Argulus papuensis n. sp., a new fish louse (Crustacea: Branchiura) from Papua New Guinea
Sophie K. Rushton-Mellor Department of Zoology, The Natural History Museum, Cromwell Road, London SW 7 5BD, UK
Accepted for publication llth May, 1990
Abstract
A new species of Argulus (Crustacea: Branchiura) is described from a sleeper, Bunaka herwerdeni (Weber), in Papua New Guinea. It is characterised by the shape of the respiratory areas, the number and shape of supporting sclerites in the suckers of the first maxilla, as well as the accessory copulatory structures on the third and fourth legs of the male.
Introduct ion
Crustacean ectoparasites of the genus Argulus M(iller are found world-wide but few have been reported from the Australasian zoogeographical region. This is the first record of a species of this genus from Papua New Guinea, although few studies of the parasites of fresh and brackish water fishes have been carried out in this region. The specimens in question represent a new species which is described below in detail.
Materials and methods
The Argulus were collected from the sleeper, Bu- naka herwerdeni (Weber), caught in the Sepik River by Dr I.L. Owen of the Central Veterinary Laboratory, Boroka, Port Moresby, Papua New Guinea. They were examined and dissected in lactophenol. Drawings were made with the aid of a drawing apparatus. Specimens for scanning electron microscopy were dehydrated through graded acetone, critical point dried, sputter co- ated with gold and examined under a Hitachi 800 electron microscope.
Argulus papuensis n. sp.
Description
Adult female. General body form squat (Fig. 1); carapace sub-oval, comprising about 85% of total body length. Mean body length 5.50 mm; range 3.42-7.61mm (based on 8 specimens). Ventral surface of head ornamented with numerous irreg- ularly arranged spicules. Lateral lobes of carapace partly overlapping abdomen, each bearing paired respiratory areas on ventral surface. Small respira- tory area located entirely anterior to large area. Compound eyes large (Fig. 2A).
Segmentation of thorax indistinct. Abdomen shorter than broad in figured specimen, but some- what variable amongst paratypes with length to width ratio ranging from 0.67-1.14. Abdominal lobes broadly rounded; furcal rami small, located adjacent to mid-line. Spermathecae small and or- bicular.
First antenna (Fig. 2B) indistinctly 5-seg- mented; first segment bearing large posterior spine but lacking anterior hook; second segment with anterior and medial spines, plus large lateral hook. Distal section of antenna extending beyond
68 S.K. Rushton-Mellor
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Fig. 1. Argulus papuensis n. sp. , paratype female . Ventral v iew. Scale-bar: 1.5 mm.
lateral hook, comprising third to fifth segments; fourth segment subdivided; fifth bearing 3 apical spines.
Second antenna (Fig. 2B) 5-segmented with prominent posterior spine; second segment swollen and bearing 5 setae; third with 3. Fifth segment armed with 2 apical spines. First antenna with 2 pairs of well-developed post-antennal
spines present on ventral surface of cephalo- thorax, lateral larger than medial.
First maxillae forming large suckers; supporting rods comprised of 5-6 sclerites, all of similar size and shape (Figs 2C, 5B). Periphery of suckers fringed with tiny spinules. Retractile pre-oral stylet located midway between maxilliary suckers (Fig. 2D). Mouth tube half as broad as long with
A new fish louse from Papua New Guinea 69
F
B
INT
5 0 0
l O O
C
G
2 0 0 2 0 0 j
Fig. 2. Argulus papuensis n. sp., paratype female. A, dorsal view; B, First and second antennae, post-antennal spines, ventral view; C, Supporting sclerites of maxilliary sucker, male, ventral view; D, Pre-oral styler, ventral view; E, Mouth tube, male, ventral view; F, Second maxilla, female, ventral view; G, Ornamentation on second segment of second maxilla, ventral view. Scale- bars are in micrometres unless otherwise stated. Abbreviations: INT, interior of sucker; EXT, exterior of sucker.
