed was about 12 mm in greatest dimension. The column in live fully expanded specimens is up to 10 mm in height, widely expanded proximally and becoming more or less cylindrical above where its diameter is about 2 mm, divisible into scapus and scapulus ( Fig. 1 ). The scapus is covered by brownish cuticle whose surface is almost free of foreign particles apart from occasional epibionts (mostly ciliophores Folliculina sp. , seen as black dots in Fig. 2A , or Bryozoa). Mesenterial insertions are apparent, especially at the edge of the flattened proximal part of the column ( Fig. 1C, D ). The scapulus is smooth, lacking cuticle, not coloured apart from a set of short longitudinal white stripes, usually grouped by three in six groups, about halfway between the oral disc and the scapus ( Fig. 1B, D ). Wider strip in the middle of each group corresponds to primary endocoels. The oral disc is small, circular and flat, of the same or a bit greater diameter as the scapulus. The oral disc is either colourless and translucent ( Fig. 1B ) or has patches of white pigment. The distribution of these white patches on the oral disc is the same on all individuals of the same cluster. For example, in all specimens of the cluster shown on Fig. 1A, C, D the ventral third of the oral disc (the area between ventro-lateral pairs of the mesenteries of the first cycle, including these pairs themselves) is white, while the remaining two-thirds of the disc is translucent with thin white lines along insertion of the mesenteries between the bases of the tentacles. These white lines and white colour of the oral disc may continue on the distal part of the scapulus ( Fig. 1D ). The tentacles are elongate and slender, up to 11 mm in large specimens and about 0.4 mm in diameter at their base, tapering distally, translucent. The tentacles are arranged hexamerously in three cycles on the outer part of the oral disc, usually up to 24 in number, but occasionally up to 30 due to the duplications sometimes occurring in the second cycle.

Preserved specimens are much flattened with short elevated central part, the largest specimen is about 10 mm in diameter and 5 mm in height. The tentacles and scapulus are not visible ( Fig. 2A ). The tentacles are capable of invagination. The ectoderm on the scapus beneath the cuticle is very thin, in some places no more that 1 µm thick, but occasionally up to 10 µm and more, especially in the folds. The ectoderm of the scapulus is much thicker, 19–35 µm ( Fig. 2C ). The mesogloea of the scapus and scapulus is up to 300 µm in thickness, but much thinner on the base. Mesogloea of the invaginated part of scapus and scapulus forms six prominent ridges ( Fig. 2D ). The cuticle covering the scapus is thin (3–5 µm), not stratified, attached to column on areas with modified ectoderm with mesogloeal strands reaching the cuticle (as in tenaculi, Fig. 2E ). At the base cuticle is attached by large crowded mesogloeal strands distributed along the whole base ( Fig. 3F ). Endoderm contains numerous gland cells which may form almost continuous layer ( Fig.3F ). The marginal sphincter is mesogloeal, alveolar, not strong, rather long (up to 2.5 mm), situated in the scapulus and continues proximally up to the middle part of the scapus, where it lies closer to endoderm. The sphincter is separated from endodermal circular muscles of column and from ectoderm by a layer of mesogloea. On transverse section of the sphincter the individual muscle meshes are rather sparse and lie mostly in the middle layer of the mesogloea ( Fig. 2C ). Radial muscles of the oral disc and longitudinal muscles of the tentacles are ectodermal ( Fig. 2F ).

