Psolus squamatus ( Müller, 1776 ) var. segregatus Perrier, 1905

Davey, Nicola, 2013, The Psolidae of New Zealand and some additions to the Macquarie Ridge fauna (Echinodermata: Holothuroidea: Psolidae), Memoirs of Museum Victoria 70, pp. 51-67 : 59-60

Psolus squamatus ( Müller, 1776) var. segregatus Perrier, 1905

Table 1, Figure 1, 4D–F

Psolus squamatus, Düben and Koren, 1846 (var.?).— Théel, 1886: 89–90, pl. 15-figs 1–2, pl. 6-fig. 2.

Psolus antarcticus .— Ludwig, 1894: 98 (in note) (part).

Psolus pauper Ludwig, 1894 . (Synonymy in Deichmann, 1941.)

Psolus squamatus .—H.L. Clark, 1901: 165; 1901: 491. (Synonymy in Deichmann, 1941; non- Psolus squamatus (O.F. Müller, 1776) .)

Psolus squamatus var. segregatus Perrier, 1905: 59–65 .

Psolus segregatus .— Vaney, 1906: 26–30, pl. 1-figs 14–15, pl. 2-figs 19–20.

Psolus squamatus (O.F. Müller, Koren) var. segregatus Perrier, 1905 .— Ekman, 1923: 1–59, 37 text-figs.— Ekman, 1925: 136–139, fig. 33.

Psolus squamatus (Koren) var. segregatus Perrier. — Deichmann, 1941: 147–148, pl. 30-fig. 7.

Psolus squamatus ( Koren, 1845) .— Pawson, 1969: 129 (not Psolus squamatus (O.F. Müller, 1776)) .

Psolus aff. squamatus (O.F. Müller, 1776) .— Massin and Hendrickx, 2011: 419–420.

Material examined. New Zealand, Chatham Rise : NIWA 27619 (2) Stn TAN0701/14, 43.35°S 179.58°E, 409–423 m, 31/12/2006 ; NIWA 43709 (1) Stn TAN0801/4, 43.26°S 178.05°E, 320–339 m, 28/12/2007 ; NIWA 43714 (1) Stn TAN0801/37, 44.22°S 179.1°E, 484–492 m, 03/01/2008 ; NIWA 44805 (5) Stn TAN0501/90, 43.36°S 178.53°E, 371–384 m, 14/01/2005 ; NIWA 49919 (1) Stn TAN0301/64, 43.92°S 179.7°W, 405–420 m, 10/01/2003 ; NIWA 76127 (8) Stn TAN0201/20, 43.28°S 178.27°E, 348–358 m, 01/01/2002 ; NIWA 76128 (1) Stn Z10972, 43.12°S 175.81°E, 467 m, 04/09/2001 ; NIWA 76129 (4) Stn Z10931, 43.13°S 175.83°E, 441 m, 30/10/2001 ; NIWA 76130 (4) Stn Z10929, 43.12°S 175.81°E, 467 m, 4/09/2001 ; NIWA 76131 (27) Stn Z9618, 43.36°S 178.91°E, 393 m, 04/01/1999 ; NIWA 76132 (6) Stn Z10829, 43.26°S 178.42°E, 374 m, 30/12/2000 ; NIWA 76133 (2) Stn Z10585, 43.05°S 178.29°E, 341 m, 30/12/2000 ; NIWA 76134 (1) Stn Z10583, 43.32°S 178.56°E, 398.0 m, 12/01/2001 ; NIWA 76424 (2) Stn TAN0601/10, 43.31°S 178.26°E, 324–340 m, 29/12/2005 .

Description. Follows Perrier (1905) and Ekman (1923) with additional details based on the specimens examined. Psolus species up to 61 mm long, 30 mm high, 39 mm wide. Body form oval, mid- to high-domed profile with raised oral and anal valves, higher anteriorly. Oral opening surrounded by 7–12 long, irregular, triangular to oblong oral plates or plate fragments, inconsistent in shape and number, imbricating slightly, thickly calcareous, granular surface, demarcation between body scales and oral plates variable, usually some body scales encroaching at base of oral plates. Anal opening a series of small scales continuous with dorsal and lateral scales, no distinct plates, heavily imbricating in circular formation surrounding the anus.

