The larval development of the West Indian sponge crab Dromidia antillensis (Decapoda: Dromiidae)

J. Zool., Lond. (1966) 149, 297-319

The larval development of the West Indian sponge crab Dromidia antillensis (Decapoda : Dromiidae)

ANTHONY L. RICE* A N D ANTHONY J. PROVENZANO, JR.

Institute of Marine Science, University of Miami, Florida, U.S.A. 7

(Accepted 8 March 1966)

(With 15 figures in the text)

Larvae hatched in the laboratory from a berried female of the sponge crab Dromidia anfizzensis Stimpson have been reared through metamorphosis. The larval development in the laboratory consisted of six zoeal stages and a megalopa. These larvae 'are compared with published descriptions of those of Dromia personatus which is the only other species of the Dromiidae of which larvae have been described.

Contents Page

Introduction . . . . . . . . . . . . . . . . . . . . . . 297 Methods . . . . . . . . . . . . . . . . . . . . . . 298 Results . . . . . . . . . . . . . . . . . . . . . . 298 Discussion . . . . . . . . . . . . . . . . . . . . . . 312 summary . . . . . . . . . . . . . . . . . . . . . . 319 References . . . . . . . . . . . . . . . . . . . . . . 319

Introduction

The Dromiidae and other dromiacean crabs have long been recognized as primitive and have been considered by some authors to be close to the stock from which the highly evolved Brachyuran crabs arose. The study of larval development has been extremely valuable in indicating relationships among invertebrates but little attention has been given to larvae of the dromiids.

Within the Dromiidae abbreviated development has been reported in Cryptodroniia octodentata Haswell and Petalomera lateralis (Gray) (as Paradromia lateralis) by Hale (1925) who suggested that this might be the case also in Epipedodromia (= Platydromia) thomsoni (Fulton and Grant). The only described larvae of known parentage in this family are stages of Dromia personatus (Linn.) of the Mediterranean (Cano, 1893; Lebour, 1934; both as D. vulgaris Milne Edwards). No descriptions of complete larval development based on laboratory rearings are available for any species of this important family.

Dromidia antillensis Stimpson is distributed in the Western Atlantic from Bermuda and North Carolina southward to Brazil from the shore to 170 fathoms (about 3 10 m) (Rathbun,

* Present address: British Museum (Natural History), Cromwell Road, London, S.W.7, England. t Contribution no. 688 from the Marine Laboratory, Institute of Marine Science, University of Miami. This

research was supported by research grants RG-16298 from the National Science Foundation and GM-11244-01 from the Public Health Service, and a Harkness Fellowship from the Commonwealth Fund.

297

298 A N T H O N Y L. R I C E A N D A N T H O N Y J. PROVENZANO, JR.

1937). Characteristically, it carries upon its back a colonial invertebrate, usually a com- pound ascidian or a sponge but sometimes zoanthoid polyps. No details of its biology are known.

The present report is based on experiments in which larvae were reared from hatching through metamorphosis.

Methods On 9 February 1963 a berried female of D. antillensis was collected from the north east shore of

Key Biscayne off Miami, Florida. The specimen was kept in running sea water in the laboratory and several hundred larvae were hatched on 13 and 14 February 1963. Of these, 216 were placed in plastic compartmented trays, one animal per compartment, 18 compartments per tray. Each compartment contained approximately 50 cm* of filtered sea water. Single trays of starved animals were placed at 25", 20" and 15°C in 100% sea water and additional trays in 75 % and 50% sea water at 20°C. Fed animals were reared in 100 %, 75 % and 50 % sea water at both 25" and 20" but only in 100% sea water at 15°C.

The sea water in which the larvae were reared had been collected on three separate occasions in the Gulf Stream several miles offshore and stored in 5-gal. glass carboys. The salinity of this water was determined by hydrometers to be 37.5 ",,,&0-1%,, and distilled water was used to make lower experimental salinities.

