Research Article |
Corresponding author: Traudl Krapp-Schickel ( traudl.krapp@uni-bonn.de ) Academic editor: Michael Ohl
© 2015 Traudl Krapp-Schickel, Wim Vader.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Krapp-Schickel T, Vader W (2015) Stenothoids living with or on other animals (Crustacea, Amphipoda). Zoosystematics and Evolution 91(2): 215-246. https://doi.org/10.3897/zse.91.5715
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This paper describes new or little known species of Stenothoidae, collected from sea anemones, bivalves or hermit crabs. A key to world Stenula species is provided.
Taxonomy, Amphipoda , Stenothoidae , new species, revalidated species, associations with other animals
Associations between amphipods and other animals are probably not all that rare, but few have been recorded hitherto, mainly because collection methods earlier were too crude. With the advance of Scuba-diving, new associations are being discovered at a rapid pace. The present paper adds a few more examples from the family Stenothoidae.
All specimens in alcohol were studied under a Reichert and Wild M5 dissecting microscope, then drawn from preparations (dissected and stored in glycerine or Faure’s medium) under a Wild M20 microscope. The pencil drawings were partly inked by hand, and partly with the software Adobe Illustrator CS 3, using a Wacom A4 drawing board. The material is lodged at the Museums of Verona (MVR, Italy), Copenhagen (
A1, 2, antennae 1, 2; art, article; Cx, coxa; Ep, epimeral plate; Gn 1, 2, gnathopods 1, 2; Md, mandible; Mx1, 2, maxillae 1, 2; Mxp, maxilliped; P 3–7, peraeopods 3–7; U 1–3, uropods 1–3.
In this paper the following terms are applied (see also
Stenothoe valida Dana, 1852
The diagnosis of this genus is summarized, it shows few eminent features: Md palp lacking totally, P 5 basis linear, P 6–7 basis widened, T laminar. The genus contains many apparently free-living species and others that are living in symbiosis with other marine invertebrates; these latter in many cases show greatly diminished sexual dimorphism.
Stenothoe species are mainly found in the Atlantic and Mediterranean, while few are living in the Pacific, in the region of Australia-New Zealand or in the Indian Ocean (
Vader 1983: 146 sub Stenothoe n.sp.
female ov. 3 mm, Florida, Monroe County, Cross Key: from Bartholomea annulata (Lesueur, 1817), 4/10/1971, J. Thomas coll. Slide MVRCr 7716, 7717.
one female front part, slide MVRCr 7718; several hundreds, same locality, same date, in alcohol, deposited at MVRCr.
Florida, Monroe County, Cross Key.
after the host anemone Bartholomea annulata (Lesueur, 1817), from where it was collected.
Sexual dimorphism lacking. Gn 1 and Gn 2 propodus similar in shape, propodus hind margin rounded, in Gn 2 without clear palmar corner. P 6, 7 basis posterodistal corner lengthened and rounded; merus posterodistally widened and lengthened, reaching half length of carpus. U3 peduncle < ramus. T with or without submarginal spines and marginal setae.
Length 2.5 – 3 mm.
Head. Eyes round, medium. Mouthparts: Md with acute hook on the place where a palp would have inserted; molar absent, incisor and lacinia mobilis strong, spine row present. Mx 1 palp with 2 arts, Mx 2 plates sitting upon each other. Mxp IP small, OP vanishing. Antennae: subequal, A1 flagellum about 15 arts, A2 flagellum about 10 arts.
Peraeon. Gn 1 basis about 3 times as long as wide, merus triangular, distally rounded and beset with spines, nearly reaching end of carpus; carpus triangular; propodus somewhat wider and clearly longer than carpus, anteriorly beset with long setae; palm well defined by a group of spines and palmar corner. Cx 2 tongue-shaped, posteriorly excavate. Gn 2 basis 3 –3.5 times longer than wide, rectangular; merus rectangular-trapezium-shaped, distally pointed, carpus triangular, distally with stiff short and long pectinate setae, propodus oval, posterior margin regularly rounded, palm defined by some robust spines but palmar corner lacking, with one or more small triangular elevations.
