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APRIL 9, 1975



W. E. MartInt

Apstract: A new hydroid, Hydrichthys pietschi, was found on a myctophid fish, Ceratias

holboelli Kréyer, collected off the leeward shore of Oahu, Hawaii. hydroid erodes the pigmented epidermis and underlying tissues of the host.

The basal plate of the The literature

on commensal and parasitic hydroids is reviewed.

Although the phenomenon is relatively rare, commensalism and parasitism involving hydroids and fish have been found in Russia (Ussow, 1887); Rumania (Dimitru, 1961); India (Alcock, 1893; Lloyd, 1907); Africa (Warren, 1916); European Atlantic Ocean (Damas, 1934; Jones, 1966); New England Atlantic (Fewkes, 1887, 1888; Gudger, 1928): Eastern Pacific (Heath, 1910; McCormick, Laurs, and McCawley, 1967); Japan (Franz and Stechow, 1908; Komai, 1932; Miyashita, 1941); New Zealand (Hand, 1961); and Hawaii (present paper). Some of these asso- ciations apparently are commensal without invasion of the host, with the polyps possessing tentacles and obtaining nourishment as do free- living species. Others are parasitic with invasion of the host, with polyps lacking tentacles and with reduction or loss of nematocysts. How the para- sites obtain their food is of some interest. Warren (1916) reported that the non-tentacled polyps of Hydrichthys boycei ingested host red corpuscles and even connective tissue. Jones (1966) found that a hydroid, which he thought probably was Ichthyocodium sarcotretis Jungersen, 1911, at- tached to copepods, Sphyrion lumpi (Kr@yer), parasitic on the redfish, Sebastes mentella Travin, fed on the fish hosts’ blood and tissue. Damas (1934) suggested that the inner ectoderm of Hydrichthys cyclothonis, which is much thicker than the outer ectoderm, absorbed nutrients from the fish host, Cyclothone signata (Garman). The ribbon-like which

stolon of Polypodium hydriforme,

occurs in the ovarian eggs of certain

Russian and Rumanian sturgeons, must be nour- ished through its outer layer which is believed to be endoderm! The latter species has a remarkable life history with some aspects. still unknown. The cycle has been reviewed by Raikova (1958), and Smol’yanoy and Raikova (1961). A young stage invades the ovarian eggs of sturgeons in the Volga, neighboring rivers, and the Danube, then develops into a ribbon-like stolon which undergoes multiple budding. The buds form polyps by developing tentacles internally from the ectoderm, detaching from the stolon and turning inside out to bring the body layers to their usual position. After the fish spawns, the polyps and what remains of the stolon escape from ruptured eggs. The polyps usually bear 6, 12, or 24 tentacles (Lipin, 1909). Most polyps become male or female but a few are hermaphroditic. Eggs are released into the gastrovascular cavity. Male polyps, each bearing four testes near the aboral end, can become attached to small stur- geons. The ectoderm over each testis produces adhesive material which firmly attaches this area. Then the testes are released from the polyp and resemble buttons attached to the fish. After the four testes are released the polyp seems to dis- integrate. Raikova (1965) photometry to determine the

used Feulgen cyto- deoxyribonucleic acid content of the various cells of this hydroid.

Ectoderm and endoderm have the diploid content.

“Dept. Biology, Univ. Southern California, Los Angeles, California 90007.


The two nuclei of the “spermatids” are unequal, the smaller haploid (n), the larger 2 to 6n. Nurse cells of the ovary are 8-32 n but the eggs are diploid when released. The youngest stage found in the sturgeon egg has two unequal nuclei, one about 400 n that forms a capsule around the embryo cells, and the other haploid. The early embryo cells also are haploid. This led Raikova to conclude that there is no fertilization and that diploidy is restored in later embryogenesis. Ques- tions remain unanswered. If there is no fertiliza- tion, what role is played by “spermatids?” How is diploidy restored in later embryogenesis, etc.? It is apparent that further work needs to be done on this unusual type of development. Are stur- geons in parts of the world other than Russia and Rumania hosts of this parasite?

