Spatulate Tips Research Articles

The structure and arrangement of echinoid tubercles

Tubercles and spines of 33 species of extant irregular echinoids were studied to provide data for interpreting tubercle structure and arrangement in fossil echinoids. Tubercle morphology is analysed functionally. It is possible to infer much about the posture, movement and function of the associated spine from tubercle morphology. The development and direction of areole enlargement and the structure of the platform are the most important features in this respect. Surface stereom porosity is used to differentiate tubercles and miliaries, which bear either spines or pedicellariae, from granules, which have no such appendages. Tubercles of regular echinoids are usually radially symmetrical and can be broadly separated into fixed-pivot and sliding-pivot systems. In irregular echinoids, spines are usually modified for a particular function and tubercle morphology is correspondingly varied. The power stroke of the oral spines is radial in pygasteroids and holectypoids, whereas, in clypeasteroids and cassiduloids, it is posterior. This is reflected in their different burial and locomotory behaviour. Oral spine and tubercle arrangement in Cassidulus resembles that found in spatangoids and this again is reflected in its behaviour. Spine and tubercle differentiation becomes quite pronounced in certain clypeasteroids. It is argued that lunules and notches are modifications which allow sand dollars to feed on the organic-rich surface layer of sediment while remaining infaunal. Tubercle and spine diversity is most pronounced in the spatangoids and is described in detail for Echinocardium. Each group of spines with a particular function is associated with morphologically distinct tubercles. Tufts of spines are readily recognizable from the tubercle arrangement. The considerable variation in the arrangement of spines and tubercles within the anterior ambulacrum is thought to reflect the varying emphasis placed on adoral transportation of sediment. Fasciole arrangement shows no correlation with depth of burial or grain size of the substratum. Aboral tubercle density is correlated with sediment grain size. To maintain a water-filled space between the tip of the spines and the test surface, echinoids increase spine density and develop a uniform covering of spines with either distally swollen or spatulate tips. In spatangoids, a more effective coverage is achieved by development of curved or oblique aboral spines, and the aboral mucous coat prevents fine particles from falling between spines and clogging the burrow. The structure and arrangement of tubercles can be extremely useful in palaeobiological studies.

本邦産Puerulusの2型、特にゴシキエビのPuerulusについて

As to the puerulus of Panulirus japonicus (v. SIEBOLD), detailed morphological and some ecological descriptions have been made by the present writer. Wherefore some informations mostly on the puerulus of Panulirus versicola (LAIR.) ?=P. fasciatus, DE HAAN, 1850? will be given in this article. Nine pueruli and 2 first-young-forms were dealt with. Of these pueruli, 5 obtained from Japan (Izu, Shizuoka Pref. and Misaki, Kanagawa Pref.) in September and October, and the rest from Palau Islands. The fact that the puerulus of P. versicola has been found from Japanese waters is new to science. The body-lengths run from 19.0-22.6mm in the puerulus, from 20.7-21.0mm in the first-young-form (Table 1). The puerulus is greatly characterized by having vestigial exopodite of the third maxilliped, much longer (2.1-2.2 times as long as body-length in P. versicola, about 1.3 times in P. japonicus) antennae with spatulate tip stained with rather deep brown colour (in alcoholic specimens) in distal 6-8 segments (Fig. 3.), and eighth thoracic sternite armed with a large acute spine on ventral side of each lateral edge. The puerulus of P. versicola differs from that of P. japonicus by the following traits besides those given above, viz., the carapace has more elevated median carina, and largely has the spine-f (Fig. 1), and the endopodite of the maxillae is provided with 2 lobes on inner distal margin (Fig. 4, I). Some descriptions in regard to the puerulus of P. versicola have been given by ORTMANN (1894), CALMAN (1909), and DE MAN (1916). But no one has given description on the signal feature of the antennae.