Introduction

Barnard and Karaman (1991: 694 ff.) list 23 species belonging to the genera Metopoides and Proboloides, which were always difficult to differenciate. Since this publication the number of species has increased, while our knowledge on character states did not grow the same way. The results of a phylogenetic analysis of the entire family Stenothoidae sensu lato by Krapp-Schickel and Koenemann (2006) showed not only that the genera treated therein had many plesiomorphic character states, but also that too many characters were still unknown or poorly described. Thus before further studies of the phylogenetic relationships, several species required redescription or at least checking of new characters not described so far.

Material and methods

As many species as possible of this group were studied and redescribed, in order to replace the (initially numerous) question marks in the start-up matrix. Species were borrowed from different Museums.

Acronyms for Museums

AMS Australian Museum Sydney

BMNH British Museum (Natural History), London

MNVCr Museo civico di Storia Naturale Verona

NMV Museum of Victoria, Melbourne, Australia

ZMUC Zoological Museum, University of Copenhagen or Købnhavn

Abbreviations in taxonomical descriptions as well as figures

A1, 2 antenna 1, 2

acc. accessory

art article

Cx coxal plate

Ep epimeral plate

flag flagellum

Gn1, 2 gnathopod 1, 2

IP inner plate

LL lower lip

Md mandible

Mx1, 2 maxilla 1, 2

Mxp maxilliped

OP outer plate

P3-7 peraeopod 3–7

ped peduncle

T telson

U1–3 uropod 1–3

UL upper lip

Us urosome

Character matrix

The chosen characters were as follows:

Head

(1.) A1 length (0) > A2; (1) ≤ A2

(2.) A2 peduncle article 1 ratio length: breadth (0) ≤ 3; (1) > 3

(3.) ratio A1: body length (0) ≥ 0.66% body; (1) < 0.66% body

(4.) A1 flagellum acc. (0) many articles; (1) 2–1 articles; ; (2) lacking

(5.) A1 peduncle art 2 (0) < article 1; (1) ≥ article 1

(6.) A1 peduncle art 1 (0) < ceph.; (1) = ceph.; (2) > ceph.

(7.) A1 peduncle art 3 (0) ≤0.3 art 1 ; (1) 0.3–0.5 art 1; (2) ≥ 0.5 art 1

(8.) A1 flagellum arts (0) <10; (1) 11–20; (2) 21–30; (3) >30

(9.) A2 peduncle art 5 (0) < flag, ; (1) = flag.; (2) > flag.

(10.) A2 peduncle art 4 (0) >art 5; (1) =art 5; (2) <art 5

(11.) A2 nr. flagellum arts (0) <9; (1) 10–15; (2) >15

(12.) Lateral cephalic lobes (0) rounded; (1) subacute, blunt

(13.) Eyes (0) medium; (1) small to absent; (2) large

Mouthparts

(14.) Mandible palp art 3 (0) ≥ half art 2; (1) < half 2 or lacking

(15.) Mandible palp art 2 (0) ≥3 setae; (1) 3–1 setae; (2) lacking

(16.) Mandible palp art 3 (0) ≥2 setae; (1) one distally; (2) lacking

(17.) Maxilliped outer plate : merus (0) ≥ 0.5; (1) 0.5–0.2; (2) <0.2

Coxal plates

(18.) Ratio length Cx2 : Cx1 (0) <2; (1) 2–2.5; (2) 2.5–3; (3) >3

(19.) Cx2 ratio length : breadth (0); ≥1.5; (1) < 1.5

(20.) Cx4 ratio length : breadth (0) l>b; (1) l=b; (2) l<b

(21.) Cx4 distally excavated (0) no; (1) yes

Gnathopods

(22.) Gnathopod 1 dactylus (0) ordinary; (1) spoon-shaped

(23.) Gn1 palm (0) < half propodus length; (1) ≥ half propodus

(24.) Gn1 palm angle about (0) no one = 180°; (1) blunt = 180–150° ; (2) acute = 120°; (3) transverse = 90°

(25.) Gn1, 2 propodus shape (0) similar; (1) different

(26.) Gn 1 propodus shape (0) rounded; (1) linear-rectangular; (2) triangular

(27.) Gn1 carpus (0) short, length< 2 breadth; (1) l=2b; (2) l<2b

(28.) Gn1 merus (0) short; (1) elongate; (2) freeprojecting

(29.) Gn1 ratio carpus : propodus (0) < prop.; (1) = prop.; (2) > prop.