The assignment of specific names to such hydroids is difficult because of the relative paucity of diagnostic characters. If host speci- ficity exists the problem would be greatly sim- plified. McCormick, et al., (1967) argued against host specificity because they found presumably the same species of hydroid on two species of fish, Tarletonbaenia crenularis (Jordan and Gil- bert, 1880) and Diaphus theta (Eigenmann and Eigenmann, 1890). Also they found the hydroid on a copepod, Cardiodectes medusaeus (Wilson, 1908) parasitic on D. theta and another fish, Lampanyetus leucopsarus (Eigenmann and Eigen- mann, 1890). The attachment of the hydroid to a parasitic copepod may not be relevant to host specificity because Jones (1966) found that a hydroid attached to a copepod parasite still fed on the fish hosts’ blood and other tissues. McCormick, et al., (1967) examined more than 2000 Pacific specimens of the fish genus Cyclothone includ- ing C. signata without finding any hydroids. Yet Damas (1934) found 24 hydroid colonies on 21 of over 2000 Cyclothone signata from the Atlantic. If host specificity does not exist, why did not McCormick, et al., find hydroids on C. signata? Warren (1916) also reported finding several species of fish hosts to Hydrichthys boycei. But again was only one species of hydroid in-


volved? (1893) found Stylactis minoi on the fish, Minous

In support of host specificity, Alcock

inermis, but not on Minous coccineus or other |

fish in the same trawl. Komai (1932) found this hydroid also only on Minous inermis in Japan. The following have been reported from only one species of fish:

Hydrichthys mirus |

Fewkes, 1888 on Seriola zonata; H. cyclothonis

Damas, 1934 on Cyclothone signata; Podocoryne bella Hand, 1961 on Congiopodus leucopaecilus;

Perigonimus pugetensis Heath, 1910 on Hypsag-

onus quadricornis; Stylactis piscicola Komai, 1932 on Erosa erosa; Nudicola monocanthi Lloyd, 1907 on Monocanthus tomentosus; Hydrichthys pacificus Miyashita, 1941 on Xesurus sp. Poly-

podium hydriforme Ussov, 1885 parasitizes only |

sturgeons. It is possible, however, that a wider

search might show more than one species of fish |

hosting the same hydroid. The question of host specificity has not been settled.

Ecological factors may determine whether or not a species of fish plays host to hydroids. Heath (1910) found twenty-five per cent of the fish, Hypsagonus quadricornis, bearing the same hy- droid, Perigonimus pugetensis, in Puget Sound but outside the sound the same species of fish was negative. the rate of infection with hydroids was higher

McCormick, et al., (1967) stated that

in species of fish that migrated to the surface at

night. The purpose of this paper is to describe another

hydroid parasitic on a fish. Theodore Pietsch,

presented a lantern fish, Ceratias holboelli Kr@yer, 1844, about 15 cm long, that had a small patch of

tiny, finger-like polyps dorsal and slightly anterior | to the left eye (Fig. 1). This fish was collected | with an Isaacs-Kidd midwater trawl at a depth | of about 95 meters off the leeward side of Oahu,

Hawaii on March 1, 1971. stained with Mayer’s paracarmine and mounted

in Canada balsam. A portion of the colony was sectioned, stained with hematoxylin and triosin |

and mounted in Canada balsam.

made with the aid of a camera lucida unless

Figure 1.

Sketch of Ceratias holboelli, C, location of coelenterate colony; E, eye. Figure 2.

Section of uninfected fish skin, EP, pigmented epidermis; S, spine-like scale. Magnification scale same as figure 4. Figure 3. Part of coelenterate colony and surrounding host skin, B, basal plate; P, polyp. Figure 4. Section through part of basal plate and host skin, I, inner ectoderm; O, outer ectoderm; S, spine-like scale; T, host cell response. Figure 5. Optical section of bud and stalk, projecting from polyp wall, EC, ectoderm; EN, endoderm.

A few polyps were

Drawings were |


Cases Bese PRE


otherwise indicated. Measurements are expressed in microns unless otherwise indicated.

Hydrichthys pietschi, new species

Figures 3-5

Polyps project from basal plate, some bearing buds on the aboral half of body (Fig. 3). Polyp 490-1,010 long; 112-168 wide. Ectoderm thin (about 3) endo- derm 8-9 thick enclosing many granules 0.8—9 in diameter. Nematocysts and mesoglea not seen. Medusa bud (Fig. 5) stalked, 87-106 long, 68 wide. Mass of cells at distal end probably developing manubrium. Bud endoderm also contains granules. Bud stalk 40-50 long; 47 wide.

Basal plate (Fig. 4) approximately 4,800 in diam. with outer thin, 3, and inner thick, 16-22, ectoderm. Thickened inner ectoderm contains granules and may function in digestion as suggested by Damas (1934). Endoderm thickness 8—25, with numerous granules, encloses shallow gastrovascular cavity. Maximum plate thickness 137 which is about equal to the greatest penetration into the host. In this penetration the pigmented epidermis and some of the underlying tissues of the host are eroded. The granules of the hydroid and of the host epidermis are very nearly the same size. Possibly the hydroid obtains its gran- ules from the host. There is a definite tissue response of the host to the parasite with a massing of cells beneath the inner ectoderm (Fig. 4) which is not seen in uninfected skin (Fig. 2).

