Psolidae Forbes

O’Loughlin, P. Mark & Ahearn, Cynthia, 2008, Australian species of Psolidium Ludwig (Echinodermata: Holothuroidea: Psolidae), Memoirs of Museum Victoria 65, pp. 1-22 : 1-3

Key to genera of Psolidae Forbes

1. Dorsal and lateral scales imbricating, conspicuous, lacking calcareous towers; scales of ventro-lateral body clearly demarcated from the thin calcareous sole that lacks scales 2 — Dorsal and lateral multilayered ossicles (scales) embedded in integument; some scales with conspicuous projecting calcareous towers; ventro-lateral body not clearly demarcated from sole Echinopsolus Gutt, 1990

2. Tentacles 15; oral valves 5, radially situated Ceto Gistel, 1848

— Tentacles 10; oral valves situated interradially if present 3

3. Mid-body tube feet absent dorsally and laterally Psolus Oken, 1815

— Mid-body tube feet present dorsally and laterally 4

4. Dorsal and lateral scales covered by ossicles that include hour-glass shaped and/or tower ossicles Lissothuria Verrill, 1867

— Hour-glass shaped and tower ossicles not present amongst the dorsal and lateral ossicles 5

5. Mouth and anus lie in the plane of bilateral symmetry Psolidium Ludwig, 1886

— Mouth and anus lie in a plane at right angle to the usual plane of bilateral symmetry Ekkentropelma Pawson 1971b

Psolidae Forbes

(synonymy of systematic records)

Psolidae Forbes,1841:201 –02, 206.— Agassiz,1845:11.— Agassiz, 1848: 905.

“Psoline sub-family” Bell, 1882: 642 (no family or other sub-family nominated).

Psolida (uncredited).— Haeckel, 1896: 380, 441, 442.

Psolinae R. Perrier, 1902: 493, 512 (sub-family of Cucumariidae , with Cucumariinae).

Psolidae Perrier, 1902 .— Pawson and Fell, 1965: 4.— Pawson, 1969a: 129.— Pawson, 1968b: 19.— Pawson, 1968c: 347.— Tommasi, 1969: 8.— Pawson, 1970: 28.— Pawson, 1971a: 33–34.— Pawson, 1971b: 115, 118.— Tommasi, 1971: 3–4.— Pawson and Valentine, 1981: 450.— Carriol et Féral, 1985: 50.— Gutt, 1988: 22–23.— Gutt, 1990: 112–13.— Massin, 1992a: 317.— Massin, 1992b: 179.— Lambert, 1996: 21.— Massin, 1997: 101.

Psolidae Ed. Perrier (undated).— Thandar, 2006: 35 (R. Perrier was the author of Psolinae).

Psolidae (uncredited).— Mortensen, 1927: 413.— Deichmann, 1940: 206.— Deichmann, 1941: 73, 135–36.—H. L. Clark, 1946: 385, 412–13.— Deichmann, 1947: 336: 336.— Deichmann, 1954: 401.— Hickman, 1962: 60.— Pawson, 1964: 461–62.— Pawson, 1967: 1–2.— Baranova and Belyaev, 1968: 236.— Pawson, 1968a: 142.— Pawson, 1969b: 38, maps 3, 5.— Cherbonnier, 1974: 601, 605.— Dartnall, 1980: 13, 77.— Pawson, 1982: 815.— Cannon and Silver, 1987: 10, 11, 29.—Rowe (in Rowe and Gates), 1995: 317.

Diagnosis (most recently by Lambert, 1996, quoting Pawson, 1970). Body flattened, with well-defined ventral sole. Dorsal surface of body invested by imbricating scales. Ventral sole soft, surrounded by tube feet. Mouth and anus dorsally turned.

Type genus. Psolus Oken, 1815 (original designation; = Lepidopsolus Bronn, 1860 , and Lophothuria Verrill, 1866 ; synonymy by Théel, 1886).

Other genera. Ceto Gistel, 1848 (= Cuvieria Jäger, 1833 , Callisto Gistel, 1848 , Stolinus Selenka, 1868 , Hypopsolus Bell, 1882 , and Theelia Ludwig, 1892 ; synonymy by Pawson, 1971a); Lissothuria Verrill, 1867 (= Thyonepsolus H. L. Clark, 1901 ; synonymy by Pawson, 1967); Psolidium Ludwig, 1886 ; Ekkentropelma Pawson, 1971b ; Echinopsolus Gutt, 1990 .

Remarks. The family Psolidae was erected by Forbes (1841), who based his family on the genus Psolus Oken and remarked that Cuvieria Peron (= Ceto Gistel , by Pawson, 1971a) should be included in Psolidae . The family was recognised by Agassiz (1845, 1848). Bell (1882) referred to a “Psoline sub-family”, without reference to family or additional sub-family. Perrier (1902) erected 2 sub-families for Cucumariidae : Cucumariinae and Psolinae. Subsequently no author (including Perrier himself) has referred to Psolinae Perrier, 1902. Perrier (1905), Mitsukuri (1912), and Ohshima (1915) referred species of Psolidium Ludwig, 1886 , and Psolus Oken, 1815 , to Cucumariidae , without reference to Psolidae . Mortensen (1927) referred Psolus and Psolidium species to Psolidae , without indication of family author. Many authors followed Mortensen (1927). Pawson and Fell (1965) incorrectly nominated Perrier (1902) as the systematic author of the Psolidae . Subsequent authors incorrectly referred to Psolidae Perrier, 1902 .

