The crustacean lacinia mobilis: a reconsideration of its origin, function and phylogenetic implications

~oologizal Journal of the Linnean Socieb (1982), 74: 133-146. With 15 figures

The crustacean lacinia rnobilis: a reconsideration of its origin, function and phylogenetic implications

ERIK DAHL

Department of <oology, University of Lund, S-223 62 Lund, Sweden

AND

ROBERT R. HESSLER

Scripps Institution of Oceanography, La Jolla, California 92093, U.S.A.

Accepted for publication June I981

The lacinia mobilis of the Crustacea Malacostraca is a more or less spine-like movable appendage of the medial mandibular edge, inserted near the base of the incisor process. It occurs in two or possibly three eumalacostracan superorders hut is retained in the adult stage only in the Peracarida. The lacinia has been interpreted as the distal member of the spine-row found in many adult Malacostraca and/or their larvae, or alternatively as a derivative of a certain cusp (‘cusp b’) of the biting edge of the primitive lophogastrids. The distribution, ontogeny and function of the lacinia were studied in a variety of Eumalacostraca. There is great variability in the guiding and locking mechanisms involved in biting, within the subclass and even within single orders. A lacinia-based guiding and locking system is likely to function only in weak mandibles. New evidence is produced in favour of derivation of the lacinia from the spine-row, and the ‘cusp b’ derivation hypothesis is rejected, ‘cusp b’ being only a highly specialized lacinia. Doubt is cast upon the unity of the superorder Peracarida mainly because the place of the order Amphipoda within it is regarded as insecure.

‘KEY WORDS :-Crustacea - Malacostraca - lacinia mobilis - evolution.

CONTENTS

Introduction . . . . . . . . . . . . . The occurrence of the lacinia mobilis among the Eumalacostraca .

Peracarida . . . . . . . . . . . . Eucarida . . . . . . . . . . . . . Syncarida . . . . . . . . . . . . . Hoplocarida . . . . . . . . . . . .

Biting in the Eumalacostraca . . . . . . . . . Conclusions . . . . . . . . . . . . . Acknowledgements. . . . . . . . . . . . References. . . . . . . . . . . . . .

. . . . . . 133

. . . . . . 134

. . . . . . 134

. . . . . . 135

. . . . . . 137

. . . . . . 137

. . . . . . 138

. . . . . . 144

. . . . . . 145

. . . . . . 146

INTRODUCTION

Ever since Calman (1904, 1909) defined the eumalacostracan divisions, the 133

002&4082/82/020133 + 14 $02.00/0 0 1982 The Linnean Society of London

134 E. DAHL AND R. R. HESSLER

main diagnostic features of the Peracarida have been considered to be the presence of oostegites in the adult female and of a mandibular lacinia mobilis in adults.

Other features listed by Calman are shared by other divisions, in particular the Syncarida, or have in other ways lost their significance as a result of the expansion of knowledge. This is the case with the number of articles present in the antennary protopod, supposed by Calman to be typically three in the Peracarida. However, this number is not found in all mysids, for the Stygomysidae have two articles. In cumaceans, isopods and amphipods, the antennary peduncle consists of five articles, but probably the three proximal ones can be taken as representing the protopod. In Tanaidacea and Spelaeogriphacea, on the other hand, the protopod consists of two articles.

More recently, Fryer (1964) concluded that the absence of oostegites does not exclude the Thermosbaenacea, placed by Siewing (1956) in a separate division, the Pancarida, from the Peracarida. This arrangement was also accepted by Hessler ( 1969).

All this tends to put still more emphasis upon the lacinia mobilis as the single diagnostic feature uniting the Peracarida. Therefore a fresh appreciation of the derivation, function and systematic distribution of the lacinia seems necessary.

