Amphipholizona perplexa ( Nielsen, 1932 ) Nielsen, 1932

Gondim, Anne Isabelley, Christoffersen, Martin Lindsey, Dias, Thelma Lúcia Pereira & Solís-Marín, Francisco Alonso, 2016, Taxonomic status of the genera Amphipholizona H. L. Clark, 1915 (Ophiuroidea, Ophiolepididae) and Amphigyptis Nielsen, 1932 (Hemieuryalidae): systematic placement and synonymy, Zootaxa 4097 (3), pp. 381-395 : 388-393

Amphipholizona perplexa ( Nielsen, 1932) new comb.

Figures 4 A–G, 5A–L, 6A–F

Amphigyptis perplexa Nielsen, 1932: 306 –307, fig. 22a–b.― Fell, 1960: 12 (key).― Solís-Marín et al., 2005: 128; 2013: 564 (list).

Type material. Zoological Museum of Natural History Museum of Denmark. Two syntypes: ZMUC OPH 251 (examined from photographs provided by Dr. Jørgen Olesen).

Type locality. South of San José, Perlas Islands, Pacific Panama, 45.72 m.

Material examined. ICML-UNAM 3.41.0, 1 spm. (dd = 4.19 mm), E. of San Marcos Islands, Gulf of California, coll. Hancock Pacific Expedition, 14 March 1936; ICML-UNAM 3.41.4, 1 spm. (dd = 3.28 mm), North of Isla Tiburón, Gulf of California, St. 27, coll. Dr. Maria Elena Caso, Hendrichx Van der Heidel, Toledano G., Álvaro Cortés, 0 7 May 1982; ICML-UNAM 3.41.1, 1 spm. (dd = 4.0 mm), Punta San Marcial, Gulf of California, St. 0 8, coll. Dr. Maria Elena Caso & Laura Calva Benítez, Cortés Cruise III, 30 May1985; ICML- UNAM 3.41.2, 1 spm. (dd = 3.61 mm), Ponta Arboleda, Gulf of California, St. 16, coll. Juan Torres Vega, Cortés Cruise III, 12 March 1985; ICML-UNAM 3.41.3, 1 spm. (dd = 4.11 mm), La Paz Bay, Baja California Sur. USMN E 30907 , 5 spms. (dd = 2.13, 3.34, 3.51, 3.61, and 3.63 mm), Off Southern California, California, USA, coll. Wolfson, F. H.

Diagnosis. Interradius covered by a single row of large polygonal plates. Arms short, flattened dorso-ventrally. Dorsal arm plate triangular or pentagonal. Ventral arm plate pentagonal and swollen. Dorsal and ventral arm plate with simple and fine stereom and some tubercles on central regions of plate. Tentacle scale lacking.

Description. Disc circular (dd = 4.19 mm), covered by few, flattened, polygonal, large plates ( Fig. 4 A, D). Radial shields large, approximately twice as long as wide, united along their full length, swollen at their distal adradial corner ( Fig. 4 A, D, G). A triangular plate separating distal extremities of radial shields sometimes present ( Fig. 4 D). Interradius covered by a single row of 2-3 large polygonal plates ( Fig. 4 A, D, G), marginal plate larger, wider, and trapezoid. Central region of disc covered by 10 to 20 flattened, polygonal plates ( Fig. 4 A, D), sometimes with small triangular or square plates occurring between them. Ventral interradius covered by imbricating scales smaller than the dorsal plates ( Fig. 4 B, C, F). Bursal slits short, localized on lateral margin of oral shields ( Fig. 5 B, C, F). Jaw short ( Fig. 4 C). Oral shields small, diamond shaped, longer than wide, with proximal angle sharp and distal angle rounded ( Fig. 4 C, F). Madreporite not differentiated. Adoral shields large, tumid, as long as wide, fully united proximally ( Fig. 4 C, F). Infradental papillae rectangular ( Fig. 4 C, F). Two oral papillae, distal longest and opercular, proximal most small and slightly rectangular ( Fig. 4 C, F).

