Siphonophora setaepromissa, Read & Enghoff, 2019

Read, Helen J. & Enghoff, Henrik, 2019, Siphonophoridae from Brazilian Amazonia. Part 2 - Two new treeclimbing species of the genus Siphonophora, including one showing pilosity polymorphism (Diplopoda, Siphonophorida), European Journal of Taxonomy 496, pp. 1-26 : 9-15

Siphonophora setaepromissa sp. nov.

urn:lsid:zoobank.org:act:4C3C08E9-C6F9-464C-8E01-A9D0399F769D

Figs 1 , 3–6 , 8C , 9B

Diagnosis

A medium-sized species, although very variable, with paddle-shaped claws. Very setose (and some males with very long setae on metazonites), but not especially tuberculate and coxae smooth. Pleurite ventral edge clearly bilobed, hind margins with some tubercles. Accessory claw short and arising from the ventral side of the claw. Anterior gonopods relatively long, with spines at the apex and a projection mesally.

Etymology

The specific name, meaning uncut or unruly setae, refers to the long setae on some of the males

Material studied (total: 96 ♂♂, 152 ♀♀)

Holotype BRAZIL • ♂; Amazonas Province, Rio Tarumã Mirím, Igapó , inundation forest; 03°02′ S, 60°17′ W; TM50C; 2 Sep. 1976; J. Adis leg.; INPA.

Paratypes

BRAZIL • 1 ♂, 1 ♀; same collecting data as for preceding; ZMUM • 4 ♂♂, 5 ♀♀; same collecting data as for preceding; INPA • 1 ♀; same collecting data as for preceding; NHMD • 7 ♂♂, 6 ♀♀; same collecting data as for preceding; TM50D; NHML • 4 ♂♂, 7 ♀♀; same collecting data as for preceding; TM50B ; NHMD .

Referred non-type material

Approximately 40 collections examined as part of this study can be attributed to this species. They are all from the same locality with dates ranging from 16 Sep. 1975 to 12 Jun. 1987. Most were from photoeclectors collecting invertebrates walking up or down trees. A small number from 1987 were collected as part of a study of standing crop, but from the same location. Specimens have been distributed between INPA, NHMD, NHML, NHMW and ZMUM.

Description

MEASUREMENTS. Body length: ♂: 5.5–18 mm, ♀: 7–19 mm. Body width: ♂: 0.44–1.12 mm, ♀: 0.45– 1.04 mm. Number of podous tergites: ♂: 35–81, ♀: 28–82. Number of apodous tergites: ♂: 1–2, ♀: 1–2.

COLOUR. Yellow to pale brown, some specimens slightly darker, especially dorso-laterally on prozonites. Small specimens generally uniformly pale white/yellow.

BODY SHAPE. Generally parallel-sided, widest point just slightly posterior of mid-point. Some narrowing behind head and towards the telson.

HEAD. In dorsal view, more or less triangular in shape, with slight depressions for the bases of the antennae, rostrum relatively clearly demarcated from rest of head. In lateral view, dorsally gradually tapering from top of head to tip of rostrum, head not domed and with no clear demarcation between rostrum and rest of head. Rostrum prominent and clear but relatively short, rostrum tip to base roughly same distance as rostrum base to antennal bases. In lateral view, rostrum slightly down-curved relative to rest of head.The ‘mouth’ was open in one female specimen and was examined under SEM. Mandible tip was sponge-like and fitted into gnathochilarium at base and rostrum at tip. Length of rostrum (to antennal base), ♂: 0.28–0.42 mm, ♀: 0.26–0.4 mm. Width of head (between antennal sockets), ♂: 0.18– 0.34 mm, 0.2–0.28 mm. Head setose and with tubercles laterally and posteriorly, but rather sparse dorsally. Larger setae on gnathochilarium at base of rostrum and smaller ones along sides of rostrum to tip.

ANTENNAE. Approximately of same length as rostrum, generally appearing shorter. Overall length: 0.63– 0.82 mm. Length:width ratio of segments 0.92, 0.75, 0.73, 0.76, 0.95, 1.35 and 0.47, antennal cones not measured (3 specimens examined). Antennal pits on segments 5 and 6 present and containing sensilla, but smaller and less clear than in species of Columbianum .

COLLUM. With abundant setae but no tubercles, although bases of setae situated very closely together, giving it a rugged look. Wide, with anterior margin forming very gentle curve. In some specimens V-shaped margin visible with SEM. Posterior margin almost straight.

