Synallactidae, Ludwig, 1894

O'Loughlin, P. Mark & Ahearn, Cynthia, 2005, A review of pygal-furrowed Synallactidae (Echinodermata: Holothuroidea), with new species from the Antarctic, Atlantic and Pacific oceans, Memoirs of Museum Victoria 62 (2), pp. 147-179 : 149-150

Key to species of pygal-furrowed Synallactidae

(The generic assignment of Pseudostichopus profundi Djakonov is unresolved. The species is distinguished by the unique presence of curved mesh-like narrow plates in the tube feet.)

1. Tube feet not in prominent series on paired radii; longitudinal muscles flat, broadly attached to internal body wall; gonad tubules arising from common source at end of gonoduct, branched..... Molpadiodemas Heding. .. 2

— Tube feet or papillae in prominent series on paired radii; longitudinal muscles cylindrical, narrowly attached to internal body wall; gonad tubules in series along gonoduct, unbranched............ Pseudostichopus Théel. .. 17

2. Tube feet hair-like or thin, thread-like..............3

— Tube feet cylindrical, prominent or inconspicuous.... 4

3. Body lacking brim; tube feet hair-like, over whole body, sometimes matted ventrally, anteriorly, pygally, frequently withdrawn ventrally; tentacle ossicles never plate-like rods with close fine spines........ Molpadiodemas villosus

— Body with rounded lateral brim, sometimes with pustulose bulges; tube feet soft, flaccid, thread-like, sometimes matted on small specimens, readily lost with outer body layer; tentacle ossicles include wide plate-like rods with close fine spines.......... Molpadiodemas porphyrus

4. Body with one, sometimes two, deep transverse constrictions; no tentacle ossicles......................................... Molpadiodemas constrictus

— Body lacking deep transverse constrictions; tentacle ossicles present.............................. 5

5. Body typically with one or two concave depressions created by epibiotic attachments; body strongly posteriorly tapered; tentacle ossicles include thin, lumpy rods..................... Molpadiodemas epibiotus

— Body lacking concavities; body not strongly posteriorly tapered; tentacle ossicles not including thin lumpy rods... 6

6. Ventrolateral margin with distinct raised protuberances... 7

— Ventrolateral margin lacking distinct raised protuberances ........................................... 8

7. Margin serrated by transverse creasing of body; ventrolateral protuberances lacking tufts of tube feet; body wall wrinkled, with small digitate projections on low reticulate ridges; tentacle ossicles include rods; body typically encrusted with globigerines or small stones................................... Molpadiodemas involutus

— Ventrolateral margin with pustules surmounted by nipple-like protuberances; tube feet in tufts on posterior pustules; body wall not wrinkled, lacking low reticulate ridges; tentacle ossicles lace mesh only; some globigerine attachments.............. Molpadiodemas pustulosus

8. Body wall thin, translucent; gonad ossicles predominantly thin lace mesh, not developed along primary rods............................. Molpadiodemas translucens

— Body wall not translucent; gonad ossicles, if present, not predominantly thin lace mesh, if mesh, developed along primary rods................................. 9

9. Body wall thick, gelatinous; ventrolateral brim thick, rounded................. Molpadiodemas depressus

— Body wall not thick, gelatinous; lacking thick, rounded brim...................................... 10

10. Cylindrical tube feet concentrated in conspicuous ventrolateral band; frequently contiguous, matted ventrolaterally..........................................11

— Tube feet not contiguous or matted ventrolaterally... 13

11. Tube feet typically 2.0 mm long, 0.4 mm diameter; frequently tubercles and divided pygal lobes posteriorly.......................... Molpadiodemas crinitus

— Tube feet typically less than 2.0 mm long, 0.4 mm diameter; lacking posterior tubercles and divisions of pygal lobes................................ 12

12. Body short, diameter large (about 2:1); tube feet typically 1.6 mm long, 0.3 mm diameter; longitudinal muscles wide; gonad ossicles long, thin rods........................................... Molpadiodemas neovillosus

— Body elongate, diameter small (about 5:1), long tapers distally; tube feet typically 1.0 mm long, 0.25 mm diameter; longitudinal muscles narrow; lacking gonad ossicles................. Molpadiodemas pediculus

13. Tube feet cylindrical, most evident as lateral band, not matted..................................... 14

— Tube feet around body, not more evident as lateral band. .......................................... 15

14. Tube feet dark reddish brown creating a lateral spotted appearance; lacking gonad ossicles......................................... Molpadiodemas morbillus

— Whole body dark brown, scorched appearance; gonad ossicles present............ Molpadiodemas ustulatus

15. Tube feet soft, scattered, lying all over body in larger specimens, sometimes erect orally and pygally; tentacles with large, conical, pointed peripheral digits..................................... Molpadiodemas helios

— Tube feet not soft, scattered, lying all over body in larger specimens; tentacle digits not large, conical, pointed.. 16

16. Even cover of small tube feet, frequently in pits or not evident, cylindrical and firm if extended; tentacle ossicles lacking knob-like central swelling; high frequency of gonad ossicles comprising rods with extensive lateral mesh....................... Molpadiodemas atlanticus

— Even cover of small, soft, cylindrical tube feet, evident only on small specimens, never erect; many tentacle ossicles with knob-like central swelling; rare presence of gonad ossicles............ Molpadiodemas violaceus

17. Body densely encrusted with sponge spicules or globigerines or shells or small stones................. 18

— Body not encrusted with attachments............. 22

18. Body covered predominantly with dense mat of sponge spicules.................................... 19

— Body covered predominantly with globigerines (foraminiferans) or shells or stones.............. 20

19. Large dense mesh ossicles in pygal lobes; lacking gonad ossicles................ Pseudostichopus hyalegerus

— Lacking mesh ossicles in pygal lobes; gonad ossicles include complex branching rods......................................... Pseudostichopus spiculiferus

20. Predominantly pointed shells with globigerines and sand cover; closely knobbed tentacle rod ossicles; lacking ossicles in gonads......... Pseudostichopus echinatus

— Predominantly globigerine or small stone cover; tentacle ossicles not closely knobbed rods; ossicles frequently in gonads.................................... 21

21. Ossicles in pygal lobes and respiratory trees; pygal lobe ossicles irregular perforated plates, sometimes double layered................. Pseudostichopus occultatus

— Lacking ossicles in pygal lobes and respiratory trees............................ Pseudostichopus peripatus

22. Body with radial series of tubercles ventrolaterally or on paired radii................................ 23

— Body lacking radial series of tubercles........... 24

23. Double series of tubercles on paired radii; ossicles present in papillae, lacking in gonads. Pseudostichopus papillatus

— Single series of lateroventral tubercles; ossicles in gonads, lacking in tube feet........ Pseudostichopus tuberosus

24. Paired radii with long tapering papillae (frequently more than 10 mm long)........... Pseudostichopus elegans

— Paired radii with short tapering papillae (up to 5.0 mm long)...................................... 25

25. Ossicles in tube feet, perianally, lacking in gonads................................ Pseudostichopus mollis

— Ossicles in gonads, lacking perianally and in tube feet.......................... Pseudostichopus aemulatus