Ceriantheomorphe brasiliensis by original designation (Carlgren 1931).

Number of valid species: 3

Moluccas (Maluku) Islands, Indonesia, shallow waters.

Only known from shallow water at the type locality.

The original description made by Kwietniewski (1898) is very simple and based only on external characters. McMurrich (1910) obtained two specimens from the same area and conducted a more detailed anatomical study. Carlgren (1931), based on McMurrich’s description, moved the species to the newly erected genus Ceriantheomorphe. There has been no other subsequent research performed on this species. This species is commercially exploited for the international aquarium trade (exported from Indonesia), perhaps owing to its vivid orange color (S. Stampar pers. obs.).

Not found in this study.

Baía de Guanabara, Rio de Janeiro, Brazil.

Brazil (Espírito Santo (20.5°S) to Rio Grande do Sul (33.7°S) states); Uruguay (35°S), and Gulf of Mexico (dubious record, 24–29°N), shallow waters (at < 40 m depth).

This species was first described as Cerianthus brasiliensis by Mello-Leitão (1919) from Guanabara Bay, Rio de Janeiro, Brazil. This description is quite simple and based on only a few external morphological characters. Oskar Carlgren visited the Museu Nacional do Rio de Janeiro (MNRJ) at the time of description of the genus Ceriantheomorphe sometime between 1925 and 1929, but he was unable to find the type material designated by Mello-Leitão. However, the type material (MNRJ 100) of Cerianthus brasiliensis is available and, based on our examinations, every mesentery, except for the directives, is fertile. Thus, based on this, the species described by Mello-Leitão should be moved to the genus Ceriantheomorphe. Carlgren (1931) mentions that the species (with this name) as described by him in that publication may be a junior synonym of C. brasiliensis Mello-Leitão 1919, as Lopes et al. (2019) have shown. Hertwig (1882) recorded a specimen of Cerianthus americanus from the Uruguayan coast whose external shape appeared to be very similar to that of Ceriantheomorphe brasiliensis. However, that specimen was not available at the time of the present study and may be lost.

Museu Nacional do Rio de Janeiro – MNRJ 100 (Holotype).

off Port Aransas, 32 km south off Corpus Christi, Texas, United States of America.

Gulf of Mexico (Northern Mexico) to North Atlantic (North Carolina, United States of America), shallow waters.

A very large species, which for many years was considered to be synonymous with C. brasiliensis even without biogeographic justification. Recently, Lopes et al. (2019) have indicated morphological differences that support the distinction between both species. Apparently, this is a species with very low incidence, since several sampling attempts have been unsuccessful (S. Stampar pers. obs.).

Smithsonian National Museum of Natural History NMNH 50015 (holotype).

Ceriantheopsis americana by original designation (Carlgren 1912a)

Number of valid species: 4

Off Charleston, South Carolina; Beaufort, North Carolina, United States of America (not specified).

Atlantic coast of United States and Canada, Gulf of Mexico, and Caribbean Sea, at 2–250 m depth.

This species is probably the most extensively studied among the Ceriantharia. There are appropriate descriptions of specimens (McMurrich 1910; Carlgren 1912a) and there is much biological information, especially related to ecological aspects (Shepard et al. 1986; Kristensen et al. 1991; Holohan et al. 1998). One important issue that still needs be studied is the possible occurrence of this species in the deep sea. Several photographic records, especially from ROV surveys below 400 m depth are available on the internet, but, to date, no such deep specimens have been collected for study.

Museum of Comparative Zoology (Harvard) – Invertebrate Zoology 243 and SCOR-1245 and Peabody Museum of Natural History (Yale) – YPM IZ 000977.CN (syntype).

Off Cape Town, South Africa.

Only known from shallow waters at the type locality (8–15 m depth).

This species was recently described and therefore little is known about it beyond a detailed morphological description. One of the most interesting features of the species is the wide range of colors (Molodtsova et al. 2011). This species occurs in waters around Cape Town. Interestingly, this species is found close to industrialized coastal development, such as marinas and ports (S. Stampar pers. obs.), which may have provided a special habitat.

Zoological Museum of Moscow State University – ZMMU No. Ec-105 (holotype).

off Quequén, Buenos Aires, Argentina.

Warm temperate south-western Atlantic, from Argentina (Buenos Aires State) to Brazil, Laje de Santos (São Paulo State), at 5–130 m depth.

This species was recently described, and little is known beyond a detailed morphological description. Similar to Ceriantheopsis austroafricanus, this species shows considerable variation in color pattern (Stampar et al. 2015b). The deepest record of the species is 130 m from a dredging expedition (Stampar et al. 2015b). However, it is possible that the species occurs at even greater depths.

Museu de Zoologia da Universidade de São Paulo – MZUSP 2686 (Holotype).

Benguela Upwelling System, Namibia.

Only known from deep water at the type locality (145–240 m depth).

