Phyllodesmium crypticum Rudman, 1981

フィロデスミウム・クリプティクム Phyllodesmium crypticum

Location: Torpedo Alley, Komodo, Indonesia
Date: 2014/09/08
Length: 10mm
Depth: 6.0m
Water temperature: 26.5℃

Description

A relatively large Phyllodesmium with the body almost completely obscured by closely packed large cerata. Oral tentacles long and tapering; rhinophores smooth, about two-thirds the length of the oral tentacles. The foot is wide, with paired recurved tapering anterior corners and a narrow tapering tail. Cerata occur in up to eight clusters per side: a single pre-cardiac arch, then a post-pericardial arch (double-rowed on the limbs and single mid-dorsally), with three single-rowed posterior arches and three reduced posterior groups. The cerata are dorsoventrally flattened and quadrangular in cross section, with rows of nodules along the four edges and scattered nodules on the flat sides — a unique form that mimics the tentacles of the Xenia colonies on which the species feeds. Body whitish translucent with pale orange to yellow-brown viscera; the upper third of the oral tentacles and most of the rhinophores are white-pigmented. Digestive gland branching shows through the dorsum as a brown midline. Ceras edges and tips are whitish, sometimes tinged blue or brown to match the host Xenia. Reaches 60 mm in body length (holotype 45 mm). Radula 0.1.0, with 36 teeth in a 45 mm specimen; bluntly pointed central cusp with paired ventral limbs and flanges bearing up to 30 large denticles. Jaw plates bilobed with coarsely serrated cutting edges.

Distribution

Type locality is a large rock pool at Angourie, northern New South Wales, Australia (October 1979, near Xenia colonies). Originally known only from northern NSW (Angourie, Broomes Head, Minnie Waters, Woolgoolga Headland). Subsequent records extend more widely across Australia and into the Red Sea, Indonesia, the Philippines, and Japan, although the identity of all extralimital records may not be fully resolved.

Etymology

The specific epithet crypticum (originally spelled cryptica) is Latin for hidden or cryptic, referring to the remarkable resemblance of the cerata to the tentacles of the host Xenia on which the animal feeds (verbatim from the original description).

Remarks

Feeds on the alcyonarian soft-coral genus Xenia (a bluish form). The animal crawls on or near the colony and, unlike Phyllodesmium hyalinum, does not nestle in basal cavities. Symbiotic with zooxanthellae: TEM observation confirms intact zooxanthellae (with cell walls, chloroplasts, and starch granules) inside digestive-gland cells, and the stomach, digestive-gland ducts, and lumen are full of zooxanthellae. The species, with Phyllodesmium hyalinum and Phyllodesmium pecten, retains zooxanthellae in digestive-gland cells in a symbiotic relationship, with rapid turnover replenished from Xenia. When disturbed, the animal autotomises its cerata; detached cerata exude a sticky secretion and wriggle. Japanese specimens that have been called "Kusenia-umiushi" by some authors are referable to Phyllodesmium orientale rather than to Phyllodesmium crypticum, following Baba 1991, which distinguishes the two species on radular and reproductive characters.

Photographed by KIMOTO Nobuhiko

Description

Distribution

Etymology

Remarks

References

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Seasonality

Shooting Locations

Photos of Phyllodesmium crypticum

Same Genus Nudibranchs

Similar Colors Nudibranchs

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