111. General Part

Ekidia sp. 3 Belyaev, 1971 EEpidia sp. 4 Belyaev, 1971 Belyaev 1971, pp. 357-358, fig. 19. Belyaev 1971, p. 358, fig. 20. A few skin fragments taken in the Romanche A skin fragment taken in the Peru-Chile Trench Trench at 7340 m. Deposits up to 0.85 mm long; at 2140 m. Deposits up to 0.71 mm long, as diam. of axis c. 0.04 mm. robust as the ventral deposits of E. atakama. 111. GENERAL PART A. THE TAXONOMIC CHARACTERS AND fimbriata (9-60 mm), and an unidentified spe- THEIR VARIATION cies of Peniagone from St. 626 (9-10 mm). The papillae and tubefeet increase in number In order to estimate the importance of the dif- with advancing age in the species Laetmogone ferent taxonomic characters the range of varia- maculata, L. fimbriata, and Orphnurgus glaber. tion within each species should be known. An In Laetmogone violacea the papillae increase in examination of a large number of specimens of number, while the tubefeet number does not many species showed that there was a pronounced increase to any appreciable degree. As a rule, the variation in most taxonomic characters. number of ambulacral appendages increases with An individual variation is unambiguously the size of the specimens in those species of the revealed by differences between specimens from Deimatidae and Laetmogonidae in which they one and the same station. If two stations are are present in a large number. involved, the differences might be due to local Juvenile giant crosses are found in Psychropo- variation. tes longicauda, but otherwise an age variation in The range of individual variation in a taxo- the calcareous deposits is unknown in the Ela- nomic character may differ from one locality to sipoda. In many molpadonians the deposits be- another. This is clearly shown by the variation come irregular in shape and decrease in num- in number of dorsal papillae in Oneirophanta ber with the age of the specimens. Similar changes mutabilis. In the 14 specimens from St. 654 in were found in some aspidochirotes (e. g. Mitsu- the Kermadec Trench the papillae were surpris- kuri 1897a). In the Antarctic dendrochirote, ingly constant both in number and arrangement, Staurocucumis liouvillei, several generations of while in the 30 specimens from St. 716 in the deposit types were found in specimens ranging eastern Pacific the papillae varied greatly in from 0.7 to 13 mm in length (Ekman 1927). number and showed no regular features in the arrangement and type of reduction. The calcareous deposits A local variation seems to be of common oc- currence among the Elasipoda. Striking examples The endoskeleton in holothurians consists of are shown by four species of the Kermadec isolated calcareous bodies, the deposits. Synonym- Trench, in particular Oneirophanta mutabilis (p. ous terms are ossicles, sclerites, and spicules, the 243). latter term usually designating small and pointed A geographic variation, i. e. a variation of a bodies, as found in the Elpidiidae and Psychropo- larger scale, was found in practically all the tidae. widely distributed species known from many Diiben & Koren (1844a, b) were the first to use specimens. the deposits consistently in the description of the An age variation has been found in a few spe- species. Working on Scandinavian species they cies only. This may to some degree be ascribed found that these could be most clearly distin- to the almost complete absence of small speci- guished by their deposits. This high evaluation mens in the material (p. 10). Specimens smaller of the deposits as specific characters has been than 20 mm were caught in five species only: adopted by subsequent authors, sometimes to Ellipinion galatheae (17 mm), Elpidia glacialis such a degree that the deposits were the only (11-35 mm), E. theeli (7-12 mm), Laetmogone feature illustrated. The importance of the deposits in characteriz- 2. Interrelationship of the different types of de- ing genera and higher categories of holothurians posit. has been differently estimated. ThCel (1882), (1) The prinzary cross. Most holothurian depos- when creating his system for the Elasipoda, its begin as a rod with a bifurcation at either end attached little generic importance to the depos- - a primary cross. It has been commonly assumed its, while considerable attention was paid to that the types of deposit which cannot be traced them in the systems of R. Perrier (1902) and back directly to a primary cross are secondarily Hkrouard (1923). The interrelationship of the transformed. Only the wheels of the Apoda have different types of deposit and its bearing on the been regarded as a possible exception (Ludwig taxonomy of the Elasipoda was discussed by 1889-1892). Hkrouard (1923) and Ekman (1926). The bifurcation of the primary cross generally continues into successive dichotomous rami- fications, leading to the various types of reticu- 1. Intraspecific variation. lated plates which occur in all five orders of the The range of intraspecific variation in the depos- Holothurioidea. The large and feebly differen- its, contrary to that in other taxonomic