\/t’ith respect to the morphological derivation two main hypotheses exist. Boas 11883) was of the opinion that the lacinia mobilis represents an enlarged terminal spine in a row of such spines found in the majority of adult peracarids between the incisor and molar processes. Manton (1928) instead chose as her starting point the strong biting mandible of the Lophogastrida, which lacks a spine-row, and derived the typical lacinia mobilis from the movable cusp (‘cusp b’) on the biting edge of the mandible. Gordon ( 1964) categorically refuted other possible interpretations.

The object of this paper is to make a fresh evaluation of the evidence concerning the derivation and function of the lacinia mobilis and to discuss related problems of phylogeny and systematics.

THE OCCURRENCE OF THE LACINIA MOBILE AMONG THE EUMALACOSTRACA

Peracarida

A well-developed lacinia mobilis is a normal feature of the mandible within all peracaridan orders. Generally there is a lacinia on both mandibles, but as a rule there are notable differences between the left and the right lacinia, the left one being in most cases larger and stronger. Sometimes the right lacinia is missing (or is indistinguishable from spine-row elements) and in certain specialized forms both may be absent. This is the case in certain isopods and amphipods. On the whole there seems to be much adaptability to functional demands.

Along the medial edge of the peracarid mandible the following elements are typically to be found, starting distally and going in a proximal direction. i 1) Incisor process. As a rule the incisor process is provided with a number of cusps

and teeth, but sometimes it has a perfectly smooth and very sharp cutting edge. In certain forms with piercing and sucking mouthparts (praniza larvae of gnathiid isopods, the amphipod genus Acidostoma), the distal part of the mandible may become lancet- or almost needle-shaped. Obviously the incisor process shows great adaptability to functional demands.

12) Lacznia mobilis. This structure is inserted just proximal to the incisor process

CRUSTACEAN LACINIA MOBILIS 135

and generally in line with and very near the last spine in the spine-row (see below), as seen, for example, in marsupial young of Gammarus pulex (L.) (Fig. 1). The actual shape of the lacinia varies considerably. Generally it broadens distally, where it is often serrate or provided with sharp teeth or blunter cusps. Sometimes its lateral margin is comb-shaped.

(3) Spine-row. In most cases the space between the lacinia and the molar process (see below) is more or less completely taken up by a row of spines. These spines often have an armature of their own in the shape of teeth, prongs, setules or comb- like structures. Sometimes their number is reduced or much increased. In the latter case they become hair-like and tend to form felt-like strips going up to and sometimes enveloping the molar process. For the pancarid species Monodella argentarii Stella, Fryer (1964) uses the term “lifting spines” for the spine-row, and this term probably could be applied universally. In amphipods of various species we have found evidence that the spine-row is involved in transferring food particles from the incisor region to the molar process, and there is good reason to suppose that this is its normal function. (4) Molar process. The typical peracarid molar process has a flat surface,

provided with various triturating devices such as ridges, spines and cusps. Marginally, especially along the dorsal margin, it is provided with setae of varying length. Like the incisor process, the molar process is also very adaptable and can disappear more or less completely or become so modified that only its position reveals its identity.

A mandible of the shape described above can be found in its typical form in members of all okders of Peracarida and is well exemplified by the mysid species Hemimysis lamornae as figured by Cannon & Manton (1927).

Eucarida

Adult Eucarida have strong mandibles, adapted for dealing with large and tough food items, and lack more delicate mandibular structures such as the lacinia

0.1 mm ~

Figure 1. Posterior view of the mandibles ofmarsupial juvenile ofGammarurpulcx (L.). llm, rlm, Left and right lacinia mobilis.


mobilis and the spine-row. These types of structure are sometimes found in the more lightly built mandibles of their larvae.

