Ameiropsis martinis, Gee, 2009

Gee, J. Michael, 2009, Some new and rare species of Ameiridae (Copepoda: Harpacticoida) from the Isles of Scilly, UK, Journal of Natural History 43 (45 - 46), pp. 2809-2851 : 2810-2820

publication ID	https://doi.org/ 10.1080/00222930903373991
persistent identifier	https://treatment.plazi.org/id/FC5A87B8-FF84-7D34-FE3F-B0F59390F641
treatment provided by	Felipe
scientific name	Ameiropsis martinis
status	sp. nov.

Treatment

Ameiropsis martinis sp. nov.

( Figures 1–5 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 )

Material examined

Holotype. Adult ♀ dissected onto five slides, NHM Reg. No. 2009.51.

Paratypes. Twenty-seven adult ♀♀ (1 dissected onto 3 slides, 1 dissected onto 1 slide and 25 spirit preserved) and 15 ƋƋ (2 each dissected onto 3 slides, 1 dissected onto 1 slide and 12 spirit preserved) NHM Reg. Nos 2009.145–147; 2009.148–157; 2009.158–159.

Description of female

Body. See Figure 1 View Figure 1 . Length 0.593 –0.870 mm (mean 0.759 mm, n = 10) semi-cylindrical, widest at posterior margin of cephalothorax, tapering gradually posteriorly and without clear distinction between prosome and urosome. Cephalothorax tapering slightly anteriorly, ornamented with a few pores and sensilla. All prosomites with sensilla on posterior margin and plain hyaline frills. Urosomites -2 and -3 (genital double somite) completely fused, line of fusion marked only by a short lateral subcuticular rib ( Figure 1B View Figure 1 ) and a dorsal row of very small fine spinules ( Figure 1A View Figure 1 ), posterior part of double somite with a dorsal and lateral row of very small, fine spinules. Genital apparatus ( Figure 1D View Figure 1 ) with median ventral copulatory pore near posterior margin of anterior part of genital double somite, a relatively long seminal duct leading to a long oval seminal receptacle; anterior gonopores joined by genital slit and covered by vestigial P6s each bearing one plumose seta. Hyaline frills of all urosomites minutely dentate. Urosomites -4 and -5 posterior margin with dorsal and lateral row of minute spinules and median ventral row of larger spinules. Anal somite ventrally with anterior row of spinules ( Figure 1C View Figure 1 ) and a few minute spinules near base of caudal rami; dorsally bearing smooth, semi-circular, operculum. Caudal rami about as long as broad, tapering posteriorly, with a row of setules on inner margin and seven setae (lateral seta-I small, lateral seta-II and terminal setae -III and - VI slender, terminal setae -IV and - V well developed, dorsal, posterior seta-VII triarticulate) GoogleMaps .

Rostrum. See Figure 1E. A View Figure 1 small elongate oval plate fused to cephalothorax, with two sensilla near anterior margin, latter only reaching to midpoint of first antennular segment.

Antennule. See Figure 1F View Figure 1 . Slender, eight-segmented, segment-2 longest. All setae naked, aesthetascs on segments -4 and -8. Setal formula as follows: 1-(1), 2-(9), 3-(8), 4-(2+(1+a)), 5-(2), 6-(2), 7-(4), 8-(5+(2+a)).

Antenna. See Figure 2A View Figure 2 . Well-developed coxa with row of minute spinules on anterior margin. Basis unarmed but ornamented with row of spinules and a few setules on abexopodal margin. Exopod two-segmented, proximal segment large, oval, with row of spinules on inner distal margin and a large, minutely dentate seta at outer distal corner; distal segment small with two, strong, minutely dentate, setae on distal margin. Endopod two-segmented, proximal segment unadorned and unarmed; distal segment with row of spinules, two strong spines and a seta on outer margin, a row of setules near inner margin and on distal margin, a row of setules and six setae (five geniculate setae and one plain seta fused at base to inner geniculate seta).

Mandible. See Figure 2B View Figure 2 . Coxal gnathobase well developed, relatively slender, cutting edge with large bicuspid tooth at outer corner, a large unicuspid tooth medially, an array of small multicuspid teeth and a plumose seta at inner distal corner. Basis armed with three robust setae (two strongly dentate) and with well-developed rami. Exopod with two lateral and two distal plumose setae. Endopod with one lateral plumose seta and five setae distally (one plumose and four naked, three of which fused at base).

