Anthosoma crassum (Abildgaard, 1794)

Caligus crassum Abildgaard, 1794, p.46, pl. 5, figs. 1-3 (non vide)

Anthosoma smithii Leach, 1816, p.406, pl. 20, figs. 1-6

Anthosoma smithii Leach, Kirk, 1888, p.31

Anthosoma crassum (Abildgaard) Thomson, 1889, p.365.

Material

On Lamna nasus: from Cook Strait, 20 females and one juvenile female, nine males and one juvenile male, collected by the author, 23 August, 1960; no data, 17 females and eight males, Dominion Museum collection; from between Cape Campbell and Kaikoura, 11 females and five males, collected by A. Dickinson, 21 November, 1963, Dominion Museum Collection; from Kaikoura, five females, one juvenile female and one male, collected by R. Baxter, 30 November, 1955; from Napier (?; label damaged), two females, three males and one juvenile male, collected by A. Hamilton, — November, 1837, Otago Museum collection, deposited by G. M. Thomson, 1910.

On Isurus oxyrinchus: from Bay of Islands, three females and two males, Dominion Museum collection, 14 March, 1957; from Paraparaumu, one female and four males, collected by J. M. Moreland, 23 April, 1953, Dominion Museum collection; from Makara, one juvenile male, collected by J. Garrick, 29 June, 1955; from Marnoo Bank, four females collected by the Fisheries Laboratory, Marine Department, 30 November, 1964; from Kaikoura, four females, collected by T. Garbes, forwarded by Dr. J. Bradford, 23 April, 1964.

On Carcharodon carcharias: from Chatham Is., two females, collected by F. Abernethy, 1 August, 1949, Dominion Museum collection; from South Bay, Kaikoura, one female, collected by H. G. Upston, forwarded by Dr. J. Bradford, 9 January, 1965.

On Galeorhinus galeus: from Tory Channel Whaling Station, 21 females and seven males, collected by J. Garrick, 1955.

Description

Female (figs. 78-89)

Overall length 11.2mm - 16.1 mm (14.1 mm).

Cephalothorax three-quarters as wide as long (7.4 mm - 10.2 mm × 5.7 mm - 7.3 mm), subovate, widest posteriorly, the margin entire except for a shallow groove one-sixth distance from anterior margin, which is associated with a ridge running across dorsum of cephalothorax, dorsum otherwise smooth. Posterior margin of cephalothorax overlying remaining thoracic segments and anterior part of genital segment.

Third thoracic segment similar to second but slightly longer and narrower (1.9 mm - 2.4 mm × 0.5 mm - 1.2 mm), and lacking plates.

Fourth thoracic segment difficult to discern. Shiino (1955, p.54) states that it is fused with the genital segment. Lewis (1966, p.69) says it is indistinctly fused and similar to two preceding segments although partly or completely covered by the swollen genital segment. In the specimens I have examined it appears to be very reduced and totally concealed by the genital segment in dorsal view although there is a small subtriangular area ventral to the anterior part of the genital segment indicating the position of this segment.

Genital segment subovate, width two-thirds length (4.7 mm - 7.7 mm × 3.8 mm - 4.7 mm), with a slight narrowing at its midpoint.

Abdomen, length half width (0.6 mm - 1.0 mm × 1.3 mm - 1.6 mm) narrowing slightly posteriorly, with caudal rami on posterolateral angles.

Caudal rami subovate, width four-tenths length (1.4 mm - 1.8 mm × 0.45 mm - 0.75 mm), with scattered very small spines irregularly over surface.

Egg string 35 mm - 68 mm in length.

First antenna of six segments, third and fourth segments subequal in length, otherwise segments becoming shorter distally so that distal segment is one-quarter basal segment length, basal segment partially divided by a groove running medially and proximally along the outer margin; second and third segments each with single setae, distal segment with several very small setae.

Second antenna of four segments, proximal half capable of being withdrawn into carapace (as noted by Lewis, 1966, p.70) the proximal half a flexible membrane, first and third segments subequal in length, second segment a little shorter, distal segment one-third length of third segment, claw-like, sharply curved, closing against a projection near midpoint of third segment.

Associated with the bases of the antennae is a suboval, chitinised structure (1.2 mm × 1.1 mm) which projects, lappet-like, beyond the cephalothorax. Lewis (1966, p.72) suggests that these may be homologous with the adhesion pads of pandarids and the processes of trebiids, euryphorids and caligids which are found in an approximately analogous position.

Mouth tube 2.0 mm in length, 0.9 mm in basal width, rounded distally.

