Discochiton quadratum (Green)
Chris J. Hodgson & Douglas J. Williams, 2018, Revision of the soft scale genus Paralecanium (Hemiptera: Coccomorpha: Coccidae) with the introduction of three new genera and twenty new species, Zootaxa 4443 (1), pp. 1-162: 58-61
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|Discochiton quadratum (Green)|
Discochiton quadratum (Green) comb. n.
( Fig. 21 View FIGURE 21 )
Lecanium expansum quadratum Green, 1904 , 236. Type data: SRI LANKA: Balangoda on cultivated nutmeg and Kalutara on undetermined tree. Syntypes, Type depository: BMNH, London, England, U.K.
Paralecanium expansum quadratum ; Sanders, 1906, 9. Change of combination.
Paralecanium quadratum ; Takahashi, 1955, 239. Change in status.
Material examined. Lectotype f and paralectotype ff (here designated): SRI LANKA (as Ceylon): top labels: TYPE in red on small round label + Lectotype on narrow label; bottom label: Lecanium / expansum / Green /
Kalutara / Ceylon (BMNH): 1/3adff (f, but all missing some venter; lectotype right-hand most specimen; envelope states coll. E.E.G.). Labelled TYPE. Sri Lanka (as Ceylon), bottom label: Lecanium / expansum / Green / from cultivated / nutmeg ( Myristica ) / Balangoda, Ceylon / III.99 (BMNH): 2/4adff (f-p; envelope states Coll. E.E.G.; also Myristica moschata ; probably part of type series). Sri Lanka (as Ceylon); bottom label: Lecanium / expansum / v. quadratum [latter in a different handwriting] Green / from nutmeg / Balangoda / Ceylon (BMNH): 1/4 adff (f-p; envelope states Paralecanium expansum – quadratum Green ; coll. E.E.G).
Other material. SRI LANKA (as Ceylon), Kalutara, on unknown plant, no date, E.E. Green ( USNM; 6893): 1/2adff (f, heavily stained, both missing venter, labelled Paralecanium expansum (Green) ; possibly part of type series). Sri Lanka (as Ceylon), Balangoda, on nutmeg, no other data ( BMNH): 1/4adff (p; all missing venters; probably part of type series; envelope states Coll. E.E.G.). Sri Lanka (as Ceylon), Peradeniya, on Garcinia sp., July 1912, E.E. Green ( BMNH; BM1916, 138): 4/6adff (fg, but venter damaged; identified as Paralecanium expansum ) + 1/1adf (fg, as P. expansum quadratum ) + 1/7 first-instar nymphs (g). Sri Lanka (as Ceylon), Padukka, on nutmeg, no date or coll. ( BMNH): 1/4 adff (p). Peradeniya, on M. fragrans , May 1909, no coll. ( USNM): 1/1adf (fg; labelled Lecanium expansum quadratum ). Maskeliya, no host or date, J. Pole ( BMNH): 1/ 2adff (f).
Note. The following description is taken from all three type specimens in the BMNH collection, with some data from other specimens, particular regarding the structures on the venter.
Slide-mounted adult female. Body almost round. Length 4.0– 5.5 mm, width 3.8–5.0 mm.
Dorsum. Derm rather uniformly sclerotised; without a band of short ridges or elongate areolations with their axes running parallel to margin submarginally (as in P. expansum ); dermal areolations submarginally obscure, round to oval but becoming more distinct submedially and medially, where showing some indication of a polygonal pattern. Marginal radial lines faint, mainly indicated by pores and setal distribution, with 13 anteriorly on head, each side with 5 on thorax and 13 on abdomen; stigmatic rays present. Abdominal clear areas numbering 4 pairs and 1 at inner ends of each anterior stigmatic ray. Derm with a polygonal pattern of pores and setae. Most setae each appear to be associated with a large pale area of derm (possibly a pore?) about 22 µm wide, although most of these pale areas lack setae but do have a sclerotised ring that could represent a setal socket (see dorsal setae on apex of membranous tubes in section on morphology); setae possibly rather few, each finely spinose, mostly narrowing to a blunt apex but sometimes more pointed, each about 13–16 µm long with a broad basal socket about 5 µm wide; if pale areas are related to setae, then frequent submarginally, becoming less frequent submedially and absent medially. Preopercular pores, each about 5 µm wide with a sclerotised margin, present in groups around anterior 3 clear areas on abdomen as follows: CA1 with 6–13, CA2 with 12–18 and CA3 with 12–19; CA4 without preopercular pores. Small simple pores, each about 2 µm wide, also frequent within polygonal pattern throughout, also present medially in about 6 or 7 transverse lines. Anal plates rather square, with anterior and posterior margins subequal in length; each plate with 3 minute setae near posterior apex plus 1 small pore medially; length of plates 170–180 µm, combined width 160–165 µm. Anogenital fold with 3 minute setae at each corner of anterior margin, each lateral margin with 1 seta anteriorly and another posteriorly. Anal ring with 6 setae, longest about 205 µm long.