Peraeopods: Cx 3 rectangular, distal margin not much longer than proximal one. Cx 4 triangular, clearly wider than long. P 3, 4 similar, slender, dactylus longer than half propodus. P 5 basis rectolinear. P 6, 7 basis with posterior margin rounded, postero-distal lobe well developed; merus lengthened and widened, reaching about half length of carpus; propodus > carpus, dactylus > half of propodus.
Pleon. U 1 peduncle > subequal rami, all beset with a few spines. U 2 peduncle > longer than unequal rami; U 3 peduncle about 3 times as long as wide, peduncle < ramus, ramus art 1 < art 2, with few short spines.
Telson with or without pair of submarginal spines and small marginal setae.
In
Florida, Atlantic Ocean.
living with and on the sea-anemone Bartholomea annulata (Lesueur, 1817).
Montagua Miersii Haswell, 1879: 323, pl. 24, fig. 4.
Montagua longicornis Haswell, 1879: 323, pl. 24, fig. 5.
Stenothoe miersi. —
Stenothoe ? miersii. —
Stenothoe valida. —
not Montaguana miersii. —
not Montagua miersii. —
not Probolium miersii. —
Port Jackson, New South Wales, Australia.
1 spec. from Bermagui (400 km S of Port Jackson, Australia), 8/6/1989, Wim Vader collected on a hermit crab in shallow water. Stored at the Australian Museum (
In
It may well be that this specimen lived among the encrusting hydroids and bryozoans growing on top of the hermit-crab-shell and thus had no direct association with the crab; it was the only Stenothoe specimen found among many hermit crabs.
Members of Metopa are mainly distributed in the Atlantic and Arctic, only very few are living outside. They can be divided into three groups by looking at their Gn 1 palmar corner:
L Gn 1 locking, palmar corner 120°, propodus widened
SI simple, Gn 1 palmar corner absent, propodus hind margin straight
N normal, Gn 1 palmar corner 150–160°, propodus hind margin rounded
Atlantic Ocean and Arctic:
M. abyssalis Stephensen, 1931 N
M. aequicornis Sars, 1879 N
M. affinis Boeck, 1871 SI/N
M. alderi (Bate, 1857) N
M. boeckii Sars, 1892 N
M. borealis Sars, 1883 SI
M. bruzelii (Goës, 1866) SI
M. clypeata (Krøyer, 1842) SI
M. cristata Gurjanova, 1955 L
M. eupraxiae Krapp-Schickel, 2009 L
M. gigas Just, 2013 SI
M. glacialis Krøyer, 1842 L
M. groenlandica Hansen, 1888 L
M. hearni Dunbar, 1954 N
M. invalida Sars, 1892 SI
M. latimana Hansen, 1888 N
M. leptocarpa Sars, 1883 L (Md palp lacking?)
M. longicornis Boeck, 1871 SI
M. longirama Dunbar, 1942 SI
M. normani Hoek, 1889 N
M. norvegica (Liljeborg, 1851) L
M. palmata Sars, 1895 SI
M. propinqua Sars, 1892 SI
M. pusilla Sars, 1892 SI
M. quadrangula Reibisch, 1905 SI
M. robusta Sars, 1892 SI
M. rubrovittata Sars, 1883 N
M. samsiluna J.L. Barnard, 1966 N
M. sinuata Sars, 1892 N
M. solsbergi Schneider, 1884 N
M. spinicoxa Shoemaker, 1955 N
M. submajuscula Gurjanova, 1948 L
M. spitzbergensis Brüggen, 1907 SI
M. tenuimana Sars, 1892 SI
M. wiesei Gurjanova, 1933 SI
Pacific Ocean:
M. abyssi Pirlot, 1933 Pacific N
M. angustimana Gurjanova, 1948 SI
M. bulychevae Gurjanova, 1955 L
M. cistella J.L. Barnard, 1969 SI
M. colliei Gurjanova, 1948 L
M. dawsoni J.L. Barnard, 1962 SI
M. exigua Krapp-Schickel, 2009 N
M. japonica Gurjanova, 1952 L
M. kobjakovae Gurjanova, 1955 L
M. koreana Gurjanova, 1952 SI
M. layi Gurjanova, 1948 N
M. majuscula Gurjanova, 1948 L
M. mirifica Gurjanova, 1952 L
M. samsiluna JL Barnard, 1966 L
M. timonovi Gurjanova, 1955 L
M. torbeni Krapp-Schickel, 2009 SI
M. uschakovi Gurjanova, 1948 N
Many authors have cited Metopa rubrovittata:
Chevreux 1900 erected a new genus Stenothoides for stenothoid species with present, but reduced mandibular palp.