Host: Ceratias holboelli Kr@yer, 1844. Habitat: Skin. Type locality: Leeward side of Oahu, Hawaii. Holotype: No. 7115, deposited in the Hancock Parasitology Collection, University of Southern California. DISCUSSION

Hydrichthys pietschi differs from other members of the genus in apparently lacking nematocysts and mesoglea, in having a thicker inner ectoderm of the basal plate, and in a deeper penetration of the host. The only other report of a hydroid on a myctophid fish is that of McCormick, et al., (1967), a species which has a thick mesoglea, a thinner inner ectoderm and only slight invasion of the host.

After this paper was accepted for publication, Polypodium sp. was reported in Acipenser fulves- cens collected in the Black River near Cheboygan, Michigan (Hoffman, Raikova, and Yoder. J. Parasit., 60:548-550. 1974).


I am indebted to Theodore Pietsch for presenting the ©

infected fish and to Vladimir Triffin, Library Staff, USC for Russian translation.


Alcock, A. 1893. A case of commensalism between a gymnoblastic anthomedusoid (Stylactis minoi) and a scorpaenoid fish (Minous inermis). Ann. Mag. Nat. Hist., ser. 6, 10:207—214.

Damas, H. 1934. MHydrichthys cyclothonis (nov. sp.), hydroid parasite du poisson, Cyclothone signata (Garman). Bull. Musée Roy. Hist. Nat. Belgique, 10:1—10.

Dimitru, B. 1961. podium hydriforme Ussov, 1885 la cega (Aci- penser ruthenus L.) din Dunare. Bul. Inst. Cercet. Pisc., 20:54-59.

Fewkes, J. W. 1887. Nature, 36:604—605.

1888. On England. Bull. Mus. Comp. Zool. Harvard Coll., 13:209-240.

Franz, V., and E. Stechow. 1908. Symbiose

zwischen einem Fisch und einem Hydroidpolypen. |

Zool. Anz., 32:752-754.

Gudger, E. W. 1928. colonial hydroides and fishes. Hist., ser. 10, [:17—48.

Ann. Mag. Nat.

Hand, C. 1961. Podocoryne bella (Hydractiniidae), living on the pigfish, Congiopodus leucopaecilus. Roy. Soc. N. Z., 1:91-94.

Heath, H. 1910. Association of a fish with a hydroid. Biol. Bull., 19:73-78.

Jones, D. H. 1966. ring on Sphyrion lumpi (Kr@yer). Nat. Hist., (13)9:173-181.

Komai, T. 1932. On two species of athecate hy-

droids associated with scorpaenoid fishes. Con- | trib. Seto Mar. Lab. no. 30., Annot. Zool. Japan, |



A hydroid parasite on a fish. |

Association between sessile |

A new species of athecate hydroid, |

Trans. |

A gymnoblastic hydroid occur- | Ann. Mag.

Un caz de Infestatie cu Poly-

certain medusae from New |


Lipin, A. 1909. Ueber den Bau des Siisswasser- Coelenteraten Polypodium hydriforme, Uss. Zool. Anz., 34:346—-356.

Lloyd, R. E. 1907. Nudicola monocanthi, the type of a new genus of hydroid parasitic on fish. Rec. Indian Mus., 1:281—289.

McCormick, J. M., R. M. Laurs, and J. E. McCauley. 1967. A hydroid epizoic on myctophid fishes. J. Fish. Res. Bd. Canada, 24:1985—1989.

Miyashita, Y. 1941. On the occurrence of a new Hydrichthys in the Pacific coast of Japan. Annot. Zool. Japan, 20:151—153.

Raikova, E. V. 1958. [The life cycle of Polypodium hydriforme Ussov (Coelenterata)]. Zool. Zh., 37:345-358 (Russ., English sum.).


1965. [A cytophotometric study of DNA content in cell nuclei of Polypodium hydriforme Ussov (Coelenterata) at various stages of its life

cycle]. Zh. obshch. Biol., 26:646-652. (Russ.. Engl. sum.). Smol’yanov, I. IL, and E. V. Raikova. 1961. [The

_ occurrence of sexually mature Polypodium hydri- forme Ussoy (Coelenterata) on sturgeon juve- niles]. Dokl. Akad. Nauk Biol., 141:1271—1274. (Russ. ).