Fed animals were given freshly hatched Artemiu nauplii and transferred to freshly prepared trays every second day. Trays were examined daily and exuviae and dead larvae were removed, washed in fresh water, and preserved in 70 % ethanol with glycerine added. A separate vial was used for preserving the exuviae and final dead specimen for each animal.

Casts and specimens to be examined microscopically were stained with Mallory's acid fuchsin red or lignin pink and dissected in 85 % lactic acid. All drawings were made with the aid of a camera lucida and details were checked at higher magnifications. In addition to the 216 experimental larvae, a smaller batch from the same brood was reared at 25°C and 100 % sea water to serve as a source of live material for drawings of whole animals. (In the illustrations the secondary setulation is frequently omitted for clarity.)

Measurements were made with the aid of the camera lucida. Total length (TL) was measured from the tip of the rostrum to the posterior border of the telson, exclusive of the telson processes. Carapace length (CL) was measured from the tip of the rostrum to the most posterior lateral margin of the carapace. All measurements are based on small numbers of specimens (less than 5), and therefore should be considered only as an indication of approximate ranges. The term stage is used herein in the sense of instar or intermoult. The female from which the larvae were obtained is deposited in the Museum of the Institute of Marine Science.

Results None of the starved animals moulted successfully into the second instar, but some lived

a t 25°C until six days after hatching, a t 20°C until seven days and at 15°C up to nine days after hatching. In 50 % sea water even fed animals failed to moult but survived longer than did starved animals, living for up to 12 days at each temperature.

Table I gives the numbers of fed animals which moulted into successive stages under the various experimental conditions. None of the larvae at 15°C survived to the iifth zoeal stage. At 20°C larvae kept in 100% sea water survived to the megalopa. At 25°C larvae survived to the megalopa in 75% as well as 100% sea water. The two individuals which moulted into a seventh zoeal instar died without moulting again, and all six megalopas obtained were produced directly from stage VI larvae.

L A R V A L D E V E L O P M E N T O F D R O M I D I A A N T I L L E N S I S 299

TABLE I

No. of larvae of Dromidia antillensis surviving into each instar under various experimental conditions

25°C 20°C 15°C Stage 100% s.w.* 75% S.W. 100% S.W. 75% S.W. 100% S.W.

I I1 111 IV V VI VII Megalopa Young crabs

18 18 15 12 11 6

2 2

-

18 16 13 13 12 9 1 2 -

18 18 14 11 8 5 1 2 -

18 11 8 6 2 0

18 13 2 1 0

* S.W., Sea water.

Table I1 gives the mean duration in days of the larval stages under the experimental conditions used, based on specimens which moulted successfully into the succeeding stage. The duration of the stages increased with decreasing temperature so that the time required to reach megalopa at 20°C (36 and 37 days) was 50 % greater than at 25°C (23 and 25 days).

TABLE I1

Mean duration in days of the larval instars of Dromidia antillensis under several experimerltal conditions ~~

25°C 20°C 15°C Stage 100% s.w.* 75% S.W. 100% S.W. 75% S.W. 100% S.W.

I 3.8 3.8 5.3 5.3 10.8 11 4.2 4.1 5.7 5.6 11.0 I11 4.5 4.0 5.5 5.3 10.0 IV 4.6 4.0 5.6 5.5 - V 4.3 4.1 6.8 VI 4.0 4.7 7.3 Megalopa 14.5

_. - _. -

- - _. -

* S.W., Sea water.

(Some earlier rearing experiments on Dromidia antillensis were carried out by one of us (A. J. P.) under rather less critical conditions in May and June 1962 and the results are worthy of mention. The animals were reared in 100 % sea water, the temperature of which varied between 25" and 28"C, and were fed brine shrimp nauplii. The average duration of the various stages under these conditions were; stage I, 3.0 days; stage 11, 2.8 days; stage 111, 2.5 days; stage IVY 2.9 days; stage V, 3.1 days, stage VI, 3.5 days and the megalopa 12.0 days.)