Five short arms, approximately 2.5 times the diameter of the disc, slightly flattened dorso-ventrally ( Fig. 4 A, B, G). Dorsal arm plate pentagonal or triangular, two times wider than long, with distal margin straight ( Fig. 4 D, G). Simple and fine stereom with minute thorns, with some tubercles in central area of plate ( Fig. 5 F). Lateral arm plate visible dorsally and ventrally, with simple stereom ( Fig. 4 A, B, 6A), pairs united dorsally and ventrally. Isolated plate from proximal arm about twice as high as wide, simple stereom with minute thorns on distal portion ( Fig. 5 A). Inner side of lateral plate slightly differentiated, with vertical and sinuous ridge, reaching middle of length of plate, flat knob on lower proximal part, inner perforation not discernible ( Fig. 5 B). Arm spine articulation formed by two lip-shaped parallel ridges of equal length, slightly curved, separated at both ends, two large openings of nearly equal size between them (muscle and nerve opening) ( Fig. 5 C). Ventral arm plate pentagonal, swollen, 1.5 times wider than long, proximal angle strongly pointed and distal margin straight ( Fig. 4 B, C, F), largely separated from following plate. Simple and fine stereom with minute thorns, with some tubercles in central region of plate ( Fig. 5 G). First ventral arm plate very small, narrow, pentagonal, twice longer than wide ( Fig. 4 C). Three to six arm spines, thin; the dorsal one is the longest (as long as one arm segment), remaining ones decrease in ventral direction ( Fig. 4 A). First arm segment with two arm spines, second with three, third with four, and from fifth onwards, six arm spines. Distal segments with only three arm spines. Arm spines with minute thorns ( Fig. 5 D, E). Tentacle pore large. Tentacle scale lacking ( Fig. 4 F).

The vertebrae are slightly longer than wide, non-keeled, with dorsal median groove V-shaped, a welldeveloped lateral curved groove, and a zygospondylous articulation ( Fig. 5 H, I, J, L). In proximal view the aboral muscle area (am) is slightly smaller than the oral muscle area (om), which is concave in distal direction ( Fig. 5 I). A well-developed suture line in dorsal and ventral view ( Fig. 5 J).

Adradial genital plate long, over the three first arm segments and in contact with the two first lateral arm plates by means of a long groove. Abradial genital plate scale-like, articulated laterally to the adradial genital plate ( Fig. 4 E).

Variations. Examined specimens measured between 3.28 and 4.19 mm in disc diameter (dd). Small morphological variations were observed. Only one specimen of 3.61 mm dd presented the primary plates well developed ( Fig. 6 D), these were the only plates present at the central region of the disc. The dorsal arm plate can vary from triangular to pentagonal. Usually, dorsal arm plates of triangular shape are observed on the first arm segments.

Color. Specimens preserved in alcohol are whitish. There is no information regarding color of living specimens.

Distribution. Gulf of California and Panama (Pacific Ocean).

Depth range. From 45.72 to 143 m ( Nielsen 1932; Solís-Marín et al. 2013). Solís-Marín et al. (2013) record the occurrence of this species from shallow waters. This may be a mistake, since no specimens analyzed in this work come from this depth.

Remarks. Nielsen (1932) described Amphipholizona perplexa on the basis of two specimens, with a disc diameter between 3 and 3.5 mm ( Fig. 6 A, B, C), from Perlas Archipelago (Pacific Panama) at 45.72 m depth. This species has been rarely cited since its original description, being considered extremely rare. Amphipholizona perplexa is currently known from only 10 specimens collected along the coast of California and Panama Bay, Pacific Ocean.

Amphipholizona perplexa (junior synonymy Amphigyptis perplexa ) was originally placed in the family Hemieuryalidae (see comments for the genus), on the basis of the shape of the arm plates, of the oral structure, and of the shape of the bursal slits. However, this classification is incorrect. Amphipholizona perplexa differs from Hemieuryalidae in several characters, among which are: the presence of a circular disc, infradental papillae, six arm spines, tentacle scale lacking, and arm spine articulation formed by two parallel, slightly curved, ridges of equal length, and abradial and adradial genital plate long and similar in size. All these characters concur with the pattern seen in Amphiuridae , and fit perfectly with the new diagnosis provided for the genus Amphipholizona . Consequently, we propose the new combination Amphipholizona perplexa and recommend transferring this genus to the Amphiuridae .

According to Thomas (1966), A. perplexa is similar to Amphipholis pentacantha H.L. Clark, 1915 . However, according to our observations, this similarity is restricted to the absence of a tentacle scale beyond the fourth arm segment in A. pentacantha (there are two tentacle scales on the first segment and one on the second and third arm segments). In all remaining characters (e.g. disc covering, radial shields, dorsal and ventral arm plates, oral and adoral shields) these species are very different (see H.L. Clark 1915: 241, 242, pl. VI, figs. 1–2). Amphipholizona perplexa is very closely related to A. delicata . However, A. perplexa differs from this latter species for having a short and slightly dorso-ventrally flattened arm, no tentacle scales along the arm and by the shape and ornamentation of the dorsal and ventral arm plates ( Table 1 ). Furthermore, the two species have a well-defined geographical distribution, A. perplexa occurs in the Pacific Ocean, while A. delicata is only known from the Atlantic Ocean. We thus consider the differences sufficient for maintaining A. delicata and A. perplexa as distinct species.

Ecological notes. This species is found in muddy, sandy or rocky bottoms ( Solís-Marín et al. 2013).

