Macrophiothrix caenosa, Hoggett, Anne K., 2006

Hoggett, Anne K., 2006, A new species of Macrophiothrix (Ophiuroidea: Ophiotrichidae) common in northern Australia, Zootaxa 1326, pp. 17-24 : 18-22

Macrophiothrix caenosa n. sp.

( Figs 1–12 )

Macrophiothrix caenosa: Hoggett, 1990: 103 ; Miller, 1997; Hart & Podolsky, 2005.

Macrophiothrix longipeda: Hoggett, 1991: 1103 (part), fig. 14B (not figs. 14A, 14C–F, 15A–C).

Type material: Holotype, NTM Q4925, 8 paratypes, NTM Q4926, Q4927, Q4928, Q4929, Q4930, Q4931, Q4932, Q4934. All type specimens from East Arm, Darwin Harbour, Northern Territory, Australia, muddy sand and rocky reef, low intertidal, under rock, collected by A. Hoggett and C. Johnson, 9 Oct. 1986.

Other material: 79 specimens. Australian Museum: Capricorn Group, Queensland, Australia — J2340 (1), J7046 (1). Northern Territory Museum: Darwin, Port Essington and Orontes Reef, Northern Territory, Australia; Lizard Island, Queensland, Australia; Broome, Western Australia; Japan; intertidal to 18 metres — Q3853 (6), Q3872 (1), Q3877 (1), Q3899 (1), Q3902 (1),Q3903 (1),Q3904 (1), Q3907 (1), Q4531 (1), Q4540 (2), Q4541 (1), Q4706 (1), Q4735 (1), Q4740 (1), Q4769 (1), Q4770 (1), Q4771 (1), Q4779 (1), Q4825 (1), Q4826 (1), Q4827 (1), Q4828 (1),Q4830 (1), Q4831 (1), Q4834 (1), Q4848 (1), Q4849 (1), Q4850 (1), Q4851 (1), Q4857 (1), Q4882 (1), Q4884 (2), Q4889 (1), Q4890 (1), Q4897 (1), Q4912 (1), Q4960 (1), Q4961 (1), Q4962 (1),Q5260 (8), Q5423 (1), Q5477 (1), Q5669 (1), Q6171 (1), Q6172 (1). Western Australian Museum: Walsh Point, Point Cloates, North West Cape, Coral Bay, Abrolhos Islands, Warroora, and off Port Hedland, Western Australia; Thursday Island, Queensland, Australia; Singapore; intertidal to 30 metres — 949­76 (1), 87­77 (1), 323­77 (1), 447­77 (1), 363­78 (1), 656­78 (2), 810­78 (2), 863­81 (1), 867­81 (1), 871­81 (arms), 877­81 (2), 196­84 (1), 377­87 (1), 378­87 (2).

Distribution: Northern Australia, from the Abrolhos Islands, Western Australia, to the Capricorn Islands, Queensland; Singapore; Japan. Intertidal to 30 m.

Habitat: Under slabs of rock or coral rubble that overlie sandy or muddy substrates. The animals move swiftly into deeper substrate when the slab is lifted.

Etymology: From the Latin caenosus (= muddy), referring to the habitat in which this species lives at the type locality.

Diagnosis: Based on all material examined. A species of Macrophiothrix with disc diameter up to 24 mm; arms 9 to 20 times disc diameter. Wide trapeziform dorsal arm plates (2.0 to 2.6 times wider than long; Figure 10 ). Multifid disc stumps (1.5 to 2.5 times higher than wide). Radial shields bearing short multifid stumps or rugose granules. Seven to 10 dorsoventrally flattened arm spines, the upper ones with thorns along whole length of both sides, terminating in a truncate or slightly expanded, but not clavate, tip. Longest arm spine second or third from uppermost, 0.9–1.3 times corresponding dorsal arm plate width. Ventral disc armament sparse or absent near genital slits. Genital plates usually lack armament. Oral shields without spinelets ( Figure 12 ). Dental plate with distinct central constriction, adoral part broader than aboral part ( Figures 3–6 ). Lateral edges of adoral part of dental plate with a single row of conspicuously taller and more pointed dental papillae, enclosing a group of smaller rounded papillae ( Figures 4–6 , 12 ). Ripe female gonads golden yellow and ripe male gonads pale orange in living specimens, both fading to white on preservation.

