Lissothuria imbricata, Solís-Marín & Arriaga-Ochoa & Villa & Laguarda-Figueras, 2018

Solís-Marín, Francisco Alonso, Arriaga-Ochoa, Julio Adrian, Villa, Cristian Moises Galvan & Laguarda-Figueras, Alfredo, 2018, Lissothuria imbricata sp. nov., a new species of sea cucumber (Echinodermata: Holothuroidea) from the central-eastern Pacific Ocean, Zootaxa 4438 (2), pp. 373-380 : 374-379

Lissothuria imbricata sp. nov.

( Figs. 1–3 )

Types. Holotype ICML-UNAM 18000, 16.46 mm Total Length (TL), Isla Cocinas , Chamela Bay, La Huerta, Jalisco, Mexico, Pacific Ocean 19° 32′ 44.8″ N, 105° 06′ 34.3″ W, 3–6 m depth, November 14th 2014.

Paratypes: ICML-UNAM 12135, 13 specimens, same data as the holotype; LEMA-CEQ627, 4 specimens, Isla Cocinas, Chamela Bay, La Huerta, Jalisco, Mexico, Pacific Ocean, 19° 32′ 45.71″ N, 105° 06′ 27.73″ W, 7 m depth, June 25th 2013; LEMA-CEQ632, 7 specimens, Isla San Pedro, Chamela Bay, La Huerta, Jalisco, Mexico, Pacific Ocean, 19° 32′ 01.01″ N, 105° 05′ 17.97″ W, 5 m depth, June 26th 2013.

Type locality. Isla Cocinas, Chamela Bay, Jalisco, Pacific Ocean, Mexico 19° 32′ 44.8″ N, 105° 06′ 34.3″. Non-type material. 153 specimens from Chamela Bay, La Huerta, Jalisco, Mexico, Pacific Ocean. See table 1 for details.

Diagnosis. Body wide almost the half of the body length. Dorsal scale covering complete, with 11 to 16 scales between the mouth and anus, 20 pointed narrow valves surrounding the mouth; the anus is surrounded by a varying number of rounded valves. Ten short tentacles, the two most ventral tentacles are smaller than the others. Sole elongated, fringed by an outer peripheral single series of smaller tube feet; inner peripheral series with three rows of closely crowded tube feet, which form a continuous margin, mid-ventral radius with a double row of tube feet, becoming crowded anterior and posteriorly. Sole leathery, translucent. Ossicles of dorsal surface are perforated plates, knobbed baskets; each dorsal scale covered by 7–20 short, wide, massive towers with a slightly spiny apex, giving the dorsal area a granular appearance. Ossicles of sole are perforated plates, which are smooth or knobbed; baskets with knobbed margin. Tentacles with irregular, perforated, flattened rods, and few rosettes.

Etymology. The specific epithet imbricata in Latin means “imbricated, overlapping”; it refers to the conspicuous appearance of the imbricated dorsal scales.

Holotype description. 17.2 mm total length (TL) and 4.4 mm high at the central part of the body (16.8 mm sole length, 8.4 mm wide). Elongated body; well calcified test. Mouth and anus elevated ( Figs. 1A, 1D ). Tentacles contracted ( Fig. 1A ). Dorsal surface with thick imbricating scales approximately 600–900 µm in diameter; 11 scales between oral and anal openings, the marginal scales are smaller ( Fig. 1D ). Scales perforated for passage of inconspicuous tube feet ( Fig. 1A ; Fig. 2A–B ); 20 pointed narrow valves surrounding the oral opening; anal valves are small and rounded varying in number ( Fig. 1D ). Sole leathery, translucent, elongated, fringed by a single outer peripheral line of small tube feet; inner peripheral series with three rows of closely crowded tube feet, which form a continuous margin, the mid-ventral radius with a double row of tube feet scarce in the midventral area and becoming crowded anterior and posteriorly ( Fig. 1B ). Dorsal tube feet distributed in all dorsal surface, those located in the ambulacra are numerous and conspicuous ( Fig. 1A ). Ten dendritic tentacles, the two ventral most are smaller than the rest. Calcareous ring simple, slim, low, radial and interradial plates about the same size and well calcified. Radial plates are larger than the interradials, in the upper part they have a small and narrow slit for the insertion of the retractor muscle; ventral and dorsal radial plates are equal in size and shape. The interradial plates have a shallow groove in the lower part; dorsal and ventral interradial pieces are equal in shape and size. One Polian vesicle. Color in alcohol yellow to light purple, tentacles white. Well-developed gonads that occupy most of the coelomic cavity.