Morphological characters Species The genus Amphipholizona is clearly an Amphiuridae in several morphological aspects. However, this genus shares some characters with other, apparently non-related genera. One example is the morphology of the lateral arm plate, which has spine articulations, particularly the knobs on the inner side, which are typically amphiurid, while the general outline of the plate and especially the outer surface ornamentation are similar to the pattern found in some species of Ophiolepis (see Thuy & Stöhr 2011: 36, Fig. 21), Ophiozonella Matsumoto, 1915 , and Ophiozonoida H.L. Clark, 1915 (Ophiolepididae) (Ben Thuy and Daniela Y. Gaurisas personal communication).

Amphipholizona seems to be more closely related to Amphipholis than any other genus of Amphiuridae . Both share a very similar pattern in the shape and arrangement of the oral frame and have one or no tentacle scales. It should be stressed that the great majority of species of Amphipholis have two tentacle scales. The arrangement of oral papillae is presently considered important in separating genera in Amphiuridae ( Martynov 2010) , and the presence of oral papillae appear to represent a conservative pattern within the Amphiuridae ( Hendler 1988) . They may thus be indicative of deep phylogenetic affinities. Notwithstanding, the absence of tentacle scales is recorded in species across the Ophiuroidea, which suggests that this absence may be homoplastic. Only a thorough phylogenetic study may confirm possible historical relationships between these genera and will be able to clarify the affinities of this genus with some genera of Ophiolepididae .

With the present study we have clarified the systematic position of the genus Amphipholizona , and have contributed to the systematics, at least in part, of the families Ophiolepididae and Hemieuryalidae . Further efforts are needed in order to characterize these less-known taxa and to reconstruct phylogenetic relationships within Ophiuroidea.

Figures

FIGURE 4. Morphological characters of Amphipholizona perplexa (Nielsen, 1932) new comb. (A) Dorsal view; (B) Ventral view; (C) Detail of the oral frame; (D) Detail of the disc; (E) Genital plates; (F) Ventral view of the arm; (G) Dorsal view of the arm. Abr: abradial genital plate; Adr: adradial genital plate; ADS: adoral shield; AS: arm spine; BS: bursal slit; DAP: dorsal arm plate; IP: infradental papillae; IT: interrradius; LAP: lateral arm plate; OP: oral papillae; OS: oral shield; RS: radial shield; TS: tentacle scale; VAP: ventral arm plate. (Photos 5 A, B, F and G courtesy of Rafael B. Moura).

FIGURE 5. SEM photographs of internal skeletal characters of Amphipholizona perplexa (Nielsen, 1932) new comb. (A) External view of lateral arm plate, detail of the ornamentation; (B) Internal view of lateral arm plate; (C) Distal view of lateral arm plate, detail of spine articulation; (D) Arm spines; (E) Base of arm spine showing articulation, detail of the minute thorns; (F) Dorsal arm plate; (G) Ventral arm plate; (H) Distal view of vertebra; (I) Proximal view of vertebra; (J) Ventral view of vertebra; (L) Lateral view of vertebra. MO: muscle opening; NO: nerve opening.

FIGURE 6. Images of type material of Amphipholizona perplexa (Nielsen, 1932) new comb. and pictures of distinct specimens showing some diferences in the patterns of dorsal plates of the disc: (A – B) Photos of syntypes ZMUC OPH 251; (C) Illustrations provided by Nielsen (1932) in original description of species; (D) juvenile specimen showing the primary plates; (D – E) specimens without defined primary plates. (Photos of syntypes courtesy of Tom Schiøtte and 6 F courtesy of Rafael B. Moura). CPP: centrodorsal plate; RPP: radial primary plates; RS: radial shield.

Tables

TABLE 1. Comparison of morphological characters of Amphipholizona delicata H. L. Clark, 1915 and A. perplexa (Nielsen, 1932) new comb.

	Amphipholizona delicata	Amphipholizona perplexa new comb.
Disc	Circular	Circular
Interradius	3 rows of plates. Marginal region with 3 plates	1 row of plates. Marginal region with 1 large, trapezoidal, plate
Radial shields	Large	Large
Oral shields	Small and diamond-shaped	Small and diamond-shaped
Adoral shields	Large and swollen	Large and swollen
Infradental papillae	Present	Present
Number of oral papillae	Two, distalmost opercular	Two, distalmost opercular
Arms	Long (6x disc diameter), and cylindrical	Short (1 ½ to 2.5x disc diameter), and dorso- ventrally compressed
Dorsal arm plate	Fan-shaped. Stereom with minute thorns	Pentagonal or triangular. Stereom with minute thorns and with some tubercles in central region of plate
Ventral arm plate	Pentagonal and flat	Triangular and swollen
Number of arm spines	3 to 6	3 to 6
Tentacle scale	Present, restricted to first five arm sgments	Absent
Discussion