Humphreysella styx (Kornicker & Iliffe 1989)

Danielopolina styx

ETYMOLOGY.—From the Latin and Greek Styx (river in the nether world).

MATERIAL.—Holotype: Sta 87–005: USNM 193439, 1 instar IV, appendages on 1 slide, carapace in alcohol.

Paratypes: Sta 87–005: USNM 193421, 1 instar III, appendages on 1 slide, carapace in alcohol. Sta 87–018: USNM 193436A,B, 2 instar III, undissected, in alcohol; USNM 193437, 1 instar II, appendages on slide, carapace in alcohol; USNM 193438, 1 instar I, appendages and 1 furcal lamella on slide, carapace and 1 furcal lamella in alcohol.

DISTRIBUTION.—Santa Cruz Island, Galapagos Islands: Deep Grieta east of Tortuga Bay, at 6–12 m water depth (type locality); Grieta de Caleta la Torta at 17–29 m water depth.

MATURITY OF SPECIMENS.—Previously described species of Thaumatocyprididae have on each lamella of the furca of the adult 2 articulated claws on the anterior margin followed by 3–6 nonarticulated ventral claws. The furcae of the 4 stages of D. styx in the present collection have only 1 articulated anterior claw. Therefore, the furca is a different type than previously described. Because of this, the number of nonarticulated claws cannot be used with certainty to estimate the age of the specimens. However, because the number of nonarticulated ventral claws increases by 1 in each of the 4 stages, it is reasonable to believe that the stages are in sequence. In 2 previously described species of Thaumatocyprididae, D. bahamensis and Thaumatoconcha radiata, the 6th limb (bearing bristles) appeared first in instar III, and for the latter species the 7th limb appeared first in instar IV. Instar IV is not known for D. bahamensis, but since the 7th limb is absent in instar III and present in instar V, it may also be present in instar IV (Kornicker and Iliffe, in press a, table 2). By using the first appearance of the 6th and 7th limbs on the 4 stages of D. styx, the stages are interpreted to be instars I to IV (Table 11).

The total number of growth stages in the ontogeny of D. styx is unknown. Within the Thaumatocyprididae, species with 5 and 7 growth stages have been described (Kornicker and Iliffe, in press a). If D. styx is assumed to have either 5 or 7 growth stages, its instar IV would be either the A-1 or A-3 stage, but it is not known which. The ventral edge of each lamella of the furca of instars I–III, but not instar IV, bears a small triangular process that could be the site of a claw present on the following stage. Its absence on instar IV may indicate that instar IV is an adult, but because no genitalia were observed that conclusion cannot be made at this time; however, the possibility cannot be eliminated, because female genitalia are small and could be overlooked.

DESCRIPTION OF INSTAR IV (Figures 11, 12).—Carapace similar in shape, ornamentation, selvage, and central adductor muscle attachments to those of instar III described herein.

Size: USNM 193439, length with anterior process 0.68 mm, length without anterior process 0.59 mm, height 0.51 mm.

First Antenna (Figure 11a,b): Limb with 8 joints. 1st joint with 1 bare dorsal bristle and 1 longer, bare, backward pointing, lateral bristle near ventral margin. 2nd joint with 1 bare dorsal bristle and distal medial spines. 3rd joint defined from 4th by slight indentation in ventral margin but without medial or lateral sutures, and without separation of sclerotized frame at ventral and dorsal margins, with spines forming 2 rows on ventral margin. 4th joint with none or 1 short ventral bristle; ventral edge of 3rd joint longer than ventral edge of 4th joint, but dorsal margins of 3rd and 4th joints without discernible boundary separating them. 5th joint about same length as ventral margin of 4th joint, with 3 ventral bristles (2 long, 1 minute, medial) (Figure 11b). 6th joint bare, slightly shorter than 5th joint. 7th joint slightly longer than 6th, with 2 long ventral b-, and c-bristles, and 1 short, dorsal a-bristle with small marginal spines. 8th joint about half length of 7th, with 3 bristles (2 long ventral e-, and f-bristles, 1 shorter dorsal d-bristle).

