Astrodendrum juancarlosi, Calero & Ramil, 2023

Calero, Belén & Ramil, Fran, 2023, Euryalida (Echinodermata, Ophiuroidea) from Northwest Africa, European Journal of Taxonomy 870, pp. 46-75 : 59-67

Astrodendrum juancarlosi sp. nov.

urn:lsid:zoobank.org:act:ECD0622E-6FAF-4C72-B102-F1B94D8ECBFB

Figs 3E–F , 7–9

Diagnosis

Species with small granule-like external ossicles, ending in a crystalline point, covering the dorsal and lateral interradial areas of the disc. Ventral disc areas and arms covered by domed granule-like external ossicles without any crystalline point. Two or three terminal projections on each arm spine; one secondary teeth on each valve.

Etymology

The specific epithet ‘ juancarlosi ’ was chosen as a tribute to Mr Juan Carlos Calero, father of the first author.

Material examined

Holotype

GUINEA BISSAU • 2 specs, 40.43–56.81 mm dd; 10°18′55″ N, 16°25′07″ W; depth 79 m; 4 Nov. 2008; Bissau-0810 exped.; stn BS200; Bissau-0810-06403; MNCN 29.02/1534 .

Paratypes

GUINEA BISSAU • 2 specs, 28.20–51.16 mm dd; 11°08′07″– 11°09′33″ N, 17°15′20″– 17°15′44″ W; depth 109 m; 29 Oct. 2011; CCLME-1110 exped.; CCLME-1110 exped.; stn BT53; MHN USC-10132 -1 and 2 • 1 spec., 40.43 mm dd; 10°18′55″ N, 16°25′07″ W; depth 79 m; 4 Nov. 2008; Bissau-0810 exped.; Bissau-0810 exped.; stn BS200; MNCN 29.02/1535 .

WESTERN SAHARA • 1 spec., 44.62 mm dd; 26°26′23″– 26°25′06″ N, 14°25′30″– 14°26′23″ W; depth 67– 58 m; 29 Nov. 2011; CCLME-1110 exped.; CCLME-1110 exped.; stn BT215; CFM-IEOMA-7776 . • 1 spec., 46.70 mm dd; 14°57′00″– 14°58′09″ N, 17°39′08″– 17°38′13″ W; depth 797 m; 25 May 2012; CCLME-1205 exped.; CCLME-1205 exped.; stn BT368; CCLME-1205-03248 ; LZM-UV.

Additional material

GUINEA BISSAU • 1 spec., 10.07 mm dd; 11°05′09″– 17°03′15″ N, 11°04′15″– 17°03′10″ W; depth 46–47 m; 26 Oct. 2008; Bissau-0810 exped.; stn BS151; Bissau-0810-06146 ; LZM-UV .

Description (holotype)

DISC. Five-lobed in shape, slightly excavated inter-radially ( Fig. 8A ), with no peripheral calcareous plates on rim. Radial shields tumid, long (almost raising the centre of disc) and narrow, which is deeply sunken ( Fig. 8C ). Radial shields completely concealed by external ossicles, bar-shaped, as wide proximally as distally, but more separated distally, converging towards centre of disc. Distally, radial shields end on enlarged, slightly concave and oval-shaped plate covered by minute granules ( Fig. 8C–D ). Dorsal disc covered by small granule-like external ossicles ( Fig. 8A, C–D ), each one ending in terminal crystalline point. At edge of disc, ossicles more densely packed and without crystalline point ( Fig. 8C ), and bigger in size between radial shields ( Fig. 8C–D ). Ossicles concealing radial shields similar to those from dorsal disc but more densely packed.Ventral inter-radial areas densely covered by mosaic of small irregular flat plates with granule-like external ossicles without terminal point. Oral shield, adoral shield, oral plates, along edge of mouth frame and ventral arm plates more densely covered by similar external ossicles. Mouth frame sunken ( Fig. 8E ). Interradial surface of lateral disc covered by external ossicles similar but smaller than those covering dorsal disc. Two large genital slits on each interradius running almost vertically along first five or six brachial segments after first fork ( Fig. 8F ). Conical external ossicles with terminal crystalline point more developed on adradial edge of genital slits. One oval-shaped and well-developed madreporite located just outside mouth frame ( Fig. 8E ). Both, tooth and oral papillae spiniform, especially larger apical ones. Mouth and infradental papillae form continuous series along mouth frame ( Fig. 8E ). Teeth varying in position and size, being irregular in outline and more or less irregularly disposed.