P 5 basis slender; P 6, 7 basis broad; Md palp with 1 article; Mx1 palp with 1 article.
In the European register of marine species
S. carinatus (Gurjanova) was transferred to Metopa and renamed M. eupraxiae sp. n. by
Thus at the beginning of this study 14 species belong to Stenula. Judging from the illustrations of the mandible in
Tandberg & Vader could demonstrate in
There are also various transitions within the maxillae, having two (Stenothoe) or one (Metopa, Stenula) articles in Mx1 palp, where often one cannot clearly decide if and where an articulation is present; while the Mx2 plates may sit in tandem-position (many Metopa like M. affinis, aequicornis, groenlandica, glacialis, clypeata) or riding position (in some Stenothoe and Stenula), with all steps in-between.
In three species we have no information about the mandible palp at all: S. rubrovittata, S. modosa, S. peltata. The following have a short stump, about as long as the width of the mandible-incisor: S. angusta, S. bassarginensis, S. ratmanovi. All other species have a uniarticulate mandible palp which is clearly longer than the mandible-incisor: S. alexanderi, S. arctica, S. beringiensis, S. incola, S. serripes, S. ussuriensis, and also Metopa derjugini Gurjanova, 1948, which is therefore here also transferred to Stenula (see above).
Stenula species could also be divided by the ratios of articles in Gn 1, having propodus subequal to carpus, or clearly much longer resp. clearly shorter. The first group is formed by the majority: S. beringiensis, S. derjugini, S. incola, S. latipes, S. modosa, S. peltata, S. ratmanovi, S. serripes; propodus is longer than carpus in S. angusta; propodus is shorter than carpus in S. arctica, S. bassarginensis, S. nordmanni, S. ussuriensis and also
S. alexanderi (this species is very aberrant also in the shape of Gn 1 dactylus).
It is the great help of a cladistic analysis that one can test the states of many characters together, and if a group of characters is changing together, it is more probable that a naturally related clade is found. But in the above listed species there are A1 subequal A2 or much different, Gn 1 propodus simple, rounded or with strong palmar corner, Gn 1 carpus short or extremely lengthened, Gn 2 propodus regularly rounded or deeply excavated, P 6, 7 strongly rounded or with widened but parallel margins, telson spinose or naked. And even using more than 60 characters as in the very exhaustive phylogenetic analysis of Tandberg & Vader (
At the moment there is nothing else to do than to continue „making order“ within this complicated family of Stenothoidae in describing as completely as possible its single members.
First we tried to find material of Metopa rubrovittata Sars from the northern North Atlantic (type loc. Christiansund and Finnmark) for comparing it with material of Stenula latipes (Chevreux & Fage) from the English Channel (type loc. Saint Vaast la Hougue, see
Christiansund (W Norway) and Vadsø (Finnmark)
–7 spec. in alcohol, 2 on slide: Surtsey (Vestmannaeyjar) off Iceland, 63.30 N, -20.60 W. NA 30 m 18/8/1971 leg. Sigurdsson, det. J. Just.
–1 spec. 20/8/1971 same locality as above,
– 4 spec. North Sea without date, 4 spec., 57.266667 N 5.5 E.