Maxillule. See Figure 2C View Figure 2 . Praecoxal arthrite with a row of spinules proximally and a seta medially on inner margin; dorsal surface with row of spinules and two surface setae; distal margin with three pairs of curved spines and one(?) seta. Coxal endite with two naked and one plumose setae. Basis with one naked seta proximally and on distal margin two naked setae and one strongly spinulous seta. Endopod minute, fused to basis, with one naked seta; exopod with three plumose setae.

Maxilla. Figure 2D View Figure 2 . Syncoxa with rows of spinules near proximal margin on anterior and posterior face and two endites on distal margin, inner endite broad with two pinnate setae, outer endite slender with two naked setae and a pectinate spine. Allobasal endite with group of setules basally and distally a fused pectinate claw and an articulating pectinate spine. Endopod with three naked setae.

Maxilliped. See Figure 2E View Figure 2 . Syncoxa with rows of spinules proximally and one plumose seta on distal margin. Basis oval, unarmed but ornamented with row of spinules on palmar margin and medially and distally on outer margin. Endopod represented by a well-developed claw slightly longer than basis, with row of spinules on distal inner margin and two accessory setae proximally.

P1. See Figure 3A–B View Figure 3 . Intercoxal sclerite small, bilobed and unadorned. Praecoxa (not illustrated) small, triangular with row of spinules on anterior margin. Coxa almost square, with four rows of spinules on anterior face and a row of setules near outer margin on posterior face. Basis with small row of spinules on distal margin and at base of inner and outer spine. Exopod three-segmented, proximal segment slightly the longest, all segments with row of spinules on outer margin; exp-2 without inner seta but with setules on inner margin; exp-3 with two plumose geniculate setae on distal margin and three spines on outer margin. Endopod three-segmented, enp-1 elongate, reaching distal margin of exp-3, with row of spinules on inner margin and a short stout plumose seta inserted at 65% of segment length; enp-2 only half length of enp-3, with row of setules on outer margin and, in holotype two but in other specimens one, seta on inner margin; enp-3 about half length of enp-1 with one plumose seta, a geniculate seta and a spine on distal margin.

P2–P4. See Figures 3C View Figure 3 and 4 View Figure 4 . Intercoxal sclerites bilobate and unadorned. Praecoxa and coxa as in P1. Basis of P2 with row of setules on inner distal margin and spinules on distal margin and at base of outer spine; basis of P3 and P4 without inner setule row and with outer element a naked seta. All rami three-segmented and all segments with row of spinules on outer margin. P2 and P3 exp-1 with spinule row on posterior face; exp-2 with attenuated outer distal corner; enp-1 with short inner seta and enp-3 reaching to middle of exp-3. P4 exopod segments more elongate than in P2 and P3; exp-2 without attenuated distal outer corner; exp-3 with three inner setae, middle one very well developed and spinulose, distal inner seta extremely fine, articulating on posterior face of segment; enp-1 with long inner seta and enp-3 only reaching to middle of exp-2. Setal formula of swimming legs is presented in Table 1.

P5. See Figure 1G View Figure 1 . Baseoendopods of each side not fused medially and exopods also separate. Baseoendopod with well-developed endopodal lobe, reaching to middle of exopod, with outer peduncle bearing a slender seta and with five setae on distal margin, four inner setae finely spinulose and outer seta very small and naked. Exopod oval, about twice as long as wide; with a spinule and a tube pore on proximal outer margin and five setae, inner seta finely spinulose, terminal setae long and naked, middle outer seta very small.

Description of male

As in female except for urosome, antennule, P1 basis, P5 and P6.

Body. Slightly smaller than female, length 0.534 –0.646 mm (mean = 0.595 mm, n = 5) and urosomites -2 and -3 not fused. Body ornamentation as in female except urosomite-3 with median ventral row of larger spinules ( Figure 5A View Figure 5 ).

Antennule. See Figure 5B View Figure 5 . Eleven-segmented, haplocer with slightly swollen segments -6 to -8 and major articulation between segments -8 and -9. Segment-2 is a short segment bearing one seta. Aesthetacs on segments -6 and -11. Setal formula tentatively given as follows: 1-(1), 2-(1), 3-(10), 4-(8), 5-(2), 6-(6 + (1+a)), 7-(1 modified spine), 8- (1 + 1 modified spine), 9-(3 spines + 1 seta), 10-(4), 11-(5 + (2 + a)).