(30.) Ratio length propodus Gn1 : Gn2 (0) ≥0.75; (1) 0.75–0.33; (2) <0.33

(31.) Gn2 ratio propodus : coxa male (0) ≥1; (1) 1–0.66; (2) <0.66

(32.) Gn2 ratio propodus:basis male (0) ≥1; (1) 1–0.66; (2) <0.66

(33.) Gn2 ratio propodus:basis female (0) ) ≥1; (1) 1–0.66; (2) <0.66

(34.) Gn2 ratio propodus : coxa female (0) ≥1; (1) 1–0.66; (2) <0.66

(35.) Gn2 palm male (0) smooth; (1) toothed-serrated; (2) incision(s)

(36.) Gn2 palm female (0) smooth; (1) toothed-serrated; (2) incision(s)

(37.) Gn2 carpus shape (0) short, l<b; (1) ; elongate, l≥b

(38.) Gn2 merus shape (0) not lobate; (1) lobate

Peraeopods

(39.) P4 ratio posterior margin of merus : propodus (0) ≤1.33; (1) >1.33

(40.) P5 basis (0) ovoid widened; (1) rectangularly widened; (2) slim like basis P4

(41.) P5 ratio anterior margin of merus : propodus (0) ≤1.25; (1) >1.25

(42.) P5 merus tip reaching (0) no carpus; (1) 0.25–0.75 carpus; (2) full carpus

(43.) P5 basis posterodistally (0) no lobe; (1) small lobe; (2) medium lobe; (3) lobe wide and deep, reaching merus

(44.) P5 basis width ratio maximum : minimum (0); 1–1.1 (1) 1.1–1.4; (2) 1.4–1.6; (3) 1.6–1.8; (4) >1.8

(45.) P6 basis (0) ovoid widened; (1) narrow like P5; (2) rectangularly widened

(46.) P6 basis hindmargin (0); harmonically rounded (1) straight

(47.) P6 basis posterodistal corner (0) rounded lobe; (1) no lobe

(48.) P6 merus length anterior: posterior margin (0) =1; (1) >1

(49.) P7 basis shape (0) rounded; (1) narrow like P5; (2) rectangularly widened

(50.) P7 merus reaching (0) no carpus; (1) <0.5 carpus; (2) >0.5 carpus; (3) all carpus

(51.) P7 ratio dactylus: propodus (0) <0.5; (1) ≥0.5

(52.) P7 basis posterior margin (0); convex; (1) concave; (2) straight Epimeral plates, Uropods + Telson

(53.) Ep3 posterodistally (0) rectangular corner; (1) acute, 60–70°

(54.) U1 rami (0) equal; (1) very different

(55.) U1 ratio peduncle : longer ramus (0) ≤1; (1) 1–1.33; (2) >1.33

(56.) U2 ratio of rami (0) > 66%; (1) ≤ 66%;

(57.) U2 ratio peduncle : longer ramus (0) < 1; (1) > 1

(58.) U2 peduncle spination (0) no to weak; (1) strong

(59.) U3 ramus ratio art 1 : art 2 (0) <1; (1) =1; (2) 1.1–1.9; (3) >2

(60.) U3 ramus spination (0) no; (1) 1–3 spines; (2) many

(61.) Telson (0); length : breadth ≤2 (1) ; length : breadth >2 (2) 3-dimensional

Schiecke (1973: 80 ff.) published in his doctoral thesis many suggestions about the morphological characters and their states in stenothoids in general. He surmises that the enlarged coxal plates are an advantage in a very densely structured environment such as cylindrical ramified branches in hydroids, bryozoans or algae, allowing stenothoids to “ride” on a branch gripping it with the paired anterior peraeopods from one side and with the posterior peraeopods from the other one, and hiding eggs or juveniles as well as the (usually) very thin posterior legs and uropods. Many species are known as associates with hydroids or bryozoans where they are observed to “steal” the little crustaceans collected and already paralyzed by the host from the tentacle-crown. But of course with stronger enlargement of Cx4 the vagility gets diminished and species with very large coxae are certainly very bad swimmers and probably detritus feeders, However, many stenothoids are excellent swimmers with an enlarged propodus on Gn2 and often with a long basis which affords great mobility, while Gn1 (inclusively Cx1) is extremely small.

It is remarkable that all mouthparts are always unusually long and narrow and it could be imagined that they all together function as a sucking device (it is said that the name steno-thoids stems from the narrow mouthparts, stenos meaning narrow in Greek). Mxp has reduced plates and Md has more or less reduced molars and palps, while pars incisivus and lacinia mobilis are very well developed with acute and robust “teeth”; also both maxillae have robust setae, which could help to divide the food parts already cut by the mandible.