It seemed strange that the sharp eye of Chevreux would have overlooked the synonymy between M. rubrovittata (cited by him in the same work
In fact, the studied material shows a classical mandible palp of Metopa species with 3 articles, though it has to be admitted that it was quite a difficult task to see always the articulations. But nevertheless, already the length of the mandible palp is very different in the material from the Channel (cf. Fig.
For control Jean-Claude Sorbe sent us material from the Bay of Biscay, and the single specimen he had collected affirms this decision.
Grandcamp-les-Bains (Calvados), on the shell of Eupagurus bernhardus (L.); very common in a dredge of 20m depth in Saint-Vaast-la-Hougue. English Channel.
1 spec. 3 mm, Survey OXYBENT 9 STN OB9–B–TS04; 43.8175 N, 2.042 W; Bay of Biscay, Capbreton Canyon; 500–510 m; 22/06/1999; coll. Sorbe.
4 spec. Denmark, Anholt (Kattegat) without date, 17,5 fathoms = 31,5 m.
Smith 1872 in: Smith and Harger 1872: 29, pl. 3, fig. 5–8;
? synonymous to
St. George’s Banks, 55 m depth. Near Cultivator Shoal.
one specimen
As the original paper is not easily accessible and as there is some confusion about the authors, I repeat herewith the type-description by Smith:
Female. Eyes round and nearly white in alcohol. Antennulae (=A1) considerably shorter than epimera of the 4th segment (Cx 4); first article of the peduncle stout, subequal to head, the second shorter, the third very short and similar to the arts of the flagellum; flagellum scarcely longer than the peduncle, with 8 arts. Antennae (=A 2) slightly longer than antennulae; peduncle art 4, 5 about equal in length; flagellum subequal to flagellum of antennulae. Cx 2 (fig. 5) nearly ovate, twice as high as broad; Cx 3 somewhat rectangular, not wider than the second but considerably deeper; Cx 4 (fig. 6) very large, slightly deeper than Cx 3 and 1/3–1/4 longer than deep, being about as long as the first five segments of the thorax, the inferior margin regularly curved and the posterior convex in outline. Gn 1 (fig. 7) small and slender; merus triangular and distally broader than the carpus, which is not quite twice as long as broad and has the lateral margins parallel; propodus narrower but slightly longer than the carpus and narrowed distally; dactylus about half as long as the propodus. Gn 2 (Fig.
Length of largest specimen, from front of head to tip of telson, about 6 mm.
The mandibles are without palp or molar tubercles, and in all other characters the species agrees with the genus Stenothoe as restricted by Boeck, but it seems to be very distinct from either of the European species.
The hint after the original description, that this species should belong to Stenothoe as it has no mandible palp, was not convincing: no Stenothoe is described from the region off Massachusetts or Connecticut, nor from the entire Atlantic, with gnathopods similar to the ones illustrated.
The incomplete illustrations of S. ratmanovi (Gurjanova, 1948) are very similar to what little we know about ?Stenothoe peltata, and the two species may well be synonymous, in spite of the large geographic distance between the type localities. In that case the older name Stenula peltata (Smith, 1874) would become the valid name of the taxon.
We hoped to get more information by studying the single type specimen (see Fig.
A sample in the collections of the Smithsonian Inst. (Washington) raised new hope to shed light in this situation: there could exist a Stenula sp. from the coelenteron of Haliactis arctica. Will this be S. peltata?
Stenula peltata (Smith, 1872): illustration of the single type specimen; A 1, 2 antenna 1, 2; Mx 1 maxilla 1; Mxp maxilliped; Gn 1 gnathopod 1 without propodus and dactylus; Gn 1’ dactylus, propodus and carpus enlarged; Gn 2 gnathopod 2; Gn 2’ dactylus and propodus enlarged; Gn 2’’ gnathopod 2 tip of carpus enlarged.
Vader 1983: 146, sub Stenothoe sp.
male 3 mm in alcohol;
male, female on 2 slides, both 3 mm.
