ZOOLOGY

A RHIZOCEPHALAN PARASITE OF THE CR AB PTYCHOGNATHUS

BARBATUS (A. l\I. E.) FROM TERNATE

DY

H. BOSCHMA

(Communicated at the meeting of October 28, 1950)

During one of the visits of the Snellius Expedition to Terriate in the Moluccas, on the beach of the island numero us small Grapsid crabs (af ter­wards pro ving to belong to Ptychognathu8 barbatu8 (A. M. E.)) were found on the coarse sand and between and under pebbles. A great number of these crabs were infested by a parasite described here 'as anew species.

Sacculina ternatensis nov. spec.

Snellius Expedition, Ternate, September 27 -29,- 1929, 86 specimens.

Specific characters. Male genital organs in the posterior part of the body, outside the visceral mass. Testes of about equal size, globular, passing with a narrow' canal with internal chitinous co vering into the wide oval vasa deferentia. Colleteric glands with a very small number of branched canals. External cuticle without excrescences. Retinacula unknown.

The parasites are of small size, their greater diameter varying from 1.7 to 5 mm; they are, liowever, large in comparison to the size of their hosts, and almost invariably they are but partly covered by the abdomen. The smaller specimens (fig. 3 u, v, w) are of an oval shape; during further development the larger diameter increases more pronouncedly than the antero-posterior diameter, so that they become largely oblong, whilst of ten the central parts of the lateral surfaces remain narrower than the dorsal and ventral regions, so that then the shape of the animals may become distinctly panduriform (fig. la, b, c, dl. The mantie opening lies at the top of a short tube in the central part of the anterior margin ; it is slightly turned towards the left side (the surface of the parasite th at is facing the thorax of the host).

Though as a rule the parasites of the larger crabs are larger than those of the smaller, there is not a direct proportion between the size of the parasite and th at of the host. The following table refers to parasites on crabs which show a shape of the abdomen not noticeably differing from that of normal female crabs. In this table "No." means the specimen as indicated in the figures land 2; "S." is the length (in mm) of the proximal border of the penultimate segment of the abdomen of the host; "P." is the greater diameter (in mm) of the parasite.

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OaCJbOCJ

Fig. 1. Sacculina ternatensis nov. spec. a-d, left side of four specimens detached from their hosts; e-z, right si de of various specimens, each partly covered with

the abdomen of its host. X 6.

No. S. P. No. S. P. No. S. P. 1 e 2.5 4.7 1 f 2.8 4.7 2a 2.9 4.2 Iw 2.6 3.6 li 2.8 5.0 2d 2.9 4.7 Ik 2.7 4.7 1 r 2.8 3.7 2i 3.0 4.3 1 l 2.7 4.4 18 2.8 3.4 1 g 3.0 4.3 10 2.7 3.9 2j 2.8 4.2 Im 3.0 4.7 2n 2.7 4.2 In 2.9 4.4 1 t 3.3 3.8 Ih 2.7 4.6 lp 2.9 4.0 1 i 3.3 5.0

Here the crabs are arranged according to size; it is evident that there is no direct correlation between the si ze of the hosts and that of the parasites. The same obtains wh en the parasites are measured that occur on crabs possessing an abdomen not differing in shape of that of normal male crabs. In the following table "S." and "P." have the same meaning as in the table above, whilst " No." refers to the specimen as indicated in fig. 3.

No. S. P: No. S. P. No. S. P. 3 t 0.9 2.6 3x 1.1 2.8 3w 1.3 2.1 3v 0.9 2.2 3q 1.2 3.7 3z 1.3 3.0 38 1.0 3.3 3y 1.2 2.7 3r 1.3 3.6 3u 1.1 1.7 3p 1.2 3.2

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Fig. 2. Sacculina ternatensis nov. spec. Right si de of various specimens, each partly covered with the abdomen of its host. X 6.

Here again there is no direct correlation between the size of the hosts and that of the parasites.