Ussow, M. 1887. Eine neue Form von Siisswasser- Coelenteraten. Morph. Jahrb., 12:137—153.

Warren, E. 1916. droid parasitic on fishes. Novit., I:172-187.

On Hydrichthys boycei, a hy- Ann. Durban Mus.

Accepted for publication March 13, 1974.



ABSTRACT: The mesostigmatid mite, Gammaridacarus brevisternalis has been found on both decomposing wrack and on the beach amphipods Orchestoidea corniculata and O. californiana. The percentage infestation of the host population increased with size of hosts and varied from 1.5 percent (hosts 3-7.9 mm) to 83.07 percent (hosts 16-19.9 mm). Mites showed no preference for male or female hosts. The number of mites per infested host increased slightly with amphipod size. Mites were found attached by gnathosoma exclusively on the ventral side of the host. The mites left hosts within 2—9 hours after death of the host and mites without hosts can crawl over sand at an average rate of 3 inches per minute. After leaving dead hosts, G. brevisternalis attach to new, living hosts. The mites traveled at least 30 cm in finding new hosts and observations suggest that the mites possess chemo-

tactic senses for locating hosts at a distance.

In California sandy beach communities, members of the amphipod genus Orchestoidea are among the most abundant macrofauna. At night these beach hoppers leave their sand burrows and feed in large numbers on stranded seaweed. As early as 1912 small, apparently ectoparasitic mites had been found on these gammarids (Hull, 1912), and in later studies of Orchestoidea both

McClurkin (1953) and Bowers (1954) noted

their occurrence. In Oregon and Washington, Canaris (1962) found Orchestoidea californiana Brandt, 1851, infested with males, females, and deutonymphs of a mesostigmatid mite which he Canaris,

named Gammaridacarus brevisternalis

‘Hopkins Marine Station of Stanford University Pacific Grove, California 93950 (Present add 2106 Avenida Soledad, Fullerton, Californi

6 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 74 (eve Saal [ | 20 3s Average no. mites 9 % of O. corniculata =o 5 £ iS es) fos Tl 7 15 per infested host 2 2 af = infested 2 2 $ 208? 4lQ 2 33 «7 be iT} o 9 os 34 = 5S AL oa 10 ol 3| 50 fos = ot 2 8 3 Ht . 5 z : : ee se x 25 a ld n=63 jo) ‘s = Ls J 3-79 8-119 12-15.9 16-19.9 20-23.9 3-79 8-119 12-15.9 16-19.9 20-23.9 : Size classes (body length, mm) Size classes ( body length, mm) Figure 2. Average number of mites per host on

Figure 1. Percentage of the Orchestoidea corniculata population, by size class and sex, found infested with mites. Sex of members of the smallest size class could not be determined. Females of the largest size are scarce.

1962. These mites have also been found in sandy beach wrack by Newell (pers. comm., 1972) and the author.

This investigation was undertaken to extend our knowledge of the relationship between the parasite and host. Studies were carried out at Hopkins Marine Station of Stanford University, Pacific Grove, California from April to June, 1972. All collections were made on the Monterey Boatworks beach located just east of Mussel Point, Pacific Grove. This beach was found by Bowers (1964) to contain a beach hopper population consisting solely of Orchestoidea corniculata Stout 1913. All amphipods collected were identified using keys in Bousfield (1959). Only O. cornicu- lata was found on this beach.

Occurrence of mites on the host.—Investigations were made to discover the extent to which the host population was infested by mites, and to see whether or not the mites showed a preference for hosts of a particular size or sex. A total of 275 hosts was collected. Each amphipod was immedi- ately placed in a separate vial of 75 percent ethyl alcohol, thus any mites that became detached could be counted and attributed to a single amphi- pod.

In the laboratory, the contents of each vial were examined under a dissecting microscope. Each amphipod was identified by species and sex, and the number of mites and their positions on the host were noted. Occasionally mites were found to have come free of their hosts and were loose in the vials of alcohol. The sex of the youngest hosts could not be determined. In the case of brooding

infested Orchestoidea corniculata, according to host size class and sex. Each column shows mean, range, and 95 percent confidence limits of the mean. Sex of members of the smallest size class could not be determined.

female hosts, the eggs or young were also checked for mites. The body length of each amphipod was then measured by straightening the body and recording the distance from the front of the rostrum to the tip of the telson. The O. corniculata collected ranged in length from 3 mm, the size when the young first leave the marsupium (McClurkin, 1953), to 24 mm, the size of the largest males.

