Echinoderes angustus Higgins & Kristensen 1988

Echinoderes angustus

DIAGNOSIS.—Middorsal spines on segments 6–10 increasing uniformly in length posteriorly; lateral spines on segments 7–11, round to oval cuticular scars (pores?) in L–4 (adhesive tube) and SD-4 spine positions; lateral terminal spines moderately long, 140–198 μm, 29.4–54.6 percent of trunk length; nearly complete midventral cuticularization present on segment 4; pectinate fringe on posteroventral margin of segment 3 fine, uniform in size; perforation sites on ventral surface of segment 3 in 2 poorly defined rows, adjacent to posterior margin; turgal furcae long, curving away from midline.

DESCRIPTION.—Adults (Figures 1–16) trunk length 320–475 μm; MSW-8 (maximum sternal width of segment 8), 62–77 μm, 15.1–21.2 percent of trunk length; SW (standard width) at segment 12, 48–60 μm, 12.2–21.2 percent of trunk length.

Segment 2 consisting of 16 placids, 16–20 μ long, x 22 (mean of 22 measurements) = 18.7±1.1 μm); midventral placid truncate, wider (~16 μm) than others (~8 μm); ventral trichoscalid plates (of head segment) overlapping alternate placids, broadly expanded at posterior margins; dorsal trichoscalid plates uniformly narrow (Figures 3, 4, 7, 8).

Segment 3, 33–44 μm long, x 22 = 38.4±2.6 μm; middorsal cuticular scar near anterior margin, subdorsal cuticular scars slightly anterior to middorsal cuticular scar; ventral surface with small crescentic muscle scars on both sides of ventral midline, additional crescentic muscle scars more laterally; perforation sites (hair origins) widely scattered over dorsal surface, ventral perforation sites in two rows near posterior margin; pectinate fringe fine, uniform in width (∼ 1 μm wide) and length (∼10 μm), along posterior margins of both dorsal and ventral surfaces.

Segment 4, 32–40 μm long, x 22 = 35.6±2.5 μm; middorsal cuticular scar near anterior margin, subdorsal cuticular scars on both sides, slightly posterior middorsal cuticular scar, smaller cuticular scars lateral to subdorsal scars; round to oval cuticular scars (pores?) at presumptive site of missing lateral spines (adhesive tubes), slightly mesial to projected tergosternal articulation zone of adjacent posterior segment; additional cuticular scars more laterally situated; perforation sites in 3 rows on both dorsal and ventral surfaces; pectinate fringe as in segment 3, but slightly less prominent; pachycyclus well developed, cuticularization extending along ventral midline, partially divided along ventral midline.

Segment 5, 34–42 μm long, x 22 = 38.9±2.2 μm; middorsal cuticular scar less prominent than that on segment 4, subdorsal cuticular scars also less prominent and lying slightly more posterolaterally; crescentic muscle scars lateral to mesial cuticularization of ventral plates; perforation sites in 4 poorly defined rows on dorsal surface, in better defined 3-row pattern on ventral plates; pectinate fringe as in segment 4.

Segment 6, 35–50 μm long, x 22 = 42.3±3.2 μm; middorsal spine 38–58 μm long, x 21 = 48.6±5.7 μm; subdorsal cuticular scars on each side of dorsal midline, slightly anterior to middorsal spine; larger, more prominent, slightly oval scars posterolateral to middorsal spine; small cuticular scars lateral to mesial cuticularization of ventral plates, near anterior margins; perforation sites in 3 poorly defined rows dorsally, in 3 or 4 rows ventrally; pectinate fringe as in segments 4 and 5.

Segment 7, 37–52 μm long, x 22 = 45.3±3.9 μm; middorsal spine 42–72 μm long, x 22 = 60.5±8.3 μm; lateral spines, possibly adhesive tubes, 8–24 μm long, x 15 = 16.1±4.3 μm, near lateroventral margins of tergal plate; small subdorsal cuticular scars anterior to middorsal spine as in segment 6, but more prominent; posterolateral cuticular scars absent; small muscle(?) scars near lateral limits, ventral scars as in segment 6; perforation sites on dorsal surface in 4 rows, in less-defined rows on ventral plates but with slightly V-shaped pattern (Figure 1); pectinate fringe as in segment 6.