Chukchi Sea, Arctic. From coelenteron of Haliactis arctica.
the epitheton should remind on the shape of the propodus Gn 2, which looks somewhat like a small fist, in Latin „pugilla“; it is used as noun in apposition.
Length 3 mm.
Head. Eyes round, normal. Mouthparts: Md with very short palp, length about half of width of incisor. Mx 1 palp with one art, Mx 2 plates in tandem – position. Antennae: subequal, A 1 and A 2 flagellum about 10–12 arts. Mxp length of inner plate about half length of ischium, outer plate about 1/3–1/2 of merus.
Peraeon. Gn 1 basis on anterior margin setose, merus with short stiff setae, carpus with long setae and pectinate spines, propodus hind margin setose, somewhat rounded to nearly straight.
Cx 2 tongue-shaped. Gn 2 male and female basis on both margins beset with setae; merus rectangular, naked, carpus triangular, with stiff setae posterodistally, propodus medially widest with setose palm, defined by thumb-shaped protrusion.
Peraeopods: Cx 3 narrow, distally rounded, posteriorly with some setae; Cx 4 distally about 3× wider than Cx 3. P 3 dactylus clearly longer than in other peraeopods; P 3–7 merus somewhat widened and not much lengthened; P 6, 7 basis widened, with parallel margins.
Pleon. U 1 peduncle spinose, > slightly unequal rami; U 2 rami subequal; U 3 peduncle = ramus art 1 = ramus art 2.
Telson naked, triangular.
Female: subsimilar to male.
The note ‚from the coelenteron of Haliactis‘ on the label of this sample may as well just have meant that the sea anemones had contracted on collection.
Within the above discussed criteria of dividing Stenula species into groups, the new species belongs to the majority having Gn 1 propodus subequal to carpus (together with S. solsbergi, see below, here transferred to Stenula) and to the few members having a very short stump of mandible palp. The shape of Gn 2 palm male and female defined by a thumb-like hump is unique and quite helpful in identifying this species.
Metopa solsbergi Schneider, 1884: 71;
one specimen, 3 mm, from the vicinity of Tromsø, N Norway (without date), collected together with Chlamys. The material was dredged in an area with much Metridium.
Malangenfjord, Norway; 18 m depth.
Vader 1983 reported already Metopa solsbergi from the North Atlantic:
This seems to be the very first time that the mouthparts were checked, and a reduced, uniarticulate mandibular palp could be illustrated, moving also this species to Stenula.
At the end of our study, we now know 16 members of the genus Stenula, as S. invalida, S. solsbergi and S. pugilla sp. n. are added, S. arctica given in synonymy with S. nordmanni, S. latipes revived and S. rubrovittata put back into Metopa:
S. alexanderi Tzvetkova & Golikov, 1990; Siberia
S. angusta (Shoemaker, 1955); Alaska, N Pacific
S. bassarginensis (Gurjanova, 1948); Arctic
S. beringiensis (Gurjanova, 1948); Bering Sea, N Pacific
S. derjugini (Gurjanova, 1948); Bering Sea, N Pacific
S. incola J.L. Barnard, 1969; California, Pacific
S. invalida (Sars, 1892); Atlantic
S. latipes (Chevreux & Fage, 1925) (type); Atlantic
S. modosa J.L. Barnard, 1962; California, Pacific
S. nordmanni (Stephensen, 1931); Greenland, ?SW-North Sea (fide
?S. peltata (Smith, 1872); Atlantic (generic allocation doubtful)
S. pugilla sp. n.; Chukchi Sea, Alaska
S. ratmanovi (Gurjanova, 1948) (could be junior synonym of S. peltata)
S. serripes (Gurjanova, 1955); Kurile Isl., NE Pacific
S. solsbergi (Schneider, 1884); N. Norway, N. Atlantic
S. ussuriensis (Gurjanova, 1948); Japan Sea, NE Pacific
The amphipod genus Stenula is probably not a monophyletic entity (cf. Tandberg and Vader 2011, this paper), and it is at present not possible to decide which taxa belong to it. In this key we have therefore cast our nets widely, and we include all species in the Metopa-Stenula complex with a uniarticulate mandible palp. This palp is very short in what we might call ‚typical Stenula‘, a bit longer, but still shorter than the incisor of the mandible, in a number of other species, also traditionally placed in Stenula, and still a bit longer, but clearly uniarticulate, in a few Metopa species: M. hearni, M. palmata and M. sinuata.