Results of the survey (Fig. 1) show there is a positive correlation between host body size and the percentage of the host population infested. In fact, only one mite (a deutonymph) was found among the 63 amphipods of the smallest size class examined. The smallest amphipods have less exposed ventral surface area for mite attachment, and also show a pattern of behavior slightly different from that of the larger hosts. The youngest amphipods are more active than the larger ones during the days and can sometimes be found hopping above the surface at that time (Bowers, 1964, and pers. observations). Mites are very susceptible to desiccation (Cheng, 1964: 545) and conceivably, this host daytime behavior could subject the mites to desiccation.

The percentage of infested males of the largest size class was lower than that of the next smallest size class. The females of the two largest sizes showed similar percentages of infestation. The decrease found in the largest males might be attributed to their tougher outer covering. Fe- males of the largest size class were close to the lower length limit of this range (20 mm) and so were almost members of the next smaller class.

| } |

1975 5 N=275 cs °o c= ° C) z [nleties meats QO 2 4 6 8 ) TS 16° 52 34

No. of mites per host

Figure 3. Degree of infestation with mites of all O. corniculata examined.

The average size of the mite population on individual infested hosts increased slightly with host body size (Fig. 2). This is not surprising since larger hosts have more room for parasites, and have had a longer time in which to acquire them. One male in the largest size class carried 33 mites. Among those O. corniculata which were infested, small mite loads were more com- mon than large loads (Fig. 3).

Distribution and attachment of mites on the host body.—When live hosts were examined, unattached mites occasionally were observed crawling on the ventral or dorsal side of the host, or on its appendages. This probably explains why mites were sometimes found detached from their hosts following preservation in alcohol.

Attached mites, however, when observed on hosts preserved in alcohol, were found only ven- trally on the amphipod body; here they ranged longitudinally from the area between the first gnathopods to a position directly above the first pleopods. Mites were found in every possible position on this flat, thin skinned surface, and also On sites on the five pairs of gills (Fig. 4). The ventral surface forms part of a protected and probably humid chamber when the amphipod curls its body and crosses its gnathopods and peraecopods across its ventral side during its daily resting period in its sand burrow.

The number of mites on the ventral surface was greater anteriorly on the hosts while the number on the gills was higher posteriorly, where the gills are larger. In heavily infested hosts, mites tended


No. of mites on ventral side

Ventral surface position

No. of mites on gills


Gill pair


Figure 4. Positions on host body at which attached mites were found in a survey of 275 amphipods. An O. corniculata (male) is shown with appendages of the left side removed. Gill pairs are numbered 1 through 5 from front to rear. In addition, eight mites were found on female oostegites.

to cluster into dense packs in the ventral mid-line. The ventral surface of the host is weakly sclero- tized; also, a large blood sinus passes close to the cuticle (Cussans, 1904). The five pairs of gills also offer a rich blood supply. If the mites feed on blood, better sites could not be found on the host.

Mites were never found attached to the host’s abdomen or telson, probably because of the am- phipods’ mode of locomotion. When a_ beach hopper jumps, it curls its posterior end forward under the body, then straightens it suddenly in springing away.

On brooding females, mites (8) found on the four pairs of oostegites or brood plates which retain the eggs or young. No mites

were also

were found on eggs or young of brooding females.

Mites were found most often attached to the host by their mouth parts: their remaining append- ages were held extended, but not attached. This However, the

position feeding. even

more heavily infested hosts showed no obvious


signs of weakness, damage, or even inconvenience caused by the mites.

The behavior of mites during molting of the likely th

this presents few problems to the ectopar:

host was not observed, but it seems


Orchestoidea, after molting, remain dormant for a period and then proceed to eat their shed exo- skeletons (McClurkin, 1955). This behavior would appear to permit the mites to detach from the old cuticle and find a place on the new, soft cuticle.

Transfer between healthy hosts——Experiments were conducted to determine if mites shift from one living host to another, or from dead to living hosts. One investigation was initiated to discover if the mites remain with their hosts even in the presence of other living amphipods. Live amphi- pods were first anesthetized with ethyl ether fumes and then were examined very carefully under a dissecting microscope. Both mites and amphipods quickly recovered from the anesthetic.

Amphipods were maintained in the laboratory using the methods of McClurkin (1953). Cotton pads moistened with seawater were placed in two 2 X 9 cm glass vials and the tops of the vials were covered with cotton gauze to prevent escape of the amphipods. One infested and one uninfested O. corniculata were placed in each of the two containers. After one to two days, each previously uninfested amphipod bore at least one mite.

