CH1TOXIDJE. 



CHITONIDJJ. 



IMP 



e 



Shelly plate* or valves of Ohilon. 



Acephalous Molliuks, between Fuialann and llalanm. Poli, in Inn 

 magnificent work on Ibe 'Testacea utriusque Siciliie,' in giving the 

 anatomy of a Mediterranean species, became a valuable ally ; for 

 although he still retained Linnes clam of Multivalves, and although 



in hu anatomical detail* he 

 aid nothing of the nervous 

 system, a branch of animal 

 organisation essentially ne- 

 ceeaary to be known for 

 assigning an animal its true 

 place, he demonstrated 

 enough clear'yto show that 

 the Chiton bore no relation 

 to the other Multivalves of 

 I.innirtis. M. De Blainville 

 however, resting upon the 

 generative faculty of the 

 Chitons, proposed, in oppo- 

 Mti. n to these views of 

 CuvieT and Lamarck, which 

 had been adopted by almost 

 all zoologists, to form a 

 sub-type of Mollusks under 

 the name of Malentozoaria, 

 in which each of the Lin- 

 n;ran genera Lrpai and 

 Chiton constitutes a class; 

 the first tbe Lepadians, or 

 Lrpadicra, the second the 

 Polyplaxiphores, or Poly- 

 plaj-ipkorn. These almost 



/v>A UV A. singular views of De 



Aj iA Blaiuville have not pre- 



P^ll irll vw vailed among zoologists; 

 and Cuvier, in the last 

 edition of the ' Regne Ani- 

 mal,' arranges the Chitons 

 at the side of the Patella, forming from these two genera hia small 

 family of Cyclobranchinns. 



Deshayes, in the article ' Oscabrion,' in the ' Kncyclop&iie Mdtho- 

 dique,' enters at large into the organisation of the Chitons, and 

 diacusaes with much learning and acuteness the conflicting opinions 

 of Cuvier and De Blainville. 



The following is a summary of the structure of this family : 



Digestive Organs. No projecting head, in which the Chitons 

 resemble the Phyllidians. No tentacula, which are replaced by a 

 kind of veil which surrounds the mouth. Kyes, as in many other 

 Mollusks, the Pteropoda for example, wanting. Mouth and oesopha- 

 gus furnished with a very long tongue rolled spirally and armed with 

 norny teeth, a good figure of which is given by Poli. Loven has 

 pointed out that the teeth, especially the central one on the lingual 

 riband, are of great importance in determining the species. Stomach 

 intestine, and liver like those of the other Gasteropods. Vent at the 

 posterior extremity of the body, as in the Phyllidians, Dorii, Ac. 



Respiratory and Circulating Organs. The branchiae of the Chitons 

 consist of a range of small triangular leaflets placed, as in the Patella 

 and Phyllidia, in the furrow which separates the foot from the 

 mantle. The number and extent of the branchial laminae are of 

 importance in determining the species. The heart is situated poste- 

 riorly in the mesial and dorsal line ; it in symmetrical, and composed 

 of a single ventricle and two auricles. 



Their organs of generation are symmetrical, and repeated on each 

 aide of the mesial line, and there are a pair of sexual orifices. 



Shelly plate* or valve* of CMotirllvi. 



Animal of Chiton tqtuimona. 



a, the animal and (hell aeen from above ; b, the animal teen from below ; 

 r, aide view of the hell and animal In a creeping or adhering Hate ; rf, portion 

 of branch!* macnlned. 



The nervous system consists of wliat may be termed a complete 

 OBSopbagean ring, and of various branches, which are given off 

 divergingly towards the several organs. 



The locomotive organs consist of an oval foot, more or less wide, 



according to the species, and extends the whole length of the 

 animal. 



The shell is compowd of eight narrow, transverse, calcareous 

 pieces, overlapping each other, and strongly implanted on each .-idc 

 in a thick and fibrous border of the mantle, which surrounds the 

 whole body, and is sometimes, as we have observed, naked, but more 

 generally covered with small scales, spines, or hairs. These pieces are 

 not immoveable, as the animal can roll itself up or stretrh i:-.-if out 

 again for the purpose of progression or adhesion. 'I'.. ..rk this 

 machinery, there are three muscles given off from the first piece to 

 the second, three others given off from the second to the third, and 

 so <>M throughout, BO as to make the mechanism of this scalea 

 complete. One of tln-se muscles occupies the mesial and dorsal 

 line, the other two are lateral and oblique. Dr. J. K. Gray regards 

 the posterior plate as the homologue of the limpet nhell. 