Second Antenna: Protopodite with long spines at posteroventral corner (Figure 11c). Endopodite (Figure 11d): 1st joint elongate with 1 distal bristle; 2nd joint slightly shorter than 1st, with 1 short, dorsal, lateral bristle and 4 terminal ventral bristles (3 long, 1 short); 3rd joint short, with 4 terminal bristles (2 short, 2 minute). Exopodite with 9 joints (Figure 11c): 1st joint divided by medial suture into long proximal and short distal parts; joints 2–8 each with long bristle with distal natatory hairs; 9th joint small, with 2 bristles (1 long, 1 medium), both with distal natatory hairs; some long bristles with few widely separated marginal spines.

Mandible: Coxale endite similar to that of instar III (Figure 11e,f). Basale (Figure 11g): tooth of endite with 5 triangular cusps with small marginal teeth; posterior edge of endite with 2 distal tubular bristles; anterior margin with 1 distal bristle; lateral side of endite with 3 long bristles near posterior margin, 1 long bristle near anterior margin, and 1 short distal knife-like bristle; medial side with 1 proximal bristle near dorsal margin (only proximal part shown in illustrated limb) and proximal and distal hairs. Endopodite (Figure 11g): 1st joint spinous, with 1 dorsal bristle at midlength; 2nd joint spinous, with 2 distal dorsal bristles, and 3 or 4 distal ventral bristles; 3rd joint spinous, with 6 bristles.

Maxilla (Figure 11h–j): Coxale with stout plumose dorsal bristle. Basale with slender medial tubeformed bristle. Endopodite: 1st joint with proximal ventral bristle with long spines, 3 dorsal bristles, and 3 distal bristles on or near ventral margin; end joint with 1 stout, unringed, nonarticulated, terminal claw and 5 articulated ringed bristles. Endites obscure but each with about 6 or 7 bristles, some tubular.

Fifth Limb (Figure 12a–c): Epipodite with bristles forming 3 groups, each with 4 or 5 hirsute bristles (Figure 12c). Protopodite and endopodite with 16 or 17 bristles (Figure 12a); distal endopodial joint with additional short tooth-like medial bristle. Exopodite 3-jointed: 1st joint divided into proximal and distal parts by weak medial suture; proximal part with 3 ventral bristles at joint midlength, 1 medial bristle at joint midwidth, and 1 long terminal dorsal bristle; distal part with 2 terminal ventral bristles and 1 medial bristle at joint midwidth; 2nd joint with 1 ventral bristle at joint midlength, and 1 medial bristle at joint midwidth; end joint with 3 bristles (midbristle 50–59 percent and smallest bristle 35–42 percent length of longest bristle) (Figure 12b).

Sixth Limb (Figure 12d,e): Epipodite with 14 bristles forming 3 groups (proximal dorsal group and distal ventral group, each with 5 bristles, middle group with 4 bristles).

Protopodite with 3 distal, spinous, ventral bristles. Basale with 2 spinous ventral bristles. Small endopodite with 2 long spinous bristles. Exopodite: 1st and 2nd joints fused (bare on right limb (Figure 12d), left limb with 2 distal bristles (1 ventral, 1 at midwidth (Figure 12e)); end joint with 2 bristles (smaller bristle 71–72 percent of longer bristle).

Seventh Limb (Figure 11k): Elongate with 2 long spinous terminal bristles.

Furca (Figure 11l): Each lamella with 1 long anterior articulated claw and 4 short ventral nonarticulated claws; all claws with minute, anterior and posterior spines; each lamella with medial and lateral spines (not shown in illustration; similar to those on furca of instar III); stout unpaired process (with minute marginal spines) on posterior of body just proximal to lamellae.

Bellonci Organ: Absent.

Lip: Upper lip hirsute, in lateral view projecting posteriorly (Figure 12f–h; posterior edge with 2 tubular bristles and 2 stout spines (Figure 12h. Esophagous narrow then broadens at anterior gut (Figure 12f). Lower lip comprising lateral flap on each side of mouth (Figure 12i).