This species was recently described and has not been the subject of any study since the original description of the species by Molodtsova (2001a). Recorded only from a restricted area in Namibia, this species occurs sympatrically with two other species, Botrucnidifer shtokmani and Cerianthus malakhovi. These three species were found in the same upwelling system, which suggests that they can also occur in deeper areas.

Zoological Museum of Moscow University – ZMMU UE-97 (Holotype).

Cerianthus membranaceus (Spallanzani, 1784)

Number of valid species: 18

off Port Blair, Andaman and Nicobar Islands, India.

Only known from shallow water at the type locality.

The species description is based on three specimens from Port Blair in the Andaman Sea (Alcock 1893); it is very simple with scant information on anatomy. The only two useful pieces of published information are related to the size of the preserved specimens (up to 10 cm in length), and the number of marginal tentacles (up to 160). The specimens observed by Alcock (1893) should be placed within the family Cerianthidae, but currently it is not possible to state that this species is truly part of the genus Cerianthus, and a systematic examination of this species is needed. The material recorded by Haldar (1981) is probably not the same species since the biogeographical region is different, but owing to the absence of a detailed description no definite conclusions can be drawn.

(?) Indian Museum.

Deep sea, North Atlantic (35° 26’N 50° 53’W), at 5000 m depth.

Only known from deep water at the type locality.

This species is one of the smallest tube-dwelling anemone species known. The described specimens are only 2.5 cm long and lived in a very long membranous tube of more than 11 cm in length. The description is not detailed but provides some information on the anatomy, indicating a very long hyposulcus (especially in figure 17, Moseley 1877). Molodtsova (2001b) proposed that this species should be placed within the family Arachnactidae, however we are uncertain about this classification as some species of Cerianthidae have comparatively long hyposulcus regions, and the small size of this species may be misleading. Additionally, the description of the tube is much more consistent with the organization of Cerianthidae (see Stampar et al. 2015a). Thus, we choose to maintain this species as valid until additional studies say otherwise.

Not found in this study, but the original description provided a graphic representation.

Aburatsubo Bay, Miura, Japan.

South Japan, South Korea, Korea (East China Sea), and China (Yellow Sea), at 1–50 m depth.

There are some detailed descriptions about this species (e.g., Nakamoto 1923; Carlgren 1924). Uchida (1979) described the color variation of specimens from Japan (Kushimoto) and some ecological aspects. The same author also compared C. filiformis to other specimens described from the same area and concluded that all specimens belonged to the same species. This assumption includes the specimen from Okinose Bank, Sagami Bay (Kanagawa, Japan) described by Wassilieff as C. orientalis Verril, 1865. This specimen is deposited in the Zoologische Staatssammlung München (ZSM; 173/D65) and does not belong to the genus Cerianthus but to Ceriantheomorphe (S. Stampar pers. obs.). It is not very well preserved, but the overall organization of the mesenteries is quite consistent with that of Ceriantheomorphe ambonensis (Kwietniewski, 1898). The occurrence of Ceriantheomorphe in Japanese waters was also discussed by Molodtsova (2001b).

Lund Museum of Zoology – MZLU L930/3095b (Syntype).

North Sea (not specified).

Arctic Ocean, Norway, and Iceland, at 650–1185 m depth.

Cerianthus incertus has a complicated taxonomic history and was originally described as C. danielsseni by Levinsen (1893) based only on its external morphology. Carlgren (1896) discussed this problem and, later, Roule (1905), based on specimens from nearby locations, described a new species using the same name. However, at this point, the name C. danielsseni became a homonym and was no longer available according to the rules of the International Commission on Zoological Nomenclature (ICZN). Thus, Carlgren (1932) suggested a new name (Cerianthus incertus) to solve both situations. Molodtsova (2014) postulated that C. incertus is a junior synonym of C. vogti, but there are no data available to confirm this hypothesis. Despite discussions on the past taxonomic confusion, this species is still understudied.

Not found in this study.

Aburatsubo, Misaki (Sagami Bay), Japan.

Sagami Bay and Miyazaki, Kyushu Island, Japan; North Hamgyong Province, North Korea, at 10–100 m depth.

The original species description was based on two small specimens, one from North Korea (North Hamgyong Province) and the other one from Japan, Aburatsubo, Misaki (Sagami Bay). The description is quite adequate and presents the most important characteristics of the species. However, as noted by Molodtsova (2001b), differences between C. japonicus and C. punctatus Uchida, 1979 are very subtle. There are only two reliable characters that can be used to differentiate the two species: (1) the organization of the tentacular pseudocycles and (2) the number of mesenteries attached to the siphonoglyph. The first is a plastic character and intraspecific variation has been reported (Carlgren 1912a; Arai 1965), while the second seems to be consistent (Stampar et al. 2016). However, figure 4 by Carlgren (1924) does not allow verification if the third pair of mesenteries (P3) is in contact with the siphonoglyph or not. If the siphonoglyph format is the same as indicated by Uchida (1979), the P3 is probably also connected. Most data indicate that C. punctatus is synonymous to C. japonicus, which currently cannot be confirmed based on the available data.