300 A N T H O N Y L. RICE A N D A N T H O N Y J. PROVENZANO, JR.

General morphology of the zoeal stages

Stage Z (Fig. 1, I and Fig. 2, I) CL 1.2 to 1.25 mm; TL 2.0 to 2.25 mm The carapace carries a well-developed, forwardly-directed, rostrum and a row of about

25 acute teeth on each postero-lateral margin, In the midline there is a blunt dorsal projection behind which there is a transverse groove and two pairs of lateral grooves. The whole surface of the carapace is sculptured with many striations running mainly posteriorly and towards the midline. These features of the carapace do not change appreciably throughout development.

The eyes are sessile at this stage. The second to fifth abdominal somites have each a pair of blunt dorsal projections and somite five carries a prominent seta at each posteriolateral corner. The telson and somite six to which it is fused have paired longitudinal ridges on the dorsal surface. The telson (Fig. 3, I) is triangular and its posterior margin has a marked medial notch, a fused spine at each corner, a hair-like second process and five pairs of long articulated setae.

The larva has a general orange appearance produced by many concentrated red chromatophores and diffuse yellow ones. The chromatophore pattern, like the carapace striations, was not seen to change appreciably during development and both these features are therefore illustrated only in the sixth zoea (Fig. 1, VI and VI(a)).

Stage ZZ (Fig. 1, I1 and Fig. 2, 11) CL 1.3 to 1.4 mm; TL 2.6 to 2.7 mm The carapace now carries a pair of antero-lateral spines at the base of the rostrum. The

eyes are free and there is a small antero-dorsal protruberance on each eye-stalk. The surface of the eye-stalks are now marked by striations similar to those on the carapace. The posterior margin of the telson (Fig. 3, 11) has an additional medial pair of setae, making a total of 8+8 telson processes.

Stage 111 (Fig. 1, 111) CL 1.5 to 1.6 mm; TL 2.7 to 2.9 mm The carapace and first five abdominal segments are essentially unchanged from the pre-

vious stage. The sixth abdominal segment in now separated from the telson which is more nearly square than in the previous stage and carries one less plumose seta on its posterior margin (Fig. 3, 111). It is apparently the third pair of processes, not the recently added eighth pair, which is lost. (In two specimens the third pair of processes were very much reduced but still visible.) The uropods are now free with the endopods unarmed while the exopods each carry 17 to 21 marginal setae and two sub-marginal ones. In two of the eight stage I11 zoeas examined in detail, the endopods were articulated with the basal segment while in the other six specimens there was no septum in this position.

Stage ZV(Fig. 1, IV) CL 1.7 to 1.8 mm; TL 2.9 to 3.3 mm The carapace is relatively broader and the rostrum relatively shorter than in the previous

stage. The lateral margins of the telson are now almost parallel. Both branches of the

FIG. 1. Dorsal views of the six weal stages of Dromidia antillensis. In VI the carapace grooves of the terminal zoea are indicated by the dottedlines. On theleft-hand side of this illustration the chromatophore pattern is shown, asterisks representing red chromatophores and the stippled areas representing the more diffuse yellow chromatophores. The bar scale represents 1.0 mm.

FIG. l S e e caption opposite.

302 A N T H O N Y L. R I C E A N D A N T H O N Y J. P R O V E N Z A N O , JR.

uropods (Fig. 3, IV) are now articulated with the protopodite which carries a small spine dorsally on its distal margin. The exopods carry 20 to 24 marginal setae and four sub- marginal ones and the endopods carry seven to ten marginal and two or three sub-marginal setae.

The pleopods make their appearance for the first time in this stage, generally as unsegmented biramous buds on abdominal segments two, three, four and five. However, in one specimen examined, the posterior two pairs were uniramous and very small and in another specimen pleopods were entirely missing from the fifth abdominal somite.

