Ophioderma unicolor H.L. Clark, 1940

Humara-Gil, Karla J., Granja-Fernández, Rebeca, Bautista-Guerrero, Eric, Solís-Marín, Francisco A. & Rodríguez-Troncoso, Alma P., 2024, Delimitation of Ophioderma teres (Lyman, 1860) and Ophioderma unicolor H. L. Clark, 1940 stat. nov. (Echinodermata: Ophiuroidea), including the description of two new species, European Journal of Taxonomy 947, pp. 130-174 : 150-153

Ophioderma unicolor H.L. Clark, 1940 stat. nov.

Figs 5 , 7 ; Tables 1–2 , 4

Ophioderma teres var. unicolor H.L. Clark, 1940: 342 .

Ophioderma teres – Ziesenhenne 1955: 191 (partim, non Lyman, 1860). — Hickman 1998: 24 (partim, non Lyman, 1860).

Ophioderma teres var. unicolor – Downey 1969: 115 (partim). — Granja-Fernández 2019: 275–279, fig. 37g –l (partim).

Ophioderma teres unicolor – Humara-Gil et al. 2022: 373, fig. 4k, table 1 (stat. nov.).

Diagnosis

Radial shields naked. DAPs divided into multiple pieces (mean = 2, maximum = 6). Coloration uniform brown (preserved specimens).

Material examined

Holotype

ECUADOR • dry preserved specimen; Galapagos Islands, Charles Island ; 1872; Hassler Expedition leg.; MCZ IZ OPH-114 .

Paratype

NICARAGUA • 1 spec. (preserved dry); Corinto , Cardon Island; 12°28′28′′ N, 87°10′51′′ W; 3.6 m (2 fathoms) depth; 29–30 Dec. 1937; Zaca Expedition leg.; MCZ IZ OPH-6153 .

Other material See Supp. file 1.

Designation of the new status as species

Ophioderma teres unicolor was initially considered a variety of O. teres (H.L. Clark, 1940) and later categorized as a subspecies based on the ICZN ( ICZN 1999, Art. 45.6.4) ( Humara-Gil et al. 2022). However, the detailed examination of both taxa revealed differences in characters that are diagnostic at the species level within the genus. Ophioderma teres unicolor has naked radial shields, DAPs divided into up to six pieces, and a uniform brown coloration. On the other hand, O. teres presents radial shields that may be covered or naked, DAPs divided into up to 13 pieces, and a speckled color pattern. Given the differences in these relevant characters, a new status for O. teres unicolor is herein proposed, raising its rank from subspecies to species: O. unicolor stat. nov.

Description

Holotype

DD = 35.7 mm, AL = 128 mm, AL:DD = 3.6. Disc pentagonal, covered by minute rounded granules, slightly separated from each other. Granule size increasing from center to periphery and decreasing close to arm base. Some granules rubbed off, leaving scales visible. Dorsal disc granule density 39 per mm 2. Radial shields naked; visible section approximately 1.5 × as long as wide, oval; distance between radial shields about 3 × width of shield ( Fig. 7A ). Small, oval plates of variable size (up to six) close to arm base ( Fig. 7A, D ). Ventral interradii covered with small granules of uniform size, separated from each other. Four genital slits per interradius. Proximal genital slits oval, in contact with distal section of oral shields and 1 st LAP. Distal genital slits oval, slightly longer than proximal ones, placed between 7 th and 9 th arm segments; surrounded by granule-bearing scales and naked scales next to the arm ( Fig. 7B ).

Oral shields 1.2× as wide as long, rounded triangular; proximal edge convex forming a rounded apex; lateral edges rounded; distal edge straight to concave. Madreporite rounded, broken in two pieces (a probable artifact of preservation), with a central depression; distal edge slightly concave. Adoral shields covered by small granules slightly separated from each other. Jaws with 9–11 oral papillae: LyOs the largest, 2 × as long as wide, angled upwards; AdShSp rounded triangular, pointed; 2°AdShSp similar in shape but slightly smaller than AdShSp; LOPas 3–6, conical, slender; IPa similar to LOPas, more robust; TPa 2–3 at jaw apex, pointed, robust. Teeth five, robust, rounded triangular to quadrangular. OPRSp not evident due to closed mouth. Oral plates covered with granules larger than those covering the adoral shields ( Fig. 7C ).