Museum of Evolution- Evolutionsmuseet (Uppsala University – ZTY 2516) (Holotype).

Menai Strait, Irish Sea, United Kingdom.

North Sea, Norwegian Sea, Barents Sea, Greenland Sea, Bay of Biscay, and (?) Sea of Okhotsk; (?) depths from 2 m to the deep sea,

This species has been the subject of many studies. There have been several morphological descriptions (e.g., Gosse 1860; Carlgren 1912a; Molodtsova and Malakhov 1995a) and several aspects of its ecology and life cycle have been investigated (e.g., van Beneden 1924; Nyholm 1943; Molodtsova and Malakhov 1995b). However, two points still need further attention. The first is related to the distribution of the species, as the presence of some disjointed records in the Pacific Ocean raise the possibility of a disjunct distribution (e.g., more than one species contained in these records). However, the presence of larvae in plankton for long periods of time (Nyholm 1943) may explain the very large occurrence areas as already known for other Ceriantharia species (Stampar et al. 2015c). Braber and Borghouts (1977) reported the occurrence of this species from an estuary system (salinity around 16 psu), and Çinar et al. (2014) from the coast of Turkey, although the second record is questionable. The second point is related to the position of the species within the genus Cerianthus. Preliminary studies (unpublished) based on molecular data indicate that perhaps this species is more related to the genus Ceriantheopsis than to Cerianthus.

Not found in this study.

Close to Torra Bay and Mowe Bay, Skeleton Coast Park, Namibia; at 300–350 m depth.

Only known from deep water at the type locality.

This species has been described in detail relatively recently based on five collected specimens. The original description, in Russian, contains no information on living animals because the material examined was already fixed at the time of diagnosis. This is a species that requires attention, as it can occur in deeper waters and may contain very important evolutionary information.

Zoological Museum of Moscow University, ZMMU EC-102 (Holotype).

Al-Qusair (Red Sea), Egypt.

Only known from shallow water (at < 5 m depth) at the type locality.

This is another species with only little available data, and these are quite contradictory. This species was described as a sea anemone (order Actiniaria) by Klunzinger (1877) based only on the external morphology. Andres (1883) described some aspects of the external morphology based on work by Klunzinger (1877) and indicated that this must be a species of family Cerianthidae. Cerfontaine (1891a) argued that this species may be the same as C. oligopodus (= Arachanthus oligopodus) found in Italy, and furthermore the specimen observed by Klunzinger (1877) was not in good condition. However, it is not possible to make more statements about this species due to the absence of material available from the region. On the other hand, the indication that this species is a member of the family Arachnactidae as stated by Cerfontaine (1891a) seems to be incorrect. The few characters present in the descriptions are not consistent with those of the Arachnactidae, but instead with those of the Cerianthidae. This is a species that requires additional sampling from the type locality for further examination, especially as some specimens identified as Pachycerianthus maua Carlgren, 1900 have been subsequently collected from the same region (Krempf 1905; Fishelson 1970).

Not found in this study, but the original description provided a graphic representation.

Mediterranean Sea, Italy (not specified).

Mediterranean Sea (Italian coast), shallow waters.

This is one of the most well-known cerianthid species, but at the same time there are many questions about the taxonomic consistency of past works. This was the first species of Ceriantharia described (type locality Italy); however, this has caused many records from the Mediterranean Sea being incorrectly attributed to this species. For example, Pax (1908) argued that C. (Saccanthus) maderensis (= Isarachnanthus maderensis) Johnson, 1861 is synonym of C. membranaceus based on the two species’ original descriptions. However, the descriptions presented and discussed by Johnson (1861) and Pax (1908) are incompatible with C. membranaceus and more likely describe a species of the family Arachnactidae, perhaps a member of the genus Isarachnanthus. In addition, I. maderensis is very common in Madeira and the Azores (Stampar et al. 2012; Stampar and Morandini 2017). Haque (1977) recorded C. membranaceus from Bangladesh and Pakistan, but these records are biogeographically incongruent and probably these specimens from the Indian Ocean are another species. In short, C. membranaceus is a species that requires a comprehensive review of all its records, especially for the presence of cryptic species, and to assess if the different morphotypes reported truly belong to just one species or to a species complex.

Not found in this study.

Paniquian Island, Mindoro, Philippines.

Only known from shallow water at the type locality.

This is a very intriguing species as the two specimens described in the original description are very different in shape. The organization of the mesenteries is not coincident on both sides of the body, indicating a considerable difference in the development of mesenteries (Carlgren 1924). This sort of large variation is not commonly reported in tube-dwelling anemones. The mesentery organization and associated structures indicate a strong correlation of these specimens with the genera Cerianthus and Pachycerianthus. Thus, this species may be important in the ongoing discussion about the validity of the genus Pachycerianthus (Torelli, 1961). Unfortunately, these are the only two specimens collected from the type locality (Philippines). Other specimens examined from this area (S. Stampar pers. obs.) are not similar to the specimens described by Carlgren (1924).

Department of Zoology, University of Stockholm, Sweden (holotype) (?).

