Parastichopus regalis ( Cuvier, 1817 )

Khodja, Ihcene, Mezali, Karim & Thandar, Ahmed S., 2021, Multiple records and polymorphism of Parastichopus regalis (Cuvier, 1817) (Echinodermata: Holothuroidea: Stichopodidae) along the Algerian coast, Zootaxa 5032 (4), pp. 549-562 : 554-556

Parastichopus regalis ( Cuvier, 1817) spotted morph

Figures 4–5 , Table 2

Material examined. LPVCMRMS2019.305; LPVCMRMS2019.306, Mostaganem, Algeria, 36° 05.077’ N, 00° 00.490’ E, 225 m, 03 June 2019 , 2 specs. LPVCMRMS2019.307, Mostaganem, Algeria, 36° 02.611’ N, 00° 01.823’ O, 117 m, 03 June 2019, 1 spec. LPVCMRMS2019.311; LPVCMRMS2019.312, Bouzedjar , Algeria, 35° 38.068’ N, 01° 08.766’ O, 96 m, 04 June 2019 , 2 specs. LPVCMRMS2019.310, Arzew , Algeria, 35° 55.444’ N, 00° 00.490’ E, 77 m, 04 June 2019, 1 spec.

Description. Specimens ( Figures 4A and 4B ) preserved length 14–24.90 cm, contracted width 4–7.50 cm; total weight 25.07–143.50 g. Each with 5–7 brownish to dark red blotches on the bivium when alive ( Figure 4A 1 ) disappearing after storage in ethanol. Morphological characters similar to non-spotted specimens described above. Dorsal body wall 1.23–6.19 mm thick; ventral body wall 1.22–6.77 mm thick. Polian vesicle single, average length 17.57 mm; stone canal also single, average length about 10.71 mm. Calcareous ring about 13 mm in diameter. Longitudinal muscles flat, attached to body wall, about 6.75 mm in thickness ( Table 2).

Ossicles. Anal region ( Figure 5A ), dorsal ( Figure 5B ) and ventral surfaces ( Figure 5C ) present the same type of ossicles as non-spotted specimens. Table discs ( Figures 5 Aa; 5Ba; 5Ca) 97.926 µm in average diameter and 7099.090 µm ² in total area. Spire 4-pillared, about 67.521 µm high, 64.691 µm wide, with 3–4 cross-bars. Papillae and pedicels include perforated rods ( Figures 5 Ab; 5Bb; 5Cb) as in the non-spotted morph, 265.026 µm in average length. Complete pedicel end plates ( Figure 5 Cc) circular, average diameter 439.218 µm; oval end plates 197.766 µm in mean length and 84.328 µm in mean width. Cloaca ( Figure 5D ) presents dichotomously branched rods. Tentacle rods ( Figure 5E ) elongated ( Figure 5 Ea), or arched ( Figure 5 Ec), branched ( Figure 5 Eb) and dichotomously branched rods ( Figure 5 Ed).

Remarks. Both spotted and non-spotted Parastichopus regalis individuals degrade very quickly if they are not immediately preserved in ethanol, after collection. The dermis rapidly disintegrates and the texture of the body becomes gelatinous, spreading out on the support on which the specimen is placed ( Figure 4C ). This reaction is probably due to the stress during fishing operation and/or exposure to light or change in pressure and/or temperature, since fished from waters more than 36 m deep. The ability to lose a piece of dermis from the body wall when in danger has been observed in many holothuroids ( Kropp 1982).

The use of formalin, although good for fixation, does not allow for better preservation because the body does not keep its original shape and the ossicles tend to corrode rapidly. Hence, alcohol is recommended although the bright red colour of the ventral surface as well as the dark spots on the dorsal surface (when present) do disappear. The thickness of the body wall can vary from one individual to another since the general texture of the body wall is very soft, thus not rigid enough to maintain the original form.

Figures

FIGURE 1. Sampling stations of Parastichopus regalis along the Algerian coast (the numbered circles represent the sampled stations - see Table 1 for details of the stations).

FIGURE 4. Morphological characters of spotted P. regalis. A. Dorsal view, blotches indicated by arrows (1). B. Ventral view spotted individual (note no blotches). C. Degradation of the dermis after 2 hours (individual not immediately preserved in ethanol). Scale bar = 1 cm.

FIGURE 5. Ossicles of P. regalis (spotted) from different parts of the body. A. Anal region. a. Tables. b. Rods. B. Dorsal surface and papillae. a. Tables. b. Rods. C. Ventral surface and tube feet. D. Cloaca. a. Tables. b. Rods. c. End plates. E. Tentacles. a. Elongated rods. b. Branched rods. c. Arched rods. d. Dichotomously branched rods. Scale bar = 100 µm.