Cactosoma abyssorum Danielssen, 1890

Cactosoma abyssorum Danielssen, 1890 View in CoL

Tables 1 View Table 1 , 2 View Table 2 ; Figs. 1–4 View Fig View Fig View Fig View Fig .

Cactosoma abyssorum Danielssen, 1890: 82 View in CoL ; Carlgren, 1921: 124.

Phellia crassa Danielssen, 1890: 60 (part).

Isophellia crassa : Carlgren, 1900: 72.

Phelliomorpha crassa View in CoL : Carlgren, 1902: 44.

MATERIAL EXAMINED. Drifting Station   GoogleMaps NP-22 (North Pole 22), Station 112, 75°15′ N, 171°03.3′ W, 450– 460 m, 10– 11.03.1979, collectors I.F. Afanasiev and L.I. Moskalev, one specimen.

Additional material examined.

Cactosoma abyssorum : holotype, ZMBN 9797 View Materials .

Phellia crassa : syntypes, ZMBN 585 View Materials , five specimens and ZMBN 2351 View Materials , three specimens (one specimen from ZMBN 585 View Materials is here selected as a lectotype and received museum number ZMBN 105402 View Materials , all other specimens become paralectotypes).

DESCRIPTION. Our specimen is 19 mm in height. The column is 9 mm in diameter in its middle, 4 mm in diameter in its distal and proximal ends. The column is divisible into base, scapus and scapulus. Naked base is flattened and somewhat invaginated, well demarcated from the scapus ( Fig. 1D View Fig ). The scapus is covered by thin cuticle incrusted by sand grains ( Fig. 1A View Fig ); it has numerous tenaculi ( Fig. 2F View Fig ). The upper part of column is not invaginated into the body and the scapulus and the tentacles are visible externally. The scapulus is naked, free from sand, and has six well defined scapular ridges, hexagonal in outline ( Fig. 1C View Fig ). Ectoderm of the scapulus is thicker (50–80 µm) than the ectoderm of the scapus (10–30 µm) and the mesogloea of the scapulus is much thicker (up to 300 µm) than that of the scapus.

Twenty four tentacles are arranged hexamerously in three cycles (6+6+12). In contracted state they blunt tipped, up to 2 mm long and 1 mm in diameter. The oral disc is small and hidden by the tentacles.

The marginal mesogloeal sphincter muscle is compact and small; on longitudinal sections it has rhomboid shape, 300 µm in length and up to 40 µm in thickness in its middle part. It is located at the bases of the outer tentacles, ( Fig. 2A, B View Fig ), close to ectodermal side. It is separated from the ectoderm by very thin (1–1.5 µm) mesogloeal layer, and separated from the endoderm by much thicker layer of mesogloea (10 µm and more). The sphincter is mostly reticular, but alveolar at its proximal end. The longitudinal muscles of the tentacles are ectodermal and well developed ( Fig. 2G View Fig ). The radial muscles of the oral disc are ectodermal. Circular endodermal muscles of the column are well developed.

The actinopharynx is long (9 mm) with 12 longitudinal ridges corresponding to insertions of macrocnemes ( Fig. 1B View Fig ) and with two shallow siphonoglyphes supported by two pairs of directives. The mesenteries are arranged hexamerously in two cycles (6+6 pairs), all are present along the whole length of the body, from the base to margin ( Fig. 1E, F View Fig ). The mesenteries of first cycle are macrocnemes, those of the second cycle are microcnemes. Large vertically elongated marginal stomata, up to 1.5 mm in length and small oral stomata, up to 0.25 mm, are present on macrocnemes. The retractor muscles of macrocnemes are strong, restricted, and reniform. The parietal part of the macrocnemes has well defined flap ( Fig. 2C View Fig ), which is better developed in the proximal part of the body, below the actinopharynx, but disappears at the base. The microcnemes resemble in the shape the parietal part of macrocnemes, but have no flaps. There is a concentration of muscle fibers running along the insertion of the mesenteries into the base ( Fig. 2D View Fig ).

All macrocnemes are fertile, containing ova up to 0.5 mm in diameter.

Cnidom. Cnidom includes spirocysts, basitrichs, p -mastigophores (see Table 1 View Table 1 and Fig. 3 View Fig ). Numerous basitrichs form a dense basitrichs pad in the distal part of scapulus ( Figs 2E View Fig , 3B View Fig ). Spirocysts are present only in the tentacles and almost absent in the scapulus (several spirocysts were found only in most distal part of the scapulus). We failed to determine the type of p - mastigophores in the actinopharynx and filaments, the structure of unfired p -mastigophores is not visible clearly on examined old material and there were no fired capsules.

