"Hymenodora glacialis, (Buchholz).
Syn. Pasiphaë glacialis, Buchholz, Die zweite Deutsche Polarfahrt. Zool. Pag. 279, Pl 1, fig. 2.
Hymenodora glacialis, G. O. Sars, Prodromus descriptionis Crustaceorum et Pycnogonidarum etc., No. 24.
Specific Character. — Carapax uniformly arcuate, with the dorsal carina, along the anterior part, bearing from 4 to 6 small teeth. Rostrum exceedingly short with the extremity pointed and the lower margin unarmed. Eyes almost conical with the point rounded off, and furnished with an opaque white pigment. Peduncle of 1st pair of antennæ short, cylindric, with the basal joint largest; outer flagellum longer and more powerful than inner; scale of 2nd pair of antennæ one-third longer than peduncle of 1st pair, broadest in the middle, with the outer margin smooth and terminating anteriorly in a dentiform projection; flagellum more than twice the length of the whole body. The 2 foremost pairs of legs precisely similar, alike in size and structure, with the chelæ but slightly incrassated and the dactyli shorter than the palm. Terminal joint on the 2 succeeding pairs elongate and tapering, on the last pair linear, and densely clothed with hair. Telson somewhat dilated at the point, which is armed with 7 spines, the 5 median of one length, but the 2 outer ones more than 3 times as long, and strongly diverging. Colour a deep blood-red. Length reaching 83mm.
Locality. — Stats. 33, 34, 35, 40, 52, 54, 137, 183, 205, 295, 297, 303, 343, 362.
Remarks. — This interesting and very peculiar form was first met with on the Second German North Pole Expedition, one specimen only having however been secured, which, in the aforecited work, Buchholz has recognizably described and figured. The said example having had to be handled with the greatest possible care, to admit of reserving it as a type-specimen, Buchholz could not of course undertake a comprehensive anatomical examination: and hence he failed to learn aught concerning the structure of the oral appendages, in which the generic difference between this form and Pasiphaë is most salient and conspicuous.
Description. — Form of body, contrary to what is observed in Pasiphaë (see figs. 1, 2), rather clumsy and almost round, not compressed from the sides as in that genus. The anterior division of the body measuring about one-third of the total length, and the posterior division tapering rapidly and uniformly backward.
All the integuments are remarkably thin and flexible, nay almost membranaceous; and hence the animal will rarely retain its form unchanged unless handled with the greatest care.
The carapax is comparatively large, covering the whole of the anterior division of the body. It is uniformly arched, with the height and breadth about equal, and the length well-nigh twice as great. Faintly marked lines indicate divers regions on the surface. That occupying the anterior part, viz. the gastric region, is most distinctly marked, and somewhat prominent, as also cut off by a sharply defined line from 2 smaller lateral areas — the hepatic regions. Along the middle, it is furnished with a distinct keel, which, on its anterior part, has from 4 to 6 small, anteriorly directed teeth. In front, this keel protends as an exceedingly short, compressed, and, at the extremity, acutely produced rostrum, of which the lower, somewhat arched, margin is perfectly smooth.
The anterior margins of the carapax exhibit under the rostrum a small incision for the eyes, bounded without and below by a triangular lobule (infraorbital spine). Beneath this lobule, are observed 2 exceedingly small dentiform projections, one placed at the side of the basal portion of the 2nd pair of antennæ (antennal spine), the other occupying the lower corner of the carapax (pterygostomial spine). The inferior margins of the carapax are uniformly arcuate, and the posterior margin, above, in the middle, is but very slight emarginate.
The posterior division of the body (see fig. 2) uniformly arched above, without the slightest trace of a keel, and without any one of the segments, in a strict sense, being hunched and projecting. The 5 anterior segments are furnished with thin, rounded epimera, exhibiting a similar relation to that in the true Caridians, the 1st pair projecting somewhat over the lateral wings of the carapax, while the 2nd pair partially overlap alike the preceding and the succeeding pairs. The 3 first pairs of epimera are as usual considerably larger and broader in the females than in the males. The terminal segment is exceedingly narrow, and in length about equal to the 2 preceding ones taken together.