In the larvae of the euphausiaceans “Vyctiphanes australis G.O. Sars and Euphausia superba Dana an articulated, distally broadened and serrate spine, inserted just distal to the molar process, was identified as a lacinia by Sars (1885) and Fraser (1937). Neither from a morphological nor from a functional (cf. p. 138) point of view is this spine in a proper position to correspond to the peracarid lacinia. However, as recently shown by Weigmann-Haass (1977), a true lacinia, also drawn by the writers mentioned, is present just proximal to the incisor process in Euphausia hanseni Zimmer. Before we knew about this paper we made a similar observation in Meganyctiphanes noruegica (M. Sars) and drew the same conclusion. In E . hanseni the lacinia is found in the first calyptopis and persists through the larval stages up to and including furcilia 111. In furcilia VII it has disappeared without trace (Weigmann-Haass, 1977).

In larvae of decapods, Gurney (1942) interpreted “one or more spines adjacent to the incisor part” as representing the lacinia mobilis. We have studied larvae of Dichelofiandalus bonnieri Caullery and Pontophilus norvegicus M. Sars and found what we interpret as a well-developed lacinia mobilis in both species, although only on the left mandible.

In D . bonnieri larva I (Fig. 2) a bicuspid and combed lacinia articulates with the edge of the left mandible just proximal to the incisor process. Otherwise the mandibular edge is smooth, apart’from a triangular, toothed spine just distal to the molar. The right mandible lacks a lacinia but has two triangular toothed spines about halfway between the incisor and molar processes. In later instars, the armature of the edge between incisor and molar processes on both sides becomes more and more complicated with short triangular spines and longer and more slender ones, all of them armed. In the left mandible of larva V, where the lacinia retains essentially the same shape as in larva I, two more slender spines insert on the edge near and proximal to it. The lacinia and these two spines thus come to form a closely-spaced row on the mandibular edge. In the same specimen the mandibular edge of the VI (presumably last - Lebour, 1940) larval stage can be seen through the V larval cuticle (Fig. 3) . The distal part of the edge with the lacinia appears essentially unchanged but on the proximal part of the mandibular edge the spine-row is better developed with longer and more numerous spines.

L 0.1 m m $

Figure 2. Anterior view of the mandibles of a first stage larva of Dichclopandulus bonnieri Caullery. lm, Lacinia mobilk.


Syncarida

Noodt ( 1964) tentatively interpreted two articulated setae on the mandibular edge of Paraspgocaris andina Noodt as representing a lacinia mobilis. In a postscript to the same paper, however, he changed his opinion and with some reservation accepted the interpretation of Gordon (1964) whose paper had appeared in the meantime.

Noodt was undoubtedly right in changing his views with respect to the setae in Paraspgocaris. Their position halfway between the base of the incisor and molar processes differs from that of the lacinia in other forms, and they certainly appear to be too weak and in the wrong place to be able to perform a guiding function in biting (see p. 138 below). The fact that they are articulated means nothing, for both in euphausiacean and decapod larvae the spine-row may simultaneously contain articulated setae and non-articulated spines.

Schminke (1971) discussed the types of mandible found in the Bathynellacea. In the family Parabathynellidae, some but not all species of the genera Atopobathynellu and Hexabathynella have on the left mandible close to the base of the incisor process an articulated, blade-shaped and distally serrate structure which, with respect to location, shape, and armature closely resembles a typical peracaridan lacinia mobilis. In those cases where it is present, the distal one of the normal five spines of the spine-row is missing. Judging from its position and shape as well as from the shape of the right incisor process it could, and most probably does, function (cf. p. 138) in the same way as the peracarid lacinia Schminke, 1972: figs 4, 7-9). It would be idle to speculate over the reasons for its presence or absence in closely related species. Where it is not present in the shape described above, a strong and serrate non-articulated spine, which is probably its homolog, takes its place (Schminke, 1972: fig. 3). Schminke does not accept this structure as a lacinia mobilis. He agrees with the interpretation of Gordon, according to which such a view would be out of the question. Instead he tentatively suggests that the proximal part of the incisor process might represent a lacinia. In Anaspides, Gordon (1961, 1964) is inclined to homologize a small serrate process between the incisor process and the spine-row with the lacinia mobilis of Lophogaster.

