For a modern photo of a pycnogonid by Norbert Wu, click here.
|ART. XI. -
DESCRIPTION OF A NEW ANIMAL BELONGING TO THE ARACHNIDES OF LATREILLE; DISCOVERED
IN THE SEA ALONG THE SHORES OF THE NEW SOUTH SHETLAND ISLANDS.
By JAMES EIGHTS, M. D. (Communicated September 17, 1834.)
Gen. Decolopoda [From deca, ten; 'olos perfect; poda, feet]
Thorax. Elliptical, composed of five segments, separated from each other by slightly impressed articulations; anterior one produced into a head-like process. Contracted behind, and having on its superior surface a subconic tubercle with two eyes placed on each side; segments terminated at each extremity by a tubular joint, to which are attached ten perfect legs. Rostrum longer than the thorax, tubular, clavate arcuated downward, with a triangular aperture at its apex; inserted into the anterior portion of the head-like process below. Chelicerae rather longer than the rostrum, inserted on each side of its base, above, biarticulate, and terminated by a forceps composed of a finger and thumb, much curved, and meeting only a short distance along their tips, the superior finger, alone movable. Palpi setaceous, ten jointed, longer than the rostrum, inserted beneath the chelicerae. Egg-bearing organs attached to a process at the base of the palpi, ten-jointed, with a terminal incurved nail. Legs cylindrical, composed of a three jointed coxa, one jointed femur, and a two jointed tibia and tarsus, the latter terminated by a simple, slightly curved claw. Abdomen? attached to the posterior segment of the thorax by a movable articulation, small, sub-clavate, and perforated at its extremity by an anal incision.
Entire animal of a bright scarlet; disk of the thorax convex, beneath,
slightly so; on the superior surface of the tubular joints, near the margin,
are situated about four very small, rigid spines; basal joint of the chelicerae,
elongated. Palpi with the third and fifth joints elongate, the former
of greater length than the latter. Egg-bearing organs with the three first
joints small and sub-equal, fourth and sixth elongate, the remainder nearly
equal the four terminal joints are prehensile, and have their inner margins
dentated, the teeth arranged in about four longitudinal rows. Legs bony
and nearly equal, posterior pair rather smaller; joints of the coxae short
and subequal. Thighs about twice the length of the coxae, furnished with
small spines at their superior extremity. The first joint of the tibia
equal in length to the thigh, the other rather longer. Tarsi as long as
the thigh; the last joint of the tibia, and those of the tarsi, each armed
at their extremities beneath, with four rigid spines. Eyes very small.
Habitat: sea in the vicinity of the New South-Shetland Islands.
Cabinet of James Eights.
I have placed this interesting animal in the class ARACHNIDES, in consequence of its close approximation to Latreille's second family Pycnogonoides [Cuvier, Regne Animal], of his order TRACHEARIAE; it possesses all of the characters, besides which, it has a segment supporting two additional legs, making in all five perfect pairs; this latter circumstance would doubtless bring it in the preceding class CRUSTACEA, being a character which strikingly distinguishes the animals that compose it; at all events, I think it will certainly form a connecting link in the great chain of the animal kingdom, between these two classes, passing from the CRUSTACEA into the ARACHNIDES by the genera Nymphon, Phoxichili, Pycnogonum &c. Their mode of respiration I could not determine, as no appearance of the stigmata, through which they are supposed to breathe, were visible. Of the many specimens that I obtained, I saw none but such as were furnished with what are termed the egg-bearing organs, consequently, if those are the females that are thus distinguished, they prove much more numerous than the males.
The tegument covering the body is soft and yielding, the appearance of segments and articulations are necessarily faint, indicating that little motion of the parts is required.
They are to be found in considerable numbers in connexion with the fuci, thrown up by the waves along the shores of the islands, after being detached by the motion of the large masses of ice, from the bottom of the sea.