S.K. Rushton-Mellor
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70
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Fig. 3. Argulus papuensts, n. sp . , p a r a t y p e f e m a l e . A - D , F i r s t t o f o u r t h t h o r a c i c s w i m m i n g legs , v e n t r a l v i e w s . S c a l e - b a r s a r e in m i l l i m e t r e s .
A new fish louse from Papua New Guinea 71
A
Fig. 4. Argulus papuensts n. sp., holotype male. A, Pair of mandibles in mouth tube, ventral view; B, Ventral view of whole body; C, Dorsal view of whole body; D, Third thoracic leg showing semen capsule, dorsal view; E, Fourth thoracic leg showing peg, ventral. Scale-bars: A, D, 500 txm; B, 1.8 mm, C, 3 mm.
72 S.K. Rushton-Mellor
Fig. 5. Argulus papuensis n. sp., holotype male. A, Serrated scale on ventral surface of coxa of second thoracic leg; B, Supporting sclerites of maxilliary sucker, ventral view; C, Fourth thoracic leg, ventral view; D, Accessory copulatory structure of fourth thoracic leg, ventral view. Scale-bars: A, 6 Ixm; B, 27 p~m; C, 270 Ixm; D, 75 ~m.
A new fish louse from Papua New Guinea 73
Fig. 6. Argulus papuensis n. sp. holotype male. A, Third thoracic leg showing semen capsule, dorsal. B, Cuticular ridges of semen capsule forming honeycomb pattern, dorsal. Scale-bars: A, 136 ~m: B, 20 I~m.
74 S.K. Rushton-Mellor
few spatulate scales scattered around base (Fig. 2E). Two bulbous swellings terminating in labial spines visible within mouth; lower lip edged with row of fine, hair-like filaments; denticulate man- dibles visible within mouth tube (Fig. 4A).
Second maxilla indistinctly 5-segmented (Fig. 2F); proximal section 2-segmented; distal section 3-segmented; terminal segment with 2 small claws. Three slender, sub-equal posterior spines on basal plate of second maxilla. Basal plate with numer- ous sparsely set scales and 2 long, closely set setae. Simple and pectinate scales present on surface of second segment (Fig. 2G). Third and fourth segments ornamented with simple scales only. Paired post-maxilliary spines present on ventral body surface either side of mid-line.
First to fourth pairs of legs biramous (Fig. 3A- D) and of almost equal size. Sympods indistinctly 2-segmented. Sympods of first and second legs with short spines on anterior margins, those of third and fourth legs with large setae on posterior margins. Small scales scattered over surface of sympod segments of all legs (Fig. 5A). First and second legs each possessing one flagellum ex- tending medially from origin on dorsal surface of exopod near its base. Both rami and flagella armed with 2 rows of plumose setae. Natatory lobe on fourth leg produced laterally and armed with simple spinules and long setae (Fig. 3D).
Adult male. Body form (Fig. 4B,C) similar to that of female; carapace comprising about 79% of total length; abdomen much longer than broad. Mean body length 3.97 mm; range 3.78-5.02 mm (based on 3 specimens). Small scales scattered over body surface. Testes elongate. Cephalic appendages and first 2 pairs of legs similar to those of female. Third and fourth pairs of legs highly modified by accessory copulatory structures. Third leg bearing one large, cup-shaped semen capsule (Fig. 6A) lying parallel with exopod (Fig. 4). Surface of capsule ornamented with distinctive honeycomb pattern of cuticular ridges. Patch of large overlap- ping scales present on dorsal surface of both coxa and basis of third leg. Anterior surface of basis of fourth leg (Fig. 4E) bearing peg-like structure with highly textured surface (Fig. 5C,D). Peg ex-
tends up over shallow depression on surface of basis.
Material examined: Holotype male, 2 paratype males and nine paratype females. Registration numbers BM(NH). 1990.11 (holotype), 1990.12-21 (paratypes). Type-host: Bunaka herwerdeni (Weber). Type-locality: Sepik River, Papua New Guinea.