The eyes (fig. 3) are comparatively small, and imperfectly developed. They are exceedingly narrow, and almost conical in shape, having, contrary to what is generally the case in other Macrurans, their greatest thickness at the base, whence they taper gradually and rapidly toward the extremity. Here is observed the exceedingly small, rounded ocular sphere, furnished with a very light, opaque, whitish pigment. Even the elements of vision would appear to be quite rudimentary, and the skin investing the ocular sphere exhibits but a faintly defined, irregular, reticulate (fig. 4). instead of the regular areolate, structure generally observed. On the boundary-line between the cornea and the stalk of the eye, occurs anteriorly a small tuberculiform projection. The peduncle of the 1st pair of antennæ (figs. 5, 6) is short and thick, almost cylindric in form, attaining scarcely one-fourth of the length of the carapax. Its 1st joint is largest, somewhat irregular in form, and furnished on the outer side with an exceedingly short, spiniform projection, from which a series of curved, plumose bristles extend posteriorly. The 2 succeeding joints are considerably shorter and narrower than the 1st, and about equal in size; the last is very obliquely truncate, from within to without. The 2 flagella are strongly developed; the inner quite slender and half the length of the body, the outer considerably longer, almost equalling the whole body in length, and at the base exceedingly tumid, as also densely beset with the usual riband-shaped sensory bristles.
The 2nd pair of antennæ are not, as in the forms previously treated of, attached in the same horizontal plane with the 1st pair, but are placed considerably lower down; and hence both pairs can be distinctly seen when the animal is viewed in profile (see fig. 2). The short and thick, indistinctly segmented basal portion (see fig. 7) extends, on the outer side, as a slightly projecting, triangular prolation, beset with bristles along the margin, and has on the inner side a slender, inward-directed spine (spina olfactoria).
The squamiform appendage (see fig. 7) is well developed, about one-third longer than the peduncle of the 1st pair of antennæ, and oblong in form, having its greatest breadth, which about equals one-third of the length, in the middle; the outer margin quite straight, the inner very considerably arched. The extremity is slender-obtuse, and, like the whole of the inner margin, beset with a closely arranged series of plumose bristles. In the outer corner of the scale occurs an exceedingly short, dentiform projection.
The flagellum is remarkably developed, more particularly in the males (see fig. 1), attaining upwards of twice the length of the body. Its peduncle (see fig. 7) is thick and muscular, composed of 3 articulations, the last being the largest.
The labrum (fig. 8) forms a somewhat galeate-projecting, fleshy lobule, of an irregular, quadrate form, on which can be distinguished a larger, arcuate median portion and 2 narrower lateral wings.
The labium (fig. 9) is deeply cleft, with the lateral lobules dilated toward the extremity, which is abruptly truncate, and in the outer corner produced to a point. Along the inner margin, these lobules are finely ciliated, whereas the outer and anterior margin is perfectly smooth.
The mandibles (fig. 10) are powerfully developed, and have, as in Pasiphaë, the part turning in toward the mouth lamelliform dilated, with the cutting edge sharpened, and divided into a great number of small acute teeth. Posteriorly, this part exhibits a somewhat inspissated region, armed with smaller and more closely arranged denticles, corresponding to the molar protuberance in other Macrurans. The right and left mandibles differ somewhat, on closer examination, as regards the character of the cutting edge. On the left side, the latter is perceptibly angular, while on the right it is more uniformly arched, and the molar protuberance on the left mandible appears, too, more abruptly truncate than on the right.
The presence of a distinctly developed, though exceedingly short, palp, essentially distinguishes the mandibles in the present form from those in Pasiphaë, which, as we know, has not this character. The said palp (fig. 11) consists of 3 well-defined articulations, of which the 2nd is the largest, the last quite small, oval in form, and beset with numerous diverging bristles.
The 1st pair of maxillæ (fig. 12) have all three branches distinctly developed. The median branch is, as usual, the strongest, compressed from the sides, and armed along the margin, obliquely truncate and directed toward the mouth, with a large number of short spines. The inner branch is likewise lamelliform and rather broad, as also densely setiferous along the inner margin. The outer branch is lanceolate, and directed anteriorly, without distinct bristles.