Gut Content: Unrecognized granular particles.

DESCRIPTION OF INSTAR I (Figure 13).—Carapace similar in shape (illustrated carapace somewhat distorted (Figure 13a), ornamentation, and central adductor muscle attachment scar to that of instar III.

Size: USNM 193438 (shell distorted), length with anterior process 0.29 mm, length without anterior process 0.27 mm, height 0.27 mm.

First Antenna (Figure 13b): Limb with 8 joints similar in proportions to those of instar II. 1st joint bare. 2nd joint with distal medial spines. 3rd and 4th joints similar to those of instars II and III. 5th joint with small ventral bristle not reaching distal end of 7th joint. 6th joint bare. 7th joint with 2 bristles (1 long ventral, 1 short dorsal); 8th joint with 2 long bristles.

Second Antenna (Figure 13c): Protopodite bare. Endopodite 3-jointed but with 2nd and 3rd joints fused: 1st joint elongate, bare; fused 2nd and 3rd joints with 1 filamentous short unringed ventral bristle and 4 ringed bristles (2 long, 2 short). Exopodite similar to that of instar III, 8th joint with 2 bristles.

Mandible: Coxale endite similar to that of instar III (Figure 13d. Basale (Figure 13e): 4 terminal teeth and 2 posterior tubular bristles similar to those of instar III; anterior margin with 1 long distal bristle; lateral side with 1 long bristle distal to midlength; indistinct short proximal medial bristle near dorsal margin. Endopodite (Figure 13e): 1st joint bare; 2nd joint with 1 dorsal bristle; 3rd joint with 4 bristles.

Maxilla (Figure 13f,g): Endite I with about 6 bristles; endite II with 1 proximal and 4 terminal bristles; endite III with 1 proximal and 3 terminal bristles; at least 1 tubular bristle on each endite. Coxale with spinous dorsal bristle. Basale with 1 or 2 bristles near ventral margin (1 medial, 1 lateral). Endopodite: 1st joint with no or 1 proximal ventral bristle and 2 distal bristles (1 ventral, 1 dorsal); 2nd joint with 1 stout nonarticulated claw-like bristle, and 2 or 3 slender bristles. (Sutures between joints indistinct so that exact location of some bristles uncertain.)

Fifth Limb (Figure 13h,i): Epipodite with bristles forming 3 groups (not all bristles shown on Figure 13i. Protopodite and endopodite with 7 or 8 bristles including short tooth-like bristle on distal endopodial joint. Exopodite 3-jointed but with 1st and 2nd joints fused: 1st joint with 1 long terminal dorsal bristle, and 2 bristles (1 ventral, 1 medial near ventral margin); 2nd joint bare; 3rd joint small with 1 terminal bristle.

Sixth and Seventh Limbs: Absent

Furca (Figure 13j): Each lamella with 1 long anterior articulated claw followed by 1 short nonarticulated claw on anteroventral corner of lamella; a small triangular process at midlength of ventral margin of each lamella; lateral and medial surfaces of each lamella with spines forming rows; stout unpaired process on posterior of body just proximal to lamellae.

Bellonci Organ: Absent.

DESCRIPTION OF INSTAR II (Figure 14).—Carapace similar in shape, ornamentation and central adductor muscle attachment scar to that of instar III (Figure 14a,b).

Size: USNM 193437: left valve, length with anterior process 0.50 mm, length without anterior process 0.46 mm, height 0.40 mm; right valve, length with anterior process 0.48 mm, length without anterior process 0.46 mm, height 0.40 mm.

