The Bathyal Holothurians of the New Zealand Region
Ilyodaemon Theel, 1879
Ilyodaemon Theel, 1879
Diagnosis : Tentacles 15, large, non-retractile. Ventrolateral pedicels large, in a single row throughout each radius. Midventral radius naked. Dorsal radii each with a crowded series of very numerous retractile slender processes, usually in a double row.
Type Specimen: Ilyodaemon maculatus Theel.
Remarks: The genus is widespread in the Indo-west-Pacific ( I. fimbriatus, I. maculatus and I. abstrusus) and off Japan ( I. ijimai and I. muriense) in depths ranging between about 159 metres and 1,000 metres. The fact that Ilyodaemon is now known to occur in New Zealand waters considerably extends the known range of distribution, and it seems likely that the genus will be found to have a far wider distribution than formerly has been supposed.
Ilyodaemon embraces five species, which may be distinguished as follows:
1 (4) | Deposits include dichotomously branching "rosettes". | |
2 (3) | Approximately 140–150 processes in each dorsal radius | I. maculatus Theel |
3 (2) | Approximately 100 processes in each dorsal radius | I. muriense Ohshima |
4 (1) | "Rosettes" lacking. | |
5 (8) | Less than 50 pedicels in each ventrolateral interradius. | |
6 (7) | Dorsal radii each with approximately 140–160 processes. Colour in alcohol violet to dark violet | I. abstrusus Sluiter |
7 (6) | Dorsal radii each with approximately 100 processes. Colour in alcohol whitish-grey | I. ijimai Mitsukuri |
8 (5) | At least 50 pedicels in each ventrolateral radius | I. fimbriatus Sluiter |
Ilyodaemon abstrusus Sluiter Text-fig. 5, figs. 1–4
Ilyodaemon abstrusus Sluiter, 1901a, p. 24; 1901b, p. 69, Pl. IV, figs. 1–3, Pl. IX, fig. 9.
Material Examined: Marine Dept. Stn. 23, 1 specimen; Stn. 31, 4 specimens.
Description: Total length ranges from 108mm to 142mm. Body elongate, approximately four times as long as broad. Bodywall extremely slimy, thick, gelatinous. Midventral radius naked, lateral ventral radii each with a single row of soft triangular processes, of average length 10mm. Processes regularly spaced along radii, numbers varying between 16 and 20 in each radius, although 18 processes is usual number. Lateral dorsal radii each carry approximately 55 pairs of short (5mm long) processes, regularly arranged; thus there are two rows of processes in each dorsal radius. Mouth ventrally turned, anus terminal.
In five specimens tentacle numbers are 11, 10, 15, 14, 14. Anterior end of each specimen damaged, normal tentacle number indeterminate, although there are probably more than 15.
Colour in alcohol dark purple overall, dorsal processes violet, ventrolateral processes lighter in colour. Tentacles dark brown, with leathery circular terminal discs. Intestine purplish-black, describing a large S-shaped loop. Polian vesicle large, bulbous. Gonad consists of small deep purple tufts of caeca.
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Text-fig. 5.— Ilyodaemon abstrusus Sluiter: Fig. 1, rods from dorsal processes; Fig. 2, large wheels; Fig. 3, rods from tentacles; Fig. 4, small wheels. ?Laetmogone violacea juv.: Fig. 5, rods from ventral pedicels; Fig. 6, small wheel; Fig. 7, large wheels.
Dorsal processes contain only small wheels in large numbers scattered irregularly. Ventral processes contain large wheels near bases; toward the distal extremities these are replaced by numerous rods of varying shape (Text-fig. 5, fig. 1) up to 0.5mm in length. Some rods bear a few small spines. In stems and discs of tentacles are curved rods (Text-fig. 5, fig. 3) up to 0.6mm long, with weakly spinous ends.
Remarks : These specimens are representatives of Ilyodaemon abstrusus, a species first described by Sluiter (1901a). Sluiter's largest specimen was 170mm in length, and the number of pairs of dorsal processes was given as 70 to 80. It is possible that this number increases with growth. However, none of the present specimens have less than 50 pairs of dorsal processes. The tentacles in Sluiter's specimens are violet, while here they are brown. In spite of such differences, it is apparent that the New Zealand specimens represent Sluiter's species.
In the specimen from Marine Dept. Stn. 31, five nematodes were found in the coelomic cavity, near the posterior end of the intestine. They were free and unattached, lying entwined in the small muscle fibres supporting that part of the intestine. Total length of these worms ranges from 16m to 30mm. The colour in alcohol approximates that of the intestine, although two of the specimens are light brown. These specimens are as yet unidentified. This is possibly the first record of the presence of nematodes in an elasipod holothurian.
The relationship between the "host" and its "parasites" is not clear. The intestine of the specimen contained no other nematodes, nor was there any evidence of damage to surrounding tissues in the region in which the nematodes were found. As there are no respiratory trees, it is difficult to imagine how the nematodes came to enter the coelomic cavity, unless they penetrated the wall of the intestine, or somehow entered the water-vascular system.