TERGITE 2. Narrower than collum but more than 0.5 × length of collum.

MID- BODY RINGS. When plotted ( Fig. 1 ) this species has a relatively large number of segments for the body width although both increase as overall body size increases. No obvious paranota, although difficult to see in some specimens because of dense cloak of setae. Metazonites standing slightly proud of prozonites giving a slight ‘castellated’ appearance in lateral view, at least anteriorly, posteriorly with less contrast so that dorsal outline is rather more even. Relative width of pro-/metazonites 0.82–0.95. Mid-body metazonites (from about tergite 20 onwards) in some, mostly larger, males covered in very dense and very long, almost tangled, setae, appearing clearly different to pubescent covering in most other siphonophorids. Especially between body rings 12–20, setae can be up to 0.31 × body width. Some males and all females have a shorter type of setal covering, some males intermediate (see graph Fig. 4 ). Metazonites with tubercles, but irregular in both occurrence and structure; may be more pronounced partway along body length. Prozonites lacking setae and quite smooth. Under SEM cytoscutes on prozonites are visible but not very pronounced. Channel between prozonites and metazonites bearing single line of setae and some collapsed tubercles. Limbus with membranous edge and not serrate. Pleurites with clearly bilobed ventral margin supporting setae and few irregular tubercles. Hind edge from inside not serrate. Ozopores starting on tergite 5 and ending on the penultimate. Position along tergal ridge seems variable, generally high above pleura-tergal margin; difficult to see any possible protuberance because of setae. Spiracles appear normal.

LEGS. Length 0.64–0.7 of body width (♂), 0.66 (♀). Length:width ratio of podomeres, prefemur to tarsus (analysed specimens = 5): 1.08–1.4, 1.2–2.0, 0.79–1.18, 1.4–1.64, 3.0–4.3, 1.86–4.3. Coxae without tubercles; coxal pores particularly large in some specimens. Claws of paddle-like shape anteriorly but by leg pair 50 just appearing longer than ‘normal’. Extent of this paddle-like shape variable, both between individuals and along the body of a single individual; most pronounced on the anterior legs of larger males but also found to a lesser degree on females and small males. Accessory claw shorter than claw (reaching just less than halfway along) and situated ventrally on claw.

TELSON. Length:width ratio 1.7–1.9.

ANTERIOR MALE LEGS. Legs 1 and 2 with slightly shorter tarsus than normal walking legs.

ANTERIOR GONOPODS. Impossible to determine number of segments, even under SEM, as several appear partially fused. Normally bent into rather uneven S-shaped curve with groove for posterior gonopods to lie in visible under SEM and appearing more or less spoon-shaped towards apex. Several strong and quite long setae on more basal segments of posterior side and probably some on anterior side in same area, but difficult to be sure of their distribution. Median lobe as described by Shelley (1996) for S. portoricensis present on one of basal segments as expansion of distal margin of segment just on mesal side; this is, however, interpreted here as modification of shape of segment to allow complicated flexure and may not be particularly significant. Apical segment smoother in surface texture (unlike wrinkled surface of rest of gonopods), concave and spoon-like in shape. At apex narrowed, blunt-tipped and slightly curved ventrad, forming final curve of S. Strong setae towards rim of ‘spoon’ but not confined to it, some of these wide and almost ‘ribbon-like’ in form. One seta, on mesal side, larger than others, on separate base and approximately equal in length to main part of anterior gonopods.

POSTERIOR GONOPODS. Probably with 7 segments including the coxae (and assuming that the apical elongated region is just one). Segment edges easier to determine than in anterior gonopods. Segments irregular in size and shape, several appearing triangular in shape to accommodate strong anterior flexure of almost 90 o ( Fig. 6B ). No setae apparent on basal segments, although one SEM specimen shows a single seta on posterior side of 4 th segment. Apical segment very long and thin, appearing parallel-sided under light microscope but under SEM gently spirally twisted like streamer, with blunt tip and strong accessory spine approximately ¼ to ½ of length from base. No apparent setae on sternal plate from which gonopods arise, although sometimes difficult to see. Gonopods of long-haired males and shorthaired males show no apparent differences. Some of much smaller males also have identical gonopods, although others have slightly shorter tips to anterior gonopods, thus appearing shorter and squatter. The degree of anterior flexure is highly variable. Some gonopods are very tightly bent, others protrude from the body in a more relaxed and much straighter form. This probably depends greatly on the level of preservation of the specimen. In the past it has been considered that larger males showed a greater degree of flexure, but this is not necessarily true of the current collection.

