Sigsbeia oloughlini, O’Hara, 2014

O’Hara, Timothy D., 2014, A new species of Sigsbeia and additional records of ophiuroids from the Great Australian Bight, Memoirs of Museum Victoria 72, pp. 131-140 : 131-135

Sigsbeia oloughlini sp. nov.

Fig. 1 and 2.

Zoobank LSID. http://zoobank.org:act:AE0247F3-DAE5-4F5E-

B966-431AD6668EA9

Material examined. -- Australia. FR0795: stn 111, SW of Esperance , 34° 23'S, 120° 39'E, 95 m, 1995, holotype: 1 ( SAM K4005 ) .

Description. Disc 4.8 mm d.d., arms five, approximately 14 mm long. Disc round to pentagonal, covered in flat polygonal to rounded plates. Primary disc plates are distinct, separated by a series of small interradial plates. A 2nd circle of larger radial and interradial plates occurs near the proximal end of the radial shields, separated by small intercalary platelets. A long narrow plate is present at the interradial margin, 2 times as long as wide, separated from the parallel radial shields by a single series of small platelets. The radial shields are long narrow plates, 3.5-4 times as long as wide, that extend from near the arm base, around the arm, to the latero-ventral edge of the disc. They converge proximally, but do not touch, separated by the secondary radial plate. There are 1-3 tumid quadrangular to triangular plates on the lower side of each arm base, adjacent to the radial shield, which are potentially homologous to the series of plates distal to the radial shields in Ophiolepis and Ophiozonella .

The ventral interradial disc is completely covered in plates, including short wide plates at the proximal margin, probably rudimentary genital scales. The central area is dominated by 2-3 tumid to protuberant plates, surrounded by 1-2 series of small intercalary platelets. The genital slits are small, and extend from the oral shield for the length of the 1st lateral arm plate.

The jaws are wider than long, with 4 oral papillae on each side that almost completely cover the jaw slit; the inner ones are block-like (almost resembling the infradental papillae on amphiurids), the 2nd and 3rd are smaller, trapezoid, slightly longer than wide, the distal ones are enlarged, 1-5-2 times as wide as long, with an angle proximally and a sloping distal edge. There is also a tiny recurved scale wrapped around the 2nd oral tentacle pore near the apex of the slit. The oral shields are roughly pentagonal, with rounded angles and concave proximo-lateral margins, as wide as long. The madreporite is distinct and enlarged. The adoral shields are sausage-shaped, 2 times as wide as long, separated proximally by a triangular intercalary plate.

The 1st dorsal arm plates are triangular, 2 times as wide as long, and are placed where the arm is inserted into the disc, adjacent to the secondary radial plate and proximal ends of the radial shields. Subsequent plates are oblong to hexagonal, becoming progressively larger and longer from the 2nd to 4th plate, 2-4 times as wide as long with straight proximal and distal margins and a convex to angular lateral margins, fully contiguous until about the 12th plate, after which they become pronounced proximally, as wide as long, and narrowly separate. There are 1-3 accessory dorsal arm plates extending from the distolateral edge of each dorsal arm plate. The largest accessory plate is triangular and contiguous with the main dorsal arm plate. There is often a smaller triangular plate extending from the ventral corner of the larger plate to near the upper arm spine. A tiny intercalary plate is sometimes present at the distal junction of the main dorsal and largest accessory arm plate. The first 2 arm segments have only a single accessory plate angled distally with respect to the dorsal arm plate.

The lateral arm plate extends around the arm from the dorsal to ventral arm plate, having a swollen ventro-distal flange which usually bears 2 small cylindrical arm spines, the upper is 2 times as tall as wide with a blunt rounded apex, the lower is slightly longer or subequal, to 2/3rds the length of the arm segment. There is one, almost granule-like, spine on the first segment and up to 3 cylindrical spines on some segments near the arm tip.

The 1st ventral arm plate is rounded-triangular, the proximal angle forms the apex of the jaw slit, the proximolateral sides are contiguous with the adoral plates and the lateral end of the distal margin with the first lateral arm plates, the centre of the distal margin is contiguous with the 2nd ventral arm plate. The 2nd plate is bell-shaped to pentagonal, with a curved to angular proximal margin, sides recurved around the tentacle pore, and a convex distal margin. From the 3rd plate, the plates are sunken around the margin and covered in thick epithelium or connective tissue, the raised central portion of the plate is pentagonal to ovoid, the 3rd and 4th slightly wider than long, and thereafter as wide as long. The tentacle pores are oval, the base as long as the raised section of the ventral arm plate, but becoming progressively shorter. A thin sunken oval tentacle scale almost completely covers the pore.

The colour (in ethanol) is brown and white. The dorsal disc is mostly brown, except for a splash of white from the centre to one interradial margin and series of small white intercalary plates around the radial shields. Arms are banded, with 1-2 pale and 2-3 darker segments; in addition, there is a strong narrow transverse white band along the distal edge of each dorsal arm plate and adjacent accessory plates. The oral shields (often with whiter proximal apices), ventral disc plates adjacent to the oral shields and the intercalary plate separating the adoral shields are also pale. The distal ventral disc plates, raised section of the ventral arm plates, lateral arm plates, tentacle scales, adoral shields and oral plates are brown.