In many stenothoids P3, 4 are longer but weaker than P5–7, and all are kept parallel to the coxae and never twisted. Interesting are the quite often acutely lengthened meri (in P3, 4 anteriorly, in P5–7 posteriorly) which warrant an additional capacity against fallling off the substrate.

Taxonomy Cladistic analysis

Figure 13, 14.

A matrix of 38 species and 61 characters was built (Fig. 13): all presently known species in the genera Proboloides, Torometopa and Scaphodactylus were included. A hypothetical Gammarus species was chosen as out-group (see also Krapp-Schickel 2009, Fig. 5 without the species of Metopoides).

The programs MacClade 4.06 (Maddison and Maddison 2003) and PAUP 40B.10 (Swofford 2002) were applied. Using 38 taxa and 61 characters a heuristic analysis with a hypothetical Gammarus as an outgroup - species was performed and the majority rule consensus tree of 28 trees illustrated in Fig. 14. The difference between the trees concerned only the arrangement within the groupings.

Heuristic search settings:

Optimal criterion = parsimony

Characters were unweighted and unordered

Gaps are treated as “missing”

Multistate taxa interpreted as polymorphism

Starting tree(s) obtained via stepwise addition

Addition sequence: random

Number of replicates = 50

Starting seed = 1191736759

Number of trees held at each step during stepwise addition = 7

Branch-swapping algorithm: tree-bisection-reconnection (TBR)

Steppest descent option not in effect

Initial “MaxTrees” setting = 200 (will be auto-increased by 100)

Branches collapsed (creating polytomies) if maximum branch length is zero

‘MulTrees’ option in effect

Topological constraints not enforced

Trees are unrooted

Total number of rearrangements tried = 46863460

Score of best tree(s) found = 486

Number of trees retained = 28

Tree length = 483

CI = 0, 38

RI = 0, 51

RC = 0, 20

Results

At the beginning of the present analysis 16 species were cited for Proboloides:

Eight species were reported from the Atlantic or Arctic Ocean: Proboloides calcaratus, Proboloides clypeatus, Proboloides grandimanus, Proboloides gregarius, Proboloides holmesi, Proboloides schokalskii, Proboloides schuleikini, Proboloides zubovi. In most species at least the females have a pronounced palmar corner in Gn2, while Gn1 is weak and slender. In the deep-water species Proboloides calcaratus and Proboloides gregarius the males have Gn2 propodus + dactylus very much lengthened and the eyes large, Cx3 has no parallel margins, but becomes wider distally and is not much narrower than Cx 4, while Proboloides holmesi has a narrow Cx3 with parallel margins, very different from Cx4.

Proboloides clypeatus must remain a species dubia, as it is too poorly described.

The species Proboloides gregarius and Proboloides schuleikini (originally only subspecies of Proboloides gregarius) show differences only in the even more elongated Gn1 in the latter, and I think Proboloides schuleikini is a big female of Proboloides gregarius. I have also my doubts about the description of Proboloides grandimana (Bonnier), where all details match Proboloides gregarius except the big and triangular Cx1 which should be even larger than Cx2, an extremely unusual character in stenothoids; it seems quite probable that this is an error and that Cx2 is repeated. - Branch et al. (1991) illustrate a Proboloides sp. with U3 with 2 rami, which undoubtedly is also an error of the drawing.

Thus the only certain Atlantic-Arctic members are Proboloides calcaratus, Proboloides gregarius, Proboloides schokalskii and Proboloides zubovi.

There are 5 nominal Proboloides species from S-Africa and the Antarctic-Subantarctic region: Proboloides porcellanus, Proboloides rotundus, Proboloides stephenseni, Proboloides typicamimus, Proboloides typicus. The species Proboloides stephenseni and Proboloides rotundus are morphologically similar and may be synonymized; Proboloides typicus is redescribed and both could be transferred to Metopoides, as they have more plesiomorphic character states than members of Proboloides. - Proboloides porcellanus is redescribed and is the type of a new monotypic genus Malvinometopa.

The remaining species Proboloides typicamimus would then be the only member of the genus Proboloides living in the Antarctic, but it seems quite probable that also this species does not belong to this genus. But it is incompletely described though, based on a single specimen and knowledge about its character states is still very inadequate.