First Antenna (Figure 14c,d): Limb with 8 joints. 1st joint with 1 bare dorsal bristle. 2nd joint with distal medial spines and distal low bulbous process (with small spines) extending, past ventral margin of joint (Figure 14d). 3rd joint defined from 4th by slight step in ventral margin but without medial or lateral sutures and without separation of sclerotized frame at ventral and dorsal margins (slight sinuate curvature in dorsal margin probably indicates location of division between 3rd and 4th joints), with spines forming 2 rows on ventral margin, and spines forming distal row on dorsal margin. 4th joint bare. Ventral edge of 3rd joint longer than ventral edge of 4th joint but reverse on dorsal margin. 5th joint smaller than 4th, with short ventral bristle with minute terminal papilla. 6th joint smaller than 5th and without bristles. 7th joint longer than 6th, with 2 bristles (1 long ventral with few widely separated minute spines, 1 short dorsal with small marginal spines). 8th joint smaller than 7th, with 3 bristles (1 long lateral, 1 medium dorsal medial, 1 short ventral medial, all with widely separated minute marginal spines and terminal papilla).

Second Antenna: Protopodite bare. Endopodite 3-jointed but with 2nd and 3rd joints fused (Figure 14e): 1st joint elongate with 1 short distal bristle; fused 2nd and 3rd joints with 5 bristles (3 long, 1 short, 1 minute). Exopodite similar to that of instar III.

Mandible: Coxale endite folded on illustrated limb (Figure 14f), but similar to that of instar III. Basale similar to that of instar III except for absence of short distal lateral bristle, and for 1 of paired anterior bristles being short (Figure 14g). Endopodite with 1 dorsal bristle on 1st joint, 2 dorsal bristles on 2nd joint, and 4 bristles on end joint (Figure 14h).

Maxilla (Figure 14i,j): Similar to that of instar III but with fewer terminal bristles. Endites not examined in detail.

Fifth Limb (Figure 14k): Epipodite present but exact number of bristles not determined because bristles obscured. Protopodite obscured on specimen examined. Distal endopodial joint with short tooth-like bristle, 4 ventral bristles (1 stout pectinate, 3 slender). Exopodite 3-jointed: 1st joint with 1 very long terminal dorsal bristle, 1 ventral bristle, and 1 medial bristle at joint midwidth; 2nd joint elongate, without bristles; end joint small with 2 or 3 bristles (1 long, 1 or 2 short, all with marginal spines).

Sixth Limb: Not observed.

Seventh Limb: Absent.

Furca (Figure 14l): Each lamella with 1 long anterior articulated claw followed by 2 short nonarticulated ventral claws and small triangular process; all claws with anterior and posterior spines; lateral and medial surfaces of lamella with spines forming rows; stout unpaired process on posterior of body just proximal to lamellae.

Bellonci Organ: Absent.

Lip: Similar to that of instar III.

Gut Content: Unrecognized amber-colored particles.

DESCRIPTION OF INSTAR III (Figures 15–17).—Carapace subround in lateral view with straight dorsal margin in vicinity of hinge and also straight margin between anterior and anteroventral processes (Figures 15, 16a,b); ventral and posterior margins as well as anterior margin dorsal to anterior process evenly rounded; valves broadest at about midlength and midheight, in vicinity of central adductor muscle attachments. Short anterior and anteroventral processes with bases just lateral to valve edge; each process bearing fragile spine-bearing frill that easily breaks off at slight touch with dissecting needle leaving smaller firm triangular protuberance.

Ornamentation (Figures 15, 16a,b): Surface finely reticulate with reticulation walls formed of minute pustules, most with blunt tips, but few with pointed tips; on anterior part of shell pustules form rows (about 8) paralleling straight edge of shell between anterior and anteroventral processes. (Pustules break off easily, and on most specimens in collection pustules missing on parts of shell, especially near center.)

Adductor Muscle Attachment Scar (Figures 15, 16a): Scar central in location; subround with greatest diameter trending towards posterodorsal margin of shell; scar consisting of 7 or 8 wedge-shaped scars more or less radially arranged. Crescent-shaped mandibular scar located anteroventral to adductor muscle scar (Figure 16a).

Size: USNM 193421, length with anterior process 0.57 mm, length without anterior process 0.52 mm, height 0.41 mm; USNM 193436A, length with anterior process 0.59 mm, length without anterior process, 0.55 mm, height 0.46 mm; USNM 193436B, length with anterior process 0.56 mm, length without anterior process 0.53 mm, height 0.44 mm.