Distribution. Southwestern Western Australia, 95 m

Remarks. Despite being known from only one specimen, which precludes dissection, this species has characteristic features that warrant its description. We place it in the genus Sigsbeia in the family Hemieuryalidae on the basis of the coiled arms, adapted for an epizoic habit, the integration of the arms into the disc, the narrow radial shields that extend around the lateral disc margin almost to the ventral surface, the presence of accessory plates at the distal lateral corners of the dorsal arm plates, the single tentacle scale and the second oral tentacle pore hidden within the jaw slit.

Matsumoto (1915) recognised two subfamilies within the Hemieuryalidae , the Hemieuryalinae with supplementary or subdivided dorsal arm plates and the Ophiochondrinae with entire plates. Martynov (2010) reviewed several genera within the Ophiochondrinae and on the basis of their arm spine articulation morphology regarded them as belonging to the Ophiacanthidae . He thus restricted the Hemieuryalidae to those genera formerly in the Hemieuryalinae, explicitly Hemieuryale von Martens, 1867 and Sigsbeia Lyman, 1878b . To these we can add the similar genera Quironia A.H. Clark, 1934 , Ophioplus Verrill, 1899 , and Ophioholcus H.L. Clark, 1915 . Two additional genera remain problematic and require further study. Ophioleila A.H. Clark, 1949 is superficially similar to Ophioplinthaca , an ophiacanthid, and Amphigyptis Nielsen, 1932 was provisionally referred to the synonymy of the amphiurid Axiognathus (= Amphipholis ) by Thomas (1966).

The other genera of hemieuryalids are separated from Sigsbeia as follows ( Fell 1960). Hemieuryale has fragmented dorsal arm plates, Ophioholcus has 6 arms and contiguous radial shields, Quironia also has 6 arms and a single genital slit in each interradius that continues around the distal edge of the oral shield, and Ophioplus has a few accessory plates spaced along the distal edge of the dorsal arm plates. All four of these genera are monospecific, with their species restricted to the Caribbean/Western Atlantic continental shelf and upper slope.

The four previously known species of Sigsbeia differ from S. oloughlini most notably in the morphology of the disc plates, dorsal arm plates, arm spines and colour pattern. The type species, S. murrhina Lyman, 1878b (holotype: 12 mm d.d.) and S. conifera Koehler, 1914 (5 mm d.d.), both from the Caribbean, have granulated disc plates, a single rectangular to ovoid accessory dorsal arm plate, and two rounded, slightly flattened, arm spines. Furthermore, on S. conifera some of the larger dorsal disc plates are tumid and the dorsal plates non-contiguous after the basal few. Sigsbeia lineata Lütken & Mortensen, 1899 from the Galapagos and Cocos Islands has smooth disc plates without granules and the inner end of the ventral arm plates sunken like on S. oloughlini ; but has flat widened arm spines, a trapezoid accessory arm plate, and two thin longitudinal stripes running from the disc down each side of the dorsal arm surface. Finally, Sigsbeia laevis Ziesenhene, 1940 from the Pacific coast of Panama has tumid but ungranulated disc plates, small dorsal arm plates, as long as wide, barely contiguous, and flattened plate-like ovoid arm spines, and a squarish to rounded accessory arm plate. None of these species have the tumid ventral disc plates characteristic of S. oloughlini .

Different authors have disagreed about the nature of the accessory dorsal arm plates. While Lyman (1878b), Koehler (1914) and Fell (1960) have treated them as accessory arm plates, Lütken & Mortensen (1899) and Ziesenhenne (1940) considered them as highly modified upper arm spines that overlie the lateral arm plate. While the ontology of these plates cannot be fully addressed from our single specimen, here they do appear to be true plates, lying in a series confluent with the dorsal arm plate and abutting the edge of the previous lateral arm plate. They do not align with the two arm spines which emerge from a distal flange of the lateral arm plate. Moreover, where these accessory plates are missing, the underlying areas appear to be at least partially decalcified, suggesting that they are dorsal arm plates. Under this interpretation, these plates and the arm spines have converged in morphology in S. laevis and S. lineata , possibly functioning as a frictional aide to climbing.

The position of the accessory dorsal arm plates in S. oloughlini recalls Ophiolepis species such as O. elegans Lütken, 1859 or O. superba H.L. Clark, 1915b . In fact, the overall morphology is quite similar to Ophiolepis , including the integration of the arms into the disc, the form of the oral frame, and the disc plating. In particular, the row of disc plates that are placed distal to the radial shields in Ophiolepis and related genera are also apparent in Sigsbeia - the middle plate placed between the proximal ends of the radial shields and the lateral ones positioned at the base of the arm between the radial shields and third dorsal arm plate. Ophiolepis can be distinguished by its smaller radial shields, which are largely restricted to the dorsal surface and the long genital slits bordered by elongated genital scales.

This is the first record of a hemieuryalid species outside the equatorial western Atlantic and eastern Pacific. Now all recognised families of ophiuroids have been recorded from the Australian/ New Zealand region. The new record from the outer continental shelf off SW Australia may indicate a lack of sampling at these depths from this region. Three of the other four Sigsbeia have been recorded living on stylasterids. The catch description for this sample did not record stylasterids explicitly but did record abundant octocorals, ascidians, sponges, and bryozoans.

Etymology. Named after Mark O’Loughlin, teacher, mentor and friend (of TOH) for over 35 years.