REMARKS. Cactosoma abyssorum is a type species of the genus Cactosoma Danielssen, 1890 . The original description of this species, based on one specimen dredged from Norwegian Sea provided by Danielssen (1890), is rather long but may be not very accurate (see opinion of Carlgren, 1902). Nevertheless, nothing in Danielssen’s (1890) original description contradicts with the features observed in the present specimen. The figure of the living specimen, provided by Danielssen (1890, tab. VI, fig. 5), shows a specimen rather similar to the specimen we examined (see Fig. 1 View Fig ), they both have elongated body, densely covered by sand, with bare upper region with six noticeable ridges and with 24 tentacles. The arrangement of the mesenteries of our specimen is also in agreement with those described by Danielssen (1890). The holotype of this species (ZMBN 9797, Fig. 4A, B View Fig ) is now represented by a small piece of the upper part of the body which is in poor condition and not allows detailed study (see Sanamyan et al, 2015). We tried to study nematocysts of the holotype but were able only to find numerous spirocysts (24–46 × 3–4 µm) and several basitrichs in the tentacles (15–19 × 2–3 µm) and in the scapulus (about 20 µm). The size ranges of these nematocysts correspond to those of the present specimen, and the absence of spirocysts in the scapulus of both specimens (in contrast with Halcampa , where they are very numerous in the scapulus) is noteworthy.

Carlgren (1921) synonymized Phellia crassa Danielssen, 1890 with Cactosoma abyssorum and redescribed the latter species basing on type specimens of P. crassa and C. abyssorum . He sectioned a piece of the distal part of the holotype of C. abyssorum and gave figures of its sphincter muscle and transverse sections of parietal muscles of macro- and microcnemes ( Carlgren, 1921, figs.149, 151 and 152). These figures correspond well to that we see on the sections of our specimen, especially the shape of parietal muscle of the macrocnemes, which have well defined flap (compare Carlgren, 1921, fig. 151 and Fig. 2C View Fig in the present paper). Thus, the specimen described in the present paper corresponds closely to description of the holotype of C. abyssorum as provided by Danielssen (1890) and Carlgren (1921) and we have no doubt in their conspecificity.

Рис. 1. Cactosoma abyssorum , ЭкЗемплЯр с СП-22. A — дистальнаЯ половина тела; B — дистальнаЯ часть тела, продольный раЗреЗ; C — дистальнаЯ часть, вид сверху; D — аборальнаЯ часть тела; E — проксимальнаЯ часть тела, продольный раЗреЗ; F — поперечный среЗ тела ниже глотки.

СокраЩениЯ: d — направлЯюЩие пары меЗентериев.

Whether Phellia crassa was correctly synonymized with C. abyssorum is a difficult question. According to Danielssen (1890) P. crassa is based on four specimens from station 290 of Norske Nordhavs-expedition. Museum of Zoology of the University of Bergen has two lots from station 290 labeled “ Phellia crassa, Dan ”, ZMBN 585 (six specimens) and ZMBN 2351 (three specimens). These lots together contain eight polyps and one sponge (labeled by #1 to #8 on Figs. 4C, D View Fig ). Polyps belong to at least three different species, and at least some of them may be considered as syntypes of P. crassa .

The specimens #1 (figured by Danielssen, 1890, tab. XIII, fig. 6) and #2 have wide base firmly attached to bivalve shell, the scapulus not visible externally and whitish scapus has remnants of cuticle. The specimen #3 is similar, but not attached to substratum and its actinopharynx is extruded out. The specimen #2 was cut transversely by previous investigators, it has six pairs of macrocnemes and six pairs of microcnemes, its tentacles are arranged in three cycles, probably 24 in number. These three specimens are most probably conspecific.

The identity of the specimen #1a (attached to the same bivalve shell as the specimen #1 and also figured by Danielssen, 1890, tab. XIII, fig. 6) cannot be established.

The specimen #4 is a sponge.

