siderablj stronger than in Terebella and pull the lateral regions inward, so that the area
of each ventral longitudinal muscle forms a rounded and prominent ridge on each side.
The dorsal longitudinal and the ventral longitudinal muscles are about equally developed,
though from the firm boundary of the ventro-lateral spaces the latter are occasionally
thicker. Two strong muscular strands pass from the lower edge of the alimentary canal
to the circular coat in the mid-ventral line. A noteworthy feature is the attachment of
the oblique muscles (pm.) above the feet, instead of the fibres leaving the foot at its
lower border beneath the bristles. The nerve-cords lie outside the circular muscular
coat as two large and prominent areas, the ventral groove being dimpled in transverse
section. The hypoderm covering the prominent ventral ridges is remarkably thick till
it is well within the deep median furrow, where it abruptly thins off at the sides of the
nerve-cords, which appear to be covered only by a thin layer which forms a kind of
modified cuticular covering. The cords are thus in close relation to the surrounding
medium. The size of the trunks is of interest in connection with the brilliant phosphorescence
of the species. The segmental organ seems to open below the upper attachment
of the oblique muscle. The alimentary canal is typical.
In TerebeUides stroemi, Sars, the hypoderm is somewhat firm and granular. The
circular muscular coat is thin, though in the dorso-lateral regions its fibres are increased.
The dorsal longitudinal muscles are much extended, and a lateral muscle is cut off by a
powerful band which passes from the foot to the outer edge of the ventral longitudinal,
the body thus having a rounded ridge on each side ventrally. The nerve-cords are small,
and lie within the hypoderm and strong circular muscular coat between the somewhat
flattened ventral longitudinal muscles. The slender oblique are attached on each side of
the trunks, unless it be held that the strong band cutting off the lateral longitudinal
corresponds to these muscles.
The nomenclature of the Terebellids in former years seems to have been peculiar.
Thus, Dujardin’s1 Sdbellina brachycera is a form with seven tentacles and eyes on the
upper fold as in a young Terebellid. On the other hand, his Sabdlina tenuis2 in the same
paper with ten filiform tentacles and four ocular points behind them and two on the tail
resembles Ehrenberg’s Amphicora.
Hessle (1917) does not think the distinctions into fore, middle and hind brain
according to Nilsson’s view hold in the Terebellimorpha, for the cephalic ganglia are
reduced to a nervous band over the pharynx and the distinctive fusions between the parts
are absent. In most of the Terebellidse the nuchal organ is in abeyance, but in Thelepus
and allied genera it is a small ciliated groove on each side.
Nilsson thought the tentacles derived their nervous supply from the posterior region
of the fore brain, but Hessle doubts this interpretation.
The segmental organs in Terebellids occur as looped organs in the anterior region
with internal and external openings, and ranging from four to sixteen or more in
number. In Lanice conckilega, however, Cunningham8 describes four functional organs
in segments 6—9, besides traces of three others in front of these, and fused membranous
1 * Ann. Sc. nat./ 2e ser., t. xi, p. 292, pi. vii, figs. 6—8.
| Ibid., p. 291, 1839.
3 Quart. Journ. Micr. Sci., N.S., vol. xxviii, p. 250, pi. xviii, figs. 11—13.
nephridial sacs in segments 10—13. The wide internal openings of the four fully-
developed organs are attached to the body-wall close behind the ventral “ fascicles of
somites 5—8, and are overhung dorsally by a longitudinal lip furnished with a series of
small digitate processes; lower down the anterior and .posterior lips of the opening are
simple, thick-walled and ciliated. The -aperture leads into a thin tube, which passes
inward and backward, curving round the inner end of the fascicle of bristles behind the
aperture, and then, crossing the continuous tube, passes up on the inner or mediad side
of the loop, at the apex of which it is continued into the efferent wider limb of the loop,
which passes down on the outer side to open into the longitudinal tube. He found
nephrostomes attached to the anterior faces' of the«||pta behind segments 2 and 3,
but no external apertures in segments 3 and 4. Communications between successive
nephridia were found—the only case in Invertebrates and Cunningham thinks
it approximates the condition , of ithe nephridial system in Vertebrates. The gonads
are in the form iff small, indifferent cells attached %|the exterior of the seyén nephro-
stomata, and are early shed into the coelom, where they undergo further development
(CunTnihneg.hseagmm).ental organs in the Terebellids have a well-developed nephrostome and a
■ longerll shorter U-shaped canal. ifhe anterior organs with the opening of their funne|s:.
in the-diaphragms differ from the posterior, which have larger funnels and their ducts
lie in the nephridial mass (Hessle). Their variabilij|S'was notioed by Meyer (1887), the
anterior differing from the posterior in the relative length of their canals. Whilst in
most genera the organs are free, they discharge into a longitudinal connecting duct
in Lanice and Loimia, and a similar arrangement: occurs in Pista and in Laniades,. In
Amphitrite, whilst the anterior organs are free; the posterior lie very close to each other,
but ho communication has been observed. Hessle-.(19.17) utilises the .nephridia in his
classification, but they do not seem to be of special service in this respect, m \ i
Amongst interesting structural features in the Terebellids are the occurrence of
statocysts and statoliths near the cephalic ganglia, in such as Amphitrite Edumrdsi, for
example, and the presence of cardiac bodies in many.
■ The genus Terebella was founded by Linnasus for a series of red-blooded worms
sometimes embedded in sand, and at first forming a heterogeneous group from which
subsequent naturalists withdrew many speoies. In the twelfth edition of his ‘ Systema
Naturse’^767), amongst other forms he inserted TembelJd lapidmia, which had been
briefly described by Kahler, from Marseilles, in 1754.
Savigny’s (1820) first tribe of the Terebellid® under the general group of the
Serpulids was Terebellse simplices, in which the upper lip was not dilated into two lobes,
the appendages of the first and third segments forming four lateral lobes directed
forward. Branchi® three pairs, ramified to .the. base and inserted on the second, third
and fourth segments. Ex. T. oottehilega, T. mectusee, T. drrata.
His second tribe, T. PhyeeKse, was characterised by having the superior lobe dilated
at the base-in two . tentaculiferons divisions, No appendages, to. the first and third
segments. Two pairs of branchi® ramified to the base and inserted on the second and
third segments. Ex. Tevebella scyllcL, T. cincinnatd.
The third tribe was the T. IdaUae, in which there were no appendages to the first