The Syncarida thus possess a mandible where three of the four basic elements found in peracarids and eucarid larvae, viz. incisor process, spine-row, and molar are basically present. In a minority of cases the distalmost spine in the spine-row may become articulated and assume a shape indistinguishable from that of a peracarid lacinia mobilis.

Hoplocarida

The Hoplocarida have mandibles adapted for strong biting, and an arrangement very similar to that of the adult is reached very early in larval development. I n Squilla massavesis Kossmann, Gohar & Al-Kholy (1957) found an unarmed emargination between the acutely spiny incisor and molar processes in larval stage 1. In stages 3-4 this emargination is obliterated and a more or less evenly dentate biting margin borders the proximal part of the molar. The only notable change to take place later is the remarkable elongation of the molar process.

As seen from this brief description the hoplocaridan mandible is very highly I

138 E. D.WL AND R. R. HESSLER

specialized and nothing even remotely similar to lacinia and spine-row is to be found. This applies also to the earliest larval stages.

BITISG IN THE EUMALACOSTRACA

The present investigation was mainly based on the study of dead specimens. Only in certain amphipods and isopods did we have the opportunity to observe the movements of mouthparts and only in a very general way. The details of mandibular movement are obscured by the more posterior mouthparts, which in all but very small Crustacea are too opaque to permit deep focusing, as used by Fryer (1964 I in his study of living Monodella. Outside the Peracarida we rely exclusively on morphology. The lack of detailed observations of living specimens has to a certain extent been compensated by studies of series of preserved specimens where the mandibles have become fixed in positions illustrating various stages in the biting process.

:Is shown by Manton (1964), biting in the Crustacea is effected by the remotor phase of the promotor-remotor roll of the mandible. By a shifting of the mandibular axis and a selective strengthening of muscles, transverse biting can be achieved. The space within the head capsule available for musculature is a factor influencing the potential force of biting.

Biting in the Eumalacostraca is basically asymmetrical, the incisor process of the left mandible gliding obliquely or transversely over the anterior side of the incisor process on the right (Fig. 4). T o be effectkre this kind of biting demands guiding- locking mechanisms directing the mandibles into effective positions and preventing their dislocation.

The alternative to the evolution of such aiding mechanisms would be fixation of the mandibles to the head with such rigidity that the closing mandibles are kept strictly in one predetermined plane without any flexibility of movement. Unless the mandibular edges are made very strong, grave dangers of damage are inherent in such a pattern. Also, such a system would prevent the grinding movements of molars. Certain decapods with strong mandibles and a strongly grinding stomodaeum may approach this solution.

In typical peracaridan biting (Fig. 4), the right incisor process enters the gap between the left incisor process and the left lacinia, which in its turn glides into the gap between the right incisor process and the right lacinia, where the latter is present. It should be noted that this is compatible both with a shearing and a transverse closing of the incisor processes.

The function of the lacinia in biting appears to be three- or possibly fourfold. It contributes to cutting (cf. Fryer, 1964 on Monodella), i t helps guide the incisor processes into the right planes and to lock them into their final closing position. Probably a toothed or spiny lacinia also helps to hold food particles in place during the bite.

Judging by morphological criteria, the laciniae found in larvae of Euphausiacea and Decapoda fulfil the same function as in the Peracarida. The same would seem to be true of the movable terminal spine in the spine-row of certain bathynellacean syncarids. In connection with strong biting in large Crustacea, the lacinia tends to undergo structural and functional changes or to disappear completely.