P1. See Figure 3D View Figure 3 . As in female except that inner spine on basis bears a row of stronger spinules and distal portion recurved and hook-shaped.

P5. See Figure 5C View Figure 5 . Baseoendopods of each side fused medially. Endopodal lobe shaped as in female but bearing only four setae, three inner setae finely spinulose, outer seta very small and naked. Exopod more rounded than in female, less than two times longer than wide, bearing five setae, terminal seta much stouter than others and finely spinulose, middle outer seta very small.

P6. See Figure 5A View Figure 5 . Asymmetrical, with one plate fused and one plate articulating with urosomite-2, each bearing three setae.

Etymology

The specific name refers to the type locality on St Martin’s flat.

Variability

The mandibular exopod in the other dissected female has only one lateral seta and one dissected male has an inner seta on P1 exp-2 on one side only.

Remarks

This animal belongs to the group of genera in the Ameirinae characterized by a clearly biramous mandibular palp, Ameiropsis , Parameiropsis Becker, 1974 , Ameiropsyllus Bodin, 1979 , Pseudameiropsis Pallares 1982 and Biameiropsis Karanovic 2006 . Parameiropsis was established by Becker (1974) to accommodate two deep-sea forms in which the exopod of the antenna is 1-segmented bearing only two setae and the armature of enp-2 is very robust, the P1 endopod is of three equal segments and the female P5 endopodal lobe has only three setae. There is some doubt as to whether this genus should be in the Ameiridae as the short, robust antennule and the large triangular rostrum articulating with the cephalosome is very un-ameirid-like. However, the male (and the condition of the inner basal spine) is unknown for any of the three constituent species (the third species described by Itô [1983]) and until this deficiency is rectified it is to be left in this family. Biameiropsis was established by Karanovic (2006) to accommodate a freshwater Australian species, B. barrowi , in which the exopod of the antenna was also only one-segmented and was the only species in all these genera to have a seta on the abexopodal margin of the basis. On the basis of the one-segmented nature of the antenna in Ameiropsis abbreviata Sars, 1911 he transferred this species to Biameiropsis . Pseudameiropsis was established by Pallares (1982) for P. argenticus Pallares and characterized by a distinctive, very prehensile P1 endopod (in which enp-1 is much longer that the exopod and enp-2 and -3 are both very small segments) and the slight reduction in the size of enp-1 on P2–P4. Bodin (1979) also established the genus Ameiropsyllus for A. monardi Bodin on the basis of the slightly reduced size of enp-1 on P2-P4 and the absence of an inner seta on P1 exp-2. For exhibiting these characteristics Bodin included Ameiropsis ariana Monard, 1928 in Ameiropsyllus even though this latter author stated that in this species the exopod of the mandible was represented by only a seta. Characters not mentioned by Bodin which distinguish Ameiropsyllus from Ameiropsis , as presently constituted, are: (1) the presence in the former of only three setae on the endopodal lobe of the female P5 compared with four or five setae in the latter. Three setae on the P5 endopodal lobe are also found in Parameiropsis ; (2) the presence in the former of two setae on the syncoxa of the maxilliped. The details of the mouthparts for the original species in Ameiropsis are very sketchy and can only be deduced from drawings of Sars (1911, 1920) which are not reliable but it would appear that two setae on the maxilliped syncoxa had previously only been illustrated for A meiropsis abbreviata (see Sars [1911, suppl. pl. 33]) and more recently reported for Parameiropsis magnus by Itô (1983). However, while there is only one seta on the maxilliped syncoxa in all species of Ameiropsis , in Parameiropsis the number of setae on this segment varies from 0 to 2 and in Biameiropsis from 1 to 2.

