Corallimorphus rigidus Moseley, 1877

Lauretta, Daniel & Martinez, Mariano I., 2019, Corallimorpharians (Anthozoa: Corallimorpharia) from the Argentinean Sea, Zootaxa 4688 (2), pp. 249-263 : 256-257

Corallimorphus rigidus Moseley, 1877

Corallimorphus rigidus Moseley 1877 ; Hertwig 1882; Andres 1883; Andres 1884; Hertwig 1885; Hertwig 1888; Haddon 1898; Delage & Hérouard 1901;Gravier 1904; McMurrich 1904; Stephenson 1920; Stephenson 1922; Carlgren 1928; Carlgren & Stephenson 1929; Weill 1934; Carlgren 1934; Carlgren 1943; Carlgren 1949; Fautin 1984; den Hartog et al. 1993; Fautin et al. 2002; den Hartog & Grebelny 2003; Häussermann & Försterra 2005; Häussermann 2006; Rodríguez et al. 2007; Häussermann 2009; Fautin 2011; Rodríguez & López-González 2013, Sanamyan et al. 2015; Fautin 2016.

Corynactis: Hertwig 1888 ; Carlgren 1900; Stephenson 1920; Stephenson 1922; Carlgren 1943; Carlgren 1949; Rodríguez & López-González 2013; Fautin 2016.

Corallimorphus obtecus Hertwig 1888 ; Stephenson 1920; Stephenson 1922; Carlgren 1928; Carlgren & Stephenson 1929; Carlgren 1949; Fautin 1984; Fautin et al. 2002; Rodríguez & López-González 2013; Fautin 2016.

Corynactis hertwigi Haddon 1898 ; Fautin 2016.

Isocorallion hertwigi: Carlgren 1900 ; Stephenson 1922; Carlgren 1949; Fautin 1984; Rodríguez & López-González 2013; Fautin et al. 2002; Fautin 2016.

Chalmersia sp. Delage & Hérouard 1901; Stephenson 1922; Carlgren 1949; Fautin 1984; Rodríguez & López-González 2013; Fautin 2016.

STUDIED MATERIAL. MACN-IN 42226 : Two specimens . SAO, O/V “Puerto Deseado” Talud Continental expedition 38º1.913’S 53º39.268’W (St. 45), 2934 m depth ; coll. Daniel Lauretta, September 2013.

Description. External anatomy. One big and one small specimen. Oral disc circular and flat, wider than column (23–37 mm in diameter), pale pink ( Fig. 5a ); mesenterial insertions clearly visible, mesogloea much thicker than in column or pedal disc, ectoderm almost completely lost in both specimens. Mouth central, circular, to 6 mm wide, in highest part of the oral disc ( Fig. 5a ). Four cycles of non retractile tentacles plus and incomplete fifth cycle ( Fig. 5a ), mainly without ectoderm ( Fig. 6a, d ), almost all with acrospheres (most tentacles lost in small specimen). About 48 marginal tentacles and 24 discal tentacles (2:1 rate marginal: discal tentacles). Tentacles 1.5–11 mm in length. Marginal tentacles longer than discal tentacles. Up to two tentacles per endocele. Column smooth, pale pink, short, wider than taller (5–8 mm in length 21.5–35.2 mm in diameter), rather firm due to the thick mesogloea ( Fig. 6a ). Distal part of the column wider than proximal part. Pedal disc circular and flat, smaller in diameter than oral disc (17.5–30.5 mm in diameter) ( Fig. 5b ), almost entirely without ectoderm (confirm by histology sections); mesenterial insertions visible ( Fig. 5b ).

Internal anatomy. Pharynx length about 1/3 of column length. Mesogloea hyaline, much thicker than endoderm (to 550 µm in oral disc and to 90 µm in pedal disc). Mesenteries in three cycles, two perfect and one imperfect (6+6+12=24 pairs of mesenteries). Same number of mesenteries in proximal and distal part of column. All mesenteries fertile, spermatic cyst to 205 µm ( Fig. 6c, f ). No siphonoglyphs nor directives found. Retractor muscles diffuse, very weak, only visible in histological preparations ( Fig. 6c, e ). Marginal sphincter muscles and basilar muscles absent ( Fig. 6a, b ).

Cnidae. The cnidom includes spirocysts (in tentacles), holotrichs (in acrospheres, pharynx and mesenterial filaments), microbasic b -mastigophores (in acrospheres and mesenterial filaments) and microbasic p -mastigophores (in acrospheres, tentacles and mesenterial filaments) ( Fig. 7 and Table 2 ). All round microbasic p -mastigophores from tentacles and mesenterial filaments are considered contamination (see remarks).

Since both specimens were almost entirely devoid of ectoderm, and there were very few capsules in each slide made, cnidocysts from both specimens were pooled, when possible; the cnidom of the species is possibly incomplete.