ARMS. Arms branching, with first fork before disc margin and second one located at margin. Nevertheless, in smaller specimens (juvenile), first fork located on margin of disc. Arms tapering gradually towards tips, completely covered, both, dorsally and ventrally, by domed granule-like external ossicles ( Fig. 9A ); these granules somewhat bigger than disc ones and without any crystalline point. Dorsal side of arms carry pedicellarial bands along whole arms. Valves with one secondary tooth downwardly curved ( Fig. 9C ). Some sunken transverse furrow between segments, giving arms an annulated appearance. Indication observed of median furrow along arm ( Fig. 8G ). Ventral side of arms with noticeable transverse naked furrows between segments until second fork; afterwards, furrows become smaller, disappearing after third fork. First two pores without arm spine. Arm spines beginning at third pair of pores with only one small spine at third and fourth pair of pores, two arm spines (sometimes one) afterwards and three arm spines (sometimes two) after second fork. Arm spines short and wide, ending in two or three hyaline points ( Fig. 9F ). Vertebrae streptospondylous ( Fig. 9G–K ).

COLOUR. Living specimens showing varying colours, from creamish-pink to dark orange and brown to gray ( Fig. 3E–F ) with clear ventral part; preserved specimens are white.

OSSICLE MORPHOLOGY. External ossicles on dorsal surface of disc, including radial shields, are granule-shaped and ending in a crystalline point ( Fig. 9A ). Baseplates oval-shaped with three to five tubercleshaped articulations for pedicellarial ( Fig. 9D ). External ossicles on baseplates granule-like shaped, approximately 200 µm in length and 100 µm in height ( Fig. 9B ). Valves with single inner tooth downwardly directed, and reticular structure ( Fig. 9C ). Lateral arm plates long, bar-like, with tuberculous stereom, spines placed in external lobe of plate ( Fig. 9E ). Arm spines ovoid-shaped with two or three small projections, not transforming into hook-shaped spines on distal portion ( Fig. 9F ). Vertebrae with hourglass-shaped streptospondylous articulations ( Fig. 9G–K ). Branching vertebra wider and with two surfaces for articulation.

Distribution

This species has been recorded in the Northwest African coast, from the Western Sahara to Guinea-Bissau waters. Its bathymetric distribution ranges between 47 and 797 m.

Remarks

The genus Astrodendrum was established by Döderlein (1911) for Gornocephalus sagaminus Döderlein, 1902 . He realised that all species that belong to Gorgonocephalus Leach 1815 are characterised by the presence of a well-developed belt of calcareous plates at the margins of the disc. However, species of Astrodendrum have no ring of calcareous plates at the rim. Additionally, the arm spines appear before the first fork, as in Gorgonocephalus ; however, in Astrodendrum Döderlein, 1911 , these arm spines are much smaller, hardly reaching ⅓ of the segment length, and their number is reduced: with three (or rarely four) on each side. Taxonomic studies dealing with this genus are scarce, and we have only found a revision of the genus recently published by Okanishi & Fujita (2018). According to these authors, the genus is characterised by having five branching arms, with less than six segments before the first fork; lack of calcareous plates on the edge of the disc margin; variously shaped external ossicles or no ossicles on the disc; a madreporite placed on the innermost part of the interradial lateral disc; and valves from the dorsal arms with one secondary tooth.