Ossicle assemblage. Ossicles of dorsal surface include dorsal scales, with one to six perforations for the passage of tube feet ( Fig. 2A–B ). Small dorsal scales (between 500 to 700 µm) are present at the base of the test, while those of the rest of the body can reach up to 1.8 mm. Dorsal scales are oriented towards the mid dorsal line of the body; those that are surrounding the mouth and the anus, are forming concentric lines ( Fig.1D ). The dorsal dermis posses massive towers with slightly spiny apex, the base may be smooth or irregular, the base measures between 170 and 200 µm in diameter, the height can be up to 190 µm ( Fig. 2C–E ), these massive towers reduce their size when approaching the lateral areas of the test, reaching 70 and 100 µm in diameter, the height can be up to 90 µm. Big baskets are 50 to 60 µm in diameter, the edge of which is usually spiny; small baskets are 40 to 45 µm in diameter, the base and the edge of which are usually knobbed ( Fig. 2F–I ). Curved supporting rods in ventral tube feet, here are also perforated plates; end plates appear to be vestigial in the dorsal tube feet ( Fig. 2J–K ). Sole ossicles are knobbed buttons with four holes ( Fig. 3A–C ), perforated plates in various shapes with smooth or knobbed margin, they reach up to 150 µm in length ( Fig. 3D–F ), and there are also small shallow baskets 50 to 65 µm in diameter, with knobbed edges ( Fig. 3G–I ). Tentacles generally with elaborate small rosettes, 40 to 50 µm wide ( Fig. 3J–K ), flat, curved and perforated rods, up to 200 µm, most times wider in the center than at the end portions ( Fig. 3L ) and perforated plates 100 to 300 µm length ( Fig. 3M ).

Paratype variations. Specimens slightly smaller than the holotype, 10–17 mm TL and 3.3 mm high in the central part of the body (9–15 mm sole length, 3–8 mm wide). Elongated body; well calcified test. 11 scales between oral and anal openings. Mouth, anus and internal morphology same as in the holotype. Tentacles contracted. Dorsal scales approximately 500–900 µm in diameter. Shape and size of the ossicles are the same as in the holotype, except that in the smaller paratype (9.8 mm TL) ossicles are more abundant.

Ecology. Lissothuria imbricata sp. nov. inhabits rocky reefs with stone blocks, it can be found attached under or on top of rocks; it uses its tube feet to partially cover its dorsal side with algae debris ( Fig. 1C ).

Reproduction. Lissothuria imbricata sp. nov. is a gonochoric species; females have lecithotrophic eggs between 420 and 470 µm in diameter, in this case, ripe gonads occupy more than 80% of the celomic cavity. Neither brooding or external sexual dimorphism was observed.

Geographical distribution. Only known from Chamela Bay , Jalisco, Mexico.

Figures

FIGURE 1. Lissothuria imbricata sp. nov., holotype ICML-UNAM 18000, A, Dorsal view; B, Ventral view. Paratype ICML- UNAM 12135; C, In situ picture showing habitat preferences; D, Live specimen, lateral view. All scale bars: 5 mm.

FIGURE 2. Lissothuria imbricata sp. nov., holotype ICML-UNAM 18000, A, Dorsal perforated scale for passage of tube feet, scale bar: 100 µm; B, Detail of perforations in the dorsal scale; C–E, Massive towers from the dorsal side, with slightly spiny apex, scale bar: 50 µm; F–I, Baskets from the dorsal side, scale bar: 40 µm; J–K, Dorsal tube feet vestigial end plates, scale bar: 50 µm.

FIGURE 3. Lissothuria imbricata sp. nov., holotype ICML-UNAM 18000, A–C, Ventral ossicles, knobbed buttons, scale bar: 50 µm; D–F, Ventral ossicles, various shapes of perforated plates with smooth or knobbed margin, scale bar: 50 µm; G–I, Ventral ossicles, small shallow baskets, with knobbed edges, scale bar: 30 µm; J–K, Tentacles ossicles, small rosettes, scale bar: 10 µm; L, Tentacles ossicles, flat, curved and perforated rods, scale bar: 50 µm; and M, Tentacles ossicles, perforated plates, scale bar: 100 µm.