Margin. Marginal ornamentation: deep crenulations, each about as deep as setal sockets and each with radial lines or ridges. Marginal setae broadly fan-shaped; width of each fan about 30–40 µm, length 30–35 µm; with about 128–165 setae anteriorly on head between anterior stigmatic clefts, each side with 55–85 between stigmatic clefts and 115–126 on abdomen. Stigmatic clefts quite deep, each with a narrow entrance, a sclerotised inner margin and 3 elongate, blunt stigmatic spines; middle spine longest, length of middle spines each 56–60 µm; lateral spines each 45–50 µm wide. Eyespots: diameter of each lens 12 µm.
Venter. Derm membranous medially but with a complete broad dark marginal band, about 80 µm wide. Multilocular disc-pores frequent on either side of genital opening and on preceding two segments only, each side with 11–22 on abdominal segment VII, about 25–30 on segment VI and 16–18 on segment V. Spiracular disc-pores present in a narrow band mostly 1 pore wide between margin and each spiracle, with 25 or 26 pores in each anterior band and 15–20 in each posterior band (pores absent from a section of each posterior band). Ventral microducts minute, present in a group just posterior to and on either side of labium but sparse elsewhere. Ventral setae: with 1 or 2 pairs of setae between antennae; pairs of long pregenital setae on segments VII –V (that on VII 115 µm long); small setae frequent medially just anterior to vulva in abdominal segment VII, otherwise very sparse, and submarginal setae sparse and extremely short, with about 6 on each side between stigmatic clefts. Antennae reduced, each with 3 segments (segmental divisions within apical segment absent); total length 120–140 µm. Clypeolabral shield 140 µm long. Spiracles: width of each peritreme 53–58 µm. Legs entirely absent.
Comments. Green (1904, p. 236) wrote: “Differs from type [ Lecanium expansum ] in the blunter and smaller scales on anal operculum; their base and outer edge about equal length, together approximately forming a square. The antennae are also more stunted in this form. In all other characters, it agrees with the type.” “On leaves of cultivated nutmeg: Balangoda. On an undetermined tree: Kalutara.” “I have also received this variety from Java where it occurs on Myristica fragrans (‘nutmeg’) and several other plants.” There are no slides of P. expansum var. quadratum in the BMNH from Java. It seems possible that they were subsequently identified as P. expansum var. metallicum Green , as the collection data is almost identical.
Although some of the above slides under Material examined are either not labelled Syntypes or not specifically referred to as L. expansum var. quadratum , it is here considered that they all refer to this species and are part of the type series.
Adult female D. quadratum are superficially similar to those of D. expansum but differ as follows (characterstates on D. expansum in brackets): (i) anal plates almost square, anal plate length to width ratio 1:0.9 (1:0.7 for D. expansum ); (ii) a complete, darker ventral marginal band present (absent); (iii) legs entirely absent (present as leg stubs); (iv) each stigmatic cleft with only 3 stigmatic spines (3–7, frequently 4+), (v) preopercular pores present associated with anterior 3 clear areas, absent from CA4 (most abundant associated with CA4 but absent from CA1 and usually CA2), and (vi) dorsal setae longer, 13–16 µm long, and more setose (normally 10–13 µm long, parallelsided and often capitate). Discochiton quadratum is also close to D. metallicum and D. rotundum (see key for differences).
Host-plants. Garcinia sp. ( Clusiaceae ); Myristica fragrans , Myristica moschata ( Myristicaceae ). Unconfirmed host plants: Calophyllum inophyllum (Callophyllaceae); Diplodiscus paniculatus ( Malvaceae ); Scolopia oldhamii (Saclicaeae) .
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