Suruga Bay (Numazu), Japan.

Only known from shallow water at the type locality.

The available information on this species is amongst the most complete from before the advent of detailed descriptions in the 2000s. Uchida (1979) gives a complete comparison of several characters with most species of the genus Cerianthus. However, besides morphological data there is still no other information about this species (e.g., reproduction).

Saibura Marine Park Research Station (lost?), but the original description provided a graphic representation.

close to Svalbard, Norway, Greenland Sea.

Svalbard, Norway, Greenland Sea; depth unknown.

This species has a very deficient description and is represented by very few museum specimens for comparison. The description of C. lloydii by Roule (1905) (see synonymy list) may fit a range of species (e.g., Cerianthus lloydii, Ceriantheopsis americana) and thus it is not possible to discuss it based on these data. The type locality is difficult to reach, and it may be very problematic to obtain additional specimens due to the absence of precise locality data and because material is likely to be from great depths up to 5000 m (Ritzmann et al. 2004). Therefore, the validity of this species remains uncertain.

Not found in this study.

Port Lloyd, Bonin Islands (Ogasawara Islands), Japan.

Only known from shallow water (18 m depth) at the type locality.

Based on the description by Verrill (1868), this species probably belongs to the family Arachnactidae, particularly due to the description of a soft tube (see Stampar et al. 2015b). The few external characters presented are only consistent with those of the family Arachnactidae. Unfortunately, there are no specimens from the Ogasawara Islands deposited in museums, and further discussions on this point depends on finding some material that can be correlated with the type material or else new collections for the designation of a neotype.

Not found in this study.

Raha, Ambon, Moluccas, Indonesia.

Only known from shallow water at the type locality.

This species was described by Kwietniewski (1898) based on a 4 cm long and 2.5 cm wide specimen with 90 tentacles in each tentacle series (marginal and labial) and three cycles each. However, these are the only characteristics indicated. McMurrich (1910a) gave a description of a specimen collected from near the type locality. However, the description is incomplete and presents some differences compared to original description. Thus, currently, we cannot confirm if this species is valid or not.

Not found in this study.

Makassar Strait, Central Sulawesi, Indonesia.

Only known from deep water (at 724 m depth) at the type locality.

This species was described based on only one damaged specimen, which was 6 cm long, with 55 marginal and labial tentacles arranged in two and four cycles, respectively. The organization of the mesenteries was not described in detail by McMurrich (1910), who simply indicated the alternation of fertile and sterile mesenteries. There are several observations of different morphotypes that are not formally associated with any other name described from this or related areas. As there are no other species described for this region with this morphotype, it is probably a valid species, but it is not possible to certainly state that this species belongs to Cerianthus.

Possibly lost (Zoological Museum of Amsterdam, now Naturalis Biodiversity Center, Leiden).

Between Keeling and south Sumatra, Indian Ocean.

Only known from deep water (at 5000 m depth) at the type locality.

This species was initially described in a table by Carlgren (1912a). However, the same author redescribed this species in 1923 in more detail. This is a species from the deep sea; however, the detailed description allows confirmation that this species belongs to Cerianthus. This is another example of a species that needs further study, as it may present very different characters compared to species from shallow waters.

Not found in this study.

Cedros Island, Mexico (Pacific coast).

Only known from shallow to deep water (at 80 m depth) at the type locality.

This is a doubtful species, as the original description is very incomplete, and some characters are incongruent. Torrey and Kleeberger (1909) comment that Cerianthus vas is a very problematic species, but they did not discuss the problems in detail. This species may actually be valid, but due to the absence of materials from the same depth and location, it is not possible to further discuss this.

Not found in this study, but the original description provided a graphic representation.

Norwegian Sea (not specified).

Only known from deep water (at 900–1400 m depth) at the type locality.

This species is well known, even though it is a species from deeper areas. The description by Danielssen (1890) is incomplete as it presents few characters related to the organization of the mesenteries. Nevertheless, it is quite detailed in various other aspects. Carlgren (1912a) presents a slightly more complete description with more comprehensive information on the organization of the mesenteries and a comparison with C. lloydii. Jensen (1992) presents environmental and biological data about the species, especially on the occurrence of branching and fairly long tubes (tube system).

Not found in this study.

Pachycerianthus multiplicatus Carlgren, 1912a (proposed by Kelly and Keegan 2000)

Number of valid species: 16

Mission Bay, East Pacific, California, United States of America.

East Pacific, California, USA, shallow waters.

This species was described by Torrey and Kleeburger (1909) based on specimens obtained from Mission Bay, California. This description is not very detailed but relevant information about its morphology is available. Child (1908) described some information on the movements and regeneration of P. (Cerianthus) aestuarii and morphological adaptations in relation to the environment. Carlgren (1912a) moved the species to genus Pachycerianthus based on the original description. Arai (1965) described a new species of the same genus, P. torreyi, from a nearby area and claimed that this was not the same species as described by Torrey and Kleeburger (1909). This species was considered a synonym of P. fimbriatus by Arai (1971), which occurs in the same area as P. aestuarii.