Discussion
There are seven described species of the genus Argulus recorded from the Australasian region and the adjacent part of South-East Asia. A. indi- cus Weber was discovered in Indonesia (Weber, 1892) and was redescribed by Kampen (1909). A. japonicus Thiele has a world-wide distribution, but the original specimens were from Japan (Thiele, 1900). A. melanostictus Wilson was first seen in Monterey Bay, California (Wilson, 1935), but has since been found in plankton samples taken off the coast of Thailand (Wilson, 1944). A. macropterus Heegaard, A. diversicolor Byrnes and A. australiensis Byrnes were all found on fish from Australia (Heegaard, 1962; Byrnes, 1985). A. plecoglossi Yamaguti was first discovered in Japan (Yamaguti, 1937).
There are gross morphological differences be- tween A. melanostictus and the new species. The dorsal surface of A. melanostictus is covered with numerous pigment cells, whereas A. papuensis n. sp. shows no such pigmentation. The abdominal lobes of A. melanostictus are sharply pointed and not broadly rounded as in A. papuensis. The number of sclerites in the supporting rods of the maxilliary sucker exceeds 20 in the former, whereas the new species possesses only five or six per row.
A. macropterus is unusual in that the cephalic area is distinctly separated from the carapace lobes, which themselves extend beyond the range of the thoracic legs and the abdomen. The overall shape of A. papuensis is sub-oval, with the head indistinctly separated from the thorax, and the thoracic legs project beyond the span of the cara-
pace lobes. Both the antennae and the second maxillae of A. macropterus lack spines, and the maxillae are small, weak and without terminal claws. A. papuensis possesses spines on both of these limbs and the second maxillae are well de- veloped.
The anterior respiratory area of A. papuensis is much larger in relation to the posterior area than in any other species being considered. The ab- dominal lobes of A. papuensis are broadly rounded and not pointed as in A. australiensis, A. plecoglossi and A. diversicolor. In addition, these three species all possess more than eight sclerites in the supporting rods of the maxilliary sucker whereas A. papuensis has only five or six.
The males of A. indicus, A. japonicus and A. plecoglossi are all distinct from A. papuensis in that they possess extra ornamentation on the post- erior surface of the coxa of the second thoracic legs.
One of the most distinctive features of A. pap- uensis is the shape and relative sizes of the respira- tory areas. The smaller anterior respiratory area is approximately half the size of the larger, and both have a simple oval, non-indented outline. When compared with all congeners for which re- spiratory areas were figured, A. papuensis most closely resembles A. caecus Wilson, A. capensis Barnard, A. giganteus Remakrishna and A. latus Smith. A. caecus and A. giganteus differ from A. papuensis in that they lack eyes, and, in both these species and in A. latus, the number of sclerites in the supporting rods of the maxilliary sucker ex- ceeds 26, whereas A. papuensis has five to six. The abdominal lobes of A. capensis are long and tapered, unlike the new species, where they are broadly rounded. Additionally, the number of sclerites in the supporting rods of A. capensis (c.10) also exceeds the number in A. papuensis.
The semen capsule found on the third leg of A. papuensis is well developed and highly textured, and it is a distinctive feature of this species. The structure of the male copulatory organs on legs 3
A new fish louse from Papua New Guinea 75
and 4 provides useful characters for distinguishing between closely related species, but in many of the older descriptions these organs are inade- quately described or are not described at all. These structures are often robust and three di- mensional, as in A. papuensis, and are difficult to figure in line drawings. Scanning electron micro- scopy provides an excellent technique for illustrat- ing their basic form as well as their complex sur- face ornamentation.
Acknowledgements
I am grateful to Dr I.L. Owen for collecting the material and I would also like to thank Dr. G.A. Boxshall for his advice and encouragement during the preparation of this manuscript. This work was carried out during the tenure of a Natural History Museum Research Studentship.
References
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