Sea Cucumbers (Holothuroidea) are a class of Echinoderms that have
become elongated and worm-like, effectively becoming secondarily
bilaterally symmetrical. Like all Echinoderms they have a calcareous
exoskeleton, but this is greatly reduced, typically only occurring as
ossicles within the epidermis. The muscle structure of Sea Cucumbers is
instead supported by a layer of modified collegen that can be stiffened
or relaxed at will, allowing for a more flexible body than that of other
Echinoderms. The Holothuroidea fauna from the Brazilian coast is still poorly know, but efforts over the last 18 years have improved our knowledge of the Hlothuroid biodiversity.
In a paper published in the journal Zoological Studies on 4 February 2020, Luciana Martins and Marcos Tavares of the Museu de Zoologia at the Universidade de São Paulo, describe two new species of the Holothuroid genus Psolidium from São Paulo and Rio Grande do Sul. This is the first record of the genus from the Brazilian coast.
The first new species is named Psolidium lonchostinum, where 'lonchostinum' is formed by the combination of two Greek words, lonche (spear) and ostinos (bony, Latinized to ostinum), and refers to the thorn-shaped ossicles (branched rods) found in the sole. The species is described from sixteen specimens collected with the aid of a Van Veen grab and a rectangular dredge from infaunal assemblages off the coast of São Paulo.
(A)–(F) Psolidium lonchostinum. (A)–(D) Holotype (MZUSP 744). (A) upper view; (B) detail of dorsal tube feet (black arrow); (C) detail of lateral scales (white arrow); (D) ventral view; detail of ambulacral feet (note the inner and outer rows of tube feet: black and white circles, respectively); (E) paratype (MZUSP 591) detail of ventral tube feet (black arrow); (F) outline of the calcareous ring. Abbreviations: R, radial plate; IR, interradial plate. Note in (F) interradial plate entire and radial plate notched. Scale bars: (A) 4 mm; (D) 2 mm; (E) 3 mm; (F) 500 μm. Martins & Tavares (2020).
The body of Psolidium lonchostinum is flat, oval in outline, 6–8.3 mm long and 4–5.9 mm wide. The mouth and anus covered by a variable number of small and irregular scales (0.8–1 mm wide), up to two tube feet penetrate each scale dorsally and laterally. The species lacks oral and anal valves.
The marginal dorsolateral scales are 0.1–0.3 mm, smaller than the dorsal scales.The species has a thin sole, lacking scales, tube feet arranged in a double series: inner series of large tube feet and outer peripheral series of smaller tube feet close to the ventral margin, which lacks mid-ventral (sole) radial series of tube feet, except for a cluster (up to 5) posteriorly and anteriorly. The calcareous ring is simple, lacking posterior processes; radial and interradial plates united only at the base, notched only at the radial plate.
Dorsal/lateral ossicles are smooth and perforated plates, irregular in outline, with undulating margins (100–120 μm long) and round holes (5–20 μm in diameter) and branched rods (thorn ossicles) (40–60 μm long). Dorsal tube feet with perforated rods (70–130 μm long), with undulating in margins.
(A)–(F) Psolidium lonchostinum, holotype (MZUSP 744). Scanning electron microscope photomicrographs of the ossicles. (A) scale from dorsal body wall, showing canals for tube feet (white arrow); (B) smooth plate from dorsal body; (C) branched rods (thorn ossicle) (black arrow); (D) rod from dorsal tube feet; (E)–(F) knobbed plates from sole. Scale bars: (A)–(B) 50 μm; (C) 40 μm; (D)–(F) 50 μm. Martins & Tavares (2020).
The sole of Psolidium lonchostinum is covered with single-layered and elongated plates (130–150 μm long), perforated at their entire length and knobbed at center and margins, and smooth plates slightly knobbed in the margin (70–100 μm long). Ventral tube feet with perforated rods with irregular, curved and undulating margins (80–160 μm long) and an end-plate.
