VENUS 65 (1-2): 81-89, 2006

Report on the Present State of our Knowledge with Regard to the Chitons (Mollusca: Polyplacophora) of the Magellan Strait and Falkland Islands

Boris Sirenko* Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab.1, St. Petersburg 199034, Russia; [email protected]

Abstract: The chiton fauna of the Magellanic region is investigated based on material from various expeditions and collecting trips made between 1958 and 2003. In total, 15 species of chitons, including one probably undescribed species are recognized in this region. Among them, 14 species inhabit the Magellan Strait, Beagle Channel and Estados Island, and 11 species live near the Falkand Islands. Comparisons of these faunas reveal that the shallow water chiton fauna of the Falkland Islands is the most impoverished in the Magellan Strait. Eleven other species that were mentioned in the literature for the Magellanic region are discussed. Four brooding species were found with eggs and juveniles in their pallial grooves, and the brooding habit of Ischinochiton stramineus and Tonicia lebruni are reported for the first time.

Keywords: Magellan region, chitons, brooding species

Introduction

Investigations of chitons of the Magellanic Region started in the 18th century when the first species of this region (Plaxiphora aurata) was described (Spalowsky, 1795). Since then more than 35 articles about Magellanic chitons have been published (see bibliography in Castellanos, 1988). Twenty-three chiton species were recorded from the Magellanic region by Castellanos (1988). The present study is an attempt to estimate the real number of species inhabiting this region.

Abbreviations: UMIP – Universidad de Magallanes, Instituto de la Patagónia, Punta Arenas, Chile; USNM – United States National Museum, Smithsonian Institution, Washington, D.C., USA; ZISP – Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia.

Materials

Altogether more than 140 samples were examined for this work. They were deposited in the USNM (collected in 1962-1971), in the ZISP (1958-2003) and in the UMIP (1994-2000). The samples were collected mainly in the Magellan Strait, Isla de los Estados, Falkland Islands and vicinity, from the intertidal zone to a depth of 750 m. Photographs of living animals were taken by the author in 2000 during a field trip in the Magellan Strait. Of special value is the material collected by Russian, American, Chilean and British SCUBA divers.

*Invited paper to the special number of Venus for the 2nd International Chiton Symposium, Tsukuba 82 B. Sirenko

Results

List of species from the Magellan Strait and Falkland Islands

Order Lepidopleurida Thiele, 1910 Family Leptochitonidae Dall, 1889

Leptochiton kerguelensis Haddon, 1886

Material examined: USNM, Estados Id., 15 spec.; UMIP, Magellan Strait, 60 spec.; ZISP, Magellan Strait, 3 spec., Falkland Ids., 2 spec., largest 5.5 mm long (Magellan Strait). Depth range: From 2.5 to 115 m. Most specimens were found at depths from 10 to 40 m. (examined material) and 12-125 m (Kaas & Van Belle, 1985a). Distribution: Around the mainland of Antarctica (Weddell, Ross, Bellinshausen Sea and near Enderby land), Magellan Strait, Tierra del Fuego, Falkland Ids., South Shetland Ids., South Georgia, South Orkney Ids., Crozet and Kerguelen Ids., Gough Id. (Kaas & Van Belle, 1985a, with addition). Remarks: Examination of samples of L. kerguelensis revealed eggs and metamorphosed young between the sides of the foot and the gill rows of seven specimens that were collected at the end of March, 2000 from the Magellan Strait. This is second report of brooding of this species (see Sirenko & Schrödl, 2001).

Leptochiton medinae (Plate, 1899)

Material examined: USNM, Estados Id., 3 spec., Magellan Strait, 1 spec.; UMIP, Magellan Strait, 3 spec., largest 13 mm long (Magellan Strait). Depth range: From 8 to 360 m (examined material) and 15-30 m (Kaas & Van Belle, 1985a). Distribution: On both sides of southern South America, from Lat. 42˚ south to Cape Horn (Kaas & Van Belle, 1985a).

Leptochiton sp.

Material examined: USNM, Magellan Strait, 4 spec.; UMIP, Magellan Strait, 1 spec., largest 4.8 mm long. Depth range: From 98 to 110 m (examined material). Distribution: Magellan Strait. Remarks: This is an undescribed species. Its body length ranges from 3 to 4.8 mm. It differs from L. kerguelensis by having (1) flat wide granules in the tegmentum, (2) a longer anterior area of valve VIII, and (3) a tricuspid cap on the major lateral tooth of the radula.