From the above it is clear that our specimens can only be considered as belonging to the genus Ameiropsis . Three species of this genus have been recorded previously from the Scilly Isles ( Wells 1970), Ameiropsis longicornis Sars, 1907 , Ameiropsis mixta Sars, 1907 and Ameiropsis nobilis Sars 1911 . Whilst A. martinis resembles the last of these species in the baseoendopod of the female P5 (four well developed and one outer minute setae), the P5 exopod is not nearly as elongate as in the other three species and A martinis also has a reduced setal formula on the swimming legs. In this and other respects A. martinis most resembles Ameiropsis australis Kunz, 1975 , described by Kunz (1975) from shell gravels in intertidal pools around East London in South Africa. In both these species: (1) the endopod of the maxillule is a very small segment fused to the basis and bearing only one seta; in other species for which this mouthpart has been described or figured the endopod is well developed and bears two or three setae; (2) there is no inner seta on P1 exopod-2, a character that is shared only with Ameiropsis robinsoni Gurney, 1927 ; (3) there is only one inner seta on P2 exp-3 and enp-3 and P3 exp-3, a character shared only with Ameiropsis reducta Apostolov, 1973 ; (4) a third large inner (distal) seta on P4 exp-3 is not present, a character shared with A. reducta and Ameiropsis minor Sars, 1920 . In A. martinis I show that distally a very small slender seta does arise from the posterior face of the segment and it is possible that this has been overlooked by Kunz (1975) for A. australis ; (5) the female P5 exopod length/width ratio is smaller than for any other species in the genus except for A. angulifera Sars, 1911 ; (6) the male P5 baseoendopods in these two species are the only ones with more than two armature elements on the endopodal lobe; (7) the structure of the male antennule in this genus is very poorly known and has only been described in detail for the present species and figured for this species and A. australis . It is mentioned by Klie (1950) for A. brevicornis and A. longicornis as being eight-segmented and Bodin (1964) merely states that A. nobilis has no significant modifications. The antennule in A. martinis is 11-segmented, with the unusual feature of a separate segment-2 bearing one seta (in most harpacticoids segment-2 and segment- 3 in the present species are usually fused). Kunz (1975) describes the antennule of A. australis as eight-segmented but illustrates at least nine segments. This should be interpreted as at least 10 segments as the small segment-5 shown in Figure 5B View Figure 5 has almost certainly not been recognized by Kunz (1975) and it is possible that he failed to recognize that there were two proximal segments each bearing 1 seta.

Despite these similarities between A. martinis and A. australis the two species can be easily distinguished by the following characters: (1) the rostrum is rounded anteriorly in A. martinis and distinctly pointed in A. australis ; (2) in the female genital field the P6 bears one large plumose seta in A. martinis and two naked setae in A. australis ; (3) the anal operculum in A. martinis is smooth whereas in A. australis it bears about seven strong spinules; (4) in A. martinis the P1 enp-1 is equal in length to the exopod whereas in A. australis it is noticeably longer than the exopod; (5) the male P5 basendopodal lobe bears four setae in A. martinis but only three in A. australis .

Within the genus Ameiropsis , the species A. minor appears to be somewhat anomalous. It was first described by Sars (1920) as Stenocopia minor Sars, 1920 , but moved to Ameiropsis by Lang (1936) on the grounds that it did not comply with Sars’ (1907) definition of Stenocopia in the habitus, the form of the antennule (first segment much the longest) and the very slender swimming legs. He suggested that it was most like Ameiropsis abbreviata (which has now been moved from Ameiropsis , see earlier). However A. minor is the only species of Ameiropsis with the following characteristics: (1) a nine-segmented female antennule with very small segments -7 and -8, similar to the condition in Stenocopia and not like the condition in A. angulifera the other species with a nine-segmented antennules; (2) the antennal exopod is two-segmented but the distal segment is minute cylindrical with only one seta. This is unlike any other species in the “ Ameiropsis ” group of genera and most similar to the condition in Stenocopia setosa Sars 1907 ; (3) the basis of the mandibular palp has only one seta (according to the figure in Plate XLI of Sars [1920]), whereas all species of Ameiropsis for which the condition is known have two or three setae; (4) A. minor is the only species in this group of genera with only four elements in P1 exp-3, all other species have five elements on this segment; (5) in all species of Ameiropsis for which the male is known and the P5 has been figured, the outer spine of the endopodal lobe of this limb is minute, often little more than a spinule in appearance. However, Por (1964) claims that he found the male of A. minor and draws the ventral urosome, which indicates that the two setae on the P5 endopodal lobe are both well developed (and the setal arrangement on the P5 exopod is rather different to the female). However, the validity of Por’s diagnosis of the animal he so briefly described must be in some doubt as he states that this species is unusual in exhibiting no sexual dimorphism of the inner spine on the P1 basis. Thus, I suggest that when the male of this species is properly described it may be that it should be removed from Ameiropsis to another genus.