In the large carrion-feeding amphipods Hirondellea gigas (Birstein and Vinogradov) and Euythenes gryllus Lichtenstein, the incisor processes have lost their

CRUSTACEAN LACINIA MOBILIS

Figures 3, 4. Fig. 3, Photomicrograph of the mandible of a 5th stage larva of Dichlopundulus bonnieri Caullery, with the rudiment of the 6th stage mandible visible through the cuticle. The lacinia mobilis remains in the same position as in Fig. 2 but it is now the terminal element in a short spine-row. Note the bending over of the mandibular edge. x450. Fig. 4, Scanning electron micrograph of the mandibles of an isopod of the genus Sforthyngura in posterior view, showing typical peracarid biting with the right incisor gliding into the space between the left incisor and the left lacinia mobilis. li , ri, Left and right incisor parts; lm, left lacinia mobilis; sp, spine-row; rn, molar.

139


dentition and have been transformed into thin and very sharp cutting edges which close in a shearing fashion, the right one gliding along a low ledge running obliquely across the subterminal part of the posterior side of the left (Dahl, 1979). Only the left lacinia is present and it is shaped so that it helps direct the right incisor process into the shearing and closing position described above.

In the lophogastrids the mandibles are of a very peculiar shape. This shape cannot be recognized in the drawings by Manton (1928, reproduced by Gordon, 1964) of Lophogaster and Gnathophausia. In order to represent the mandibular edge in one plane it is drawn as being more or less flattened. In fact the topography of lophogastrid mandibles is very different and as far as we know unique among the Malacostraca. From the scanning micrographs (Figs 5-9) it can be seen that the distal part of the left mandibular edge of Gnathophausia ingens (Dohrn), comprising the incisor process and the lacinia mobilis, forms somewhat more than a semicircle, open medially. The shape of the edge of the right mandible is even more complicated (Fig. 6), but when the mandibles close it fits into the hollow of the half-tube formed by the margin of the left mandible. In Lophoguster ppicus M. Sars the shape of the mandibles is essentially similar with a semitubular left and a complicated right mandible, the latter fitting into the tube. As seen from Fig. 5, the lacinia of the left mandible in Gnathophausia fills nearly the whole space between the incisor process and the molar process, only a small cusp projecting between the latter and the lacinia. On the right side a long non-articulated ridge with only two low cusps completely fills the same space. The function of the lophogastrid lacinia is not clear. In mounts with the mandibles retained in situ these parts are obscured by the overlying incisor processes. It is obvious that strong biting in the lophogastrids has been achieved by strengthening the mandibular edges and by the peculiar mode of interlocking the incisor processes.

It seems to be a point of interest that in certain other strongly biting and primitive Eumalacostraca without laciniae, a gliding and closing mechanism based upon a folding of the lateroventral mandibular margin has evolved independently. This is the case in Anaspides where both mandibular margins are bent over rectangularly backwards (Fig. 10). A corresponding arrangment is also found in later lawae and adults of Euphausiacea where, however, the bending is in opposite directions (Fig. 11)-backwards in the left, forwards in the right mandible. It is foreshadowed by a slight bending over of the lateral mandibular margin in the furcilia, which still retains the lacinia.

In some penaeid and eucyphid decapods studied by us, the incisor processes of the mandibles are vaulted without any lateral folding, although a bending of the mandibular margin is indicated in the larvae of Dichelopandalus and Pontophilus (cf. Fig. 3 \ . It is not clear whether the vaulting in the adult mandibles could in itself provide a guiding mechanism for an interaction. This appears to be the case with the short and broad mandibles of Pasiphae (Figs 12-13). In Pandalus with its long and narrow incisors, the molar processes are provided with strong lateral ridges which may prevent excessive movements of the mandibles (Figs 14-15). In none of the forms studied did we find any evidence of an interaction mechanism based on interlocking of biting cusps on the mandibular edges, the strongly armed ones found in Meganyctiphanes and Pusiphae shearing past each other. No astacurans, anomurans, or crabs were included in our material.