In the majority of the specimens there is no manifestation of parasitic castration in sa far that the shape of the abdomen differs from that in normal female or male crabs. In some specimens, however, in which the abdomen still has the appearance of that of the female crab, it has become narrower in proportion to its length, thereby slightly changing towards that in the male sex (fig. Iq; fig. 2c, e, 0, p, r; fig. 3t, h). In other specimens this process has gone further, so that now the abdomen, besides being narrower than that of the normal female, has an ultimate segment of a more or less equilateral triangular shape, thereby changing still more towards that of the male abdomen (fig. 2t ; fig. 3d, l, m, n). }'inally in one specimen (fig. 3 0) the ultimate segment of the abdomen is very similar to that of the normal male, whilst the rest of the abdomen resem bles that of female crabs though being much narrower.

The parasite has not a fixed spot for penetrating the abdomen of its host. In the crabs possessing an abdomen showing the characters of the fe male sex the parasite may be attached to the proximal half of the

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Fig. 3. Sacculina ternuten.sis nov. spec. Right side of various specimens, each (cxcept i) partly covered with the abdomen of its host. x6.

abdomen (e.g., fig. Iv, x, y; fig. 28, t, z; fig. 3 j) or to the distal half (e.g., fig. 1 g, k, l, m, n, 0, q). On the other hand the parasites of crabs that have an abdomen showing the characters of the male sex almost invariably are attached to the dis tal half of the abdomen (fig. 3 p-z).

Occasionallya crab is infested by two parasites. These may be attached to the proximal half of the abdomen (fig. 2 p; fig. 3 b) or to the distal half (fig. 2 b; fig. 3 g, i). When two parasites occur on one crab they do not seem to suffer from want of space, for as a rule their shape does not differ from that of solitary specimens.

The internal anatomy could be studied in longitudinal sections of four specimens and in transverse sections of one. Especially the transverse sections distinctly show the structure of the male organs. These are found in the posterior part of the body, outside the visceral mass. Fig. 4 t repre­sents a transverse section from the posterior region. Here the male genital opening of the right si de is to be seen and the left vas deferens closely adhering to the body wall; the section moreover shows the posterior part of the right testis. In the next section (fig. 4 g) the posterior part of the left testis and the cavity of the right testis are visible besides the two vasa deferentia. The following section (fig. 4 h) in both male organs shows the narrow tube with its chitinous wall that connects the testis with its vas deferens; in the left male organ this tube leaves the vas deferens, ~n the right male organ it enters the testis. In the last section (fig. 4 i) the chitinous

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~.· . . . . ()o.·., .. ..

~

~

Fig. 4. SaccuUna ternatensis nov. spec. a -d, posterior parts of longitudinal sections of one specimen, a in thc region of the va.sa defel'entia, each following section from a slightly more ' dorsa.! region than the preceding; e, lougitlldinal sertions of the eolIeteric glands of two specimens; f - 1:, centra I parts of transverse sections of one specimen, f from the postcrior region, each following section from a slightly more anterior region than the preceding. lt, left testis; lvd, left vus deferens; rt, right

testis; rvd, right vus deferens. a -d, f -i, X 30; e, X 63.

tube joins the left "as deferens to its testis, of the right male organ the anterior parts of the vas deferens and the testis are shown. The two testes are more or less glabular; the two vasa deferentia are wide, slightly aval, their inner wall does not possess any ridges.

Of the longitudinal sections fig. 4 arepresents the central parts of the vasa deferentia. In fig. 4 b t.he chitinous tube is seen on the inner wall of the left vas deferens. Fig. 4 c shows the central part of the left testis and the chitinous tube on the inner wall of the right vas deferens. In fig. 4 d the central part of the right testis is visible. The longitudinal sections show that the male organs are contained in the posterior part of the body, outside the visceral mass.

Longitudinal sections of the colleteric gIands of two specimens are represented in fig. 4 e. In one of these the number of canals amounts to 6, these are drawn in black as the canals have no intern al covering of chitin. In the other specimen there are 5 canals possessing distinct layers of

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chitin. The sections are from regions in which the colleteric glands show their most pronounced division of the canal system.