Not found in this study, but the original description provided a graphic representation.

Georges Bank, Massachusetts, United States/Nova Scotia, Canada (not specified).

Northwestern Atlantic (Arctic Sea to North Carolina, USA), at depths of 10–500 m.

Remarks. This species was described by Verrill (1873b) based on external morphology but he did not give many details. Danielssen (1888) gave a very detailed description, including various characters concerning the internal anatomy. A century later, Shepard et al. (1986) presented a study on ecological aspects of tube-dwelling anemones from the Northwest Atlantic and included some information about Pachycerianthus (Cerianthus) borealis. Molodtsova (2001b), in her discussion of the genus Cerianthus, showed that Cerianthus borealis should be part of the genus Pachycerianthus. This species occurs at lower temperatures and apparently resists considerable variations in salinity (S. Stampar pers. obs.).

Peabody Museum of Natural History (Yale – YPM 9830, 9831, 9832 (Syntype).

Curaçao, Dutch Caribbean.

Caribbean Sea (Curaçao), at 65–75 m depth.

This species was described by den Hartog (1977) based on specimens from Curaçao. The description of this species is fairly detailed and includes a wide range of biological and morphological information. This is the only species of this genus in the Caribbean Sea and it shows no morphological similarity to congeners described from the Pacific Ocean. On the other hand, this species shares some characters with P. schlenzae, which was described from the South Atlantic (Stampar et al. 2014b). Thus, the evolutionary correlation of these two species is of biogeographical relevance.

Naturalis Biodiversity Center (former Rijksmuseum van Natuurlijke Historie, Leiden – RMNH.COEL.11359 (holotype).

off Port Jackson, Sydney harbor, Australia.

Sydney harbor, Australia, at 5–15 m depth.

This is one of two species of this genus described from Australia by Carter (1995), the other one being P. longistriathus. They co-occur in the same bay and therefore doubts about the consistency of the two taxonomic species still exist. The morphological differences between the two species appear consistent, but intraspecific variation is quite significant and thus a more thorough evaluation of the morphological characters and the inclusion of molecular data may change this view.

Australian Museum; AMG15399 (holotype).

Naples, Tyrrhenian Sea, Italy.

Tyrrhenian Sea, Italy and Aegean Sea, Greece, shallow waters.

This species was initially described from the Italian coast (Naples region) as a variation of Cerianthus membranaceus (Andres 1881). However, Lo Bianco (1909) recognized distinct differences from the material identified as C. membranaceus and suggested a new name, Cerianthus dohrni, but without giving a description. Subsequently, van Beneden (1924) gave a very detailed morphological description of the species with some observations from specimens in aquaria. Some years later, Torelli (1932) described Cerianthus viridis based on specimens with a morphology clearly related to that of Cerianthus dohrni. Carlgren (1940) relocated C. dohrni to the genus Pachycerianthus. This is one of the largest species of tube-dwelling anemones in the world with a length of more than 40 cm, which is comparable to the lengths of Ceriantheomorphe brasiliensis and Cerianthus membranaceus.

Not designated (several specimens mentioned, which can be considered syntypes).

Cebu, Philippines.

Sulu Sea and Celebes Sea, Philippines, and Indonesia, (?) Pacific Coast of US and Canada; shallow waters.

This species forms part of a taxonomic problem. The description of P. fimbriatus was based on a study of 15 specimens collected mainly from the Celebes Sea, Philippines, by McMurrich (1910). In the same study, McMurrich argued that Cerianthus elongatus was the same as the new species P. fimbriatus, and considered Kwietniewski’s (1898) description as incomplete and invalid. McMurrich (1910) also argued that Cerianthus nobilis described by Haddon and Shackleton (1893), based on specimens from North Australia, could also be the same species, but specimens were not available for comparison. Later, Arai (1965) described a new species from the Pacific Coast of North America, P. torreyi. The same author in 1971 recognized that this species was highly correlated with McMurrich’s P. fimbriatus from the Celebes Sea. Thus, Arai (1971) considered P. torreyi to be a junior synonym of P. fimbriatus. However, the geographical distribution is disjunct by 14,000 km, and it is likely that a more detailed study with the inclusion of molecular data will present different results. In our opinion, P. torreyi should be a valid species.

The provenance data of a specimen in the Natural History Museum at London, NHMUK 1889.11.25.64, is coherent with the locality and dates in the original description, but it is impossible to make an exact connection between the materials.

El Mogote, Baja California, Mexico.

Gulf of California, Mexico; shallow waters.

Although this species occurs in an area with a long history of marine research, it is still little known, and the only study focused on this species is the original description by Carlgren (1951). The species description is based only on one individual and therefore knowledge is quite limited and morphological variation is not known to date. Thus, this species still lacks taxonomic confirmation as well as other studies.

Smithsonian National Museum of Natural History – USNM 49454 (Holotype).

Los Angeles, East Pacific, United States of America.

Only known from shallow water at the type locality.