The actinopharynx has no distinguishable siphonoglyphs. Because the preserved specimens were strongly flattened and contracted it was not possible to obtain perfect transverse sections of mesenteries to illustrate their distribution and shape. As it appears on underwater photographs the first and the second cycles of mesenteries reach the oral disc and the number of mesenteries at the limbus may be about 100, i.e. at least five cycles and some mesenteries of sixth cycle present at the limbus. Schematic arrangement of the mesenteries is shown in Fig. 3A . Eight mesenteries of the first cycle, arranged as in Edwardsia , are macrocnemes.They are perfect and have retractors, filaments, gonads and acontia. The retractor muscles are strong, circumscribed, pinnate with well developed central mesogloeal lamella. Free ends of their pennons are always directed to the body wall ( Figs. 3B, D ; 4A–C ). On the opposite side the parietobasilar muscles are present; they may form a short free flap (up to 100 µm in length). Parietal muscles are not developed. The mesenteries of fifth couple (paired with dorso-lateral macrocnemes) are microcnemes but have diffuse muscles at their inner (closer to actinopharynx) parts which on some sections resemble diffuse retractors ( Fig. 3B, C ). The mesenteries of the sixth couple (paired with ventro-lateral macrocnemes) are similar to those of the fifth couple but have weaker muscles ( Figs. 3D, E ; 4A ). Mesenteries of the second and subsequent cycles are weak, without recognizable muscles on the endocoelic sides, but with discernible muscles on the exocoelic sides corresponding to parietobasilar muscles ( Fig. 3C ). Basilar muscles indiscernible ( Fig. 3F ).

меЗентерии (2 — меЗентерии второго цикла); D — поперечный среЗ череЗ вентро- латеральную пару меЗентериев первого цикла на уровне глотки; E — те же меЗентерии ниже уровнЯ глотки; F — среЗ череЗ педальный диск.

ОбоЗначениЯ: c1–c6 — билатеральные пары меЗентериев; en — Энтодерма; od — оральный диск; pd — педальный диск; sc — скапус; t — Щупальце.

All studied specimens were female. The diameter of the ova is up to 200 µm. Many images show examples of ongoing pedal laceration ( Fig. 1C ). Most probably compact clusters of similarly coloured specimens are the result of asexual reproduction.

Cnidom includes robust and gracile spirocysts, basitrichs, holotrichs, p-mastigophores A, p-mastigophores B (see Table 3 and Fig. 5 , cnidae of the column and tentacles were studied in seven specimens, those of the actinopharynx in four specimens, those of the filaments in 17 specimens, those of acontia in six specimens and those of the endoderm in two specimens; cnidae of the syntypes were studied in seven specimens). Numerous basitrichs in the scapulus ( Fig. 5F ) are larger than in scapus and form an almost solid layer ( Fig. 2G ). Large basitrichs of the tentacles ( Fig. 5J ) are concentrated at the tips.

HABITAT. The clusters of this species were found at a depth of 23 to 30 m. They were concentrated on a steeply sloping bedrock bottom.

REMARKS. The genus Octineon is the sole member of the family Octineonidae and currently contains three species: O. lindahli (Carpenter in Carpenter et Jeffreys, 1871), O. suecicum and O. chilense Carlgren, 1959 .

The type species of the genus, O. lindahli (= Ammodiscus lindahli Carpenter in Carpenter et Jeffreys, 1871), was dredged by H.M.S. “Porcupine” in 1870 off the south coast of Spain at depths from 413 to 702 m. The morphology of these specimens was described in detail by Fowler (1894) and Carlgren (1921, 1931). The information provided by Fowler (1894: 461) suggests that the specimens were rather numerous in that location (“obtained <...> a large collection of thin sand discs...”) but surprisingly the species has not been recorded again during the past 150 years. Octineon lindahli lives unattached on the sea floor, has a thin disk-shaped body densely covered by attached sand and has only 12 tentacles.

The second species, O. suecicum , is also based on a single lot of specimens. In his brief original description Carlgren (1940: 60) gives the locality as “ Sweden, Bohuslän. Väderöar, in vicinity of the Lophelia -reef, 60–70 m on small stones or shells”. A more detailed description provided by Carlgren (1942) is based on the same material. The species lives attached to hard objects, its body is free from sand and it has at least 24 tentacles in fully developed specimens, so it differs quite distinctly from O. lindahli and cannot be confused with it.

The third species, O. chilense is known only from the original description based on specimens from two stations from the region of Los Lagos, Chile, from 100 m and 50–60 m depth. This species is very similar to O. suecicum . Carlgren (1959) says it has a stronger sphincter muscle and stronger retractor. In our opinion the more significant difference is the larger size of basitrichs in acontia (62–70.5 × 5.6 µm).