Currently, only six species have been assigned to this genus. Among them, only Astrodendrum capense ( Mortensen, 1933) , described from Durban, South Africa ( Mortensen 1933; Clark & Courtman-Stock 1976), has been found in the Atlantic Ocean – Namibia ( Alva & Vadon 1989). Astrodendrum elingamita Baker, 1974 has been reported in New Zealand and Philippines ( Baker 1974; Okanishi & Fujita 2018); Astrodendrum galapagense A.H. Clark, 1916 from Galapagos Islands; Astrodendrum laevigatum (Koehler, 1897) from Colombo ( Sri Lanka); and Astrodendrum sagaminum ( Döderlein, 1902) from Japan, East China Sea and Sri Lanka ( Döderlein 1902, 1911; Clark 1911; Bomford 1913; Matsumoto 1917; Irimura & Kubodera 1998); and the recently described Astrodendrum spinulosum Okanashi & Fujita, 2018 also from Japan.

In addition to the shape, size and arrangement of external ossicles – widely used as an important specific taxonomic character ( Baker 1974, 1980; McKnight 2000) – Okanishi and Fujita (2018) included the possibility of the lack of external ossicles (as in the case of A. laevigatum ), and they also proposed three new taxonomic characters to distinguish species of Astrodendrum :

• absence/ presence of bulges on lateral ridges of proximal portion of arm

• number of terminal projections of arm spines on proximal portion of arm

• number of secondary teeth of hook-shaped arm spines on distal portion of the arm

The main morphological features of all known species of Astrodendrum , including A. juancarlosi sp. nov., are summarized in Table 2 .

Astrodendrum spinulosum differs from the rest of species by the presence of bulges on lateral ridges of proximal portion of the arm.

The new species here described, also differs from A. spinulosum by the number of terminal projections of arm spines on the proximal portion of the arm (three in the case of the new species and one in A. spinulosum ). In addition, A. spinulosun has cone-shaped external ossicles, while A. juancarlosi sp. nov. has granule like ossicles ending in a crystalline point at the dorsal surface of the disc.

Astrodendrum juancarlosi sp. nov. is more similar to A. elingamita in the shape of the ventral coverage and the lack of a scale in the first tentacle pore. Nevertheless, A. elingamita has the first fork in the margin of the disc, while it is located before the margin in our species. The polygonal plates of the ventral covering are closer in the A. elingamita than in our specimen. Our specimens also differ from A. elingamita by having one type of dome-shaped granules with 1–2 hyaline terminal points rather than two smooth types. Astrodendrum sagaminum differs from Astrodendrum juancarlosi sp. nov. in also having two types of granules and naked arms and ventral disk.

Astrodendrum capense has several medium-sized conical tubercles along the radial shields; it also has some smaller conical tubercles along the inter-radial disc margin, both ending in small thorns. Moreover, the disc is closely covered with minute and smooth plates.

Astrodendrum galapagense has a dorsal coarse armament on the disc and arms. The external ossicles on the aboral disc are plate-shaped at periphery and conical at center, both slightly in contact, while on the oral surface has a few small widely scattered granules, except in the ventral interbrachial areas.

Astrodendrum laevigatum is covered by a thin, transparent, soft and perfectly smooth tegument without any granules or spines. According to the description of this species in the literature, there are some doubts about the inclusion of this species in the genus Astrodendrum . We consider necessary to review the type material before we can reach a conclusion on this issue. Therefore, in this paper we follow Okanishi & Fujita (2018) and keep the species within the genus Astrodendrum .

Finally, our specimen has marked rectangular furrows that are absent in the rest of the species of Astrodendrum . Even though Mortensen (1933) described the underside of the arms of A. capense as flat and without any grooves, he pointed out that this “may be an indication of a transverse furrow between the segments from the first forking onwards” ( Mortensen 1933: 286).

See Table 2 for comparison of main morphological characteristics among species.