Order Chitonida Thiele, 1910 Family Ischnochitonidae Dall 1889

Ischnochiton stramineus (Sowerby in Broderip & Sowerby 1832) (Fig. 1)

Material examined: USNM, Estados Id., 10 spec.; UMIP, Magellan Strait, 2 spec.; ZISP, Magellan Strait, 15 spec., Falkland Ids., 19 spec., largest 19 mm long (Magellan Strait). Depth range: From 0 to 25 m (examined material), 0-22 m (Kaas & Van Belle, 1990). Chitons of the Magellan Strait and Falkland Islands 83

1 3 4 5

2

7 8 6

10 11

9

Fig. 1. Ischnochiton stramineus, Fuerte Bulnes, Magellan Strait, body length: 9 mm. Fig. 2. Callochiton puniceus, Fuerte Bulnes, Magellan Strait, body length: 10 mm. Fig. 3. Chiton bowenii, Fuerte Bulnes, Magellan Strait, body length: 40 mm. Fig. 4. Chiton bowenii, Fuerte Bulnes, Magellan Strait, body length: 39 mm. Fig. 5. Tonicia lebruni, Fuerte Bulnes, Magellan Strait, body length: 27 mm. Fig. 6. Tonicia atrata, Fuerte Bulnes, Magellan Strait, body length: 31 mm. Fig. 7. Tonicia atrata, Fuerte Bulnes, Magellan Strait, body length: 51 mm. Fig. 8. Tonicia atrata, Fuerte Bulnes, Magellan Strait, body length: 26 mm. Fig. 9. Tonicia smithi, Fuerte Bulnes, Magellan Strait, body length: 41 mm. Fig. 10. Tonicia calbucensis, Fuerte Bulnes, Magellan Strait, body length: 28 mm. Fig. 11. Plaxiphora aurata, Coffin Island, Falkland Islands, body length: 33 mm. 84 B. Sirenko

Distribution: Along the coast of south America, from Islay, Peru, southward along the shores of Chile, Magellan Strait, Tierra del Fuego, to Tom Bay, Patagonia. It has also been reported from the offshore islands Juan Fernandez, Falkland Ids. and South Georgia (Kaas & Van Belle, 1990). Remarks: The valves of this species are often eroded. There is one example of this species from the Magellan Strait, collected on May, 20, 2000, with metamorphosed young between the sides of the foot.

Stenosemus exaratus (G. O. Sars, 1878)

Material examined: UMIP, Magellan Strait, 16 spec., largest 18 mm long. Depth range: From 78 to 360 m (examined material), 100-2580 m (Kaas & Van Belle, 1990). Distribution: Occurs from the Arctic Ocean throughout the Atlantic to the Antarctic Seas, even penetrating into the Pacific along the SW coast of Chile (Kaas & Van Belle, 1990).

Family Callochitonidae Plate, 1901

Callochiton puniceus (Couthouy MS. Gould, 1846) (Fig. 2)

Material examined: USNM, Estados Id., 15 spec., Magellan Strait, 2 spec.; UMIP, Magellan Strait, 24 spec.; ZISP, Magellan Strait, 8 spec., Falkland Ids., 14 spec., largest 24 mm long (Falkland Ids.). Depth range: Intertidal zone to 480 m (examined material), intertidal zone – 300 m (Kaas & Van Belle, 1985b). Distribution: Magellan Province, S. Chile, Magellan Strait, Tierra del Fuego, Cape Horn, Falkland Ids., S. Argentina (Kaas & Van Belle, 1985b). Remarks: The color of this species varies from white to red.

Family Chitonidae Rafinesque, 1815

Chiton bowenii (King & Broderip, 1831) (Figs. 3, 4)

Material examined: UMIP, Magellan Strait, 2 spec.; ZISP, Magellan Strait, 12 spec., largest 40 mm long. Depth range: From 2 to 33 m (examined material). Distribution: Magellan Strait, Tierra del Fuego. Remarks: This is a rather rare species. It was found in the Magellan Strait near Fuerte Bulnes (several specimens) and near Bahia Laredo (one specimen).