Stage V (Fig. 1, V) CL 1.95 to 2.10 mm; TL 3-85 to 4.00 mm For the first time the telson is more narrow posteriorly than anteriorly (Fig. 3, V). The

exopods of the uropods now carry 22 to 26 marginal setae and four sub-marginal ones, and the endopods have 10 to 14 marginal setae and three sub-marginal ones. The pleopods are now definitely all biramous but are lacking setae.

FIG. 2. Lateral views of zoeal stages I, I1 and VI of Dromidia antillensis. The bar scale represents 1.0 mm.

Stage VI (Fig. 1, VI and VIa and Fig. 2, VI) CL about 2.15 mm; TL about 4.45 mm The telson is now very much longer than broad, and narrows considerably at the posterior

margin (Fig. 3, VI). The exopods of the uropods carry 25 to 30 marginal setae, and the endopods 14 to 17 marginal setae. The pleopods are considerably larger than in the previous stage, but are still non-setose.

Cephalothoracic appendages of the zoeal stages An tennule

The antennules of the different zoeal stages are illustrated in Fig. 4. The major features of this appendage within each stage were very constant and the only variations noted were minor ones in the number of aesthetascs and hairs on the dorsal or outer flagellum. The illustration shows the progressive changes in this appendage.

I 0.5 mm I

m

FIG. 3. Dorsal views of the tail fan in the six zoeal stages of Dvomidiu untilleiuis. The bar scale represents 0.5 mm.


L J

E E

FIG. 4. The antennule in the six zoeal stages of Dromidia antillensis. The bar scale represents 0.5 mm.


Antenna In the first zoea, the antenna1 scale (Fig. 5, I) carries ten plumose setae on the distal

two-thirds of its medial margin. The proximal one-third of the medial margin and the entire length of the lateral margin carry many fine hairs. The endopod is about two-thirds the length of the scale in this stage. It carries three terminal setae, and one sub-terminal seta.

In stage I1 (Fig. 5, II), the scale carries setae on its lateral margin, as well as on the medial margin, there being a total of 18 to 23 marginal setae. The endopod is now relatively shorter than in stage I, being only about half as long as the scale. It still carries the four setae as in stage I.

TABLE I11

Variation in the armature of the endites of the maxillule in the zoeal stages of Dromidia antillensis

Zoeal No. of specimens Coxal Basal endite stage examined endite Teeth Setae

I 3 8-10 3 -4 2-3 I1 3 8-10 4 2-3 111 4 12 5 4 IV 5 15-16 5-6 5-6 V 4 16-19 6 6 9 VI 2 19-23 5 8-10

In stage I11 (Fig. 5, HI), the scale carries 23 to 26 setae. The endopod is now considerably less than half as long as the scale. In this, and subsequent zoeal stages, the endopod is either naked or armed with a single non-plumose terminal seta.

In the fourth zoea (Fig. 5, IV), there are 25 to 28 marginal setae on the scale. The endopod may be two-segmented; it is now relatively longer than in the previous stage and is about half as long as the scale. In addition to the two spines on the protopodite which were present in the earlier stages, up to three small spinules appear at this stage. The secondary spinules on the large spine are much smaller than in the third zoea. (The illustration does not show this well.)

In the fifth stage (Fig. 5, V) the scale carries 27 to 30 marginal setae. The endopod is definitely two-segmented and is considerably more than half as long as the scale. The large spine on the protopodite is no longer armed with secondary spinules.

In the sixth stage (Fig. 5, VI) the scale again carries 27 to 30 setae. The endopod is almost the same length as the scale and may be three-segmented. There are several small spines on both the dorsal and ventral faces of the protopodite.

Mandible The mandibles are massive structures, each with a relatively flat terminal area bordered

by a raised rim carrying corneous teeth. They do not alter appreciably in form throughout the zoeal stages, except for the addition of a palp which makes its appearance for the first time as a small bud in the fourth zoea and increases in size while remaining unarmed and unsegmented in the subsequent two stages.