Mandibular palp biramous, exopod one-segmented, one-quarter endopod length, borne on an extension of the basipod, with three small spines distally; endopod subtriangular in cross section, basal width two-fifths length, narrowing almost to a point distally, with two setae two-fifths segment length borne distally.

Maxilla of two segments, first segment three-quarters length of second, subrectangular, two-thirds as wide as long; second segment one-fifth as wide as long, with two parallel flanges near outer margin, for three-fifths segment length, terminating on an outer spur-like projection of outer margin, distal fifth of segment rounded, with longitudinal striations, and a longitudinal semicircular denticulate ridge running longitudinally around it, associated with a further semicircular denticulate ridge around outer portion of its base. these denticulate ridges are derived from rows of spines clearly seen in juvenile specimens, in which this distal portion of segment is smaller, narrower and more pointed distally.

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Maxilliped of two segments, basal segment, two-thirds as wide as long, somewhat rounded distally, outer margin rounded, inner margin swollen medially and proximally, the second claw-like segment closing against and between these swellings; second segment two-thirds length of first, basal width half length, pointed distally, moderately curved.

First second and third pereiopods with basipod greatly enlarged and flattened, in each case overlapping in the ventral midline, and extending laterally to hide much of the genital segment in lateral view, the second pereiopod partly overlying the plates on the second thoracic segment, and these plates partly overlying the basipod of the third pereiopod which extends further around the body than do the other two; the basipods of the pereiopods and the plates of the second segment between them envelope much of the body, hiding from view the three thoracic segments and much of the genital segment; first and second pereiopods each with a mediodistal notch, in the apex of which are faint signs of degenerate rami, third pereiopod which no notch and no signs of rami.

Male (figs. 90-101)

Overall length 9.0 mm - 16.7 mm (smaller specimens may be less mature males).

Carapace similar in form to that of female, two-thirds as wide as long (5.2 mm - 9.5 mm × 4.0 mm - 7.3 mm).

Second thoracic segment disc-shaped, length one-third width (0.6 mm - 1.4 mm × 2.8 mm - 3.5 mm), lacking the dorsal plates found in the female.

Third thoracic segment similar in form to second, length half width (1.1 mm - 2.5 mm × 1.9 mm - 4.3 mm).

Genital segment subrectangular, angles rounded, slightly wider anteriorly, a little longer than wide (2.0 mm - 3.3 mm × 1.5 mm - 3.2 mm), with two plate-like ventral extensions of posterior margin covering much of ventral surface of abdomen, the extensions separated by a narrow V-shaped sinus; two small semicircular projections from the base of these extensions could perhaps be degenerate fifth pereiopods.

Abdomen subrectangular, two-thirds as long as wide (0.4 mm - 1.2 mm × 0.8 mm - 1.8 mm), the caudal rami carried on posterolateral angles.

Caudal rami of similar form to those in female, width one-third length (0.9 mm - 1.8 mm × 0.3 mm - 0.7 mm).

Appendages as in female, except that in the first and second pereiopods the notch in the basipod is shallow and the degenerate rami are slightly better developed; in the first pereiopod each ramus is of one segment, lying against margin of pereiopod, each subrectangular, endopod slightly narrowed distally, each with several small spines and one broader spine along outer and distal margins; rami of second pereiopod more complex, exopod subcircular, with two setae and one heavy spine distally, the spine with pigmentation over distal half, the whole ramus almost hidden by a thin hood extending around it from the basipod, endopod similar to rami on first pereiopod but broader.

Juvenile specimens (female, fig. 88, male, fig. 101) very similar to adults, but can be recognized by their smaller size, their relatively smaller genital segment and the nature of the maxilla (see above).

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Discussion

Anthosoma crassum has been recorded from many parts of the world and on a number of host species, the most frequent being members of the family Lamnidae.

Previous records include:

North-East Atlantic: on Lamna nasus—Aberdeen (Scott and Scott. 1913, p.109): Exmouth, Dartshire (Baird, 1850, p.299 and Leach, 1816, p.406 refer to same specimens); Devonshire (Leach, 1819, p.533); Φresund (Steenstrup and Lütken, 1861, p.397; Olssen, 1868, p.23); Hornbaek, Kattegat (Krøyer, 1838, p.295); Belgium (van Beneden, 1870, p.8).

• on Cetorhinus maximus—Newlyn, England (Birkett and Burd, 1952, p.392).
• on a shark, in the collection of the British Museum (Milne Edwards, 1840, p.483; Bassett Smith, 1899, p.468).
• on Mustelus mustelus—Belgium (van Beneden, 1870, p.5).