Five arms rounded, tapering distally: two almost complete, one regenerating close to arm base and two regenerating from mid-section ( Fig. 7K ). Dorsal arm base with some small scales and few granules scattered between them ( Fig. 7D ). DAPs wider than long, typically divided into three and up to six irregular pieces ( Fig. 7D–E ). DAP pieces sequence of the longest arm: first ten segments, 2, 2, 2, 1, 1, 2, 3, 4, 3, 1; 11 th –20 th, 1–5; 21 st –30 th, 2–4; 31 st –40 th, 3–5; 41 st –50 th, 3–6; 51 st –60 th, 2–4; 61 st –70 th, 3–5; 71 st –80 th, 2–4; 81 st –90 th, 2–4; 91 st –100 th, 2–4; 101 st –110 th, 1–3; 111 st –117 th, 1–3. Distalmost DAPs trapezoidal to triangular, entire ( Fig. 7F ). First VAP small, 3× as wide as long, with rounded edges ( Fig. 7B ). Subsequent VAPs quadrangular, slightly longer than wide; distal edge convex ( Fig. 7G–H ). Distalmost VAPs triangular, rounded, slightly longer than wide ( Fig. 7I ). A pair of pores between the 3–4 proximalmost VAPs in all five arms ( Fig. 7B ). LAPs conspicuous, wider than long, with up to 13 arm spines. Arm spine sequence of the longest arm (right side, including arm spine bearing segments within disc): first ten segments, 3, 3, 4, 4, 5, 6, 7, 8, 9, 10; 11 th –20 th, 12–13; 21 st –30 th, 11–12; 31 st –40 th, 11–12; 41 st –50 th, 10–11; 51 st –60 th, 10–11; 61 st –70 th, 9–10; 71 st –80 th, 8–9; 81 st –90 th, 8–10; 91 st –100 th, 7–8; 101 st –110 th, 6–8; 111 th –120 th, 6–8; 121 st –126 th, 4–5. Arm spines conical with blunt tips, flattened, ⅔ LAP length. Dorsalmost arm spine the shortest; ventralmost the longest and more robust, in contact with tentacle scales of the following segment ( Fig. 7J ). Two tentacle scales, rarely three; adradial tentacle scale oval, just over ½ VAP length; abradial tentacle scale shorter and wider, ¾ adradial scale length, triangular ( Fig. 7G–H ). In the distalmost arm section, tentacle scales oval and elongated, adradial being the longest; last arm segments with only one scale ( Fig. 7I ).

General coloration uniform brown (dry specimen) ( Fig. 7K ). Dorsal side: disc brown ( Fig. 7A ). Arms brown ( Fig. 7D–F, K ). Ventral side: interradii brown ( Fig. 7B ). Oral shields brown; oral papillae and teeth cream ( Fig. 7B–C ). LAPs brown. Arm spines brown with cream bases and tips ( Fig. 7J ).

Paratype and non-type variations

The paratype was 29.7 mm in size (DD). It overall agreed with the holotype but differed in the following aspects: its oral shields were trilobed rather than rounded triangular, the 20 proximalmost DAPs were divided into more pieces (mostly four), and the maximum number of spines was 12 instead of 13.

Non-type specimens varied in size from 17.1 to 30.2 mm (DD). In three specimens (DD = 17.1–20.7 mm), the distance between the radial shields was two times the shield width, smaller than in the holotype. In another specimen (DD = 30.2 mm), the distance was four times the shield width. One specimen (DD = 20.5 mm) presented small plates on the disc near the arm base, while the remainder only had granules. All specimens showed divided DAPs, but two of them (DD = 20.5 and 20.7 mm) had more entire rather than divided plates, with the latter composed of two pieces at most. The maximum number of arm spines varied by size, ranging from ten (DD = 17.1 mm) to 13 (DD = 30.2 mm). Finally, the coloration varied as follows: two specimens, including the one with the lightest general coloration, presented some slightly darker granules on the dorsal disc, particularly in the center; the radial shields were either darker than the disc or the same color but with a significantly darker margin.