Dorsal and lateral scales predominantly 3–5 mm wide, a few up to 12 mm wide, but decreasing in size towards anal and oral valves and at lateral edge, macroscopically evident, scales imbricate slightly; scale margin colouration consistently light (white or cream), usually with a brown centre, variable in intensity, can appear spotty; scales with coarsely granular surface, granules loose or attached, globular, up to 310 µm wide. Sole oval, without tapering anally or orally; inner series of tube feet arranged in 1–3 rows around the outer sole perimeter, crowded, can extend midventrally posteriorly and anteriorly; outer peripheral series of smaller tube feet in a spaced, single row, close to the ventral margin; midventral series of tube feet variably present, extending anteriorly or posteriorly only, or absent completely.

Dorsal and lateral ossicles mainly large multilayered plates covered in granules, as described above; some thickened plates up to 180 µm long; rare smooth perforated plates up to 130 µm long; rare single-layered plates with secondary layering in some specimens. Ventral ossicles perforated plates ranging from simple crosses without complete perforations to some with up to 15 perforations.

Colour. Preserved. Directly into ethanol: oral, anal valves and sole white; dorsal scales centrally graduating brown to cream, white on perimeter. Frozen then ethanol: cream scales, white plates, no brown centres ( NIWA 43714, NIWA 44805).

Distribution. South America, Strait of Magellan and Argentina, 256– 274 m. Extended to New Zealand, Chatham Rise, 320– 492 m here.

Remarks. The majority of the New Zealand material fits the description above, but there is variability in the number and appearance of the ventral ossicles. The variability ranges from a complete absence of ossicles (majority of specimens) to specimens with rare broken pieces of single-layered, smooth perforated plates (0–3 perforations, NIWA 76130, NIWA 76127, NIWA 76128) and two specimens ( NIWA 43714, NIWA 44805) yielding smooth perforated plates and rare broken pieces. These plates variably have marginal projections, low knobs, and can be flat to slightly concave.

Théel (1886), Ludwig (1894), Perrier (1905) and Vaney (1906) all tried but failed to find a diagnostic difference between the North Atlantic and southern American specimens of Psolus squamatus (O.F. Müller, 1776) , but the opinion was shared that a bipolar species was unlikely, and accordingly Perrier (1905) erected the variety segregatus for the southern form. Ekman (1923) presented an exhaustive comparison of Norwegian and South American specimens and confirmed the status of the variety Psolus squamatus ( Müller, 1776) var. segregatus Perrier, 1905 . In particular Ekman (1923) recognised the significant size difference in the dorsal and lateral surface granules. Deichmann (1941) and Massin and Hendrickx (2011) accepted the status of the variety. Pawson (1969) determined specimens from Chile to be P. squamatus and did not accept the distinct species or variety status .

O’Loughlin (pers. comm.) examined specimens in the Smithsonian Institution that were identified as Psolus squamatus ( Müller, 1776) , from Norway ( USNM 8583), the West European Basin ( USNM E38321), and Alaska ( USNM 24536, USNM E27846). He concluded that there are two species represented and neither is conspecific with the Californian specimens ( USNM E17011, USNM E16931), which are in turn not conspecific with southern American specimens from the Strait of Magellan ( USNM E33632, USNM E33634, USNM E33635) and Argentina ( USNM 22201). A useful character for distinguishing between the different putative species in this complex may be the presence or absence and size of surface granules. The species most similar to P. squamatus that range in their distribution from the North Atlantic and into the Pacific along the western coast of the Americas from Alaska to Cape Horn are united by the presence of larger surface granules. Overall, the dorsal surface loose granule size, and the sole ossicle perforations and sizes are the major differences between P. squamatus and P. squamatus var. segregatus . Psolus squamatus var. segregatus sole ossicles are perforated plates that are smaller (75–110 µm) compared with those of P. squamatus (150–300 µm).

The status of both the species and the variety is undergoing an extensive systematic review (Martinez, pers. comm.). Until this is complete, our New Zealand species is designated as P. squamatus var. segregatus , but with minor reservation. The largest ossicles we found (in only two specimens) ranged from 95–140 µm long, but never reached the size documented for Psolus squamatus . Also, the size of the dorsal granules for P. squamatus var. segregatus is documented at 330–470 µm compared with 150–250 µm in P. squamatus . Our New Zealand specimen’s dorsal granules were variable in size, but the loose ones were measured as predominantly 270–350 µm, with only a few larger ones variably present (up to 500 µm). Our minor reservation is the frequent absence of ossicles in the sole in our New Zealand specimens. Deichmann (1941), when discussing the variety, notes that the ossicles often disappear with age. Ossicles were predominantly absent in large specimens, hence our decision to place these New Zealand specimens in P. squamatus var. segregatus . All these examined specimens come from similar locations and depths and are of comparable sizes.