The task has been made more difficult by several factors: many species have only been partly illustrated, and at least for the species S. angusta, S. invalida, S. modosa and ?S. peltata, as well as possibly some of Gurjanova‘s species, males are still unknown.
We treat here the 16 Stenula species mentioned above, plus three species which are closely related, but until now still left unchanged in Metopa:
1 | Coxa 4 distal margin clearly sinuous; N. Norway, 4 mm | M. sinuata Sars, 1892 |
– | Coxa 4 distal margin regularly convex or almost straight | 2 |
2 | Gn 1 propodus and carpus very long and slender, dactylus broad and heavily setose; Gn 2 rectipalmate | 3 |
– | Gnathopods not as above | 4 |
3 | Gn 1 propodus < carpus, palm concave, dactylus length to width > 2; N. Norway, 5 mm | M. palmata Sars, 1892 (see note 1) |
– | Gn 1 propodus > carpus, palm convex, dactylus length to width = 3:2; Laptev Sea, 3.8 mm | S. alexanderi Tzvetkova & Golikov, 1990 (see note 2) |
4 | P 6 –7 basis and merus posteriorly serrated, hind margin of basis proximally with acute tooth; Kurile Islands, NE Pacific, 7 mm | S. serripes (Gurjanova, 1955) |
– | P 6 –7 basis not serrated nor with tooth | 5 |
5 | Gn 2 propodus in male with deep U-shaped excavation | 6 |
– | Gn 2 propodus in male not with deep U-shaped excavation | 7 |
6 | Gn 2 propodus palm in male semicircularly excavated near distal corner, rest of palm much longer than width of excavation; Japan Sea, 4 mm | S. ussuriensis (Gurjanova, 1948) |
– | Gn 2 propodus palm in male deeply and irregularly excavated, rest of palm shorter than width of excavation. Japan Sea, 5 mm | S. bassarginensis (Gurjanova, 1948) |
7 | Gn 2 propodus male palm clearly irregular, defined by strong tooth | 8 |
– | Gn 2 propodus in male smooth or slightly crenulate, convex or straight | 9 |
8 | Telson with 3 pairs of spines; Kamchatka, NE. Pacific, 3.5 mm | S. beringiensis (Gurjanova, 1948) |
– | Telson naked or with small setules; California, 2 mm. | S. incola Barnard, 1969 |
9 | Gn 2 propodus palmar corner prominent, shaped like a finger-tip; Chukchi Sea, 3 mm | S. pugilla Krapp-Schickel & Vader, 2015 |
– | Gn 2 propodus palmar corner blunt or with acute tooth | 10 |
10 | Gn 1 carpus unusually long, up to 3 × longer than wide; eyes very large | 11 |
– | Gn 1 carpus clearly not as long; eyes normal | 12 |
11 | Gn 1 dactylus not reaching half length of propodus; A1 clearly shorter than A2; P 6–7 basis with rounded hind margin; W. Greenland, 5 mm | S. nordmanni (Stephensen, 1931) (= S. arctica (Gurjanova, 1951) (see note 3) |
– | Gn 1 dactylus reaching half length of propodus. A1 and 2 subequal; P 6–7 basis with straight hind margin; California, 2 mm. | S. modosa Barnard, 1962 |
12 | Telson with 2 pairs of spines; Bering Sea, 4 mm. | S. derjugini (Gurjanova, 1948) |
– | Telson naked | 13 |
13 | Gn 1 carpus clearly shorter than propodus | 14 |
– | Gn 1 carpus subequal to propodus | 15 |
14 | P 7 very broad, posterior margin convex; mandiblepalp long, but unarticulated; Canada, 3–4 mm | M. hearni (Dunbar, 1954) |
– | P 7 basis slender, posterior margin rather straight; mandible-palp shor, Point Barrow, Alaska, 3 mm. | S. angusta (Shoemaker, 1955) |
15 | P 6–7 posterior tip on merus reaches halfway of less along carpus | 16 |