(A)–(F) Psolidium lonchostinum, holotype (MZUSP 744). Scanning electron microscope photomicrographs of the ossicles. (A) four-holed smooth plate from sole, ventral view; (B) four-holed smooth plate from sole, dorsal view; (C)–(D) multiperforated smooth plate from sole, dorsal view; (E) four-holed smooth plate from sole, lateral view; (F) rod from ventral tube feet, dorsal view. Scale bars: (A)–(B) 30 μm; (C) 40 μm; (D)–(E) 50 μm; (F) 80 μm. Martins & Tavares (2020).
The second species is named Psolidium nanoplax, where 'nanoplax' is formed by the Greek words, nano (little) and plax (plate), in reference to the reduced length of the sole plates. The species is described from two specimens collected from the offshore part of the Campos Basin of southeastern Brazil, with the aid of an ELOS dredge.
(A)–(F) Psolidium nanoplax (MZUSP 589, 592). (A) Lateral view of holotype preserved in ethanol (note anal cone in white arrow); (B) upper view of paratype-MZUSP 592 preserved in ethanol (note mouth and anus in black and red arrows, respectively); (C) detail of anal cone holotype-MZUSP 592 (note anal cone and papillae, in white and red arrows, respectively); (D) detail of dorsal tube feet holotype-MZUSP 592 (red arrow); (E) detail of lateral scales paratype-MZUSP 592; (F) ventral view detail of ambulacral feet paratype-MZUSP 592, (note the inner and outer rows of tube feet: black and white arrows, respectively); (G) calcareous ring (H) detail of retractor muscle (white arrow) and (I) outline of the calcareous ring paratype-MZUSP 592. Abbreviations: R, radial plate; IR, interradial plate. Note, only radial plate notched. Scale bars: (A) 5 mm; (B) 4 mm; (C) 500 μm, (D) 500 μm, (E) 0.5 mm; (F) 2 mm; (G)–(I) 500 μm. Martins & Tavares (2020).
The body of the first of the specimens was elongate, reaching 11 mm, the smaller was ventrally and dorsally flattened and measured 8 mm. Ths mouth and anus lack valves, the anal cone is slightly raised. The dorsal and lateral body are covered with conspicuous imbricating scales (0.8–1 mm) and without granules or tubercles at the surface. One inconspicuous tube foot is present at each scale. The marginal dorsolateral scales smaller than dorsal scales (0.1–0.3 mm). Ventral sole lacking scales, tube feet arranged in a double series: inner series of large tube feet and outer peripheral series of smaller tube feet close to ventral margin, mid-ventral tube feet absent. Calcareous ring simple, lacking posterior processes, radial and interradial plates united only at the base; radial plate notched.
The dorso-lateral ossicles are knobbed and multiperforated single plates, flat, oval in outline, heavily knobbed on one side, smooth on the other surface, knobbed edges (150–170 μm long) and rounded holes 10–20 μm in diameter.
(A)–(I) Psolidium nanoplax (MZUSP 589). Scanning electron microscope photomicrographs of the ossicles. (A) knobbed plate from dorsal body (B) supporting rod from dorsal tube feet; (C) 'cup-like' plates from sole in dorsal view; (D) 'cup-like' multiperforated plates from sole in ventral view; (E) 'cup-like' four-holed plates from sole in dorsal view; (F) 'cup-like' plates from sole in lateral view (G) knobbed plates from sole and (H)–(I) knobbed plates from ventral tube feet. Scale bars: (A)–(B) 50 μm; (C) 20 μm; (D)–(I) 30 μm. Martins & Travares (2020).
The sole is covered with with knobbed and multiperforated single plates, strongly concave, oval in outline, heavily knobbed on one side, smooth on the other surface, knobbed edges (70–100 μm long), and round holes 15–20 μm in diameter and 'cup-like' multiperforated plates, concave, oval in outline (50–70 μm long) 10–15 μm in diameter.
Dorsal tube feet with supporting rods, curved with one central perforation and one central apophysis (80–150 μm). Ventral tube feet with knobbed and multiperforated plates.
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