The Chitons then resemble the other .M<>llu>-k : 1, in the general 

 form of the body ; l!. in the orpin ..f locom, <' the nature, 



form, and position of tbe branch he ; 4, in the heart, and in the 

 distribution of the circulating vessels ; 6, in the mouth and it* 

 veil; 6, in the tongue and the rest of the digestive organs; 7, in 

 the position of the vent; and 8, last, but not least, in the nervous 

 systtm. 



What, then, are the differences ? 1 , the form of the shell composed 

 of eight pieces instead of one ; 2, the mantle, which is more fleshy 

 and fibrous than in the other mollusks ; 3, the myology ; 4, the 

 double issue of the organs of generation, allowing this difference to 

 be established, whereas it is doubted. With regard to the abw 

 eyes, that defect exists in a considerable number of molluaks. 



Professor E. Forbes and Mr. Hanley place the family Chiloniilee 

 next before the Patellidir. They say : "As our knowledge stands nt 

 present, we prefer to regard them as an abnormal family of . 

 branrhiata, and trust before long that some active obsen 

 by the coast will occupy himself with studying the dcvelopm 

 the Chitons, and endeavour to ascertain the form they axxuine in 

 their larval condition. Whoever does so will make an important 

 discovery, and do more towards fixing the tnie position of these 

 anomalous creatures than all cabinet examinations of them have yet 

 enabled us to effect." 



Geographical Distribution. The species are numerous, and there 

 are few rocky shores without some of them. As a general rule, tin- 

 largest are found in warm climates, but there are exc-e. 

 instance, Chiton tctii/er and Chiton Bovxnii (King), are found on tin- 

 shores of Tierra del Fuego, and in the Straits of MagalhaetiB ; t In- 

 former of these species grows to the length of 2J inches, and the 

 breadth of 1 f inches, and the latter to the length of S\ inches, and 

 tbe breadth of H inches. 



The species are found on rocky shores, where they adhere, and also 

 on stones and other submarine bodies. They are found at depths 

 varying from the surface to 25 fathoms. A few are found creeping on 

 the sand. 



Most zoologists are agreed that there are no differences sufficiently 

 strongly marked to make a generic distinction between Chiton and 

 Chitonetlut ; and. indeed, the gradations from the one to the other 

 are so imperceptible, that there is no point where the line can bo 

 satisfactorily drawn. In the most completely-developed form of 

 Chiton the shelly secretion greatly preponderates ; in Ckitntn/lnii that. 

 secretion is comparatively small, and the great development is in t he- 

 border of the mantle, which, in some instances, almost hides the 

 comparatively-minute shelly pieces. 



a. Species with the Mantle-Border, or marginal ligament, cori- 

 aceous and naked. Examples, C. C'hilrnrit, Fremblry, and 

 C. Blainrillii, Broderip. 



C. Chilenru. Shell oblong-ovate, opaque, thick, dark brown, smooth, 

 dull ; inside white, with pink markings on the first, second, and hu,t 

 valves. Valves with longitudinal Mri.T, crossed by irregular con- 

 centric ridges. Anterior and posterior valves scmilunate, slightly 

 punctated ; second valve subcarinated, the front margin obtusely 

 angled, lateral margins arcuate, and the posterior with n pro: 

 beak, on each side of which diverges a rather elevated grain 



ridge ; the next five valves alike, bow-shaped, with a granulate ridge 

 on each side. Border smooth, coriaceous, tough, thick, darker 

 coloured than the shell, semipellucid, broad at the sides and narrow 



at the extremities. Locality, Valparaiso, in crevices of rocks and 

 under stones. (Frembley.) 



C. Blainvillii. In this species the shape of the coriaceous border 

 itself is not only very remarkable, but it is here and there fringed, 

 though not with hair. M. Deshayes has placed this under his . 

 of those species which have the border of the mantle fringed with 

 hair or spines, probably from not having seen a good specimen. 

 Shell roundish, anterior valve obscurely rayed, the posterior one very 

 small and abrupt; the others concentrically Unrated, the whole 

 being rosy, variegated with white brown, and greenish, and inu-rnally 

 white. The mantle-border orange-red, very narrow posteriorly, and 

 enormously produced anteriorly, rounded and fringci! 

 there, especially on its anterior margin, with some short coriaceous 

 processes. Locality, Inner Lobos Island, coast of Peru. 