Tonicia lebruni de Rochebrune, 1884 (Fig. 5)

Material examined: USNM, Estados Id., 137 spec.; Magellan Strait, 1 spec.; UMIP, Magellan Strait, 9 spec.; ZISP, Magellan Strait, 88 spec., Falkland Ids., 157 spec., largest 39 mm long (Falkland Ids.). Depth range: Intertidal zone to 30 m (examined material). This species is most abundant in the intertidal zone. Distribution: Along the coast of South America from Chubut to Tierra del Fuego, Estados Id., Chitons of the Magellan Strait and Falkland Islands 85

Falkland Ids. and Dawson Id. (Castellanos, 1988, with additions). Remarks: This is the most abundant shallow water species, both in the Magellan Strait and near the Falkland Islands. It lives mainly in the intertidal zone. Examination of samples of T. lebruni revealed eggs in both pallial grooves of several specimens collected at the end of May, 2000 from the Magellan Strait.

Tonicia atrata (Sowerby, 1840) (Figs. 6-8)

Material examined: UMIP, Magellan Strait, 4 spec.; ZISP, Magellan Strait, 31 spec., Falkland Ids., 18 spec., largest 70 mm long (Falkland Ids.). Depth range: Intertidal zone (Magellan Strait) to 21 m (Falkland Ids.) (examined material). Distribution: Along the coast of southern South America from Puerto Montt, Puerto Gappler up to Tierra del Fuego, Beagle Canal, Magellan Strait, Falkland Ids. (Castellanos, 1988). Remarks: The color of the valves and girdle of this species is highly variable (see color photos).

Tonicia smithi Leloup, 1980 (Fig. 9)

Material examined: ZISP, Magellan Strait, 2 spec., Falkland Ids. 2 spec., largest 50 mm long (Falkland Ids.). Depth range: From 2 (Magellan Strait) to 21 m (Falkland Ids.) (examined material), intertidal zone (Leloup, 1980). Distribution: Pacific coast of South America from Mehuin (Chile) (Leloup, 1980) to the Magellan Strait and Falkland Ids. (examined material). Remarks: This species is very rare. Live specimens have a chestnut girdle, that quickly loses its coloration in alcohol.

Tonicia calbucensis Plate, 1898 (Fig. 10)

Material examined: USNM, Estados Id., 1 spec.; ZISP, Magellan Strait, 7 spec., Falkland Ids., 28 spec., largest 38 mm long (Falkland Ids.). Depth range: From 3 to 25 m (Falkland Ids.) and to 48 m (Estados Ids.) (examined material). Distribution: Magellan Strait, Estados and Falkland Ids. Remarks: This species was incorrectly synonymised with T. lebruni by Leloup (1956). T. calbucensis differs from T. lebruni and T. atrata by the shorter antemucronal area of valve VIII and some characters of valves, girdle and radula. The sutural laminae are white in T. calbucensis and brown in T. lebruni. Dorsal spicules are dark brown in T. lebruni and light colored in T. calbucensis. The ratio between the length of the antemucronal and postmucronal areas of the tail valves is 0.5-0.65 in T. calbucensis, 0.76-1.06 in T. lebruni, 0.71-0.81 in T. atrata and 1.07-1.09 in T. smithi

Family Mopaliidae Dall, 1889

Plaxiphora aurata (Spalowsky, 1795) (Fig. 11)

Material examined: USNM, Estados Id., 51 spec., Magellan Strait, 1 spec.; UMIP, Magellan 86 B. Sirenko

Strait, 1 spec.; ZISP, Magellan Strait, 23 spec., Falkland Ids., 32 spec., largest 86 mm long (Falkland Ids.). Depth range: Intertidal zone to 25 m (Magellan Strait, Estados Id. and Falkland Ids.). This species is most abundant in the intertidal zone. Distribution: This species was reported from such widely separated areas as the South Island of New Zealand and the Neozelanic Subantarctic Islands, Tristan and Gough Islands, the Magellan Province, up to Valparaiso on the Pacific side, to the Falkland Islands on the Atlantic side, and the adjacent Subantarctic Islands (Kaas & Van Belle, 1994). Remarks: This is the largest chiton in the studied area. The species is rather variable in the color of the valves and the sculpture of the tegmentum and there are at least 15 synonyms (see Kaas & Van Belle, 1994).