The mites are quite motile. They can shift from one living host to another, at least when the hosts are close together. This physical proximity occurs in the field especially during the night, when many closely packed O. corniculata can be found feeding on wrack.

Mite reaction to host death—A similar experi- ment was set up to determine the reaction of mites to the death of their host. Two live O. cor- niculata infested with two mites each were killed by stabbing. They were immediately placed in two McClurkin vials and left overnight. The dead hosts bore no mites the next morning, and even the cotton in the vials appeared to be free of mites.

The experiment was repeated in an aquarium tank filled with four inches of damp sand similar to that in which the amphipods burrow during the day. Five infested O. corniculata were killed by stabbing and placed overnight in shallow holes in the sand to simulate the death of amphipods in their burrows. All the amphipods were found the next day to have no mites.

Finding a new host.—Since mites leave after death of the host, other experiments were per- formed to determine whether mites can locate new, healthy hosts. In one experiment, two dead infested amphipods were placed in separate McClurkin vials, and a live uninfested O. cor-


niculata added to each vial. One dead amphipod bore one mite, and the other two mites, at the start of the experiments, but after 12 hours all the mites had transferred to the living amphipods.

A similar experiment was carried out in the sand tank. Five infested O. corniculata with one mite each were killed and placed in holes in the sand, then three uninfested live amphipods were added. After nine hours, one living O. corniculata individual bore all five mites and the remaining live and dead amphipods had no parasites.

In these experiments, contact between the dead and living hosts was possible. In the field, O. corniculata have been observed eating individuals of their own species, which should provide good opportunity for mite transfer.

Experiments were also performed to discover if mite transfer could take place without close contact between hosts. Under normal beach con- ditions this might involve mite movement across the beach. In order to test the mites’ capabilities of locomotion in sand, a round dish of beach sand was prepared. A mite was introduced at a marked spot on the sand, and allowed to move

freely. The mite’s progress was observed under | the dissecting microscope, and it appeared to have |

no great difficulty traveling on sand. The several mites timed averaged 3 inches per minute. When a living O. corniculata was placed at a point across

the dish of sand from the mite, the mite was | observed to crawl directly across the sand and ©

climb on the amphipod, suggesting chemotaxis.

With these results in mind, a more complex

experiment was performed to test mite transfer from dead to living hosts over varying distances.

A large aquarium tank was divided by metal sheets into four separate compartments or run- | ways measuring about 8 x 42 cm. Sand from | the normal environment, treated with steaming hot |

water for fifteen minutes to kill any mites, was drained, dried to the dampness O. corniculata prefers, then placed in each runway, and the surface roughly leveled. Living, uninfested

Orchestoidea were caged in cylinders of plastic | screen of 1 mm square mesh, two animals to a |

cage. A cage of amphipods was placed at one end of each of the aquarium runways. Three fresh O. corniculata, each with three mites, were killed

by piercing and placed on sand in separate run- | ways of the aquarium. One dead infested amphi- |

pod was placed 10 cm away from the cage in

runway A, one was placed 20 cm away in run- |

way B, and one at 30 cm in runway C. Runway D contained live caged uninfested hosts and no


dead host with parasites. After nine hours (overnight, in darkness), the cage in runway A contained one amphipod with two mites and one with one mite (no loss of mites over 10 cm). In runway B, one caged amphipod bore three mites, the other none (no loss of mites over 20 cm). In runway C, each caged amphipod bore one mite (loss of one mite over 30 cm). No mites were found on the caged amphipods in control runway D.

The results suggest the mites possess chemo- receptors enabling them to locate hosts over considerable distances.

Mites in environments other than the host.— The foregoing observations suggest that some part of the mite population exists apart from the O. corniculata population. Possible alternative en- vironments for these mites are: 1) other host species; 2) damp sand; and 3) damp wrack on the beach. As previously noted, mites also infest the O. californiana population. Mites that had the appearance of those infesting O. corniculata were found in older, partially buried wrack. Newell (pers. comm., 1972) has identified them as G. brevisternalis, and noted that he has found these mites in southern California exclusively in wrack. Mites from Pacific Grove wrack, which appeared identical to the amphipod mites, were introduced into a vial with live uninfested amphi- pods. A day later, they were found attached to the O. corniculata. The mites can live for prolonged periods apart from the host. Gammaridacarus brevisternalis can live more than a month on de- composing wrack placed in closed plastic bags (Helen Kompfner, pers. comm., 1972). I have kept the mites in stoppered vials containing only tiny bits of beach wrack, and also in vials containing only a pad of sea water soaked cotton for at least 3.5 weeks. In contrast, mites held overnight in an empty, corked glass vial were all dead the next morning, evidently of desiccation.