Distribution and Natural History. Previous records of this species indicate that it has a wide distribution, especially in the southern hemisphere ( Fig. 1 ). It has been recorded from the South Pacific and Indian oceans, but not from the South Atlantic; record of Cm. rigidus in Argentine basin by Fautin (1984) is incorrect. The new specimens of Cm. rigidus were found in the SAO, about 350 km off Mar del Plata city (approx. 38ºS) at 2934 m depth ( Fig. 1 ). The sample was taken with a fishing net but, inferring from the sediment collected along with the specimens (mud with a few rocks), the specimens seem to live in soft bottoms, not attached to stones or any hard substratum. Previous studies of sea anemones from the area failed to recollect specimens from this species. None took samples beyond 1200 m deep, so it is possible that the species inhabits only in deeper waters at this latitude.

Remarks. Corallimorphus is a cosmopolitan genus, ranging from 30 to 4648 m ( Fautin 2011; Rodríguez & López-González 2013; Sanamyan et al. 2015). Specimens from the group have been found in all oceans, except for the Arctic and the South Atlantic Oceans. Fautin (1984) studied specimens of Cm. rigidus and Cm. profundus Moseley, 1877 from Antarctica and discussed the status of the species known at that time, stating that Cm. atlanticus was likely to be synonymous of Cm. rigidus . This view was not accepted by den Hartog et al. (1993), who identified one specimen collected in the Azores as Corallimophus. cf. atlanticus . Our specimens present some differences with the other species recorded from the Atlantic Ocean, Cm. atlanticus , which prevent us from identifying our specimen with it. Based on the description made by den Hartog et al. (1993) our specimens have a smaller relation oral disc diameter: column length (approx. 0.22 vs 0.3), the tentacles are larger (to 11 mm vs 5 mm), the discal tentacles are small but well developed (almost vestigial in Cm. atlanticus ), they are clearly arranged in three cycles and the mesogloea is thinner. Finally, all the known records of Cm. atlanticus are located in the North East Atlantic, while our records correspond to the SAO (over 8500 km apart). When describing Cm. niwa Fautin (2011) made a redefinition of the family and a revision of the genus, but Sanamyan et al. (2015) described a new species in the genus ( Cm. karinae ) and rejected the synonymization of Cm. profundus and Cm. antarcticus (both names were suggested to be synonyms by Fautin 1984). Rodríguez & López-González (2013) accepted the synonymization of both, so the status of the species is under discussion. Other species of the genus has been reported somewhat close to Argentinean waters. Corallimorphus profundus was found in the south Pacific and Antarctic deep water ( Fautin 1984). This species is characterized by having a marginal: discal tentacle ratio of about 4:1 (vs. 2: 1 in Cm. rigidus ) and longer tentacles (up to 40 mm vs. 11 mm in our specimens), which prevents us to identify our specimens with it.

We could not find the lanceolate microbasic b -mastigophores in the acrospheres (also reported as lanceolate basitrichs by Riemann-Zürneck & Iken 2003) reported for other species (e. g. Cm. profundus , Cm. rigidus , Cm. ingens Gravier, 1918 and Cm. karinae ). This cnida type is not reported for all species, but it has been suggested to have generic significance ( Riemann-Zürneck & Iken 2003). The lack of ectoderm in our specimens prevented a more detailed study of the cnidae (as in other works), so the absence of some categories may be a consequence of the low number of capsules found.

Although tentacle cnida data between both specimens agree, all the round microbasic p -mastigophores found in the tentacles and mesenterial filaments are to be treated as contamination (possibly by feeding). There was little remaining ectoderm on the tentacles of the specimens. Histological section failed to prove the presence of cnida in the ectoderm of the tentacles but revealed some free capsules inside them (especially the round microbasic p - mastigophores). The lack of ectoderm could also explain the lack of other cnida type, like lanceolate microbasic b - mastigophores. Nevertheless, there are some differences between our specimens cnida and those reported elsewhere from Cm. rigidus . Our specimens have smaller (but overlapping) holotrichs and microbasic b -mastigophores in acrospheres, holotrichs with wider size range in the pharynx and smaller (but overlapping) microbasic p -mastigophores in the mesenterial filaments (table 2).

Figures

FIGURE 1. Distribution of Corynactis carnea and Corallimorphus rigidus. Black area corresponds to the distribution of Corynactis carnea in Argentina, the black circle corresponds to the new record of Corallimorphus rigidus and the black squares correspond to previous reports of Corallimorphus rigidus worldwide.

FIGURE 5. Shape and color of a specimen of Corallimorphus rigidus directly after collection. (a) Oral view; (b) Pedal view.

FIGURE 6. Internal anatomy of Corallimorphus rigidus (a) longitudinal section, note the lack of marginal sphincter; (b) longitudinal section showing the junction between the mesenteries and the pedal disc; (c) cross section showing the mesenteries; (d) longitudinal section of a tentacle; (e) detail of mesenterial muscle (arrow); (f) spermatic cysts. T, tentacles; SC, spermatic cyst.

FIGURE 7. Cnidocysts from Corallimorphus rigidus. Holotrichs: a, e and f; microbasic b-mastigophores: b; microbasic p- mastigophores: c, d, g and h. * cnida capsule reduce 50% of its size with respect to the scale. c and g probably contamination (see text).