Microasteropteron youngi Kornicker 1976

Microasteropteron youngi Kornicker, 1976

Microasteropteron youngi Kornicker, 1976b:15, figs. 14–19.

HOLOTYPE.—Adult female, USNM 151580.

TYPE-LOCALITY.—Between reef and Paiko Peninsula, Maunalua Bay, Oahu, Hawaii.

MATERIAL.—No new material.

DISTRIBUTION (Figure 125).—Only collected at type-locality. Depth 30–58 cm.

DIAGNOSIS.—Second antenna: Endopodite without bristles.

Seventh Limb: Each limb with 8 bristles.

Lateral Eye: Small, darkly pigmented, without ommatidia.

Upper Lip: With long spinous anterior process.

CORRECTION OF ORIGINAL DESCRIPTION.—Illustrated 1st antenna (Kornicker, 1976b, fig. 19f) shows ringed bristles on the 4th and 5th joints, these are actually hairs. Upper lip was described (page 23) as having a single lobe with large process; this probably should have been 2 lobes, each with anterior process.

Microasteropteron youngi

HOLOTYPE.—USNM 151580, adult female on slides and in alcohol.

TYPE-LOCALITY.—Sample 1, between reef and Paiko Peninsula, Maunalua Bay, Oahu, Hawaii.

ETYMOLOGY.—The species is named after one of the collectors, Dr. Richard Young.

PARATYPES.—USNM 153933, 1 A–1 female, and USNM 153934, 2 very early instars, all from sample 2, same locality as holotype.

DESCRIPTION OF ADULT FEMALE (Figures 14–19).—Carapace oval in lateral view with small shallow incisur and slightly overhanging rostrum (Figures 14, 15a); 2 lateral low ribs present, 1 near dorsal margin, other near ventral margin; these terminate posteriorly in small rounded process; a convex low vertical rib with small rounded process near middle connects with posterior ends of horizontal ribs forming together with them a U-shaped ridge; a small rounded process present in posterodorsal corner of valve dorsal to small process at posterior end of upper rib; middle of each valve with sinus in dorsal half; carapace widest posteriorly in vicinity of processes at ends of lower horizontal ribs; carapace longest and highest at middle.

Ornamentation: Surface with numerous shallow dish-bottomed fossae (Figures 15, 16b,c); minute pustulae, less abundant within fossae, visible with SEM magnifications (Figures 15f, 16).

Pores: Long bristles emerging from open pores with low lip, sparsely distributed over valve surface (Figures 15e,f, 16a); small pore present near base of some of these bristles (Figure 16a); smaller bristles emerging from closed pores also sparsely distributed; some minute pores without bristles also present (Figure 16e).

Infold: Posteroventral infold with 2 stout easily visible bristles (Figures 17a,b,d,f, 19b,c); 1 flagellate bristle present just proximal and dorsal to base of each stout bristle (Figures 17c-e, 18a, 19b,c); a 3rd flagellate bristle with more numerous and slender branches present dorsal to uppermost stout bristle (Figures 17b,c, 19b,c); upper stout bristle with 1 minute bristle just outward from base, lower stout bristle with 2 minute bristles just outward from base (Figure 17e); 11 minute bristles forming groups of 1 to 4 bristles present on posteroventral infold (Figure 19b); infold above shallow incisur with 8 long bristles forming row parallel to anterodorsal margin (Figure 19a).

Selvage: Wide lamellar prolongation with marginal fringe present along anterior, ventral, and posterior margins of valves.

Central Muscle Scars (Figures 15d, 17a, 18 b–d): Consisting of cluster of about 12 individual oval scars; scar area reflected on outside of each valve by boss with 12 round fossae (Figure 15d).

Size: USNM 151580, length 0.73 mm, height 0.52 mm.

First Antenna (Figure 19d–f): First joint with short, distal, medial spines near ventral margin and long hairs laterally near ventral margin; 2nd joint with dorsal and ventral hairs and 2 spinous dorsal bristles; 3rd joint short with 2 short spinous dorsal bristles and 1 minute ventral bristle (not seen with certainty); 4th joint with 2 terminal spinous bristles, 1 short dorsal, 1 long ventral; 4th joint with 2 long hairs ventrally; 5th joint with long hairs on lateral surface and long bare sensory bristle; sensory bristle with strong widely spaced rings proximally, weak narrowly spaced rings distally, with conelike tip; 6th limb with minute, terminal, medial bristle. Seventh joint: a- and b-bristles bare about same length as sensory bristle of 5th joint; c-bristle bare, slightly longer than sensory bristle. Eighth joint: d-bristle absent; e-bristle bare, bristlelike, about same length as a-bristle but more slender; f-bristle bare, with proximal part oriented slightly dorsal, about same length as a-bristle; g-bristle bare, slightly longer than other bristles of joints 7 and 8.

