26 



HARDWICKE'S SCIENCE-GOSSIP. 



[Feb. 1, 1S70. 



PIGMY CRUSTACEANS. 



THERE are two small species of the curious 

 family of Pycnogonidse, which I find iu toler- 

 able abundance on this coast, and as they belong to 

 a class of creatures to which very little attention 

 appears to be paid by microscopists generally, I pro- 

 pose to jot down a few particulars which I have 

 been able to glean respecting them, in the hope that 

 they may interest some of the readers of Science- 

 Gossip, and possibly induce some other seaside 

 naturalists to look up the anatomy and life-history 

 of this obscure but very singular group of crusta- 

 ceans. 



The information to be obtained from books re- 

 specting the natural history of the Pycnogonida; is, 

 so far as my experience goes, very limited. Most 

 popular writers either pass them over without notice, 

 or are content with a very casual mention of them, 

 and I have not yet been able to learn that there is 

 any full and exhaustive account of them extant. 

 The best account of their anatomy which I know of 

 is that contained in Dr. Carpenter's " Microscope 

 and its Revelations," 4th edit., pp. 636-638. 



Cuvier classed the Pycnogons among the Tra- 

 chearian arachniclce , the order to which the mites, 

 ticks, and chelifers belong — a classification which 

 is, I believe, now admitted by the best authorities 

 to be erroneous. They are considered to be true 

 crustaceans, but exhibit a singular degradation of 

 type, the digestive and circulatory organs being re- 

 duced to a very rudimentary form. 



The two species which are the subject of the 

 present paper are the Achelia Mspidata and 

 Pallene pygmcea of Hodge. They both inhabit 

 rock-pools, between tide-marks, and seem espe- 

 cially to affect the bushy tufts of Corallina officinalis, 

 which are the favourite haunts of so many forms 

 of microscopic life. A pickle-bottle full of this 

 weed brought home for examination at leisure, has 

 generally rewarded me, on careful search, with a 

 score or more of specimens, which, on being placed 

 in a tumbler of sea-water, with a few fronds of 

 coralline, soon make themselves' at home, and may 

 be kept alive and healthy for months with very 

 little trouble. Eor microscopic purposes I find 

 them improve by keeping, as they get rid of the 

 coating of diatoms and other extraneous matters 

 which, when freshly caught, frequently obscures the 

 satisfactory view of their internal arrangements. 



I have before me, in the zoophyte trough, while 

 writing, a group of some half-dozen individuals cf 

 the two species named. With a two-inch objective 

 and the dark-field illumination, a very good idea of 

 their general form and structure may be obtained. 

 At first sight they might almost be taken for dimi- 

 nutive specimens of some of the long-legged spider- 

 crabs, Inachus or Stenorhynchus, to which genera, 



in 'their" sprawling' gait and gaunt skeleton-like 

 aspect, they bear not a Little resemblance. They 

 sprawl leisurely over the weed, to which they cling 

 very tenaciously by means of their powerful hooked 

 claws; and when, as is often the case, two 

 or three individuals come into contact, the long 

 legs get mixed up into a state of most admirable 

 confusion. Two or three of the specimens before 

 me have attached to the under side of the thorax 

 one or two roundish masses of spawn. These are 

 carried in a sort of loop formed by a pair of false 

 feet, with which the females are provided, but which 

 are entirely wanting in the males. The spawn is 

 carried until hatched, after which the larvse appear 

 to reside on the body of the parent for some time, 

 probably until washed off, and compelled to shift 

 for themselves. The newly-hatched young (fig. 33) 



Fig. 33. Larva of Achelia at birth, x 160. 



are curious, active little creatures ; they are fur- 

 nished with four bristle feet and a very formidable- 

 looking pair of chela?, which they use with consider- 

 able energy. 



It is not uncommon to find females loaded with 

 spawn and young at the same time, and a very 

 curious sight it is, reminding one of the prostrate 

 Gulliver with the citizens of Lilliput climbing over 

 his body. I have not yet been able to trace the 

 development of the larvse beyond the next stage of 

 their career, I presume after undergoing their first 

 moult. In this state they present the appearance 

 shown in fig. 34. They have increased greatly in 

 size, and though their general form continues the 

 same, show a marked advance towards the perfect 

 state. The pulsations of the stomach can be plainly 

 seen, and the rudiments of the csecse of the limbs, 

 to be described presently, also make their appear- 

 ance. Beneath the thorax is seen the projecting 

 mouth, from which a short gullet passes backwards 

 to the gizzard, and a dark spot on the upper sur- 

 face of the thorax shows the position of the eyes. 

 In this stage I find them grubbing about among the 

 refuse of decaying weed, excrement of Polyzoa, &c, 

 at the bottom of the vessel in which they are kept'; 

 and, from their appearance, they do not starve. 

 There does not appear to be any marked difference 

 between the larva of Pallene and Achelia : the spe - 

 cimens figured are of the latter. 



Let us now glance at the anatomy of the adult Pyc- 

 nogon, selecting for that purpose a fine specimen of 