Description of holotype: The holotype ( Figures 1–2 ) is a female. Maximum oocyte diameter is 0.204 mm. Disc diameter is 19 mm, arm length 290 mm. Dorsal disc armament is of short (about twice as high as wide), cylindrical, multifid stumps, density 18 per square mm. Ventrally, disc stumps become shorter and have fewer points as they approach the genital plates and jaw. Stumps do not extend onto the long genital plates that border the genital slits, or onto the wing­like genital plates distal to the oral shields ( Figure 12 ). Radial shields are 6.0 mm long, 2.5 mm wide, widest 2.5 mm from distal end. Radial shields bear rugose granules, density 25 per square mm.

Dorsal arm plates are trapeziform ( Figure 10 ), some fractured near the longitudinal midline. The proximal one or two plates bear a few stumps similar to, but smaller than, those on the disc. All other dorsal arm plates lack stumps. The 17th dorsal arm plate is 2.12 mm wide, 0.84 mm long.

Arm spines are dorsoventrally flattened with small thorns along the lateral edges of the uppermost few spines. Lower spines are smooth proximally with thorns only along the distal edges. The spines have parallel edges and terminate in an abruptly rounded tip, which has slightly longer thorns on the aboral side; they are not clavate. First and second free segments each have 9 spines, 3rd to 5th segments each have 8 spines, and 10th and 20th segments each have 7 spines. Longest spine in each series is the second or third from uppermost; longest spine is 2.33 mm on segment 17, 1.1 times the corresponding dorsal arm plate width. Ventralmost arm spine is the smallest in the series and has a few short thorns near the tip.

Ventral arm plates are wider than long, with rounded distal corners ( Figure 11 ). Tentacle scales are small and rounded.

Jaw structure is shown in Figure 12 . All oral shields are bare. Dental papillae on lateral edges of the dental plate are conspicuously and abruptly taller than those in the centre and at the adoral end of the plate. The jaw of the holotype has not been dissected.

Preserved colour is pale purple with scattered darker patches on the disc and darker transverse bands on the arms at intervals of 4–5 segments. Colour in life was shades of brown rather than purple. The gonads are white in the preserved specimen but were golden yellow in life.

Figures

FIGURES 1, 2. Macrophiothrix caenosa n. sp., holotype, disc diameter 19 mm. 1. Dorsal view. 2. Ventral view.

FIGURES 3 – 9. Dental plates of Macrophiothrix caenosa and M. longipeda, ventral ends uppermost. 3 – 6. M. caenosa. 3. Specimen from Darwin, Northern Territory (NTM Q 4928, d. d. 16 mm), papillae and teeth removed. 4. Same specimen (NTM Q 4928), papillae and teeth intact. 5. Specimen from Japan (NTM Q 5423, d. d. 17 mm), papillae and teeth intact. 6. Specimen from Darwin, Northern Territory (NTM Q 4849, d. d. 11 mm), papillae and teeth intact. 7 – 9. M. longipeda. 7. Specimen from Lizard Island, Queensland (NTM Q 5421, d. d. 16 mm), papillae and teeth removed. 8. Same specimen (Q 5421), papillae and teeth intact. 9. Specimen from MacGillivray’s Reef near Lizard Island, Queensland, d. d. 11 mm, papillae and two of four teeth intact (dorsalmost tooth removed, second dorsalmost broken). Scale bar 1 mm.

FIGURES 10 – 12. Macrophiothrix caenosa, holotype. 10. Dorsal arm plates, 16 th and 17 th from disc. 11. Ventral arm plates, 19 th and 20 th from mouth. 12. Single jaw. Scale bar 1 mm.