Perhaps when the mites do not locate an amphi- pod quickly, they find in the wrack a humid environment where they can survive until they find a new host. The relationship of the mites to the wrack requires further study.



I thank Irwin M. Newell of the University of Cali- fornia, Riverside, for identifying the mite, and for his helpful suggestions. Marty Mendelson of the State University of New York at Stony Brook assisted me with the later. stages of my diagrams. Sam Johnson, a graduate student at Hopkins Marine Sta- tion at the time of this study, answered many questions about amphipods. Especially, I would like to express my deep appreciation to Donald P. Abbott for his enthusiastic guidance.


Bousfield, E. L. 1959. hoppers (Crustacea: coast of California. 1/2 2s

of beach from the Bull.,

New records Amphipoda ) Nat. Mus. Canada,

Bowers, D. E. 1964. Natural history of two beach hoppers of the genus Orchestoidea (Crustacea: Amphipoda) with reference to their comple- mental distribution. Ecology, 45:677—696.

Canaris, A. G. 1962. A new genus and species of mite (Laelaptidae) from Orchestoidea califor- niana (Gammaridea). J. Parasit., 48:467—469.

Cheng, T. C. 1964. The biology of parasites. W. B. Saunders, Philadelphia, 727 pp.

Cussans, M. 1904. Liverpool marine biology com- mittee memoirs. XII Gammarus. Williams and Norgate, London, 47 pp.

Hull, H. V. 1912. Some marine and _ terrestrial acarina of Laguna Beach. First annual report of the Laguna Marine Laboratory. Pomona College Press, 218 pp.

McClurkin, J. I., Jr. 1953. Studies on the genus Orchestoidea (Crustacea: Amphipoda) in Cali- fornia. Unpublished Ph.D. thesis, Stanford Univ. Publ., 5803 Univ. Microfilms, Ann Arbor, Michigan.

Accepted for publication October 24, 1973.




Two species of hyperiid amphipods (Hyperoche medusarum and H. medi-

terranea) were found in symbiotic associations with the ctenophore Pleurobrachia bachei. H.

mediterranea has not previously been reported from this ctenophore.

Adult amphipods

were most frequently encountered on the exterior of the host, or forming excavations in

the surface.

Immatures were most abundant

within the mesoglea of the ctenophore.

Behavioral observations on living specimens are discussed and related to the method of

entrance into the host by the amphipods.

Symbiotic relationships between pelagic hyperiid amphipods and various host organisms (medusae, ctenophores, salps) have been noted by several

authors (Bowman, Meyers, and Hicks, 1963; Brusca, 1967, 1971; Hardy, 1965; Laval, 1963, 1966, 1968; Schellenberg, 1942: Stephensen,

1923; Steuer, 1911), but few of these reports dis- cuss the nature of the associations. In at least one instance, (Hyperia galba on the scyphomedusa Cyanea capillata), post mortem gut analyses of the amphipod revealed nematocyst capsules and the relationship was reported as parasitic (Dahl, 1959). Bowman et al., (1963) reported on ob- servations of living specimens of H. galba on a live C. capillata, but actual feeding by the hyperiid was not seen, and Dahl’s conclusions remain unsupported by direct evidence. Most of the related literature consists of reports of occurrence of members of the family Hyperiidae.

We intend to elaborate on the association be- tween Hyperoche medusarum and the ctenophore Pleurobrachia bachei, previously reported by Brusca (1971), and to present observations on the association between H. mediterranea and P. bachei. We have found no mention of the latter relationship in the literature. All of the speci- mens discussed here were collected from northern California waters either with plankton nets aboard the RV/CATALYST within a few miles of the entrance to Humboldt Bay, or by finding freshly stranded ctenophores on the mud and sand flats of the bay itself. Collections were made during the months of June and July, 1972.


The genus Hyperoche is distinguished from other members of the family Hyperiidae by having


gnathopods one and two chelate, with the carpal prolongation of the second pair compressed and blade-like. In the two species discussed here, the carpal process of the first gnathopods are similar in shape.

Only about 45 specimens collected during this study were large enough to identify with cer- tainty. The remaining individuals were unpig- mented juveniles (less than 1 mm in length) and immatures (1-3 mm in length), and could not be identified or sexed. The epimeral plates of these young amphipods were observed under 430 magnification, but could not be assigned to either species as described below.