The 2nd pair of maxillæ (fig. 13) have, contrary to what is the case in Pasiphaë, the true maxillary part (endognath) well developed, and divided into 3 bristle-beset masticatory lobules. The mesognath is slender-lanceolate and furnished at the point with a few long and slender bristles. The exognath constitutes an oblong, translucent, membranous plate, beset round the margins with strong, plumose bristles, and having the posterior — narrower — portion somewhat incurved.
The 1st pair of maxillipeds (fig. 14) exhibit a widely different appearance from those in Pasiphaë, resembling rather the said parts in the typical Caridians. The endognath is divided into 2 lamelliform masticatory lobes, of which the anterior is exceedingly broad, and densely beset along the inner margin with delicate bristles. The mesognath has the same narrow and simple form as in the 2nd pair of maxillæ. The exognath constitutes an anteriorly directed oblong plate, beset along its outer margin with strong, plumose bristles. It ends obtusely rounded, without a trace of the usual terminal lash. The epignath is comparatively of inconsiderable size, and forms a small plate, of a spongious structure, attached by a slender stalk to the outer side of the basal part.
The 2nd pair of maxillipeds (fig. 15) are likewise developed in the manner common to the typical Caridians, and differ greatly from those in Pasiphaë. They consist, exclusive of the stem and its 7 distinct segments, of a well-developed exognath and epignath. From the basal joint of the stem, protends inward a bristle-beset lobule, representing the true endognath, while the rest of the stem corresponds rather to the mesognath on the preceding pair. The penultimate joint is lamelliform, nay almost securiform-dilated, and constitutes, together with the exceedingly small preceding joint, a geniculate curve. Along the outer, arcuate margin, it is beset with numerous bristles and spines. The terminal joint, which a straight suture separates from the penultimate, is considerably smaller, oval, and armed along the inward-directed margin with a series of sharp spines. The exognath, attached to the outer side of the 2nd joint of the stem and protending straight forward, has an exceedingly slender, linear form, and at the end is indistinctly articulated, and beset with bristles; the epignath exhibits a structure similar to that in the preceding pair, but a well-nigh circular form. Posterior to the latter, proceed from the outer side of the basal part a narrow, linguiform lobule, which also occurs on the succeeding pair, and on all of the legs.
The 3rd pair of maxillipeds (fig. 16) are greatlv produced, pediform, and reach, extended anteriorly, about to the point of the scale of the 2nd pair of antennæ. Of the 5 joints of the stem, the 3rd is the largest, and less distinctly separated from the preceding, as also a good deal curved. The terminal joint is not much shorter, tapers rapidly toward the extremity, which is drawn out to an awl-shaped point. Like the preceding joints, it is beset with dense fascicles of bristles, which, more particularly on the inner margin, are strongly developed; true spines, however, do not occur.
To the outer side of the 2nd joint of the stem is attached a well-developed exognath, on which can be distinguished a narrow, cylindric basal portion and a somewhat compressed, multiarticulate terminal part, beset with long, plumose bristles. The whole length of the exognath, when fully extended, equals about one-third of the length of the stem.
Finally, on the outer side of the basal joint of the stem is attached an oval or elliptic epignath, strikingly distinguished by having assumed the character of a true branchia, 8 or 9 distinct transverse folds rising from its outer surface.
All of the legs have a well-developed natatory branch (exopodite) attached to the outer side of the 2nd joint, as in the Schizopods, corresponding to the so-called exognath on the oral appendages.
The two anterior pairs are shortest, and, as in Pasiphaë, furnished with chelæ; the three posterior pairs are, on the other hand, simple at the extremity.
The 1st pair of legs (fig. 17) are scarcely as long as the last pair of maxillipeds, and comparatively feeble in structure. Of the joints, the 4th is the largest, and longer than the three preceding ones taken together. The 5th joint forms along with the 4th, as a rule, a strong, geniculate bend, and is hardly one-third as long as the latter. The 6th joint, or hand, is but little thicker than the preceding joint, and measures about one-fourth of the length of the leg. The fingers, as compared with those in Pasiphaë, are exceedingly short, scarcely half as long as the palm, somewhat slender, and at the point slightly curved (see, too, fig. 18). All of the joints are more or less densely beset with bristles, in particular along the inner margin; the bristles on the hand itself, however, are very short.