Second Antenna (Figure 19g): Protopodite with medial hairs near dorsal margin and with long distal medial bristle; endopodite consisting of slight bulge without bristles. Exopodite 9-jointed: 1st joint with minute, medial, terminal spine; bristles of joints 2 and 3 with proximal slender ventral spines and distal natatory hairs; bristles of joints 4–8 with natatory hairs; 9th joint very small, with single natatory bristle.

Mandible (Figure 19h,i): Coxale endite with few minute spines near base of ventral branch (Figure 19h); ventral branch with about 4 oblique rows of spines and 3 small terminal teeth; ventral margin of dorsal branch with small tooth just distal to tip of ventral branch, and 1 single and 2 double teeth proximal to small main spine; tip of dorsal branch hirsute and truncate with 2 spinous bristles, 1 near middle, 1 at dorsal edge; dorsal margin of branch serrate distally. Basale: endite with 3 pectinate end bristles, 1 dwarf bristle, and 1 triaenid bristle with 10 pairs of teeth distal to about 8 pairs of smaller teeth; ventral margin of basale with 1 triaenid bristle similar to that on endite and 1 long spinous bristle, both near middle of margin; dorsal margin with 2 terminal bristles; medial surface with proximal spines near dorsal margin. Exopodite very short with 2 terminal bristles, 1 short, 1 extending past distal margin of 1st endopodial joint. Endopodite: ventral margin of 1st joint with 3 long spinous bristles; dorsal margin of 2nd joint with 5 bristles, 1 proximal, 4 terminal; medial surface with long spines forming rows; end joint with 5 bristles, 4 long, 1 short; medial surface with spines forming rows.

Maxilla (Figure 19j): Tip of epipodite missing on specimen examined; dorsal margin of basale with 1 long bristle with few long marginal hairs; ventral margin of basale with 1 minute bristle near middle and 1 long spinous terminal bristle. Endopodite: 1st joint spinous, with long bare beta-bristle; 2nd joint with 3 long bare terminal bristles. Endite could be construed as 1 lobe with 5 bristles, but slight separation between proximal 2 and distal 3 bristles suggests the presence of 2 endites.


Fifth Limb (Figure 19k): Epipodite with about 49 bristles; hirsute exopodial bristle not reaching end of comb; 1 short bristle present proximal and dorsal to base of exopodial bristle; about 21 bristles present along ventral margin of comb; dorsal half of tip of comb with long hairs.

Sixth Limb (Figure 19l): Anterior margin with 3 bristles, 1 proximal, 1 near middle, 1 distal; anteroventral corner with 3 or 4 hirsute bristle; lateral flap hirsute but without bristles; ventral margin of limb with 9 bristles, some hirsute, some with long proximal and short distal spines; posteroventral corner indistinct on specimen examined, either bare or with 2 short bristles; limb hirsute.

Seventh Limb (Figure 19m): Each limb with 8 bristles, 6 proximally, 3 on each side, and 2 terminally, 1 on each side; each bristle with 3 or 4 bells; terminus with 2 large processes and proximally to these 8 spinous teeth, 4 on each side; microstructure of processes could not be resolved with light microscope.

Furca (Figure 19n): Each lamella with 7 claws; claws 1–3 separated by space from claws 4–7; claws taper distally to fine point; claws 1–4 about same width at base; claws 5–7 narrower at base than claw 4.

Eyes: Small darkly pigmented lateral eye without ommatidia (Figure 19o); medial eye pigmented, about 3 times diameter of lateral eye (Figure 19d).

Rod-shaped Organ: Elongate widening distally, with abundant spines on proximal half, tip rounded (Figure 19d).

Posterior of Body: Thumblike spinous dorsum present (Figure 19q).

Gill-like Structures: Small (Figure 19q).

Upper Lip: Consisting of single anterior lobe with large process with few marginal spines (Figure 19p), and posterior hirsute lateral flap on each side of mouth.

DESCRIPTION OF A–1 FEMALE.—Carapace similar to that of adult female. Size: USNM 153933, length 0.60 mm, height 0.42 mm.

Appendages: Not examined in detail but in general similar to those of adult female. Furca with only 6 claws on each lamella.

Comparisons: The new species M. youngi is compared in Table 1 with the only other species in the genus, Microasteropteron parvum Poulsen, 1965. Easily discernible differences are the presence of a lateral eye in M. youngi, the absence of bristles on the endopodite of the 2nd antenna of M. youngi, and the presence of 8 rather than 6 bristles on the 7th limb of M. youngi.