Nuttallochiton martiali (de Rochebrune, 1889)

Material examined: UMIP, Magellan Strait, 3 spec.; ZISP, Magellan Strait, 3 spec., Falkland Ids., 2 spec., largest 17 mm long (Falkland Ids.). Depth range: From 2.5 to 92 m (examined material), and 0 to 79 m (Kaas &Van Belle, 1987) Distribution: Along the coast of Argentina from Comodoro Rivadavia south to the Magellan Strait and Tierra del Fuego; also near the Falkland Islands (Kaas & Van Belle, 1987). Remarks: This is a rather rare species, which lives under stones.

Nuttallochiton hyadesi (de Rochebrune, 1889)

Material examined: USNM, South of Falkland Ids., 1 spec., near Estados Id., 1 spec.; ZISP, South of Falkland Ids., 3 spec., largest 57 mm long. Depth range: From 124 to 750 m (examined material), 20 m (Kaas & Van Belle, 1994). Distribution: This species inhabits Tierra del Fuego (lectotype), the Patagonian shelf including the Falkland Islands, Birdwood Bank and Crozet Island (examined material). Remarks: This is a rather deep-water species. N. hyadesi differs from N. mirandus (Thiele, 1906) by the different sculpture of the central areas of the valves, which are sculptured with fine longitudinal riblets in N. hyadesi, but with radial riblets in N. mirandus. N. hyadesi differs from N. martiali in that the central areas of intermediate valves are not terraced, but sculptured with thread-like longitudinal riblets. The records of Nuttallochiton mirandus from Falkland Islands (Dell, 1964) and from Birdwood Bank (Odhner, 1923) are seemingly in error. According to my data, only two species of the genus Nuttallochiton (N. martiali and N. hyadesi) occur off the Falklands and at Burdwood Bank. The latter is very similar to N. mirandus, and confusion may thus have occurred. The northernmost distributional limit of N.mirandus is South Georgia (Sirenko, personal observation).

Family Hemiarthridae Sirenko, 1997

Hemiarthrum setulosum Carpenter in Dall, 1876

Material examined: USNM, Estados Id., 31 spec.; ZISP, Magellan Strait, 2 spec., Falkland Ids., 1 spec., largest 8 mm long (Magellan Strait). Depth range: Intertidal zone to 92 m (examined material); low water to 380 m (Kaas & Van Belle, 1985a). Distribution: Between latitudes 45˚ S and 70˚ S all around the mainland of Antarctica: Patagonia, Tierra del Fuego, S. Georgia, S. Shetlands, S. Orkneys, Crozet, Kerguelen and Chitons of the Magellan Strait and Falkland Islands 87

Table 1. Distribution of chitons in different areas of the Magellan region. Species Magellan Strait Estados Islands Falkland Islands 1. Leptochiton kerguelensis + + + 2. Leptochiton medinae + + － 3. Leptochiton sp. + － － 4. Ischnochiton stramineus + + + 5. ?Ischnochiton pusio + － － 6. Stenosemus exaratus + － － 7. ?Stenosemus dorsuosus － + － 8. Callochiton puniceus + + + 9. ?Callochiton steinenii + － － 10. ?Chaetopleura brucei + － － 11. Chiton bowenii + － － 12. Tonicia lebruni + + + 13. Tonicia atrata + － + 14. Tonicia smithi + － + 15. Tonicia calbucensis + + + 16. Plaxiphora aurata + + + 17. Nuttallochiton martiali + + + 18. Nuttallochiton hyadesi － + + 19. Hemiarthrum setulosum + + + Species with “?” were absent in the studied material

Macquarie Islands (Kaas & Van Belle, 1985a). Remarks: This small, uncommon chiton lives on or under encrusting calcareous algae and among mussels.