features, tiated plates of many Dendrochirota and of the can be estimated from selected body samples only, genera Lleima and Oneirophanta within the and not from the examination of whole speci- Deimatidae represent the Ieast specialized type. mens. It is, therefore, important that the samples Hkrouard (1923) considered the reticulated are representative of the variation within the plate such a fundamental type of deposit that he specimen. In most species there is a consistent derived even the various spicule types of Elpidii- difference between the dorsal and ventral depos- dae from reticulated plates. The arms of the its - the ventral ones being more robust. This elpidiid spicules, according to Hkrouard, rep- difference may to some degree be phenotypic. resent zigzag-lines of internodia, emerging through Differences between deposits from different alternating reduction of one of the two branches parts of the dorsum or ventrum are usually of in each ramification. Hkrouard divided the spic- doubtful taxonomic value. The difference is ules in this family into 1) a quaternary type, with generally smaller than between dorsal and ventral the central growing point lying in the middle of deposits and is seldom refound from one speci- an internodium, and 2) a trinary type, with the men to another. Even when conspicuous differen- central growing point at a nodal point. The ces occur, as in the dorsum of one of the speci- dual origin of the spicules, according to Hkrouard, mens of Psycheotrephes magna from St. 234, they indicated that, at an early stage, the family sepa- are generally incidental. An exception is consti- rated into two distinct evolutionary trends. tuted by Orphnurgus glaber, in which the de- This complicated derivation of simple spicules formed deposits are increasingly robust towards was based wholly on speculation. No intermediary the posterior end of the ventrum. stages have been observed between reticulated The deposits of the ambulacral appendages are plates and the spicules of the Elpidiidae, and usually elongated or rod-shaped bodies which nothing in the morphology of the spicules sug- are less characteristic specifically than are the gests that their arms are constructed from a line fully developed deposits of the dorsum and ven- of internodia. HCrouard's ideas of spicule deriva- trum. They were as a rule examined in only a tions may, therefore, be left out of consideration. few specimens of each species. Ekman (1926) rejected the view of the primary Sometimes species, even belonging to different cross as the prototype of all holothurian deposits. genera, are indistinguishable by their deposits He maintained that, at least in the Elasipoda and (Oneirophanta setigera and Orphnurgus protec- Aspidochirota, some types of deposit were deriva- tus; Benthogone rosea, B. fragilis, and Laetmo- tives of a "Spitzstabchen" - a rod which is pri- gone interjacens; Laetmogone wyuillethomsoni marily undivided. This view led Ekman to re- and L. theeli; and some species of Peniagone). markable conclusions regarding the taxonomy of Nevertheless, the deposits proved to be the most the Elasipoda. reliable of the species characters. As the relationship of the different spicule The deposits are important also to the study types is of fundamental importance for an un- of geographic and local variation. derstanding of the phylogeny and taxonomy of the Elasipoda, it seems relevant to discuss Ek- tate a derivation of the former from the latter. man's views. In my opinion, the irregular "intermediary" spic- Deimatidae. According to Ekman, both spicule ules are more likely reduced stages of regular types are represented. While the reticulated plates tripartite spicules, which again may derive from and the crosses with spatulated, perforated arm a primary cross through reduction of two oE its ends were derived from primary crosses, some of arms. the rod-shaped spicules in the ambulacral appen- The rod-shaped spicules of Scotoplanes and dages in species of Orphnurgus, Oneirophanta, Ellipinion may be derived through reduction of and Deima were derived from "Spitzstabchen". tripartite spicules or directly from primary cross- As an example of a "Spitzstabchen" in Deima, es. Intermediary stages were found in Scotopla- Ekman reproduced one of the four tentacular nes clarki (Fig. 85) and S. globosa (Theel 1882, pl. spicules illustrated by Ludwig (1894, pl. PX: 1-4) XXXIV: 2). for D. pacificurn, disregarding the fact that the The spicules of Elpidia remain as the only three other illustrated spicules are intermediates type which cannot be traced back directly to a between rods and reticulated plates. primary cross. The uniqueness of these spicules is The pointed, spindle-shaped rods in the am- further underlined by their unusual optical bulacral appendages in species of the other features. Schmidt (1925), determining the position deimatid genera may seem to offer a more convinc- of the optical axis in representatives of the five ing example of c'Spitzstabchen".

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