The specimens #5, #6 and #7 are similar to each other and differ from other specimens. They have relatively small base not attached to substratum. Their smooth naked scapulus and tentacles (24 in number) are visible externally. The scapus is covered by dark cuticle with rather dense layer of sand grains and mud. These tree specimens, with heavily incrusted scapus and bare scapulus with visible longitudinal lines (mesenterial insertions), correspond most closely to figures of living specimens published by Danielssen (1890, tab. IV, fig. 9 and tab. XIII, fig. 5). The specimen #5 was studied by Carlgren (1902). His figure of this specimen ( Carlgren, 1902, Fig.7 View Fig ) is entitled “Danielssen’schen Original-Exemplare”. Basing on the study of this specimen Carlgren (1902) created a new genus Phelliomorpha and used the name Phelliomorpha crassa as a valid name for Phellia crassa . Later Carlgren (1921) synonymized Phelliomorpha crassa with Cactosoma abyssorum . This decision was made basing on the morphology of the specimen #5. Its internal features, as reported by Carlgren (1902), are in agreement with the features we found in our specimen of C. abyssorum from NP-22, and the known features for the holotype of C. abyssorum . These three specimens (#5, #6 and #7) have similar cnidom ( Table 2 View Table 2 ), the most characteristic feature of which is very numerous basitrichs (20–27 × 3–4.5 µm) in the scapulus (battery?). Danielssen (1890: 62 and pl. XIV, fig. 3b) also reported this feature: “nematocysts appear here in such great abundance that they almost entirely conceal the ectoderm”. However, spirocysts of the scapulus are very rare in the specimens #6 and #7, where they occur only in the most distal part of the scapulus (as in our specimen from NP-22), but are more common in the specimen #5. It is hard to say how important are these differences but we inclined to agree with Carlgren (1921) that the specimen he studied (#5), and also the specimens #6 and #7, may be conspecific with C. abyssorum .

Рис. 2. Cactosoma abyssorum , гистологические среЗы. A — продольный среЗ череЗ дистальную часть тела, покаЗываюЩий сфинктер (укаЗан стрелкой); B — сфинктер, увеличено; C — поперечный среЗ череЗ скапус ниже глотки, покаЗываюЩий макро- и микромеЗентерии; D — мускулы, расположенные вдоль вхождениЯ меЗентериЯ в баЗу (стрелки); E — многочисленные баЗитрихи в Эктодерме скапулюса; F — тенакулЯ; G — поперечный среЗ Щупальца, покаЗываюЩий продольные Эктодермальные мускулы. СокраЩениЯ: s — маргинальный сфинктер; sl — ЭктодермальнаЯ сторона скапулюса; t — Щупальце. Цифрами обоЗначены циклы меЗентериев.

The specimen #8 has wide base firmly attached to a stone. It has no recognizable scapulus. The column is pale, with remnants of cuticle. Its distal part is not hidden and is visible externally. It has 48 tentacles arranged hexamerously in four cycles. The number of mesenteries at base (as seen by transparency of column near the limbus) also appears to be about 48. The column of this specimen has basitrichs (14– 20 × 2.5–3.5 µm) and numerous holotrichs (21– 28 × 2.5–4 µm) on the limbus, while all other putative syntypes have on the limbus only small basitrichs (10–20 × 2.5–4 µm) of the same type as on the scapus and on the base. The presence of the holotrichs and the presence of 48 tentacles distinguish this specimen from other putative syntypes of P. crassa therefore the specimen #8 can not be considered as conspecific with them.

Taking into the consideration the fact that the putative syntypes of Phellia crassa belong to at least three species of sea anemones and one sponge we decide to designate a lectotype of Phellia crassa . The specimen #1 (figured in the original publication) and the specimen #5 (which morphology is well known) are better candidates than other syntypes. The specimen #1 was figured in the original description without doubt ( Danielssen, 1890, tab. XIII, fig. 6). However the original description of the internal features of P. crassa is not based on this specimen (specimen #1 is intact, not sectioned). The internal features of this specimen are not known and hard to access now — this old specimen become firm in preservative, flattened, and detailed examination of its internal features with necessary sectioning may significantly damage it. On the other hand the morphology of specimen #5 (including its internal features) is well known, it was redescribed in details by Carlgren (1902) and its features are known better than the features of other syntypes. The specimen #5 is in good condition now. The designation of specimen #5 as a lectotype will not change the current status of P. crassa as a junior subjective synonym of C. abyssorum View in CoL and preserves stability of Zoological Nomenclature. On the other hand, the designation of the specimen #1 as a lectotype of P. crassa will cause many problem, including potential synonymy with other species and servers no useful purpose — in this case P. crassa should be treated as valid species with an uncertain affinity (because its inner features are totally not known). Recommendation 74B of the International Code of Zoological Nomenclature (ICZN, 1999) says: “Other things being equal, an author who designates a lectotype should give preference to a syntype of which an illustration has been published”. The “other things” (sensu Recommendation 74B) are not equal in the present case and the recommendation to prefer an illustrated specimen is not applicable here. According to Recommendation 74A (ICZN, 1999) “in order to preserve stability of nomenclature an author should act consistently with [...] previously accepted taxonomic restrictions of the application of the name.” According to Recommendation 74A we designate here the specimen #5 as a lectotype of Phellia crassa (ZMBN 105402). This designation will not lead to changes in nomenclature and P. crassa stay as a junior subjective synonym of Cactosoma abyssorum View in CoL .