This is another species described from the United States’ Pacific Coast by Torrey and Kleeburger (1909) with a relatively good amount of detail; like P. insignis, there have been no more subsequent detailed or comparative studies. Arai (1971) has been the only author that has mentioned the morphological characters of this species after the original description, but even this characterization was based on the characters listed in the original description. The taxonomic status of this species is doubtful.

Not found in this study, but the original description provided a graphic representation.

off Port Jackson, Sydney harbor, Australia.

Sydney Harbor, Australia; 5–10 m depth.

As mentioned for P. delwynae, the taxonomic status between the two Australian species, P. delwynae and P. longistriatus, is not clear. Both were described from a very restricted area and the morphological variation between them is very subtle. There is a need for a more detailed study approach to understand the differences between these two currently valid species.

Australian Museum – AM G15402 (Holotype).

south of Jogashima, Sagami Bay, Miura, Kanagawa, Japan (at 1100 m depth).

Japan and China, shallow to deep waters.

The description of Cerianthus magnus by Nakamoto (1919) is quite adequate, but still very simple. Nevertheless, the author presented a scheme of the mesenteries, and two photos of preserved and dissected material, which allows an adequate comparison with other species. Uchida (1979) moved this species to the genus Pachycerianthus and performed a very detailed redescription of the species based on specimens from Sagami Bay, Japan. This species occurs in an area with several other species of Ceriantharia but is apparently consistent with regard to its taxonomy. The co-occurrence of these species in Sagami Bay may be relevant in an evolutionary context with a focus on environmental niche differentiation among Ceriantharia species.

Not found in this study, but the original description provided a graphic representation.

Mkokotoni, Zanzibar, Tanzania.

Indian Ocean (Mozambique, Madagascar, and Tanzania) and Aden Gulf (Djibouti) and Red Sea (Egypt and Saudi Arabia), shallow waters.

This species was described by Carlgren (1900), who subsequently moved this species to the genus Pachycerianthus and added some comments on its morphology (Carlgren 1912b). Krempf (1905) recorded two specimens from Djibouti, but he did not study anatomical characteristics. Much later, Fishelson (1970) recorded a great number of specimens from Eilat, Israel. However, again, the author failed to mention any anatomical characters of the specimens, and the figure of the presented specimen is quite inconsistent with the description of Carlgren (1900) or with specimens analyzed from Mozambique (S. Stampar pers. obs.). Thus, the identification of the Red Sea specimens may be misleading, and these Red Sea specimens could be classified either as another species already known to the region (perhaps Cerianthus medusula) or as an undescribed species.

Not found in this study, but the original description provided a graphic representation.

Ambon, Maluku, Indonesia.

Only known from shallow water at the type locality.

This species was described by McMurrich (1910) based on two specimens from Ambon Island, Indonesia. The information presented by the author is quite suitable for characterization of the species, especially as the mesentery organization is quite conspicuous. No further relevant information on this species is available to date.

Not found in this study, but the original description provided a graphic representation.

Two areas are mentioned – Kattegat Strait and Trondheim, Norway (not specified)

North, Inner, Celtic, Irish and Norwegian Seas, Gulf of Biscay, at < 130 m depth.

Remarks. Levinsen (1893) described this species as Cerianthus danielssen, however, this description was incomplete and did not meet the minimum characterization requirements for a cerianthid species. Thus, Carlgren (1912a) proposed the new name P. multiplicatus, while giving a detailed description of this species. Carlgren (1912b) included several records in the region as well as some biological aspects. Nyholm (1943) gave a detailed study of the life cycle of the species, including information on reproductive seasons and also on larval development (a modified planula). This is a very interesting species for ecological studies, as several reports have mentioned clusters of individuals in different regions (e.g., Jonsson et al. 2001). There is still doubt about the true distribution of the species as individuals recorded from the coast of France and Spain have never been studied in detail.

(?) Lund Museum of Zoology (MZLU) - 6570 (syntype), but not formally designated in description.

Thursday Island, Queensland, Australia.

Queensland and Northern Territory, Australia, New Caledonia, shallow waters.

A large species originally described from northeastern Australia as Cerianthus nobilis. This description is very simple and was based only on external characters and there have been no further studies based on specimens from this area. Molodtsova (2000, 2007) correctly suggest that this species does not belong to the genus Cerianthus, but to the genus Pachycerianthus. The relation with two species described by Carter (1995) (P. delwynae and P. longistriatus) is completely unknown, however, there is the possibility that all three species are, in fact, a single one, based on their overlapping morphological characters.

Museum of Zoology (University of Cambridge) – I.33575.A-B (holotype).

off Guarapari, Espírito Santo state, Brazil.

Brazil, from Bahia to Espírito Santo states (Abrolhos Bank and Royal Charlotte Bank), at 5–10 m depth.