In summing up the evidence it appears that biting with the aid of a lacinia mobilis is the mode adopted by small eumalacostracans (Peracarida, many larvae


Figures 5-8. Scanning electron micrographs ofthe mandibles ofCnathophausia zngm (Dohrn). Figs 5,6, Medial views of left (Fig. 5) and right (Fig. 6) mandibles, showing the unique lophogastrid pattern with a very strongly curved left mandible into which the right mandible can be fitted and locked. Figs 7,8, Posterior views of the mandibles. li, ri, Left and right incisor parts; fm, lacinia mobilis; c, fixed cusp on right mandibular edge corresponding to lacinia; m, molar. x 60.

141

Figures 9- 1 1. Fig. 9, Scanning electron micrograph of detail of left mandibular edge of Gnathophausia ingm (Dohm). h, Lacinia mobilis; sp, spines which may represent a compressed spine-row; m, part of molar edge. x 120. Fig. 10, Scanning electron micrograph of mandibles of Anaspides tasmaniue (Thomson) in posterior view and biting position, with posteriorly bent edges of left (I) and right ( r ) mandibles guiding and locking each other. x 240. Fig. 11, Scanning electron micrograph of mandibles of Meganyctiphaws nomegica (M. San) in posterior view. The bent edge guiding and locking system in M. norveguu diffen from that of Anaspides faman& in having only the left mandibular edge (I) bent over posteriorly and the right edge (r) anteriorly. x 120.


Figures 12-15. Figs 12-13, Scanning electron micrographs of left (Fig. 12) and right (Fig. 13) mandibles of Pasiphue sivado Risso, showing the absence of specialized locking mechanisms. x 36. Figs 14-15, Scanning electron micrographs of left (Fig. 14) and right (Fig. 15) mandibles of Pandalus propinquus G. 0. Sam, showing the complicated locking mechanism provided by the molar surfaces. x 24.

I43


of Euphausiacea and Natantia) . The situation in Syncarida is somewhat confusing but the morphological evidence suggests that a lacinia type of biting occurs in certain small forms. A lacinia does not seem to serve strong biting in large Crustacea, where other mechanisms predominate; guiding and locking by means of mandibular edge folding has been found in Anmpides, in larvae and adults of Euphausiacea, in larvae of Decapoda, and in a highly peculiar form in lophogastrids. It appears to have developed independently in various groups.

CONCLUSIONS

Manton (1928) reasoned that the lacinia mobilis was derived from a cusp of the incisor process, and not a member of the spine row. The main elements in her argument were :

(1) In Lophogaster and Gnathophausia, the lacinia mobilis is developed as no more than a slightly articulated tooth on the left mandible and corresponds to cusp ‘b’ of the right incisor process, where no lacinia mobilis is present;

(2) the cusp pattern in these lophogastrids is similar to that of Meganyctiphanes except that cusp ‘b’ of the left incisor process is immobile in the euphausiacean;

(3) the base of the spine row in Hemimysis and the syncarid Anaspides corresponds to cusp ‘c’ of the lophogastrids.

This argument gains its force from the assumption that the lophogastrid mandible is primitive in the condition of its lacinia mobilis, the lack of a spine-row and continuity between the incisor and molar processes. This assumption, made without further documentation, but presumably based on the general primitiveness of lophogastrids, is weak. The teeth of an incisor process are heavily sclerotized and rigidly fused into a single biting unit. How could the articulation of cusp ‘b‘ evolve? There could be no selective value to the intermediate stages, such as a biting cusp which is immovable but with a weakly sclerotized base. Thus, the cusp hypothesis necessitates impossibly nonfunctional hypothetical intermediates, a situation against which Manton herself has repeatedly warned. Also, notwithstanding the general primitiveness of the lophogastrids, the pattern of their mandibles is among the most highly specialized types found within the Malacostraca and is most unlikely to be basic within the subclass.

No such difficulty accompanies the spine-row hypothesis. The most distal spine in the left row can gradually evolve into a highly differentiated lacinia mobilis and be fully functional and increasingly adaptive with every stage of advancement.