The separation of H. medusarum from H. medi- terranea is based upon the shape of the epimeral plates of pleonites 1-3. Hurley (1955) described these two species from specimens taken in New Zealand waters. Figures 1 and 2 picture the epi- meral plates and gnathopods from males and fe- males, and illustrate the specific traits as observed in the animals collected during the present study.

Pleonites 1—3 possess postero-ventral points in H. medusarum (Fig. 1 A, D), whereas, these plates are generally rounded and blunt in H. mediterranea (Fig. 2 A, D). Some variation was noted when examining individuals for this char- acteristic, and the specimens figured are indi- viduals which show the described shapes. Some of the amphipods displayed less prominent, but | distinct points, and in one instance a point was | seen on the second plate; none was present on either the first or the third plate. The extent to

P.O. Box 505, Lower Lake, California 95457.

? Ministry of Fisheries, c/o U.S. Peace Corps, P.O. Box 379, 44 R. Seeneevassen St., Port Louis, | Mauritius, Indian Ocean.


Figure 1. Hyperoche medusarum.

1; C (2), gnathopod 2; gnathopod 1. 0.5 mm.

D (¢é),

which these intermediate forms are present in the natural population is unknown, but it should be of interest to examine a larger series for possible taxonomic implications.

The gnathopods of both species are similar, with the following differences. The meeting edges of the chelae appear quite heavily toothed in H. medusarum (Fig. 1 B, C, E, F) when compared with the fine setation of the respective claw margins on H. mediterranea (Fig. 2 B, C, E, F). In addition, the extension of the merus along the posterior edge of the carpus bears 5—7 large distal

Total length of 2 = 4 mn, total length of 4


A (@), epimera of pleonites 1, 2, 3; B (Q), gnathopod epimera of pleonites 1, 2, 3; E (4), gnathopod 2; F (¢),

= 6.5 mm. All scale lines =

(males), which are Hurley (1955) re- ported these spines in female H. medusarum as well, but the specimens studied here showed only a fine to moderate setation. Although H. medusarum has the Pacific, H. was previously known only from the Mediter ranean Sea, and the New Zealand. It is likely that these species will |

shown to have wider distributions as more si

spines in H. medusarum

absent from H. mediterranea.

been reported

from northeastern mediterranea

south Pacific near

become available from around the world



Figure 2.

1; C (2), gnathopod 2; D (4), epimera of pleonites 1, 2, 3; E (¢), Total length of @ = 3 mm, total length of ¢ =

gnathopod 1. = 0.5 mm.


Detailed counts were made of the amphipods associated with 50 preserved Pleurobrachia bachei. Every ctenophore housed at least one hyperiid, and one individual contained five. Thirty-two amphipods had dropped from the hosts during preservation (17 adults and 15 young) and 107 were removed from inside the ctenophores (106 young and 1 adult). The examination of the 50 specimens thus yielded a total of 139 hyperiids. This is a marked increase in density over the 1971 report by Brusca of 24 hyperiids in 135 P. bachei. Unfortunately, earlier work analyzed undated samples, so any seasonal significance to the difference remains unclear.

The specific locations of the amphipods re- moved from the preserved ctenophores were as Adults (total = 18)—H.

follows: medusarum,

Hyperoche mediterranea. A (@), epimera of pleonites 1, 2, 3; B (2), gnathopod gnathopod 2; F (¢), 5.5 mm. All scale lines

(6 specimens; dropped from surface); H. medi- terranea, (12 specimens; 11 dropped from sur- face, 1 in mesoglea). Unidentifiable young (total = 121)—15 specimens, dropped from surface; 101 specimens, in mesoglea; 2 specimens, im- bedded in surface; 2 specimens, partially im- bedded in gut wall (aboral canal); 1 specimen, | inside pharynx.

In addition to the above data on preserved indi- viduals, several living adult amphipods were ob- served on freshly collected ctenophores. Counts were not made during these behavioral studies.


About 20 living ctenophores were examined in a search for active hyperiids. Most of the amphi- pods noted were immature and imbedded in the mesoglea; these remained stationary while slowly |


moving their peraeopods and gnathopods. While some of these young hyperiids moved the gnatho- pods around the area of their mouthparts, definite feeding activity could not be confirmed.

In two instances live, unpigmented juveniles (less than 1 mm long) were seen moving about within the gut canals of the host. Although small crustaceans frequently are eaten by P. bachei, neither of these amphipods seemed to be affected by the digestive action of the gut. In the above two cases there was