The natatory branch is powerfully developed, and reaches, anteriorly extended, beyond the 4th joint. For the rest, its structure perfectly agrees with that of the exognath on the last pair of maxillipeds.
At the base of this pair of legs, as also of the three succeeding pairs, are attached 2 well-developed branchiæ, and, anterior to the latter, the basal joint forms a tuberculiform projection, furnished with a bunch of long, curving bristles.
The 2nd pair of legs (fig. 19) are similar in size and structure to the 1st, being distinguished from them merely by a somewhat different proportion in length between the 3rd and 4th joints, as also by the fingers of the chela being a trifle longer.
The 3rd pair of legs (fig. 20) are very feeble in structure, and greatly produced, their length about equalling that of the whole anterior division of the body. The 3rd joint is a trifle shorter than the 4th, and both exhibit along the inner margin a single series of sharp-pointed spines, exclusive of slender bristles. The last joint is greatly produced, and slender, tapering a little toward the extremity, and provided with scattered fascicles of bristles. The terminal claw is about half as long, falciform, and beset along the inner margin with delicate spines. The natatory branch has precisely the same appearance as that on the two preceding pairs, and not even is the bristle-beset, PG 42 tuberculiform 2Jrojection at the base wanting.
The 4th pair of legs are in no respect distinguished from the preceding pairs.
On the other hand, the last pair of legs (fig. 21) exhibit distinct deviations. They are about of the same length as the two preceding pairs, but taper less abruptly toward the end, as also the proportion in length between the different joints is somewhat different. Thus, the 3rd joint is considerably longer than the 4th, and entirely without spines, whereas the bristles on the inner margin are longer and more numerous. The 5th joint, too, is comparatively larger than in the preceding pair, and very little, if at all, shorter than the 4th. Finally, the last joint is perfectly linear in form, everywhere of the same breadth, and along both margins, but especially the inner, beset with short, scopiform fascicles of bristles. The terminal claw is quite rudimentary, obtuse at the end, and, as a general rule, entirely concealed among the bristles of the preceding joints.
The branehiæ (see fig. 22) exhibit the usual pyramidrical form aud lamellar structure, but are characterizcd by their considerable number. On eitber side occur 10, including the supplementary branchia mentioned above as found on the last pair of maxillipeds. If we except this and the hindmost branchia (see fig. 21), both of which are odd ones, the rest occur in a double series, so that each leg has 2 branehiæ (see figs. 17 and 19).
The natatory appendages of the abdomen (figs 23. 24) are powerfully developed, and consist of a thickish, muscular, and somewhat flattened basal part, along with 2 slender, lanceolate branches, or terminal plates, beset with numerous ciliated marginal bristles. Of these branches, the inner is somewhat shorted than the outer, and at the base furnished on the inner margin with a comparatively large, cylindric, or somewhat claviform, appendix (see fig.24). The 1st pair are in this respect distinguished from the rest chiefly by the said branch being exceedingly short and of a simple oval form. Some difference, too, is observed in these parts on comparing the sexes. In the male, they have on the whole a more powerful structure, with the basal portion comparatively shorter and broader, and less densely beset with bristles. The inner branch on the 1st pair (see fig. 28) is also considerably broader than in the female, and has the extremity almost truncate. On the 2nd pair (fig. 29), are seen, attached to the inner branch, 2 appendices of which the anterior and shortest corresponds to that in the female, while the other is peculiar to the male, and has the form of a narrow, linguiform plate, beset along the margins with strong, spiniform bristles.
The telson (fig. 25) is remarkably narrow and elongate in form, and projects considerably beyond the outer caudal appendages (see fig. 1). Its anterior fourth has an approximately cylindric form, and thence it rapidly and uniformly tapers in a posterior direction, the hindmost part thus becoming exceedingly narrow. The point itself (fig. 26) is somewhat dilated, and exhibits a slightly outward-curving terminal margin, to which are attached 7 spines. The 5 middle ones are uniform in size and appearance, whereas the 2 outermost are far more powerfully developed, and upwards of 3 times the length of the others, as also widely diverging to either side. Along the sides of the appendage, and somewhat nearer the dorsal surface, is observed a series of 6 exceedingly small denticles.