Segment 8, 40–58 μm long, x 22 = 49.2±3.7 μm; MSW 62–77 μx 22 = 68.1±3.2 μm; MSW/TL 15.1–21.2 percent, x 22 = 18.2±1.5 percent; middorsal spine 56–89 μm long, x 21 = 71.3 +–8.8 μm; lateral spines 40–50 μm long, x 21 = 44.4±3.7 μm; perforation sites in 4 rows on ventral plates, pattern similar to that in segment 7; all other characters similar to those in segment 7.

Segment 9, 48–64 μm long, x 22 = 50.6±5.6 μm; middorsal spine 62–94 μm long, x 20 = 79.7±8.3 μm; lateral spines 41–60 μm long, x 20 = 49.6±4.2 μm dorsolateral muscle scars larger than on segment 8; perforation sites in 5 rows; all other characters similar to those in segment 8.

Segment 10, 50–70 μm long, x 22 = 55.6±4.1 μm; middorsal spine 74–106 μm, x 22 = 89.3±8.7 μm; lateral spines, 44–60 μm long, x 21 = 52.5±4.7 μm; subdorsal muscle scars(?) near midline, posterior to middorsal spine; all other characters similar to those in segment 9.

Segment 11, 50–60 μm long, x 22 = 54.7±2.4 μm; middorsal spine absent; lateral spines 36–56 μm long, x 22 = 46.4±6.2 μm; dorsolateral muscle scars more prominent than in segment 10; perforation sites less numerous, 3 or 4 poorly defined rows on dorsal surface, 2 or 3 rows on ventral plates; all other characters similar to those on segment 10.

Segment 12, 44–58 μm long, x 22 = 50.5±3.7 μm; SW 48–60 μm, x 22 = 53.3±3.0 μm; SW/TL 12.2–21.2 percent, x 22 = 14.3 ±1.5 percent; lateral spines absent; 2 middorsal cuticular scars near anterior margin, prominent dorsolateral muscle scars slightly posterior to level of posteriormost middorsal cuticular scar; additional smaller muscle scars more posteromesial to larger muscle scars (Figure 6); small cuticular scars near anteromesial margin of ventral plates; more prominent, longitudinally oval muscle scars slightly posterior to smaller cuticular scars; perforation sites fewer and not in well-defined rows on dorsal or ventral plates; pectinate fringe barely visible.

Segment 13, 24–34 μm long, x 22 = 28.6±2.5 μm; tergal furcae lanceolate to weakly cuspidate with mesial margin slightly interrupted (Figures 5, 6, 9, 10); ventral plates with rounded posterior margins slightly fringed; lateral terminal spines 140–198 μm long, x 22 = 172.7±15.3 μm; LTS/TL 29.4–54.6 percent, x 22 = 46.4±6.5 percent; lateral terminal accessory spines of females 48–88 μm long, x 10 = 71.0±10.5 μm; LTAS/TL 13.7–21.7 percent, x 9 = 19.8±2.4 percent; LTAS/LTS 26.9–53.3 percent, x 6 = 40.3±8.6 percent; penile spines of male: P-1 30–41 μm long, x 10 = 37.0±3.3 μm; P-2 20–22 μm long, x 7 = 20.6±1.5 um; P-3 30–36 μm long, x 9 = 33.0±2.1 μm.

In addition to the lack of lateral accessory spines and the presence of 3 pairs of penile spines, males differ from females in having a slightly longer trunk length, slightly longer middorsal spines, and slightly shorter lateral spines.

Morphometric data for adult specimens are shown in Table 1.

HOLOTYPE.—Adult female, TL 410 μm (Figures 1–6, 11–15), Disko Island, sta RH 1535 (see ‘Localities’), USNM 233200.

ALLOTYPE.—Adult male, TL 375 μm (Figures 7–10, 16), other data as for holotype USNM 233201.

PARATYPES.—Two females and 3 males, TL 355–415 μm, other data as for holotype, USNM 233202; 2 females, TL 355–370 μm, Disko Island, sta RH 1527, USNM 233203; 3 females and 4 males, TL 320–400 μm, Disko Island, sta RH 1531, USNM 233204; 1 male, TL 475 μm, Disko Island, sta RH 1533, USNM 233205; 1 male, TL 420 μm, Disko Island, sta 1536, USNM 233206; 1 female, TL 350 μm, Disko Island, sta 1537, USNM 233207; 1 female, TL 340 μm, Disko Island, sta 1538, USNM 233208. Other paratypes have been deposited in the Zoological Museum, Copenhagen.