Ophioderma hybrida Stöhr & Weber & Boissin & Chenuil 2020, sp. nov.
Creators: name: Stöhr, Sabine
name: Weber, Alexandra Anh-Thu
name: Boissin, Emilie
name: Chenuil, Anne
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Ophiurida
Ophiodermatidae
Ophioderma
Ophioderma hybrida

description: Ophioderma hybrida sp. nov.
urn:lsid:zoobank.org:act: 72379251-8181-4B42-8CB6-881F0C144526
Figs 9–10; Tables 1–2
Diagnosis
Species of Ophioderma with variable morphology. Dorsal arm plates single or as several pieces. Seven to 10 equal arm spines. Eight oral papillae. Colour pattern: disc dark brown or olive dorsally and ventrally, often with white spots. Dorsal arms dark brown with light brown or white and black spots, ventrally lighter brown. Maximum known size about 19 mm dd.
Etymology
This species has likely evolved by an ancient hybridization event between two species (O. longicauda and O. zibrowii sp. nov. or their respective ancestors), which the Latin word hybrida alludes to. It also refers to the mixed morphology of the species.
Material examined
Holotype MEDITERRANEAN SEA • Tunisia, Kelibia; 36°50′7.31″ N, 11°7′6.20″ E; depth 0.3–1.5 m; 3 Jul. 2013; Zined Marzouk & Alexandra Weber leg.; preserved in 95% ethanol; SMNH-Type-9185.
Paratypes MEDITERRANEAN SEA • 11 specimens; same data as for holotype; SMNH-Type-9186 • 8 specimens; Tunisia, Monastir; 35°46′28.83″ N, 10°50′18.93″ E; depth 2–5 m; 25 Jun. 2013; A. Weber leg.; preserved in 95% ethanol; SMNH-Type-9187.
Other material
MEDITERRANEAN SEA • 3 specimens (with dorsal disc removed, but present); same data as for holotype; SMNH-178454 • 3 specimens; Tunisia, Tunis; 1849; Åberg leg.; SMNH-35614, 123374, 123375.
Description
Holotype (Fig. 9)
Disc diameter 17.4 mm, two arms cut off near disc but present (Fig. 9 A–B). Radial shields covered by disc granules (Fig. 9A). Dorsal arm plates weakly tumid, as 1–3 pieces on about first 30 joints, when single twice as wide as long, distal edge straight or concave (Fig. 9 C–D). Ten arm spines, all about equal in length, ventralmost slightly wider. Ventral arm plates overlapping, squared, distal edge convex (Fig. 9E). Two oval scale-like tentacle scales, superimposed on the ventralmost spine. Ventral disc covered by granules similar to dorsal disc. Eight oral papillae, short, weakly pointed to round, Lyman’s ossicle large, pointing into mouth slit (Fig. 9F). Tooth papillae larger than oral papillae, teeth rounded block-shaped. Oral shield almost twice as wide as long, with wide proximal angle, distal edge slightly convex. Madreporite larger, almost as long as wide (Fig. 9B). Adoral shield long, narrow, extending around the lateral edge of the oral shield, separating it from the arm (Fig. 9F). Adoral shields covered with granules, similar to disc granules. Proximal genital slits angled from oral shield to second arm joint, distal genital slits at disc edge, two arm joints long.
Disk dark brown dorsally with radiating lighter brown pattern and scattered white spots (Fig. 9A). Dorsal arms dark brown with light brown and dark spots along the distal plate edges and on some lateral edges (Fig. 9 C–D). Ventral disc and arms light greenish brown, oral shields darker (Fig. 9B).
Variation
The range of morphological variation is presented in Table 2 and on Fig. 10. The specimens vary in size from 9.8 to 18.7 mm disc diameter. Among the 23 examined specimens, the number of dorsal arm plate pieces varies considerably. Multiple plates or pieces have been found on the proximal arms, until about joint number 30, but not on all joints, and sometimes not on all arms (Fig. 10E). In most specimens, there are only two pieces, but in a few animals, multiple pieces were observed (Fig. 10E, H, N). Some specimens have only single dorsal arm plates (Fig. 10B, K). More pieces are present in the larger specimens but there appears to be only a weak size relation for this trait. Likewise, the number of arm spines and oral papillae is not related to disc diameter. All but two animals have granule covered radial shields. Colour variations are limited. All examined specimens have a dark brown or olive dorsal disc with varying white patterning (from spots to radiating lines) and a dark ventral disc, similar or lighter oral frame and ventral arms. The dorsal arms show alternating light and dark bands and a series of light and dark spots along the distal edge of the dorsal arm plates.
Other specimens
SMNH-35614 15.5 mm dd, SMNH-123374 16.3 mm dd, SMNH-123375 14.3 mm dd. Colour faded to light brown. Most of the granules rubbed off the discs, and status of the radial shields as naked/granule covered cannot be assessed, but they have an exposed area, devoid of scales. Eight oral papillae. Two to three dorsal arm plates on single joints (SMNH-123374), up to nine joints (SMNH-123375), up to 12 joints (SMNH-35614), variable between arms. Juveniles present in the bursae.
Remarks
The origin of this species through an ancient hybridization event between O. longicauda and O. zibrowii sp. nov. (or their ancestors) (Weber et al. 2019) is further supported by its high morphological variability. Multiple dorsal arm plates are typical of O. longicauda, and in some specimens of O. hybrida sp. nov. the most proximal joints bear several plates, forming a crowded mosaic pattern similar to O. longicauda. The usually granule covered radial shields are shared with all species except O. zibrowii sp. nov. (Table 1) and are probably evidence of O. longicauda (or its ancestor) being one of the ancestral species. The variation of arm spines and oral papillae overlap with both ancestral species and O. africana sp. nov., but O. guineense has a higher number of arm spines. Ophioderma hybrida sp. nov. shares the vivid colour pattern of the arms with O. zibrowii sp. nov. and O. guineense, whereas O. africana sp. nov. and O. longicauda are darker and the spots on the arms are less obvious in the former. So far, O. hybrida sp. nov. appears to be a smaller species with disc diameter under 20 mm, but more material is needed to confirm this. We believe that the reproductive mode of O. hybrida sp. nov. is brooding given that brooding individuals have been collected in Tunisia (Stöhr et al. 2009) and the ones examined in this study are morphologically more similar to O. hybrida sp. nov. than to O. zibrowii sp. nov., because they have more dorsal arm plates per joint. Yet, we cannot confirm it, as the brooding specimens from Tunisia were too old for genetic analyses (1849 and 1924; PCR amplification failed). In addition, all other O. hybrida sp. nov. specimens have been collected outside the reproductive season so examination of their gonads was inconclusive in determining their reproductive strategy.
description: Published as part of Stöhr, Sabine, Weber, Alexandra Anh-Thu, Boissin, Emilie & Chenuil, Anne, 2020, Resolving the Ophioderma longicauda (Echinodermata: Ophiuroidea) cryptic species complex: five sisters, three of them new, pp. 1-37 in European Journal of Taxonomy 600 on pages 22-24, DOI: 10.5852/ejt.2020.600, http://zenodo.org/record/3637773