Mediterranean: on Isurus oxyrinchus—Palavas, France (Delamare Deboutville and Nunes-Ruivo, 1953, p.205); Genoa (Brian, 1902, p.7); Portoferraio (Brian, 1902, p.7); Adriatic (Valle, 1880, p.62).

North-West Atlantic: on I. oxyrinchus^*, L. nasus, Carcharinus obscurus, and Odontaspis taurus—Martha's Vineyard and Woods Hole, Mass. (Wilson, 1922, p.23, 1932, p.446).

• on Carcharodon carcharias—Woods Hole, Mass. (Wilson, 1924, p.12); Padre Is., Texas (Pearse, 1952, p.28).

South-East Atlantic: on I. oxyrinchus—Angola (Nunes-Ruivo, 1956 ^**); South Africa (Hee gaard, 1962, p.181).

• on Carcharias sp. and L. nasus—Table Bay and False Bay, South Africa (Barnard, 1955, p.272).

Indian Ocean: on Carcharias sp. and L. nasus—Durban (Barnard, 1955, p.272).

• on unnamed host—Port Natal, Durban (Wilson, 1923, p.13).

South-West Atlantic: on L. nasus—Mar del Plata (Brian, 1944, p.208).

• on Cetorhinus maximus—Mar del Plata (Fontes, 1949, p. 185).

North-East Pacific: on an unnamed host—Vancouver Is., and Californian Coast (Wilson, 1932, p.446).

• probably on I. oxyrinchus—45°11′ N, 174°54′ W (Lewis, 1966, p.67).
• on Carcharodon carcharias—Pokai Bay, Hawaii (Lewis, 1966, p.67).

North-West Pacific: on L. nasus—Toyama Bay, Japan (Yamaguti, 1936, p.12); Kesennuma, Japan (Shiino, 1955, p.50).

• on L. ditropis—Kesennuma, Japan (Shiino, 1957, p.370).
• on Prionace glauca—Tyôsi, Japan,
• on I. oxyrinchus—Owase, Japan.
• on Heptranchias perla—Kannoura, Japan (Shiino, 1955, p.50).
• on an unnamed host—Japan (Wilson, 1932, p.446).

South-East Pacific: on an unnamed host—Concepcion, Chile (Brian, 1944, p.208).

South-West Pacific: on Isurus oxyrinchus—Long Reef, nr. Port Jackson, New South Wales and French Pass, Cook Strait, New Zealand (Heegaard, 1962. p. 181).

• on L. nasus—Napier, New Zealand (Thomson, 1889. p.366); Otago, New Zealand (Kirk, 1888, p.31).
• on Cardiarias sp.—probably New South Wales and on an unnamed host—Port Jackson, New South Wales (Heegaard, 1962, p. 181).

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As well as its almost complete latitudinal distribution, Anthosoma crassum has been taken from Aberdeen, Scotland (59°9′ N) to Otago, New Zealand (45°45′ S).

Despite the numerous records of this species there have been few detailed descriptions or figures given. Those available (the fullest being those by Wilson 1922, p.23, pl. 1, figs. 1-9, Shiino, 1955, p.50, figs. 1-2, and Lewis 1966, p.67, figs. 4-6) suggest there is little variation except in size. Minor morphological variations shown or described could well be due to variations in optical equipment available to the various authors, with the possible exception of the female specimen figured by Brian (1944, fig. 44), which appears to have notches in the third pereiopod and plate of the second thoracic segment, as well as in the first and second pereiopods.

Size as measured by total length varies considerably, e.g. Yamaguti (1936) gives 8.8 mm - 11.0 mm for the female compared with Brian (1944) who gives 15.3 mm - 18.0 mm for this measurement, while Wilson (1922) gives the male as 8 mm - 10 mm compared with Brian (1944) who gives 12 mm - 13 mm. However when the range in the specimens available to me is considered (9.9 mm - 18.0 mm for the female, 9.0 mm - 16.7 mm for the male) the above apparent differences can be understood as individual variation. There is some suggestion of a host specific influence on size in my material but the numbers are not sufficient for statistical analysis and it would not be surprising if geographical factors, the site of attachment and the intensity of infection were also involved.

There appears to be considerable variation in the intensity of infection. Wilson (1922, p.25) states that this species "never occurs in any number on a host, but is more often solitary, although occasionally the two sexes are associated upon the same fish". Birkett and Bund (1952, p.392) on the other hand state that their specimens were numerous and did considerable damage to the host. In the present collection the author obtained one lot of 31 specimens from a single host which had been severely damaged, particularly on the dorsal surface of the tongue, which appeared to be partly hollowed out, while other collectors reported both single and multiple infections (see Material above).