306 A N T H O N Y L. RICE A N D A N T H O N Y J. PROVENZANO, JR.

Maxillule The general form of the maxillule (Fig. 6(a) and (b)) does not change throughout the

zoeal stages. In all six stages the endopod is two-segmented and carries a total of eight setae. The coxal and basal endites each carry a number of setae and stout spines and the changes occurring in this armature during the zoeal phase are summarized in Table 111.

I 0.5 m m

I

FIG. 5. The antennae in the six zoeal stages of Dromidia antillensis. The bar scale represents 0.5 mm.

L A R V A L D E V E L O P M E N T OF D R O M I D I A A N T I L L E N S I S 307

Maxilla The form of the maxilla is shown in Fig. 6(c). The illustration is of the maxilla of a third

zoea but the basic shape of the appendage is similar in all of the zoeal stages. The endopod in all of the stages carries a total of nine plumose setae in three groups, but the armature

\ I

\

\

FIG. 6.!Dromidiu untillensis. (a) Maxillule of the first zoea; (b) maxillule of the sixth zoea; (c) maxilla of the third zoea; (d) proximal lobe of the coxal endite of the maxilla in the sixth zoea. The bar scales represent 0.1 mm.


of the rest of the appendage changes considerably during development (Table IV). The setae on the basal endite and on the distal lobe of the coxal endite are all of one type, but the proximal lobe of the coxal endite carries two types of setae, a terminal group with rather stiff secondary setules and a sub-terminal row with much finer secondary setules, (see Fig. 6(a)).

TABLE IV

Variations in the setulation of the maxilla during rhe zoeal stages of Dromidia antillensis (numbers in parentheses are the numbers of appendages examined)

Stage Scaphognathite

I 13-17 (5) I1 16-19 (7) 111 20-26 (8) IV 26-34 (6) V 29-38 (4) VI 41-48 (3)

Basal endite Distal lobe Proximal lobe

3-4 (4) 5 (3) 4 (7) 4-5 (7)

4-5 (5) 4-5 (5) 5-6 (4) 5 4 (5)

8 (2) 7 (1) 9-10 (2) 8-9 (2)

Coxal endite Distal lobe Proximal lobe

4 (3) 6-7 (3) 3-4 (6) 7-10 (7) 3-4 (6) 9-12 (7) 4-6 (4) 12-16 (5)

7 (1) 16-20 (3) 7-8 (2) 29-32 (2)

First maxilliped The course of development of the first maxilliped through the zoeal stages is illustrated

in Fig. 7. No variations in the armature of the appendage were noted in the first and second zoeas. The armature of the exopodite showed some variation in the later zoeal stages, however, there being seven or eight natatory setae in the third stage, nine or ten in the fourth stage, 10 or 11 in the fifth, and 13 or 14 in the last stage. In the first three zoeal stages, the medial margin of the basipodite carries a total of 11 setae disposed in four quite distinct groups. In the later stages, this grouping is lost and there is some variation, there being 12 or 13 setae in the fourth stage, 13 to 15 in the fifth, and 15 to 17 in the sixth. The coxa bears a single seta mediodistally in the first stage, with others being added until there are six or seven in the ultimate zoea.

Second maxilliped (Fig. 8) As in the first maxilliped, no variations in the armature of the second maxilliped were

noted in either the first or second zoeal stages. The number of natatory setae on the exopodite varied in the third and later stages, the third zoea having seven or eight, the fourth nine or ten, the fifth 10 to 12, and the sixth 12 or 13. The only other variations noted were that the fifth seta on the penultimate segment of the endopodite may appear either in the fifth or the sixth stage and that in the sixth stage this segment may be sub-divided by a rather indistinct septum.

Third maxilliped The third maxillipeds of the first, second, fourth and sixth stages are illustrated in Fig.

9. Intermediate larvae showed correspondingly intermediate degrees of development, there being six or seven natatory setae on the exopodite in the third stage, seven or eight in the fourth, 8 to 10 in the fifth and 9 to 12 in the sixth.