The cusp hypothesis also necessitates the conclusion that the spine row is a secondary acquisition, even though it is found in nearly every eumalacostracan division : all syncarids, larvae of the most primitive eucarids (euphausiaceans and natantians) and all peracarids except the lophogastrids.

The Lophogastrida are very primitive peracarids in terms of their internal anatomy (Sewing, 1958) and their possession of the fullest expression of a primitive caridoid facies, but primitive animals are rarely primitive in all ways. The condition of the mandibular biting surfaces is a likely example of this. Lophogaster, Gnathophausia and the adult euphausiacean Meganyctiphanes are large particle feeders. In these circumstances, if a lacinia mobilis were present, it might become secondarily reduced, and the cutting edge of the incisor process lengthened. This is seen in many scavenging lyssianassid amphipods (Eurythenes,


Hirondellea), where such a condition is clearly secondary (Dahl, 1979). In view of the difficulties attendant to the cusp hypothesis, the similarities in the details of dentition between the lophogastrids and the euphausids (to the extent that they exist at all) may be little more than coincidental, or at best a result of functional necessities. Indeed, in view of the fact that in Euphausia hanseni the lacinia mobilis completely disappears between furcilia VI and VII (Weigmann-Haass, 1977), it is impossible that its cusp ‘b’ could be related to the lacinia. In these terms, the cusp- like condition of the lacinia mobilis of Lophogaster is no more than one of the many ways a lacinia mobilis can become modified.

While much is made of the homologization of cusps ‘b’ and ‘c’ between major taxa (Gordon, 1964), careful reinspection shows that such an interpretation is by no means the only way the cusp patterns could be correlated (cf. figures of Gnathophausia, Anaspides, Meganyctiphanes, Pandalus and Pasiphae in the present paper). In our view, conclusions about the homology of cusps between different orders are unlikely to have a firm foundation.

The preceding considerations bear on the question of the unity of the Peracarida by showing that:

(1) a lacinia mobilis is not unique to the Peracarida; (2) it is derived from the distal member of the spine-row; (3) it may have evolved more than once. If so, then the presence of a lacinia mobilis cannot be regarded as a peracaridan

diagnostic feature. This leaves the possession of oostegites as the only peracaridan hallmark (the thermosbaenaceans not withstanding). However, taxa based on single characters should be regarded with suspicion, and there is cause to feel such concern in the present case because of the condition in the Amphipoda.

In view of the generally isolated position of amphipods as based on various features (ventrally flexed embryo; cleavage complete in early stages; maxilliped with fused coxa and lacking an epipod ; tagmatization of abdominal appendages into three pleopods and three uropods-Calman, 1909; Manton, 1928 ; Siewing, 1963), one may well question whether the placement of this group within the Peracarida’ is secure.

The present analysis emphasizes the presence of a spine-row as a common eumalacostracan feature, and reaffirms Boas’ ( 1883) hypothesis of a spine-row origin for the lacinia mobilis. One of the outcomes of this line of inquiry is to add doubt about the unity of the Peracarida. Interestingly, a lacinia does not seem to serve well in larger forms, and here a folding of the biting surfaces often seems to have evolved. Obvious throughout this research is the fact that detailed analyses of mandibular function in the Malacostraca are essentially nonexistent. In view of the exciting issues which are tied to this activity, it is hoped that this gap in our knowledge will not be left unfilled.

ACKNOWLEDGEMENTS

The present investigation was supported by grants from the Swedish Natural Science Research Council. For secretarial and technical aid we are indebted to Miss Ylwa Anderson, Mrs Ingrid Hallberg, Mr Folke Larsson, Miss Inger Norling, Dr Rolf Odselius and Mrs Inga Thomasson.


REFERENCES

BOAS, J. E. V., 1883. Studien uber die Verwandschaftsbaiehungen der Malacostracen. MorphologirchesJahrbuch,

CALMAS, M’. T., 1904. On the classification of the Crustacea Malacostraca. Annals and Magazine oJNaNatura1 8: 485-579.