– | P 6–7 posterior lobe on merus reaches clearly further than halfways along carpus | 17 |
16 | Gn 2 propodus length:width = 3. P 7 basis broad, length = 2 width.; N. Norway, 4 mm | S. invalida (Sars, 1892) |
– | Gn 2 propodus l:w = 2; P7 basis less wide, l< 2w, N. Norway, 7 mm | S. solsbergi (Sp. Schneider, 1884) |
17 | We have been unable to find reliable differences between Stenula latipes (Chevreux & Fage, 1925), a species associated with hermit crabs in W. Europe, and S. ratmanovi (Gurjanova, 1948), an only partly described species from Kamchatka in the northern Pacific. Moreover, the illustrations of this latter species and those of Stenothoe peltata (Smith, 1874) from Georges Banks, NW Atlantic, are, as far as they go, practically identical. |
This is the type species of Norman’s (1902) short-lived genus Sthenometopa.
Probably not a Stenula, to be transferred to Metopa or Sthenometopa.
In transferring Metopa nordmanni to Stenula,
Table
Amphipods | Hosts | Reference |
---|---|---|
on Sea anemones | ||
Parametopella antholobae Krapp-Schickel & Vader, 2009 | Antholoba achates (Drayton, 1846) |
|
Stenothoe barrowensis Shoemaker, 1955 Point Barrow, Alaska |
unidentified |
|
Stenothoe bartholomea Krapp-Schickel & Vader, 2015 Florida Keys |
Bartholomea annulata (Lesueur, 1817) | this paper, Vader 1983 (as Stenothoe sp. n.) |
Stenothoe boloceropsis Krapp-Schickel, Häussermann & Vader, 2015 Chiloe Island, Chile |
Boloceropsis platei McMurrich, 1904 |
|
Stenothoe brevicornis G. O. Sars, 1883 N. Norway, Newfoundland, Canada Stellwagen Bank, Canada |
Actinostola callosa (Verrill, 1882) Liponema multicornis (Verrill, 1880) |
|
Stenula pugilla Krapp-Schickel & Vader, 2015 Chukchi Sea |
Haliactis arctica Carlgren, 1921 | this paper (see also Vader 1983, as Stenothoe sp.) |
Stenula solsbergi (Sp. Schneider, 1884) W.Scotland Newfoundland, Canada |
Metridium senile (L., 1767) | (as Metopa solsbergi) |
Other large coelenterates | ||
Metopa bruzelii (Goes, 1866) Newfoundland, Canada |
Primnoa resedaeformis (Gunnerus, 1763) |
|
Proboloides calcarata G. O. Sars, 1883 Newfoundland, Canada |
Primnoa resedaeformis |
|
Stenothoe minuta Holmes, 1905 N. Carolina, USA |
Astrangia danae Milne-Edwards & Haime, 1849 |
|
Stenothoe valida Dana, 1853 Barbados, W.Indies |
Millepora complanata Lamarck, 1816 |
|
Stenula nordmanni (Stephensen, 1931) Newfoundland, Canada | Gersemia sp. |
(as S. arctica) |
Torometopa sp. Antarctic |
Primnoella sp. |
|
Hydromedusae | ||
Metopa alderi (Sp. Bate, 1857) E. Scotland Norfolk, England Bohuslän, Sweden N Norway |
Tima bairdii (Johnston, 1933) |
|
Metopa borealis G. O. Sars, 1883 W. Scotland |
Phialidium sp. |
|
Ascidians | ||
Malvinometopa porcellana (K. H. Barnard, 1932) Falkland islands |
‘pharynx of large ascidian’ |
|
Metopa groenlandica Hansen, 1888 Maine, USA W. Greenland |
Pyura ovifera (Linnaeus, 1767) Boltenia sp., various ascidians |
|
Stenothoe eduardi Krapp-Schickel, 1976 Napoli, Mediterranean |
on and in ascidians (Microcosmos) |
|
Stenothoe marina Sp. Bate, 1857 Norway |
“inside ascidians” |
|
Stenothoe minuta Holmes, 1905 N. Carolina W. France |
Styela plicata (Lesueur, 1823) |
Pirlot 1933 (as Microstenothoe ascidiae Pirlot) |