This species was recently described based on a study of several specimens from the central area of the Brazilian coast, where it is an endemic occurring along a coastline of approximately 500 km length. Some aspects of external morphology are similar to those of P. curacaoensis and may reflect a correlated evolutionary history between the two species. Although Stampar et al. (2014b) presented some biological information mainly related to the reproduction seasons, little is known about the ecology and biology of this species. The species is endangered as its range suffers from high levels of anthropogenic pressure (Miranda and Marques, 2016), which could result in the loss of its habitat.

Museu de Zoologia, Universidade de São Paulo (MZSP) – 1949 (Holotype).

off Languedoc coast, France.

Mediterranean Sea, Azores, and (?) Black Sea; shallow waters.

After Cerianthus membranaceus, this was the second species to be formally described in Ceriantharia. It was first described as an unclassified polyp with some similarities with Hydrozoa and Anthozoa (Rapp 1829a). Later, it was only characterized as a Ceriantharia by Sars (1857). This species was widely studied by Child (1903a, 1903b, 1904a, 1904b) in a series of experimental studies related to asexual reproduction, behavior, and regeneration of polyps. Carlgren (1912b) presented a detailed redescription of this species and moved it to the genus Pachycerianthus. He described several abnormalities of the species’ anatomy (Carlgren 1912a), which were attributed to asexual reproduction events that are uncommon in Ceriantharia. After this, several authors reported this species from various regions, including the Black Sea (Kiseleva 1975). If P. solitarius occurs in the Black Sea, it would show a great tolerance to brackish water. Therefore, specimens recorded in the Black Sea may not be of the same species that inhabits the Mediterranean Sea. However, there are no available specimens for comparison. Wirtz et al. (2003) recorded this species in the Azores, however a more detailed study is needed to understand if this species occurs outside the Mediterranean Sea, or whether the Azores specimens belong to P. solitarius.

Not found in this study.

Family Botrucnidiferidae Carlgren, 1912

Number of valid taxa: two genera and four species.

Botruanthus benedeni (Torrey & Kleeberger, 1909)

Number of valid species: 2

San Diego Bay, California, United States of America.

California (United States of America), Baja California (Mexico) and Galapagos Islands (Ecuador), shallow waters.

This species was described based on a study of a single specimen. This species (and genus) is characterized by possessing wart-like structures (cnidorages) organized in bunches (botrucnids) in the mesenterial filaments. Except for these structures, the anatomy is very similar to species of the genus Pachycerianthus. The holotype is not available, and we therefore here designate a neotype collected from the same region by Charles Cutress in 1955 (NMNH 49400). This specimen was studied by Stampar et al. (2017) (erroneously referred to as “holotype”) and its characters are consistent with those in the original description. Because of its importance as type species of the genus Botruanthus, the neotype designation for this species is justified. This is a poorly studied genus and there is no biological or ecological information about this species.

Smithsonian National Museum of Natural History (USNM) – 49400 (neotype).

off Veracruz, Mexico.

Gulf of Mexico, intertidal to shallow waters.

This species was recently described by specimens from the intertidal zone in reefs of Central Mexico in the Gulf of Mexico. Morphological characterization is quite easy, as the number of anatomical characters allow its distinction in relation to B. benedeni. There have been no studies on ecological or biological aspects of this species.

Museu de Zoologia da Universidade de São Paulo; MZUSP 002757 (Holotype).

Botrucnidifer norvegicus Carlgren, 1912

Number of valid species: two

Trondheimfjord, Trondheim, Norway.

Norwegian Sea, at 50–700 m depth.

This species was described by Carlgren (1912a) based on specimens from Trondheim Fjord, Norway. These are small ceriantharians (up to 4 cm long) with an expansion of the cnidoglandular tract and some botrucnidae (= cnidoragae) at the end of some mesenteries. Although the description is fairly comprehensive, knowledge of this species is limited. Other authors cite only some of the species characteristics or have reported occurrences in areas that look similar (e.g., Molodtsova 2004a). Recently, Ceriello et al. (2019) reported on the coloniality of this species, which is a newly discovered trait among Ceriantharia. This species is important in the discussion on the homology of morphological characters, particularly in relation to mesenterial structures.

Lund Museum of Zoology (MZLU) – L898/3051 and Marine invertebrate collection Norwegian University of Science and Technology University Museum (NTNU) – 40499 (syntype).

off Namibia coast (southeast Atlantic), at 130–350 m depth.

Only known from deep water at the type locality.

This species was described based on dredged specimens from off the Namibian coast. This is the second species of this genus that has been sampled beyond conventional SCUBA diving depths. The description of this species (in Russian) is very detailed and addresses all the necessary characters. As discussed by Molodtsova (2001c) some larval forms of this family are recognized from this area, however the link between larval and adult stages is only possible based on molecular or developmental approaches (Nyholm 1943; Stampar et al. 2015c).

Zoological Museum of Moscow University – ZMMU EC-100 (holotype).

Order Penicillaria den Hartog, 1977

Number of valid taxa: one family, two genera, and nine species

Family Arachnactidae McMurrich, 1910

Number of valid taxa: two genera, and nine species

Arachnanthus oligopodus (Cerfontaine, 1891)

Number of valid species: Five

Low Isles, Queensland, Australia.

