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69
Resumé.
Species examined.
I had specimens of the following species under examnation: — Myzostoma cirriferum, Leuckart; host. Antedon
petasus, Düb & Kor. M. glabrum; host. A. rosacea (a few badly preserved specimens only). M. gigas, Lütken;
host. A. eschrichtii, Mull, (a few specimens amongst which one complemental male). M. giganteum, n. sp.; host. A. celtica,
Mar. M. graffi, n. sp.; host. A. celtica; and M. carpenteri; host. A. dentata, Say (A. sarsii, Düb. & Kor.:.
Myzostoma giganteum, n. sp. (Pl. I, fig. 3, 4.)
This species very much resembles M. gigas, Liitken; in exterior as well as in its anatomy. It is, however,
distinguished by its more robust and not so flat bod}’. The dorsal surface rises from the translucent margin much more
sharply, and is considerably more arcuate, whilst in M. gigas it is flatter, and its margin not so sharply marked; so that
transversal sections of this species acquire, thus, a more lenticular appearance, which is further promoted by the ventral side
being, usually, quite flat (Pl. IX, fig. 1), whilst in M. giganteum it is, usually, not a little concave (Pl. II, fig. 1 .
The thickness of the body is dissimilar in the two species; in one specimen of M. giganteum (4 mm. broad) the thickness was
I mm.; whilst one specimen of M. gigas (4 mm. broad) had a thickness of only 0.6 mm. In M. giganteum, the ventral side
is without any prominences; whilst the specimens of M. gigas examined had, on their ventral side, a slight longitudinal
prominence in which the ventral nerve-cord, especially the middle, is partly situated ; it becomes, thus, in greater or smaller degree,
a convex ventral and a concave dorsal surface (Pl. IX, fig. 1 as well as, also, thinner; whilst the ventral cord of M.
giganteum is convex on both sides, considerably thicker, and is separated from the ectoderm by a considerable muscular layer PI.
II, fig. i . From this mesial longitudinal prominence in M. gigas, similar slight ridges radiate, one to each parapodium; these
are caused by the musculi centrales; nothing similar is to be seen in M. giganteum. Both species have, on their dcrsal
surface, tubercles distinguishable by the naked eye. The dorsal surface, in M. giganteum, appears to be a little more wrinkled,
and its parapodia are stronger and have a thicker and broader base than those of M. gigas. The situation of the parapodia,
and the segmental glatidulous sacks1) is similar to that of M. gigas. The gland openings are oval, and considerably
prominent, with radial furrows proceeding from them. The cirri appear to be a little longer, and not so deeply recessed
as they are in M. gigas. The size appears to be about the same in both species. The largest specimen of M. giganteum
examined was 6 mm. in diameter. The colour approaches to madder-brown, darkest in the middle, and paler and more yellowish
towards the margin of the body. In its anatomical structure, this species is distinguished from M. gigas by its having a
considerably more developed proboscis, and by the greater extension, and the peculiar form of the hook-glands; these are
separated into two branches, the one surrounding the hooks (chief hook, supporting rod, and reserve hooks’, and the
other; in which there is a number of vacuoli; extending towards the middle of the body (Pl. II, fig. i,h., k.). The
hook-apparatus appears, also, to be a little more developed. From the posterior part of the stomach in both. M. giganteum as
well as, also, in M. gigas, only two intestinal branches issue (Pl. IX, fig. 19). — — Host. Antedon celtica. Marenzeller
(Sladen). From Station 343, of the Norwegian North-Atlantic Expedition (Neighbourhood of Spitzbergen, Depth 743 fathoms.
Temp. — 1.2 (Celsius).
The species is one of the little migratory ones; all the specimens found were seated, on the disk of the comatula.
close to the mouth. One complemental male was found under the ventral side of one of the largest hermaphrodites
measuring about ’/a °f ’ts length.
Myzostoma graffi, n sj). (Pl, I, fig. I, 2.)
This species resembles M. marginatum, but is distinguished by its tongue-indented margin, and by the 20 cirri
situated, one upon each of the 20 tongues of the margin (Pl. I, fig. 1). The colour approaches to madder-brown, as in the last
mentioned species. The largest specimens measure up to 4.5 mm. in length. The bod)- is of moderate thickness and
circular in shape, with an arcuate dorsal surface and a translucent margin. The length of the cirri varies much, according as
they are more or less retracted. Exclusive of the tongues upon which they are situated, they measure 0.19 -0.22 mm.
in length. The dorsal surface is, usually, wrinkled and beset with tu mercies. The parapodia are situated nearer
’) What previous writers have designated suckers, I call by this, to my mind, more correct appellation.
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