Discussion

The chiton fauna in the Magellan Strait and Falkland Islands represented by the available material comprises 15 species, namely Leptochiton kerguelensis, L. medinae, L. sp., Ischnochiton stramineus, Stenosemus exaratus, Callochiton puniceus, Chiton bowenii, Tonicia lebruni, T. atrata, T. smithi, T. calbucens, Plaxiphora aurata, Nuttallochiton martiali, N. hyadesi and Hemiarthrum setulosum. With the exeption of Nuttallochiton hyadesi, all species inhabit the Magellan Strait, and 11 (all except Leptochiton medinae, L. sp., Stenosemus exaratus and Chiton bowenii) were found near the Falkland Islands. The shallow water chiton fauna of the Falkland Islands is slightly impoverished compared to the Magellan Strait. Several species that were previously reported to inhabit the Magellan Strait (Castellanos, 1988), were not included in the list. They are Chaetopleura isabellei (D’Orbigny, 1841), Ch. angulata (Spengler, 1797), Ch. peruviana (Lamarck, 1819), Chiton striatus Barnes, 1824 (= Ch. magnificus Deshayes, 1827), Ch. subfuscus Sowerby in Broderip & Sowerby, 1832 (= Ch. magnificus Deshayes, 1827) and Acanthopleura granulata (Gmelin, 1791). All of these are warm- water species and records from the cold waters of the Magellan Strait must be attributed to either mistakes on labels, or incorrect identifications. Regarding four more species (Lepidopleurus culliereti de Rochebrune, 1889, Ischnochiton exanthematus Dall, 1919, I. imitator (E. A. Smith, 1881), and Chaetopleura brucei Iredale in Melvill & Standen, 1912) that have been recorded from this area, I conclude that the first species 88 B. Sirenko a nomen dubium (probably Chaetopleura sp. according to Pilsbry, 1893); Ischnochiton exanthema- tus is a junior synonym of Callochiton puniceus according to Kaas & Van Belle (1987); I. imitator is a junior synonym of I. stramineus according to Kaas & Van Belle (1990) and Chaetopleura brucei is a very enigmatic species described from the South Orkney Islands (in water that is too cold for the genus Chaetopleura) and found later near Tierra del Fuego (Castellanos, 1953). The rare Callochiton steinenii (Pfeffer in von Martens & Pfeffer, 1886), Ishnochiton pusio (Sowerby in Broderip & Sowerby, 1832) and Stenosemus dorsuosus (Haddon, 1886) were not found. Moreover a species tentatively identified as Leptochiton cf. sykesi (Sowerby, 1903), which lives in the Concepcion Canal (Pacific coast of Chile) and in the Bransfield Strait (Antarctic Peninsula) might be collected in the Magellan region in future. After examination of the specimens reported here and review of previously published records, the chiton fauna of the Magellan Strait, Estados Islands and Falkland Islands is summarized in Table 1. According to the literature (Strack, 1987; Sirenko 1990, 1991; Sirenko & Schrödl, 2001), there are eight species in which the females deposit their eggs in the pallial groove and retain them there at least to the trochophore larval stage, and 26 species that brood their young in the pallial grooves through the final stage of metamorphosis including the development of fully- formed shell plates. The present study adds two additional species: Tonicia lebruni in the first group and Ischnochiton stramineus in the second group. Along with the previously known species, this makes four species of brooding chiton in the Magellan region: Hemiarthrum setulosum, Leptochiton kerguelensis, Ischnochiton stramineus and Tonicia lebruni. As a whole, the chiton fauna of the Magellan Strait and the Falkland Islands is relatively poor, which is perhaps due to the last large glaciation and the youth of the Magellan Strait, which opened only about 2000 years ago (Moore, 1975).

Acknowledgements

I would like to thank Prof. Kristian Fauchald for his kind permition to use the rich collections in the USNM, and Drs. Miroslav Harasewych, William Moser, Cheryl Bright, Marty Joynt, and Natasha Gray, who helped me during my stay in USNM in 1999. I am grateful to Drs. Erika Mutschke, Carlos Rios Cardosa, Captain Jorche Ramirez, Jacquie Parada and other members of Laboratorio de Hidrobiologia, UMIP for the help and providing me materials. I thank also Fred Clark (Falkland Islands) and Dr. Vladimir Laptikhovsky (Fishery Department, Falkland Islands) for the materials from Falkland Islands. I also thank both reviewers for a detail critical review of the manuscript and Dr. James H. McLean, Los Angeles County Museum for the linguistic corrections of the manuscript. The study was funded by grant 16 “Complex study of Antarctic biota” of the Russian Federal Program “World Ocean”.