L A R V A L DEVELOPMENT O F D R O M I D I A A N T I L L E N S I S 309

Pereiopods (Fig. 10) In stage I the first pereiopod is present as an unarmed, bilobed bud. In the second stage

the exopodite is cut off from the basipodite and carries four plumose setae. In the third stage it carries five setae, (Fig. 10, III), in the fourth stage, six setae (Fig. 10, IV), in the fifth stage six or seven setae, and in the sixth stage six to eight setae, (Fig. 10, VI). The

I 0.5 mm I , \, ',

FIG. 7. The first rnaxilliped in the six zoeal stages of Dromidia antillensis. The bar scale represents 0.5 rnm.


m m

FIG. 8. The second maxilliped in the six zoeal stages of Dromidia antillensis. The bar scale represents 0.5 mm.


endopodite becomes obviously cheliform in the fourth zoea and is distinctly segmented in the sixth or ultimate stage and even carries a few scattered setae.

There is no sign of the more posterior legs in the first zoea but at least the second and third pairs are present as simple buds in the second stage, and all the legs are present in the third zoea. These legs develop in a similar manner to the endopodite of the first leg, becoming distinctly segmented in the last zoea. While the posterior four pairs of legs do not develop definite exopodites, these structures are possibly represented by very small pro- tuberances on the basipodites of legs 2 and 3 in the later stages.

I 0.5 mrn

FIG. 9. The third maxilliped in zoeal stages I, 11, IV and VI of Dromidia untillensis. The bar scale represents 0.5 mm.

By the last zoeal stage the full adult complement of gills is developed in association with the legs (Fig. 10, VI). Thus the first leg has two arthrobranchs, legs 2 and 3 each have two arthrobranchs and one pleurobranch, leg 4 has one arthrobranch and one pleurobranch and leg 5 has only a single pleurobranch. In early stage six zoeas all of these are simple outgrowths which are hardly recognizable as gills, but in older examples of this stage all of the pleurobranchs and the arthrobranchs of the first leg are obviously branchiae.

Morphology of the megalopa The dorsal aspect of the megalopa is illustrated in Fig. 11. The megalopa has a furry

appearance because of setae originating from close to the bases of each of the carapace 22


spines and the presence of others as well. In the illustration the setae have been omitted, with the exception of those along the posterior border of the carapace, so as not to obscure the underlying structures.

T

FIG. 10. Dromidia antillensis. The cheliped in the third and fourth zoeal stage and all the pereiopods of the right side in the sixth zoeal stage. The bar scale represents 0.5 mm for I11 and IV and 1.0 mm for VI.

Certain features of the zoeal carapace, notably the grooves and dorsal projections have been retained in the megalopa. However, there are so many radical changes in morphology at this stage that there is little point in describing these in great detail, but all features illustrated for the zoeal stages have been illustrated also for the megalopa (see Figs 12 to 15). The telson (Fig. 15(a)) was similar in shape in all six specimens examined, but the number of telson processes ranged from 6 to 11 spaced unevenly along the posterior margin.

Discussion

There are no previously described larvae of the genus Dromidia of which the parentage is certain. However Gurney (1924) described larvae from the tropical mid-Atlantic which he

LARVAL DEVELOPMENT O F D R O M I D I A A N T I L L E N S I S 313

FIG. 11. Dromidiu antillensis. (a) Dorsal view of the megalopa; (b) lateral view of the anterior part of the carapace, the eyes, antennules and antennae having been removed. Almost all of the setae have been omitted from these illustrations for clarity. The bar scale represents 1.0 mm for (a) and 0.5 mm for (b).


attributed to the Dromiidae, stating that they probably did not belong to the genus Dromia. These larvae bear an extraordinary resemblance to our larvae of Dromidiu untillensis and it is very probable that his species is in fact a Dromidia. In more than 20 anatomical features