Stenothoe valida Dana, 1853 E. Greenland |
Boltenia sp.? |
|
Torometopa paralellocheir (Stebbing, 1888) Falkland Islands |
‘branchial sac of simple ascidian’ |
|
Bivalves | ||
Metopa alderi (Sp. Bate, 1857) Svalbard |
Musculus discors (Linnaeus, 1767), M. niger (JE Gray, 1824) |
|
Metopa glacialis (Krøyer, 1842) N. Brunswick, Canada Bear Island Svalbard Korea W. Greenland |
Musculus discors (Linnaeus, 1767) M. koreanus Ockelmann, 1980 M. laevigatus (JE Gray, 1824) |
Ockelmann 1980 |
Metopa groenlandica Hansen, 1888, E. Greenland | Pandora glacialis Leach, 1819 |
|
Hermit crabs | ||
Metopa rubrovittata G. O. Sars, 1883 N.W. Europe | Pagurus bernhardus Linnaeus, 1758 | many authors |
Metopelloides micropalpa Shoemaker, 1930 St Laurent estuary, Canada |
Pagurus pubescens Krøyer, 1838 |
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M. paguri Marin & Sinelnikov, 2012 Russian coast Japan Sea |
Pagurus pectinatus (Stimpson, 1858) & Elassochirus cavimanus (Miers, 1879) |
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Stenula latipes (Chevreux & Fage, 1925) W. France Ireland England |
Pagurus bernhardus (L., 1758) |
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Spider crabs | ||
Stenothoe symbiotica Shoemaker, 1956 Florida, USA Florida, USA |
‘large spider crab’ Stenocionops spinimana (Rathbun, 1892) |
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The situation is different for the associates of mollusks (all Metopa species) and those on sea anemones (mostly Stenothoe and Stenula species). Practically all these species appear to be obligate associates of only a single or in some cases a few hosts, and they have never been found free-living (for a possible exception see
In contradistinction to the case with sea anemones, all the stenothoid associates of bivalve mollusks are Metopa species. Once more the associations seem to be obligate ones, the amphipods are rarely found free-living (and never leave their hosts in laboratory observations) and they are confined to a single host or, in the case of Metopa glacialis, to a series of closely related host species. A partial exception is Metopa alderi, usually an associate of large hydroids and hydromedusae, that recently was found in Musculus spp in N. Spitsbergen (
In the case of the single, quite aberrant Stenothoe species that lives on a spider crab, S. symbiotica Shoemaker, 1956, its biology is as yet completely unknown, but also this association appears to be an obligate and probably species-specific one; the species has never been collected elsewhere and it has clearly prehensile peraeopods. Also the amphipod associates of hermit crabs and their tenanted mollusk shells are of unknown biology. Metopelloides paguri Marin & Sinelnikov, 2012 and M. micropalpa (Shoemaker, 1930) have slightly but clearly prehensile posterior peraeopods, and may therefore well be direct associates of their host hermit crabs (
We are grateful to Dr. Chad Walter of the Smithsonian Institution, Washington DC, who after thirty years refound the unidentified sample that contained Stenula pugilla, and lent it to us. We thank prof. R.T. Barrett, Tromsø for linguistic assistance, as well as Dr. Oliver Coleman, Naturkunde Museum Berlin, for constructive criticism.