Queensland, Australia, shallow waters.

Carlgren (1937) described this species from northeastern Australia and this is the only study so far on this species. Although the description is adequate, it does not include detailed information. In general, the Australian coast is vastly understudied regarding Ceriantharia species diversity. The taxonomic status of A. australiae in relation to Arachnanthus bockii remains to be studied in detail.

Natural History Museum (London); NHMUK – 1954.6.25.47 (holotype).

Viti Levu, Fiji.

Only known from shallow water at the type locality.

This is another species with little information, except for the morphological description. There are some characters in Carlgren’s (1924) description that allows distinction of this species in comparison to Arachnanthus australiae, however, the reduced number of specimens may be a problem to understand the intraspecific variation of these characters.

Not found in this study, but the original description provided a graphic representation.

Italian Coast, Mediterranean Sea (not specified in detail).

Mediterranean Sea, shallow waters and caves.

Arachnanthus oligopodus was initially described as a species of the genus Cerianthus by Cerfontaine (1891a), and was moved to the genus Arachnanthus by Carlgren (1912b). This is a very common species in several areas of the Mediterranean Sea, especially on the Italian Coast (Carlgren 1924; Torelli 1961). This species has a number of descriptions with appropriate levels of detail (e.g., Cerfontaine 1909; Carlgren 1912a). However, knowledge of the species is still incipient. Biological aspects, especially on the life cycle, are still quite unknown.

Not found in this study.

island near Jaz’air Sila, Saudi Arabia.

Red Sea, shallow waters.

This species was recently described from shallow Saudi Arabian waters of the Red Sea. Morphological characterization was based on internal anatomy and there have been no studies on ecological or biological aspects of this species yet.

Florida Museum of Natural History – FLMNH UF9168 (holotype).

Röberg Indalbay, Trondheim, Norway.

North Sea, at 10–200 m depth.

This species is rather common in some areas of Great Britain and Scotland and there are two detailed descriptions; the original (Carlgren 1912b) and a redescription (Picton and Manuel 1985). The life cycle has been inferred from the occurrence of larvae named as Arachnactis albida (Picton and Manuel 1985), but further study is needed to understand the relationship in detail. Not much is known about ecological aspects of this species and this should be a very interesting field of study.

Swedish Museum of Natural History (Naturhistoriska riksmuseet) – NRM 134778 (Holotype).

Isarachnanthus maderensis (Johnson, 1861)

Number of valid species: 4

Neira, Banda Island, Indonesia.

Indonesia, French Polynesia, and Hawaii (USA), shallow waters.

This species was described based on two specimens from the Banda Islands, Indonesia. The diagram of mesenteries, part of cnidome, and tentacle organization are present in the original description, however, there are some evident similarities in relation to Isarachnanthus panamensis. Furthermore, unpublished molecular data indicate similarity between these two species and studies on this clade should be prioritized.

Zoological Museum of Amsterdam (now Naturalis Biodiversity Center, Leiden) – (ZMA.COEL.000209 – Lectotype/ ZMA.COEL.000210 – Paralectotype).

Madeira Island, Portugal.

Madeira Island (Portugal), Ascension Island, Rocas Atoll (Brazil), Caribbean Sea, (?) Mediterranean Sea; at 2–30 m depth.

This species was described by Johnson (1861) from Madeira Island. However, the first detailed morphological characterization was presented by Brito (1986) (as I. cruzi). The delimitation of this species is quite complicated, as according to Stampar et al. (2012) only molecular data or morphometric data of the cnidome can be used to compare to other species of the genus. The distribution of this species is quite wide, from oceanic islands of the South Atlantic to the Caribbean Sea and the Mediterranean Sea (Stampar and Morandini 2017).

Not found in this study.

Piscadera Bay, Curaçao, Dutch Caribbean.

Caribbean Sea, South Atlantic (Argentina; Brazil), at 1–20 m depth.

This species was described by den Hartog (1977) based on specimens from Curaçao. The specific epithet is related to the nocturnal behavior of this species. This is the most studied species of the genus, as the larval development has been described and the taxonomy has been reviewed with molecular data (Stampar et al. 2012, 2015c). Molodtsova (2003) argued that this species is only a synonym of Isarachnanthus maderensis, however, based on molecular and micrometric data (Stampar et al. 2012) it has been shown that these two species are distinct.

Naturalis Biodiversity Center, Leiden (former Rijksmuseum van Natuurlijke Historie) – RMNH.COEL.11364 (Holotype).

Taboga, Panama (Pacific coast).

Only known from shallow water at the type locality

This species was described from the Panama coast based on three specimens. The description is also detailed, including two mesentery diagrams. Thus, variation in mesenterial organization is quite evident, especially in relation to the size of directive mesenteries. As discussed above, regarding Isarachnanthus bandanensis, these two species are very similar in terms of both morphological and molecular data and further studies are needed.

Zoological Museum of Amsterdam (now Naturalis Biodiversity Center, Leiden) – ZMA.COEL .000211) (holotype).