Within the history of holothuroid classification we note that Semper (1868) referred Psolus Oken to order II Pneumonophora, family Dendrochirotae , sub-family Dendrochirota Gastropoda. Théel (1886) referred Psolus Oken to order II Pedata, family Dendrochirotae , sub-family Gastropoda.

Forbes (1841) distinguished the family Psolidae as “having a soft circumscribed disk like the foot of a Gasteropodous Mollusc on which the suckers are placed for progression”. In his diagnosis of sub-family Psolinae, Perrier (1902) continued emphasis on the distinct sole with its specialised tube feet. Mortensen (1927) added the presence of large imbricating scales dorsally, sharply delimited from the thin-walled ventral sole; dorsal mouth and anus; and 10-15 tentacles. Subsequent diagnoses by Deichmann (1941), Hickman (1962), Pawson and Fell (1965), Tommasi (1969, 1971), Pawson (1970, 1982), Carriol et Féral (1985), Cannon and Silver (1987), Gutt (1988), Rowe (in Rowe and Gates, 1995), and Lambert (1996) have generally agreed with Mortensen (1927). But none has continued to include the significant point made by Mortensen (1927) that there is a sharp demarcation between the dorsal scales and the thin-walled sole. In discussing his new genus Psolidiella, Mortensen (1925) noted “a distinct ventral sole, which is, however, not limited from the rest of the body by a sharp edge”, one reason given by Mortensen for not referring Psolidiella to the Psolidae .

A second reason stated by Mortensen (1925) for not referring Psolidiella to the Psolidae was “the fact that the posterior part of the intestine, with its mesentery, is in the left ventral interradius”. He added “the situation of the posterior part of the intestine appears to be of primary importance for the subdivision of dendrochirotes, the cucumariids and the phyllophorids having it in the left, and the psolids having it in the right ventral interradius”.

Hickman (1962) noted contradictory observations by Deichmann (1941) who claimed that “ Cucumariidae seem typically to have the third mesentery attached on the right side of the midventral muscle band, the Phyllophoridae seem to have it attached to the left, and the Psolidae have it either way”. She explained that for Psolidium and Thyonepsolus (= Lissothuria ) the loop is attached in the left ventral interambulacrum, while in Psolus it is attached in the right.

Some cucumariid species were examined in this study: Apsolidium densum O’Loughlin and O’Hara, 1992 , Neoamphicyclus mutans ( Joshua, 1914) , Psolidiella hickmani O’Loughlin, 2000 . In these three cucumariid genera and species the posterior intestinal mesentery is attached to the left of the midventral radial muscle, supporting Mortensen (1925) and contradicting Deichmann (1941). O’Loughlin (2000) illustrated this position for the genus Psolidiella . Pawson (1968a) described a right attachment for the cucumariid species Pseudopsolus macquariensis ( Dendy, 1896) , and Ludwig and Heding (1935) reported a right attachment for their cucumariid species Pseudocholchirus mollis , supporting Deichmann (1941). This evidence indicates that the position of posterior intestinal mesenteric attachment is variable for cucumariids as currently assigned.

Some psolid species were examined in this study: Ceto cuvieria ( Gistel, 1848) , Echinopsolus acanthocola Gutt, 1990 , Psolidium poriferum ( Studer, 1876) (= incertum), Psolidium ravum Hickman, 1962 , Psolus antarcticus Philippi, 1857 , Psolus arnaudi Cherbonnier, 1974 , Psolus charcoti Vaney, 1906 , Psolus koehleri Vaney, 1914 , Psolus paradubiosus Carriol and Féral, 1985 . In eight of these psolid species the posterior intestinal mesentery is attached to the right of the midventral radial muscle, supporting Mortensen (1925) and Deichmann (1941) for Psolus species. But in Ceto cuvieria it is attached to the left. This evidence indicates that the position of posterior intestinal mesenteric attachment is variable for psolids as currently assigned.

Pawson (1967) noted difficulty with the Psolidae in determining whether or not some species should be considered psolids or referred to another dendrochirotid family. The cucumariid genera Pseudopsolus (see Pawson, 1968a), Apsolidium and Neocnus (see O’Loughlin and O’Hara, 1992), and Psolidiella (see O’Loughlin, 2000) include species with a sole that is not delimited by a distinct junction of ventro-lateral body wall scales with a thin-walled sole lacking scales, and lack conspicuous imbricating dorsal and lateral scales. None has been referred to Psolidae . We support this exclusion. The genus Echinopsolus Gutt, 1990 was referred to Psolidae on the grounds of the species having a distinct sole. We note that Psolus charcoti Vaney, 1906 and Echinopsolus acanthocola Gutt, 1990 lack a sharply demarcated sole, and lack macroscopic imbricating scales dorsally, and should not be referred to Psolidae . Reassignment of these taxa does not belong in this revision of Psolidium , and will be treated elsewhere.

A comprehensive revision of the relationships amongst cucumariid and psolid species is required and should be undertaken with supportive evidence from molecular genetic data.