Pentapantopus
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Kühl, Poschmann and Rust, 2013
| Pentapantopus Temporal range: | |
|---|---|
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| Diagrammatic reconstruction of Pentapantopus vogteli | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Pycnogonida |
| Genus: | †Pentapantopus Kühl, Poschmann and Rust, 2013 |
| Species: | †P. vogteli |
| Binomial name | |
| †Pentapantopus vogteli Kühl, Poschmann and Rust, 2013 | |
Pentapantopus is a genus of fossil pycnogonid (sea spider). The only known species is Pentapantopus vogteli from the Hunsrück Slate of Germany. This sea spider was thought to have had five pairs of legs;[1] however, a 2024 study disproved this. It is recognizable by its flatten, tuberculated legs with the first pair having less segments than other sea spiders.[2]
Pentapantopus is a relatively small pycnogonid with a measured body length of up to 1.2 cm. It somewhat resembles the Silurian Haliestes,[1] which was used to infer various details that are not well-preserved (e.g. cephalon, palps, ovigers, leg annulations, abdomen) on the former's redescription in 2024.[2]
The cephalon is poorly preserved. The narrowed trunk has lateral processes measured as long as wide. The segmentation of the reduced abdomen is unclear, but it might have had 3 segments based on Haliestes. The proboscis was folded underneath its body, which might reflect its mobility. The chelifores have at least 3 segments (podomere): a 2-segmented pincer and an unsegmented scape, although the original description identified a 2-segmented scape.[1] The palps and ovigers have poorly preserved segmentation, although the former may have a terminal claw.[2]
When Pentapantopus was first described in 2013, it was thought to be a polymerous (extra-legged) species that had 5 pairs of legs (hence the name). However, with the description of another specimen in 2024, this has been refuted in favour of the common arrangement of 4 pairs of legs, as the previous "fifth leg" in the incomplete specimen was likely a misinterpretation of the opposite fourth leg. Each leg begins with a possibly annulated coxa and ends with a long, hook-like terminal claw. Each podomere from the fourth segment is wide and flattened, with most of them bearing tubercles and sparse pairs of long setae along the inner side. Within this section, the first pair of walking legs has one less segment than the other three, resulting in a total count of 7 segments for the first leg, which is unusual for a pycnogonid, in contrast to the usual 8 segments of the remaining 3 pairs.[2]