First Antenna (Figure 16c): Limb with 8 joints. 1st joint with 1 bare dorsal bristle. 2nd joint with 1 bare dorsal bristle and distal medial spines. 3rd joint defined from 4th by slight step in ventral margin but without medial or lateral sutures, and without separation of sclerotized frame at ventral or dorsal margins (slight sinuate curvature in dorsal margin probably indicates location of division between 3rd and 4th joints), with spines forming 1 or 2 ventral rows, and spines forming distal row near dorsal margin. 4th joint bare; ventral edge of 3rd joint longer than dorsal edge of ventral 4th joint, but relationship reversed on dorsal margin. 5th joint smaller than 4th, with 1 long ventral bristle with few minute widely separated spines. 6th joint slightly smaller than 5th and without bristles. 7th joint about same length as 6th, with 2 bristles (1 long ventral and with few small widely separated marginal spines, 1 short dorsal with small marginal spines), 8th joint smaller than 7th, with 2 long ventral bristles and 1 shorter, dorsal bristle.

Second Antenna (Figure 16d): Protopodite with long spines at posteroventral corner (Figure 16d). Endopodite 3-jointed, but with 2nd and 3rd joints fused: 1st joint elongate, with 1 bristle; 2nd joint about ¾ length of 1st, with 2 terminal bristles (1 lateral, short, filamentous, 1 medial, long, ringed, bare); 3rd joint short, with 4 bristles (2 long, 1 short, 1 minute). Exopodite with 8 joints: 1st joint undivided; bristles of joints 2–7 long, ringed, with few widely separated minute marginal spines, and distal natatory hairs; 8th joint with 2 bristles (1 long, 1 medium), both with few minute widely separated marginal spines.

Mandible (Figure 16e–g): Coxale endite with proximal and distal sets of teeth separated by space (Figure 16e); proximal set comprising 4 broad cusps plus triangular tooth close to distal set of teeth; surface between cusps and medial and lateral surfaces just proximal to cusps with slender spines; 1 spinous bristle with base just distal to triangular tooth; distal set of teeth consisisting of 2 flat teeth, each having 4 or 5 pointed cusps; cusps of proximal flat tooth pectinate; distal flat tooth with small proximal medial tooth on medial cusp. Basale (Figure 16f): tooth of endite with 5 triangular cusps with small marginal teeth; posterior edge of endite with 2 tubular bristles (1 proximal, 1 distal, each with terminal papilla); anterior margin of endite with 2 ringed bristles (1 with medial base, 1 with lateral base); lateral side of endite with 2 slender proximal ringed bristles and 1 shorter distal ringed bristle; medial side with 1 proximal ringed bristle near dorsal margin. Endopodite 3-jointed with 1st and 2nd joints about same length and 3rd joint shorter (Figure 16f,g): 1st joint with 1 dorsal bristle at midlength; 2nd joint spinous, with 2 dorsal bristles (dorsal margin of joint narrower distal to bristles); 3rd joint spinous, with 4 bristles.

Maxilla (Figure 17a–c): Endite I with 6 bristles; endite II with 7 bristles; endite III with about 4 bristles; 1 or 2 tubular bristles on each endite. Coxale with long stout plumose dorsal bristle. Basale with slender medial tubular bristle. Endopodite: 1st joint with 2 distal bristles on or near dorsal margin and distal bristle at joint midwidth or near ventral margin. End joint with 1 anterior, stout, linear, sclerotized nonarticulated claw, and 4 articulated slender bristles.

Fifth Limb (Figure 17d,e): Epipodite with bristles forming 3 groups (Figure 17d). Protopodite and endopodite with about 11 bristles; distal endopodial joint with additional short tooth-like bristle. Exopodite 3 jointed: 1st joint with 1 very long terminal dorsal bristle, 1 ventral bristle, and 1 medial bristle at joint midwidth; 2nd joint elongate with 1 bristle on ventral margin; end joint small with 3 bristles (middle bristle 45 percent and smallest bristle 32 percent length of longest bristle).