In nearly all specimens examined the external cuticle of the mantie is entirely devoid of excrescences. Of ten this cuticle is completely smooth, in many cases it shows an outer layer that is slightly rough on 1tCeOunt of minute rugosities as represented in fig. 5 c. In one specimen a part of the external cuticle is covered with small papillae of a circular or oval shape (fig. 5 a). These have a diameter of 2 to 6 p, their height is about 2 p. In

0 0 a 0 0 0°

o 0 0 0 <::;:)

o 0 0 0 0 0 ° 0 Cl 0 C) CC) Cl

C 0 0 0 0 Cl

0 a <::;:) 0 <:::> 0 0 0 0

o a 0 ° 0 o~ C) <::l

0 0 0° a 0 <;:) <::l ~ 0

C ~ ~ <:) <::;:) 0 C)

~~~ <:::> ~ 0 0 <::;:) a

Fig. 5. Sacculina ternatensis nov. spec. a, upper surface of the external cuticle of a. specimen showing small papillae; b, upper surface of the extel'f1al cuticle of 8.

specimen showing small tubercles; c, section of the external cuticle of a specimen having the usual structure. X 530.

another specimen a part of the external cuticle shows small tubercles, very little extending above the surface, having a diameter of 6 to 11 P (fig. 5 b). These tubercles are arranged in rows.

As these peculiarities of the extern al cuticle were found in two specimens only, and in these in a small part of the cutiele only, we may safely regard these as abnormal features, and state that a smooth cuticle is characteristic of the species.

The external cuticle of the mantle is comparatively thin (thickness about 15 p), it has a tendency to appear in sections as an undulating layer (fig. 5 c), which may, however, be a result of contraction during pre­servation.

No retinacula were found on the parts of the intern al cuticle examined for this purpose.

A fairly large number of species of the genus Sacculina have, as the specimens dealt with above, an external cuticle that is devoid of excres­cences, or has a more or less uneven or roughened surface, or shows small excrescences of a very indefinite kind. Among these there are two species described by KOSSMANN (1872), Sacculina captiva of which no distinctive

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characters are known, and S. pomum of which it is stated that the two testes are united, proving that at least the latter is specifically distinct from the species described above.

In a previous paper (BoscHMA, 1937) the characters are noted of twenty species of the genus with an external cuticle without excrescences or with very insignificant excrescences. In seven of these, Sacculina caelata, S. calva, S. confragosa, S. glabra, S. pertenuis, S. rathbunae, and S. scabra, the male organs are situated in the visceral mass. The other species correspond with S. ternatensis by having the male organs in the posterior part of the body, outside the visceral mass. In contradistinction to S. ternatensis eight of these, S. anceps, S. curvata, S. flexuosa, S. gregaria, S. irrorala, S. plana, S. punctata, and S. rugosa, have colleteric glands with a weIl developed system of canals, a longitudinal section showing twenty or more of these canals. The remaining species, S. bicuspidata, S. gibba, S. pustulata, S. schmitti, and S. su lca ta , possess a smaller number of these canals. But in all of these the vasa deferentia are narrow canals, so that on account of this character they are distinct from S. ternatensis.

Among the species described by SHIINO (1943) there are six of the genus Sacculina that have an external cuticle without or with indistinct excrescences. In four of these, S. nigra, S. fabacea, S. pugettiae, and S. upo­gebiae, a longitudinal section of the most strongly branched region of the colleteric glands shows more than 20 canals. In two species, S. imberbis and S. pinnotherae, this number is smaller. These two species, however, differ from S. ternatensis by having comparatively narrow vasa deferentia.

In Sacculina robusta, another species without excrescences of the external cuticle, the number of canals in a longitudinal section of the colleteric glands is up to 23 or 24 (BoscHMA, 1948). Moreover, there are other characters separating the species from S. ternatensis.

Notwithstanding the lack of distinctive characters in the structure of its external cuticle the species described above, therefore, proves to be distinct from all other weIl known species of the genus by definite characters.

REFERENCES

BOSCHMA, H., '.rhe Species of the Genus Sacculina (Crustacea Rhizocepha.Ja). Zool. Meded., 19 (1937).

-----, '.rhe Rhizocephalan Parasites of the Crab Atergatis floridlls (L.). Proc. Kon. Ned. Akad. Wetensch., 51 (1948).

KossMANN, R., Bciträge zur Anatomie der schmarotzenden Rankenfüssler. Inaug.­Diss. (Würzburg 1872).

SHIINO, S. M., Rhizocephala of JapaIJ. Journ. Sigenkagaku Kenkyusyo, 1 (1943).