Histopy, (7713: 144-158. CALMAS, W. T., 1909. Crustacea. In R. Lankester (Ed.), A Treatise on zoology, 7(3) :I-346. London: Adam &

Charles Black.

lamornae. Transactions of the Royal Society of Edinburgh, 55: 219-253. CANNON, H. G. & MANTON, S. M., 1927. On the feeding mechanism of a mysid crustacean, Hemkysis

DAHL, E., 1979. Deep-sea carrion feeding amphipods: evolutionary patterns in niche adaptation. Oikos, 33:

FRASER, F . C.. 1937. Early larval development of the Euphausiacea. Proceedings ofthe Linnean Sock& ofLondon,

FRYER, G., 1964. Studies on the functional morphology and feeding mechanism of Monodella argentarii Stella

GOHAR, H. A. F. & AL-KHOLY, A. A., 1957. The larval stages ofthree stomatopod Crustacea. Publications of

GORDON, I., 1961. On the mandible of Paranaspides lacwtris Smith-a correction. Crustaccana, 2: 213-222. GORDON, I., 1964. On the mandible of the Stygocaridae (Anaspidacea) and some other Eumalacostraca, with

GURNEY, R., 1942. Larvae of Deacapod Crustacea. Ray Socicty London, Monograph, 129: 1-306. HESSLER, R. R., 1969. Peracarida. In R. C. Moore (Ed.). Treatise on Invertebra& Paleontology. Part R, Arthropoda 4 :

LEBOUR, M. V., 1940. The lamae of the Pandalidae. Journal of the Marine Biological Association o f the United

MASTOX, S . M . , 1928. On some points in the anatomy and habits ofthe lophogastrid Crustacea. Transactions of

MANTON, S . M., 1964. Mandibular mechanisms and the evolution of arthropods. Philosophical Transactions of the

NOODT, W., 1964. Xatiirliches System und Biogeographie der Syncarida. Gewiisser und AbwiissPr 37/38: 77-186. SARS, G. O., 1885. The Schizopoda collected by H.M.S. “Challenger”. Report on the Scient@c Results ofthe Voyage

SCHMINKE, H . K. , 1972. Evolution und Homologisierung der Mandibeltypen der Bathynellacea (Crustacea,

SIEMTING, R., 1956. Untenuchungen zur Morphologie der Malacostra. zoologisthe Jahrbucha, Abteilung f i r

SIEU‘ING, R., 1963. Studies in malacostracan morphology: results and problems. Museum ofCmnparatiue <oolog~,

WEIGMANN-HAASS, R., 1977. The Calyptopis und Furcilia-Stadien von Euphausia hanreni (Crustacea :

167- 175.

149: 89-94.

(Crustacea: Thermosbaenacea). Transactions ofthe Royal Socicg of Edinburgh, 66: 49-90.

the Marine Station, .41-Ghrdaga, 9: 85-130.

special reference to the lacinia mobilis. Crustaceana, 7: 150-157.

R36GR393. Boulder, Colorado: Geological Society of America, Inc. and The University of Kansas.

Kingdom, 24: 239-252.

the Royal Sockty ofEdinburgh, 56: 103-1 19.

Royal Society ofLondon, (Bi 247: 1-183.

of H.M.S. Challenger during theyears 1873-1876, Zoology, 13: 1-228.

Malacostraca , . zeitschriff fur zoohgirche Systrmafik und Evolutwnsforschung, 10: 1 74-1 80.

Anatmie und Onlogenie d n Ticre, 75: 39-176.

Cambridge, MassaLhusetts, Special Publication : 85- 103.

Euphausiacea). Helgolandm Wissenschaftliche Meercsuntersuchungen, 29: 3 15-327.

Documents

The crustacean lacinia mobilis: a reconsideration of its origin, function and phylogenetic implications