Sixth Limb (Figure 17f,g): Epipodite with bristles forming 3 groups (Figure 17f). Protopodite obscured on limb examined. Basale with 1 ventral bristle (this bristle could be on protopodite). Small endopodite with 2 long bristles. Exopodite: 1st and 2nd joints fused, bare; end joint short, with 2 weakly developed bristles.

Seventh Limb: Not observed.

Furca (Figure 17h): Each lamella with 1 long anterior articulated claw followed by 3 short nonarticulated ventral claws; claws with minute spines along anterior and posterior edges; 1 or both lamellae with small triangular process posterior to posterior ventral claw; anterior margin of lamella with few short spines; lateral surface of lamella with minute spines forming rows, more and longer spines on medial surface (some medial spines extending past ventral edge of lamella); stout unpaired process (with minute marginal spines) on posterior of body just proximal to lamellae.

Bellonci Organ: None observed.

Lip: Upper lip with distal spines and a short tubular bristle on posterior edge on each side of midwidth (Figure 16h). Esophagus narrow; broad anterior part of gut separated from smaller and narrower posterior part by slight restriction; anus small (Figure 16i).

Gut Content (Figure 16i): Unrecognized brown particles.

COMPARISONS.—The carapace of D. styx resembles those of D. orghidani and D. carolynae in having reticulations with walls formed by papillae. It differs from both species in not having a small posterodorsal process on each valve. The carapace of D. styx is much smaller than that of D. carolynae. Danielopolina styx bears more than the 3 short nonarticulated claws present on each lamella of the furca of D. orghidani. Danielopolina styx differs from previously described species of the Thaumatocyprididae in having only 1 instead of 2 articulated anterior claws on each lamella of the furca.

ONTOGENY.—As in Thaumatoconcha radiata and D. bahamensis the 1st and 2nd antennae, mandible, maxilla, 5th limb, and furca are already present in the 1st instar (Table 11); the 6th and 7th limbs are not present; the Bellonci organ is absent on all instars. The 6th limb appears, but with just a few bristles, in the 3rd instar, and the 7th limb in the 4th instar. The carapace of the single instar I in the collection is distorted, but all instars appear similar except for size.

First Antenna: The number of bristles on the 1st antenna increases from 5 on instar I to 12 or 13 on instar IV (Table 12). The ventral bristle of the 5th joint of does not reach past the 8th joint on instars I and II but is extremely long on instar III.

Second Antenna: The protopodite of the 2nd antenna is bare on instars I and II but bears long spines on the posterior ventral corner on instars III and IV. The exopodite has 8 joints on instars I to III and 9 joints on instar IV. The exopodial bristles bear distal natatory hairs on all instars. The 1st endopodial joint is bare on the 1st instar but bears 1 bristle on later instars (Table 13). The 2nd and 3rd endopodial joints are fused on all instars, but can be differentiated by the location of bristles on instars III and IV. The total number of bristles on the 2nd and 3rd joints increases from 5 on instar I to 9 on instar IV (Table 13). All 4 terminal bristles of the 3rd endopodial joint of instar IV are short, whereas 2 of 4 terminal bristles of instar III are very long, possibly the difference is sexual, but sex of the instars was not determined.

Mandible: The terminal teeth of the coxale and basale are similar on all 4 instars. The number of lateral bristles of the basale as well as the number of bristles of 1st and 2nd endopodial joints are higher on later instars, but the number of bristles of the 3rd endopodial joint remains at 4 (Table 13).

Fifth Limb: The number of exopodial bristles increases from 4 on instar I to 13 on instar IV (Table 14).

Sixth Limb: The 6th limb appears first on instar III, and bears rather short and weakly developed bristles, but the number of bristles is only slightly less than on the limb of instar IV (Table 14).

Seventh Limb: The limb appears first on instar IV and bears 2 terminal bristles, the same number observed on adults of other species of the genus.

Furca: All 4 instars have only 1 articulated claw on the anterior margin of each lamella. The number of nonarticulated claws increases from 1 on instar I to 4 on instar IV (Table 15). The distribution of furcal claws on other Thaumatocyprididae are presented for comparison in Table 15.