Pilosity polymorphism

A notable feature of this species is that some males, but not all, have extremely long setae on the middorsal part of the metazonites ( Figs 4–5 ). Initially, this seemed so obvious and distinct that those with the long setae were considered to be a different morphospecies. However, no females were found with long setae, and plots of the setal length against body width show a considerable but continuous variation in the males. In the females a much narrower range of setal length is shown.

Ecology

All the individuals were collected from an inundation forest, Igapó. Almost all the specimens were collected from TM50, TM51 or TM52, which were traps on trees catching downward movement. A few were from TM47 (tree traps catching upward movement and a few also from standing crop studies.

Table 2 shows the numbers of individuals found in different months (most were collected in 1976, but a small number from 1977 are also included). This forest is inundated from March/April until August/ September (see Wolf & Adis 1992 for more information). It can be seen that most individuals were found during the end of the time when the forest was inundated.

The majority of these specimens were captured walking down trees. The single male in May, one female in February and one female in November were found walking up trees. In addition, one male in June and one in July were recorded as part of standing crop surveys, together with one female in February and 7 in June. This suggests that the bulk of the movement down trees takes place in July–September, during the inundation period although towards the end. Presumably this species spends the beginning of the inundation period in the trees, but where it lives the rest of the year is not known.

It is tempting to think that the long setae and the paddle-shaped claw have something to do with the habitat of this species in the forest, which is seasonally inundated. However, the claw shape, although perhaps most pronounced in the males of this species, is also found in S. hebetunguis (details of the habitat of this species are unknown) and perhaps in a less pronounced way in S. tuberculata sp. nov. (see below). The final column in Table 2 indicates the number and proportion of ‘long-haired’ males in the samples. For this purpose, a ‘long-haired’ male is considered to be one with setae equal to or more than 0.08 mm long. From this it is apparent that ‘long-haired’ males can be found at almost any time of the year. Although more ‘long-haired’ individuals were found towards the end of the inundated period, this is also when more individuals were collected in general.

The considerable size range of the males in terms of number of body rings suggests that individuals continue moulting after attaining maturity. However, it cannot be determined from the present collection whether males moult between long and short setal forms, the long setae develop over a series of moults, or they moult into a long (or short) setal form and then continue with this morphology.

See Table 1 for comments concerning differences between this species and others from Brazil.

Figures

Fig. 1. Relationship between body width (mm) against the total number of tergites with legs for new species of Siphonophora Brandt, 1837 and S. hebetunguis (Attems, 1951).

Fig. 3. Siphonophora setaepromissa sp. nov., non-type specimen. A. Head in lateral view. B. Head in dorsal view. C. Pleurite in lateral view, anterior to left. D. Head of male in lateral view. E. Head of female in ventral view. F. Head of female in lateral view with left antenna missing. Scale bars: A–C = 200 µm; D–F = 10 µm.

Fig. 4. Siphonophora setaepromissa sp. nov., relationship between body width and setae length in males and females.

Fig. 5. Siphonophora setaepromissa sp. nov., non-type specimens. A. Mid-body rings of male with long setae, body width approximately 1 mm. B. Midbody rings of male with short setae, body width approximately 1 mm. C. SEM showing long setae in male. D. Limbus of female showing anchor-shaped tubercles. Scale bars: C = 100 µm; D = 10 µm.

Fig. 6. Siphonophora setaepromissa sp. nov., non-type specimen. A. Male gonopods in situ. B. Male gonopods in situ. C. Claws in ventral view. D. Claw in anterior view. Scale bars: A–B = 100 µm; C–D = 10 µm.

Fig. 8. A. Siphonophora fuhrmanni Carl, 1914, type specimen, habitus, body length approximately 30 mm. B. Siphonophora mjoebergi Verhoeff, 1924, non-type specimen, habitus, body length approximately 15 mm. C. Siphonophora setaepromissa sp. nov., paratype, ozopore showing ring of setae, scale bar = 0.01 mm.

Fig. 9. Claws and accessory claws in the three species of Siphonophora Brandt, 1837 studied here. A. Siphonophora hebetunguis (Attems, 1951). B. Siphonophora setaepromissa sp. nov. C. Siphonophora tuberculata sp. nov. Not to scale.