The present record of a member of the genus Octineon from British Columbia is a first record for a half century since Octineon was last recorded. This record is geographically distant from all previously known locations ( Spain, Norway and Chile). The morphology of specimens described herein corresponds closely to that of O. suecicum in most details, including the coloration of living specimens, e.g. probably characteristic for the species and rather distinctive arrangement of short longitudinal white lines grouped by three on the scapulus (see Fig. 1B, D ), Carlgren (1940: 59) describes them as “on the lowest part of the scapulus 3 opaque white, longitudinal lines, sometimes more irregularly arranged”. We examined nematocysts of syntypes of O. suecicum (SMNH 5633). Their size ranges and composition are similar to whose of the specimens from British Columbia (see Table 3 ), especially the nematocyst of the scapus and base, available without dissection of the specimens, which were studied on more specimens.

Figures

Fig. 1. Octineon suecicum Carlgren, 1940. A–D — live specimens in natural habitat. Рис. 1. Octineon suecicum Carlgren, 1940. A–D — живые ЭкЗемплЯры в естественной среде обитаниЯ.

Fig. 2. Octineon suecicum Carlgren, 1940. A — specimens from British Columbia, preserved; B — syntypes SMNH 5633 (on stones); C — longitudinal section of the distal part of the scapus and scapulus; D — transverse section of introverted part of the scapus; E — tenacula; F — transverse section of the tentacle; G — crowded basitrichs in the ectoderm of the scapulus. Abbreviations: en — endoderm; s — sphincter; sc — scapus; sl — scapulus; t — tentacle. Рис. 2. Octineon suecicum Carlgren, 1940. A — фиксированные ЭкЗемплЯры иЗ Британской Колумбии; B — синтипы SMNH 5633 (на камнЯх); C — продольный среЗ череЗ дистальную часть скапуса и скапулюс; D — поперечный среЗ череЗ ввернутую часть скапуса;E — тенакулЯ; F — поперечный среЗ череЗ Щупальце; G — многочисленные баЗитрихи в Эктодерме скапулюса. ОбоЗначениЯ: en — Энтодерма; s — сфинктер; sc — скапус; sl — скапулюс; t — Щупальце.

Fig. 3. Octineon suecicum Carlgren, 1940. A — arrangement of the mesenteries; B — transverse sections through dorso-lateral pair of the mesenteries of the first cycle; C — transverse section of the microcnemes (2— mesenteries of the second cycle); D — transverse sections through ventro-lateral pair of the mesenteries of the first cycle on the level of the actinopharynx; E — the same mesenteries below actinopharynx; F — section through the pedal disc. Abbreviations: c1–c6 — couples of the mesenteries; en — endoderm; od — oral disc; pd — pedal disc; sc — scapus; t — tentacle. Рис. 3. Octineon suecicum Carlgren, 1940. A — схема органиЗации меЗентериев; B — поперечный среЗ череЗ дорсо-латеральную пару меЗентериев первого цикла; C — поперечный среЗ череЗ микро-

Fig. 4. Octineon suecicum Carlgren, 1940. A — transverse section through the distal part of column (2 — mesenteries of the second cycle); B — transverse sections through dorsal pair of the directives; C — transverse sections through ventral pair of the directives. Abbreviations: c1–c6 — couples of the mesenteries; od — oral disc; ph — actinopharynx; sc — scapus; t — tentacle. Рис. 4. Octineon suecicum Carlgren, 1940. A — поперечный среЗ череЗ дистальную часть колюмна (2 — меЗентерии второго цикла); B — поперечный среЗ череЗ дорсальную пару направлЯюЩих меЗенте- риев; C — поперечный среЗ череЗ вентральную пару направлЯюЩих меЗентериев. ОбоЗначениЯ: c1–c6 — билатеральные пары меЗентериев; od — оральный диск; ph — глотка; sc — скапус; t — Щупальце.

Fig. 5. Octineon suecicum Carlgren, 1940, distribution of cnidae (see Table 3 for size ranges). Рис. 5. Octineon suecicum Carlgren, 1940, распределение книд (раЗмеры укаЗаны в табл. 3).