Figures

Fig. 3. A–B. Asteronyx loveni Müller & Troschel, 1842 collected from Mauritanian waters on Distichoptilum gracile Verrill, 1882. C. Asterochema inornatum Koehler, 1906 collected from Western Sahara waters on Paramuricea sp. Koelliker, 1865. D. Ophiocreas oedipus Lyman, 1879 collected from Western Sahara waters, on Acanthogorgiidae indet. E–F. Astrodendrum juancarlosi sp. nov. (LZM-UV Bissau-0810-06146), specimens collected from Guinea Bissau waters. Not to scale.

Fig. 7. Map from the study area with the location of the stations where Astrodendrum juancarlosi sp. nov. were collected during the ten surveys off Northwest Africa.

Fig. 8. Astrodendrum juancarlosi sp. nov. (MNCN 29.02/1534). A. Dorsal view. B. Ventral view. C. Detail of dorsal view. D. Detail of disc granules. E. Detail of ventral view. F. Interradial surface of lateral disc and genital slits. G. Arm. H. Arm, ventral view.

Fig. 9. SEM photographs of internal skeletal characters of specimens of Astrodendrum juancarlosi sp. nov. (MNCN 29.02/1534). A. Granule-shaped ossicles from disc. B. Ossicle from baseplates. C. Valve. D. Baseplate. E. Lateral arm plate. F. Arm spines. G. Distal view of vertebrae. H. Proximal view of vertebrae.I. Ventral view of vertebrae. J. Lateral view of vertebrae. K. Dorsal view of vertebrae. Abberviations: DT = depression for tentacle; NC = nerve canal; WC = water canal.

Tables

Table 2 (continued on next page). Key features for species of Astrodendrum Döderlein, 1911 mainly based on the original descriptions; references included in the Table indicated different sources. “–” means no data.

	A. capense ( Mortensen, 1933)	A. elingamita Baker, 1974	A. galapagense A.H. Clark, 1916	A. laevigatum (Koehler, 1897)	A. sagaminum ( Döderlein, 1902)	A. spinulosum Okanashi & Fujita, 2018	A. juancarlosi sp. nov.
disc armament	closely covered with small granular external ossicles, fully in contact	closely packed with dome-shaped granules of two distinct sizes	mostly naked integument, but with widely scattered coarse granules	no ornamentation	widely covered with small granules	covered by conical external ossicles, but separated and scattered at periphery of the disc	covered by small granule-like external ossicles ending in a crystalline point.
radial shields	covered with large conical external ossicles, separated and scattered, ending in a number of small thorns	distinct, narrow at proximal end, widening distally	bar-like, covered by skin and external ossicles, almost reaching the centre of disc ( Okanishi & Fujita 2018)	smooth, large and narrow	well-differentiated	bar like, completely concealed by external ossicles, not reaching disc centre	bar-shaped and densely covered by granule-like ossicles ending in a crystalline point.
VIA	closely covered by small flat polygonal plate-shaped ossicles together with some scattered large conical ossicles ending in a number of small thorns, on lateral marginal edge of the disc	covered with granule-like ossicles of two distinct sizes	covered by sub- equal granule-like ossicles.	covered by a thin and smooth tegument	oral disc surface covered by flat, polygonal external ossicles, fully in contact on oral plate; slightly tumid, round and slightly in contact on adoral plates ( Okanishi & Fujita 2018)	the oral surface of disc covered by polygonal plate- shaped external ossicles, fully in contact; interradial surface of lateral disc covered by conical external ossicles and skin	densely covered by small granule-like external ossicles
mouth frame	covered by irregularly polygonal flat plates	closely covered with slightly domed polygonal granule- like plates; adoral plates without this covering	only a few small and widely scattered granules	–	oral shields, adoral shields, oral plates and ventral arm plates completely concealed by external ossicles ( Okanishi & Fujita 2018)	oral shields, adoral shields, oral plates and ventral arm plates completely concealed by external ossicles	covered by small granules
jaw	small plates granule- like	–	only a few small and widely scattered granules	–	–	–	sunken; jaw covered with small granules