FIG. 12. Dromidiu untiZlensis megalopa. (a) Antennule; (b) antenna; (c) mandible; (d) maxillule; (e) maxilla; (f) first maxilliped; (g) second maxilliped; Q third maxilliped. The bar scale respresents 1.0 mm.

described by Gurney, his larvae are identical with those of Dromidia antillensis, as herein described, except that the endopodal lobe of the antennule appeared in his third zoea, whereas in our larvae it was first evident in the fourth stage, a minor point indeed. (As pointed out by Lebour (1934), Gurney’s specimens evidently represent the second, third and fourth zoeal stages and not the first, second and third, as he stated.) The gill formula


given by Gurney differs from ours in that there is only a single arthrobranch on legs 2 and 3 in his larvae, but even this discrepancy could be explained by his admittedly uncertain interpretation of the lobes.

Boone (1927) described a megalopa which she attributed to Dronzidia antillensis. Though her illustrations are rather inadequate her description is not inconsistent with our material.

FIG. 13. Dromidia antillensis megalopa. Right cheliped. (a) Ventro-lateral view; (b) dorso-medial view; (c) medial view of the palm. The bar scale represents 1.0 mm.

The only other genus in the family for which zoeal stages are definitely known is Dronziu. The first larva of the Mediterranean species of Dromia ( D . personatus, under the name D. vulgaris) was described by Cano (1893) who studied the embryology and early post- embryology of this species. The work of Lebour (1934) at Plymouth on the same species however, is in more detail. She was able to hatch first stage larvae in the laboratory, and some of these moulted to the second stage.

In addition to these definitely identified larvae there are a number of descriptions in the literature of zoeas and megalopas taken in the plankton and attributed to this species with varying degrees of certainty (Claus, 1876; Boas, 1880; Cano, 1893; Gourret, 1884; Lebour, 1934 and Pike & Williamson, 1960). The main differences between the larvae of Dromidia antillensis and those of Dronzia personatus (information mainly from Lebour and from


Pike & Williamson) are summarized in Table V. Since information is available for only a single species in each genus it is not yet possible to say which of these characters, if any, are generic.

TABLE V

Diferences between the larvae of Dromia personatus and Dromidia antillensis

Stage Character D. personatus D. antillensis

General

Zoea I

Zoea I1

Zoea I11

Terminal zoea

Megalopa

Postero-lateral carapace spines Postero-lateral carapace

serrations Supra-ocular spines Eye-stalk papillae Ridges on abdominal somite 6 Spine on protopod of uropods Total length * Maxpd. 3, endopod * Maxpd. 3, exopod

Legs Total length Ant. 1, endopod subterminal

Maxpd. 3, endopod Maxpd. 3, exopod Leg 1, exopod Other legs

seta

Pleopods Total length 3rd telson process Ant. 2, endopod Mandibular palp Maxpd. 1, exopod Legs Total length Maxpd. 1, exopod Maxpd. 2, exopod Maxpd. 3, exopod Maxpd. 3, endopod Carapace length Carapace L/W ratio Carapace greatest width Posterior telson margin Dactyl of P,

Epipod on PI

Present Absent Absent (Lebour) Present (Pike &Williamson) Present Absent Absent Absent Absent 2.9-3.2mm Naked Smaller than endopod 2

setae All present as buds 3.2-3.6mm Absent

5 setae 6 setae 5 setae Exopod buds on P,P,

Present as buds 4.0 mm Present but reduced 4 length of scale Present 6 setae Exopod buds on P,-P, 64mm 8 setae 8 setae 8 setae 5 segments 3.24mm > 1.5 Nearer posterior margin Straight or convex

Present from stage I1 Present from stage I1 Present Present from stage IV 2.0-2.25 mm 2 setae Larger than endopod naked

Only PI present 2-6-2-7 mm Present

2 setae 5 setae 4 setae Only PI and P, present as

Absent 2.7-2.9mm Lost ct length of scale Not until stage IV 1-8 setae No exopod on P, 4.45mm 15-17 setae 12-13 setae 9-12 setae 2 segments 2.5 mrr~ < 1.25 Nearer anterior margin Concave

buds-no sign of exopods

Not markedly different from Sickle shaped and sub-chelate

Present Absent P, and P,

* It is possible that Lebour (1934) and Pike & Williamson (1960) misidentified the parts of this appendage.