References

Castellanos, Z. J. A 1953. Los quitones del Museo de la Ciudad Eva Perón. Notas del Museo de la Ciudad Eva Perón, Tomo 16, Zoología N 138: 173-183. Castellanos, Z. J. A. 1988. Catalogo descriptivo de la Malacofauna marina Magallánica I. Los placoforos (Mollusca-Placophora). 41 pp. La Plata Provincia de Buenos Aires Comisión de Investigaciones Científicas, La Plata. Dell, R. K. 1964. Antarctic and Subantarctic Mollusca: Amphineurea, Scaphopoda and Bivalvia. Discovery Report 33: 93-250. Kaas, P. & Van Belle, R. A. 1985a. Monograph of Living Chitons. Vol. 1 Order Neoloricata: Lepidopleurina. 240 pp. E. J. Brill/ W. Backhuys, Leiden. Kaas, P. Van Belle, R. A. 1985b. Monograph of Living Chitons. Vol. 2. Suborder Ischnochitonina: Ischnochitonidae: Shizoplacinae, Callochitoninae & Lepidochitoninae. 198 pp. E. J. Brill/ W. Backhuys, Leiden. Kaas, P. & Van Belle, R. A. 1987. Monograph of Living Chitons. Vol 3. Suborder Ischnochitonina: Ischnochitonidae: Chaetopleurinae, and Ischnochitoninae (pars). Additions to Vols. 1 and 2. 302 pp. Chitons of the Magellan Strait and Falkland Islands 89

E. J. Brill/ W. Backhuys, Leiden. Kaas, P. & Van Belle, R. A. 1990. Monograph of Living Chitons. Vol. 4. Suborder Ischnochitonina: Ischnochitonidae: Ischnochitoninae (continued). Additions to Vols. 1, 2 and 3. 298 pp. E. J. Brill/ W. Backhuys, Leiden. Kaas, P., Van Belle R. A. 1994. Monograph of Living Chitons. Vol. 4. Suborder Ischnochitonina: Ischnochitonidae: Ischnochitoninae (continued), Callistoplacinae; Mopaliidae. Additions to Volumes 1-4. 402 pp. E. J. Brill, Leiden. Leloup, E. 1980. Polyplacophores Chiliens et Brésiliens. Bulletin de l’Institut royal des sciences naturel- les de Belgique 52 (16): 1-12. Moore, D. M. 1975. The alpine flora of Tierra del Fuego. Anales del Instituto Botánico A. J. Cavanillo. 32: 419-440. Odhner, N. H. 1923. Die Chitonen. Further Zoological results of the Swedish Antarctic expedition 1901-1903 1 (3): 1-4. Pilsbry, H. A. 1893. Manual of Conchology, vol. 15, 133 pp. Academy of Natural Sciences, Philadelphia. Sirenko, B. I. & Schrödl, M. 2001. Molluscs biodiveristy and ecology. Berichte für Polarforschung 402: 85-95. Sirenko, B. I. 1990. New species of chitons of the genus Leptochiton (Mollusca, Polyplacophora) of the shelf and the slope of the Kurile Islands. Proceedings of the Zoological Institute, Leningrad 218: 96-104. (in Russian) Sirenko, B. I. 1991. New way of a direct larval development of chitons and addition to the brooding species. Proceedings of the Zoological Institute, Leningrad 228: 4-11. (in Russian) Spalowsky, J. 1795. Prodromus in Systema historicum Testaceorum. 88 pp. Strack, H. L. 1987. The Polyplacophora of Gran Canaria including a worldwide survey of the brooding species. Iberus 7: 179-187.

(Received April 14, 2004 / Accepted May 10, 2005)

マゼラン海峡とフォークランド諸島の多板類相研究の現状

B. I. シレンコ

要 約

1958 年から 2003 年までに各種探検調査等で収集された標本をもとに，マゼラン海峡とその周辺海域 の浅海性多板類相を研究した。合計 15 種の多板類が認められ，そのうち 1 種は未記載種と考えられる。 これらのうち 14 種はマゼラン海峡，ビーグル水道，エスタドス島に分布し，11 種がフォークランド諸 島に分布している。このような各地域の多板類相の比較の結果，フォークランド諸島の多板類相はマゼ ラン海峡の多板類相から構成種数が減っただけのものであることが判った。上記 15 種以外にこれまでマ ゼラン海峡から記録のあった 9 種について再検討を行ったところ，8 種は標本ラベルの間違いや誤同定 によって誤った記録，1 種が実体不明であった。また記録はないが，本海域をはさんでコンセプション 水道と南極半島ブランズフィールド海峡から報告されているサメハダヒザラガイ属の 1 種 Leptochiton cf. sykesi は今後本海域でも採集される可能性がある。 本海域に分布する種のうち 4 種に保育習性が観察された。このうち Tonicia lebruni と Ischnochiton stramineus は本研究が初めての報告となる。前者は雌が卵をトロコフォア幼生まで保育し，後者は殻板が 全て形成される時期まで保育することを記録した。