Distribution and habitat

Ophioderma unicolor stat. nov. was previously recorded in Mexico, Nicaragua, and Ecuador as O. teres var. unicolor (H.L. Clark 1940; Downey 1969; Mireles-Velázquez et al. 2021). This study confirms its presence in Nicaragua (Cardon Island) and Ecuador (Galapagos Islands) (see Supp. file 1). On the other hand, the records from Mexico are invalidated as they correspond to a new species described below ( O. aija sp. nov.). The northernmost record of O. unicolor is from Cardon Island, Corinto, Nicaragua (12° N), and the southernmost from Chatham Island (also known as San Cristóbal Island), Galapagos Islands, Ecuador (0° S) ( Fig. 5 ). This species has been collected in rocks, sand, and algae, at depths from 3.6 to 45.7 m.

Remarks

While establishing O. unicolor stat. nov., H.L. Clark (1940: 342) designated MCZ IZ OPH-114 as “the type” (= holotype) of the then variety ( ICZN 1999, Art. 73.1.1). He also noted that a specimen from Cardon Island, Nicaragua, “very similar” to the holotype, was in the same collection, along with two other specimens (MCZ IZ OPH-6153) (H.L. Clark 1940). H.L. Clark (1940) did not formally acknowledge the latter three specimens as paratypes but neither excluded them from its type series ( ICZN 1999, Art. 72.4.6). Downey (1969) treated those specimens as paratypes of O. unicolor but reported the lot with two specimens instead of three; the third specimen was likely lost. In accordance with the ICZN, Downey’s (1969) inclusion of these specimens in the type series was appropriate at the time ( ICZN 1999, Art. 72.4.1). Nonetheless, the recent examination of the material revealed that one of the specimens (currently MCZ IZ OPH-167471, DD = 10.6 mm) did not correspond to O. unicolor but to a different species (see O. aija sp. nov. Remarks). Consequently, the type series of O. unicolor now comprises the holotype and one paratype.

Ophioderma unicolor stat. nov. has often been misidentified as O. teres ( Ziesenhenne 1955; Hickman 1998; Granja-Fernández 2019; KJHG pers. obs.), but there are morphological differences between both species (see Designation of the new status as species). Despite the frequent confusion with O. teres , O. bichi sp. nov. from the EP (described below) and Ophioderma cinereum Müller & Troschel, 1842 from the western Atlantic are more similar in appearance to O. unicolor . The three species share the covered adoral shields, DAPs divided into multiple pieces, and brown coloration. However, they differ in the following: 1) naked radial shields (sometimes with a darker margin) in O. unicolor and O. cinereum but covered in O. bichi ; 2) section between the arm and distal genital slits with naked and granule-bearing scales in O. unicolor and O. cinereum , and only with granule-bearing scales in O. bichi ; 3) arms uniformly brown in O. unicolor and O. bichi but banded in O. cinereum ; and 4) O. unicolor is distributed in the Pacific coast of Central America and the Galapagos Islands, O. bichi in the Gulf of California and the Revillagigedo Islands, and O. cinereum from the Bahamas to Brazil ( Hendler et al. 1995; Hernández-Herrejón et al. 2008; Gondim et al. 2013).

Figures

Fig. 5. Distribution of Ophioderma teres (Lyman, 1860), Ophioderma unicolor H.L. Clark, 1940 stat. nov., Ophioderma aija sp. nov., and Ophioderma bichi sp. nov. in the eastern Pacific. A. Gulf of California. B. Revillagigedo Islands. C. Mexican Tropical Pacific. D. Central America and Colombia. E. Galapagos Islands.

Fig. 7. Ophioderma unicolor H.L. Clark, 1940 stat. nov., holotype (MCZ IZ OPH-114, DD = 35.7 mm). A. Dorsal disc. B. Ventral disc (inset: section between the arm and the distal genital slit). C. Closeup of a jaw. D. Proximalmost dorsal arm. Arrowheads indicate the extra plates on the arm base. E. Median dorsal arm. F. Distalmost dorsal arm. G. Proximalmost ventral arm. H. Median ventral arm. I. Distalmost ventral arm. J. Lateral arm plates and arm spines. K. Dorsal view. Abbreviations: 2° AdShSp = secondary adoral shield spine; AdShSp = adoral shield spine; IPa = infradental papilla; LOPas = lateral oral papillae; LyOs = Lyman’s ossicle; RS = radial shield; TPa = tooth papilla; vT = ventralmost tooth.