There are two nominal Pacific species of Proboloides remaining, Proboloides tundus and pacificus, which may well be synonymous: the shape of Gn2 matches (the only illustrated detail of the first), and the written description of the shape of P5-7 merus in Proboloides tundus “narrow, scarcely produced” matches the description by Shoemaker 1964 for Proboloides pacificus “very slightly expanded”. Furthermore both species were found off California at greater depth (302 fathoms = 552 m and 718 fathoms = 1313 m, among hydroids on the back of a spider crab). Shoemaker describes and illustrates Proboloides pacificus with slender P5–7 merus, but at the end of his remarks he adds: “as shown here, the merus [of the last peraeopods] is widely expanded”, which must be a lapsus linguae.

Proboloides anophthalmus is the only species living in the Indian Ocean (Madagascar). It is very similar to the Atlantic species Proboloides? holmesi, however there are some differences in the shape of T, the presence of pearls on the Cx3 margin and the shape of A1, 2. This deep-sea species has no eyes.

Two species can be added here:

“Metopa nordmanni” sensu Shoemaker 1955: 128 fig. 10 a-j (non Metopa nordmanni Stephensen) has to be described as new member of Proboloides, but as I could not see the material it must be cited as Proboloides sp. (Shoemaker, 1955) for the time being.

Proboloides aequicornis (Stephensen, 1931), as explained above.

After the thorough check of 16 species, eight (plus one doubtful member) remain belonging to Proboloides and show that the title in this series of papers is no longer appropriate, as none of them was found in the Austral-Antarctic region:

aequicornis (Stephensen, 1931: 198 fig. 59); between Faroes and Iceland, N-Atlantic.

anophthalmus Ledoyer, 1986: 965–66 (Madagascar, 335–450 m); Indian Ocean.

calcaratus (Sars, 1882: 92, t.4 sub Metopa calcaratus, 1895: 247, t. 85 sub Probolium. c.; 1992: 247 t. 85), Atlantic.

gregarius (Sars, 1882: 93; 1895: 245 pl. 84), Atlantic; = probably grandimanus (Bonnier 1896: 638 sub Probolium grandimanum), species dubia, Atlantic; = probably schuleikini Gurjanova 1946: 283 sub Proboloides gregarius ssp. schuleikini, Arctic.

? holmesi Bousfield 1973: 89 fig. 16/2, Atlantic.

pacificus (Holmes, 1908: 524), Pacific O, = ? tundus JL Barnard 1962: 147–149, Pacific.

schokalskii Gurjanova, 1946: 283, Arctic, Kara Sea

sp. Shoemaker 1955: 128, Arctic, Point Barrow

zubovi Gurjanova 1951: 412–13, Arctic, Kara Sea

Species dubia.

Proboloides clypeatus (Stimpson, 1853: 51 sub Stenothoe clypeata), Atlantic.

Species incertae sedis.

? Metopoides typicamimus Andres 1995: 355–364, Antarctica. [This species may very well belong to Metopoides, but has very elongate antennae and lacks OP on Mxp, or at least not seen with certainty, both advanced character states. More material is needed for solving this question].

? Proboloides holmesi Bousfield 1973: 89, fig. 16(2). [Aberrant member of this genus. May belong in Metopa].

Species transferred to Metopoides.

Metopoides rotundus (Stebbing, 1917) (= ? Proboloides stephenseni Ruffo, 1949)

Metopoides typicus (Walker, 1906)

Key to 15 members of Metopoides species (including ?Metopoides typicamimus) Key to 9 members of Proboloides (including ? Proboloides holmesi and Proboloides sp.)

The habitus sketches added to the resulting tree in Fig. 14 (from above: Proboloides, a large Scaphodactylus, Torometopa with A1> A2, Torometopa with A1 < A2, small Scaphodactylus and Metopoides) may give an idea about the differences in the body shapes in this basic group of stenothoids: e.g. members of Proboloides have a disto-posteriorly lengthened and widened merus on the last three peraeopods, which is much less the case in all other groups. Ed Bousfield (in litteris) opines that this must have an important hydrodynamic function, which could well be imagined. Also the relative length and width of Cx 4 (in Scaphodactylus gigantocheirus strikingly small) or the relation of the antennae (in the group near Torometopa antarctica and Torometopa crenatipalmata with the second one always being longer and stronger) could tell us something about the swimming (or even digging?) ability, if we would know more about their life style. However, it seems probable that Proboloides members are mainly free-living and do not live in association with, or at least not inside of, other animals; they ought therefore to be good swimmers and have a rather strong sexual dimorphism.

The remaining species in Fig. 14., not belonging to the genus Proboloides, will be treated in the following and final part.