Colossendeis cf mycterismos Bamber, 2004

Staples, David A., 2007, A new species of Colossendeis (Pycnogonida: Colossendeidae) together with records from Australian and New Zealand waters, Memoirs of Museum Victoria 64, pp. 79-94 : 91-92

Colossendeis cf mycterismos Bamber, 2004 .

Figure 6A–G

Colossendeis mycterismos Bamber, 2004:7–9 . Fig, 3 (A–E)

Material examined. NORFANZ Stations. Holotype: Lord Howe Plateau, 34°12.20'S, 162°41.44'E, 751 m, 26 May 2003, (Tan 0308, stn 084), NMV J48824 (1 specimen).

Paratype: West Norfolk Ridge, Wanganella Bank , (34°37.20'S, 168°57.03'E), 521 m, 3 Jun 2003, (Tan 0308, stn 154), NMV J53080 (1 specimen) .

Diagnosis. A fine, delicate species. Leg span to about 55 mm. Proboscis almost 1.5 times length of trunk, greatest diameter in proximal 3rd, down-curved throughout length, strongly tapered distally. Ocular tubercle with apical point, 2 or 4 eyes, pigmented or unpigmented. Legs slender, terminal claw of all legs short, less than one-third propodus; tarsus, shorter than propodus, propodus ratio variable.

Distribution. East coast of Taiwan; Lord Howe Plateau, Tasman Sea.

Remarks. This material enables additional observations to compliment the original description. The proboscis is gently down-curved through its length but more so in distal one-third and articulates from about horizontal, downwards, to what appears to be a more natural position of about 45°. Palp segment 5 is longest, about 1.2 times longer than segment 3, segment 6, 1.1–1.2 times longer than segment 7 and segments 8, 9 and 10 progressively increase in length. The distal four palp segments were covered in numerous spinules of uniform size; segment 10 is about 4 times as long as wide. The terminal oviger claw is straight, smooth and a little longer than half the length of segment 10, finely crenulate spines on segments 7 to 10 are in single row, and number 7:6:6:9. The length of the tarsus relative to the length of the propodus decreased from the 1st pair of legs to the 4th pair in 1 specimen, but in no particular order in the other; the length of the tarsus ranged from 48–97% of the propodus length, the main claw ranged from 27–46% of propodus length. The longer leg segments are gently curved, tibia 1 is equal to, or marginally longer than the femur and tibia 2 is 24–35% longer than tibia 1. The tarsus and propodus have a row of short spines along ventral margin; all segments are covered in short spines, the larger spines interspaced among more numerous shorter spines. Coxal pelliculae were not evident. The ocular tubercle is slightly taller than its basal width, with a variably developed apical point. The four darkly pigmented eyes are of equal size and have convex lenses. Lateral sensory organs were not evident. The genital pores are tiny and placed on the distoventral surface of coxa 2 of all legs. The abdomen is fusiform, curved with a convex dorsal surface and distinctly clavate distally. Differences between the holotype and the Tasman Sea specimens can be summarized as follows. The holotype is about one-third larger than the Tasman Sea specimens and has only one pair of unpigmented eyes; palp segments 3 and 5 are of equal length and segments 6 to 10 are subequal. The femur of the 3rd leg of the holotype is almost 30% shorter than tibia 1, and tibia 2 is only 10% longer than tibia 1. The proboscides of the Tasman Sea specimens are uniformly inflated proximally with a tapered, curved distal region; Bamber’s figures (3A, B) show a distinct bulge at one-third the proboscis length and minimal distal curvature. The holotype abdomen was not described, but based on the same figures, it is of uniform width and somewhat convex dorsally. The oviger claw is nearly half the length of the 10th segment and has a ‘flattened expansion’ along its ventral margin (fig. 3C). The number of oviger spines in the holotype was not documented for comparison. Oviger and palp glands are not evident.

The status of these specimens will have to be reassessed on examination of additional material, particularly as both the holotype and these specimens are recorded from similar depths and are adult, decreasing the chances of differences being attributed to heterogonic growth. Characters of particular significance are the unique variability in the number of eyes from 2 to 4; the differences in the proportions of longer leg segments and differences in the supposed characteristic shape and orientation of the proboscis for which the species was named. Should the proboscis orientation and shape of the C. mycterismos holotype prove to be an artefact of preservation, then apart from differences noted above, differences are relatively minor. Rather than introduce another species into a genus already bedevilled by species complexes, I have provisionally referred the specimens to C. mycterismos . The specimen from stn 154 was enveloped in a clear, diatomembedded slime.

Additional measurements and illustrations are provided for future comparison.

Measurements (in mm). Length trunk (frontal margin cephalic segment to tip 4th lateral process) 2.64; width across 2nd lateral processes 0.88; length proboscis (lateral) 3.25; greatest width proboscis 0.50; length abdomen 0.43. Third leg: coxa 1, 0.38; coxa 2, 0.48; coxa 3, 0.38; femur 7.43; tibia 1, 7.43; tibia 2, 9.80; tarsus 0.80; propodus 0.98; claw 0.28.

Oviger; seg. 1, 0.10; seg. 2, 0.25; seg. 3, 0.27; seg. 4, 2.27; seg. 5, 0.62; seg. 6, 3.60; seg. 7, 0.44; seg. 8, 0.35; seg. 9, 0.25; seg. 10, 0.25; claw, 0.16. Palp segments (in mm). seg. 1, 0.02; seg. 2, 0.09; seg. 3, 1.78; seg. 4, 0.18; seg. 5, 2.10; seg. 6, 0.50; seg. 7, 0.44; seg. 8, 0.31; seg. 9, 0.34; seg. 10, 0.40.

Two other species share a similar proboscis shape with C. mycterismos ; Colossendeis pipetta Stock, 1991 and C. sinuosa Stock, 1997 . As noted by Bamber, the tarsus in both species is longer than the propodus and the proboscides are more tubular distally in both species. Colossendeis pipetta can further be distinguished by the higher numbers of spines on oviger segments 7 to 10. Stock described the lateral processes of this species as being separated by twice their own diameter; however his fig. 28B shows them to be separated by about their own diameter. Also, his reference to oviger segments 3 and 5 should be to segments 4 and 6. Stock’s brief description of C. sinuosa does not enable adequate comparison with that species and his relative descriptions of the palps as being “less elongate” and of “different slenderness”, necessitates re-examination of the type material. In the meantime, C. pipetta can be primarily characterised by the ‘sinuous’ shape of the distal portion of the proboscis.

Figures

Figure 6. Colossendeis mycterismos sp. nov. holotype (NMV J48824): A, B, dorsal and lateral views of trunk; C, oviger; D, oviger segments 7–10; E, palp; F, leg 3; G, tarsus and propodus.