The outer caudal appendages (fig. 27) have a short and simple basal part. Of the terminal plates, the inner is lanceolate, and beset round the edge with long, plumose bristles. The outer plate is a trifle longer than the inner, and at the point somewhat obliquely truncate, with the outer margin perfectly straight and beset with short and slender bristles, the inner slightly arcuate. At the outer corner, occurs an exceedingly small and rudimentary denticle. For the rest, the plate is quite simple, without the slightest trace of a transverse suture in its outermost part.
In a living state, the whole body of the animal, together with its various appendages, has an exceedingly vivid and brilliant blood-red colour. The long flagella of the antennæ exhibit in their basal part more or less distinctly alternating rings, or transverse bands. The ocular pigment is, as stated above, opaque white.
The length of the largest individuals met with, measured from the point of the antennal scale to the tip of the telson, was 83mm. The males would as a rule appear to be larger than the females.
Development. — The very considerable size of the eggs attached beneath the abdomen of the female (see fig. 2), gives reason to surmise, that the development, either occurs direct, as in the genus Bythocaris, or that, at all events, it is merely connected with an imperfect metamorphosis. Meanwhile, roe was found in a single specimen only, and the stage of development did not admit of undertaking any investigation with the said object in view.
The smallest individuals obtained, measuring 16mm in length, exhibited in all essential characters precisely the same structure as full-grown individuals, without its being possible to detect the slightest trace of a previous larval stage.
Occurrence and Habits. — Judging from its whole organization, the form here treated of would appear to lead a kind of semi-pelagic existence; in other words, I have reason to suppose, that, unlike the forms previously recorded, this animal is not strictly confined to the sea-bottom, but can move about freely through the water. Meanwhile, the rudimentary character of the eyes indicate with absolute certainty its habitat as chiefly lying in the deeper strata, a fact to which the experience derived on the Norwegian Expedition gives full confirmation. All of the specimens collected were brought up in the dredge or trawl from the greatest depths in the cold area — 452 to 1862 fathoms. In shallower water we never took it, nor in the surface-net, which not- withstanding was extensively used on the Expedition.
Finally, I will not fail to remark that Mr. R. Collett has found the remains of this form in the ventricle of one or two deep-water fishes whose organization is such as must infallibly prevent them from ascending to any great distance from the sea-bed, viz. -- Raja hyperborea Collett and Lycodes frigidus Collett, both brought up from the great depths of the cold area.
As a remarkable coincidence, it is worthy of note, that the specimen examined by Buchholz is said to have been taken at the surface of the water. Assuming this to have actually been the case, we cannot but regard it as anomolous. The animal had probably from some incidental circumstance, by an undercurrent or in some other manner, been carried up trom the deeper strata, where the species must obviously be assumed to have its true habitat.
Though the form described above, judging from its powerfully developed natatory organs and trifling specific weight, must be deemed an exceedingly vivacious animal, the specimens we succeeded in collecting gave without exception but very faint manifestations of life, notwithstanding they were captured as a rule in a perfectly unmutilated state and as soon as possible isolated in a vessel containing fresh sea-water. The reason of this must clearly be, that the animal, on being suddenly brought up to the light of day from the enormous depths it inhabits, is placed in such abnormal conditions as cannot fail to paralyze all its vital functions. For the rest, similar phenomena may be observed, to a greater or less extent, in most other marine animals whose habitat is the great depths of the ocean.
Distribution. — The specimen described by Buchholz was taken, as previously stated, in the open sea, east of Greenland, and near the 74th parallel of latitude. On the Norwegian Expedition, the form occurred at not less than 14 different Stations, all in the cold area. Finally, Mr. R. Collett found the remains of a specimen in the ventricle of Lycodes frigidus, at Stat. 353, from which we had not recorded this Crustacean.
Hence, the known limits of its distribution are confined within the deep basin, filled at the bottom with ice-cold water, that extends between Spitzbergen, Beeren Eiland, and Norway on the one side, and Greenland, Jan Mayen, and Iceland on the other, — from the 63rd to the 80th parallel of latitude."
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