Though there has been fairly general agreement that the highly evolved Brachyura arose from within or very close to the Dromiacea, the origin of the Dromiacea themselves has been the subject of considerable discussion over the past 80 years or so. The mixture of anomuran and thalassinid characters exhibited by both the adult and larval stages of the Dromiacea has led to their being derived variously from within the Thalassinidea (Gurney, 1942; Pike, 1947), from within the Anomura (Ortmann, 1901), or from a post-thalassinid

FIG. 14. Dromidia antillensis megalopa. Lateral (posterior) views of legs 2, 3, 4 and 5 of the right side. The bar scale represents 1.0 mm.


stock intermediate between this group and the Anomura (Boas, 1880; Cano, 1893). Bouvier (1896), on the other hand, postulated a pre-thalassinid origin for the Dromiacea from Jurassic Nephropsidea. This theory was criticized by Gurney and was shown to be incorrect from palaeontological studies “by the discovery of a morphological sequence from extinct Triassic M a m a to extinct primitive Liassic Brachyura that existed before

(b) (C)

FIG. 15. Dromidia antilhsis megalopa. (a) Tail fan; (b) and (c) pleopods of abdominal somites 2 and 5. The bar scale represents 1.0 mm.

either the supposed ancestor or its supposed descendant had appeared on the scene” (Glaessner, 1960). However, the fossil record has led Glaessner to the conclusion that the Dromiacea did indeed have a pre-thalassinid origin and that both groups evolved inde- pendently from an extinct group of Reptantia, the Glypheocarida.

Pike & Williamson (1960) described the early larvae of Dromia personatus and Homolu barbata from the plankton and pointed out that Bouvier’s arguments for a pre-thalassinid origin for the Dromiacea were supported by a consideration of the known larvae of both the Droniiidae and Homolidae. Although the results reported here constitute the first description of a complete series of larval stages within the Dromiacea, the larvae of Dromidiu antillensis resemble those of Dromiu personatus so closely that this information does not add significantly to the facts available to Pike & Williamson and therefore only sub- stantiate the conclusions which they reached.


Summary

Larvae of the sponge crab Dromidia antillensis have been hatched from a berried female in the laboratory and reared under various conditions of temperature and salinity and fed on brine shrimp nauplii. Some of the larvae reared in 100 % and 75 % sea water at 25°C and in 100 % sea water at 20°C reached the megalopa stage, but at lower salinities and lower temperatures none of the animals passed through all of the zoeal stages.

The larval development in the laboratory consisted of six zoeal stages and a megalopa and these stages are all described and illustrated. These larvae are compared with published descriptions of those of Dromiapersonatus which is the only other species of the Dromiidae of which larvae have been described. There are a number of differences between the larvae of these species but it is not yet possible to say which of these differences, if any, are generic.

R E F E R E N C E S

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Boone, L. (1927). Crustacea from tropical Fast American seas. Bull. Bingham oceunogr. Coll. 1 (2): 1-147. Bouvier, E. L. (1896). Sur I’origine homarienne des crabes. Bull. SOC. philomath. Paris (8) 8: 34-110. Cano, G. (1893). Svillupo dei Dromidei. Atti Accad. Sci.fis. mat., Napoli 6 (2): 1-23. Claus, C. (1 876). Untersuchungen zur Erforschung der genealogischen Grundlage des Crustaceen-Systems. Wien :

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Documents

The larval development of the West Indian sponge crab Dromidia antillensis (Decapoda: Dromiidae)