Peripatopsis sedgwicki

Although Purcell originally described Peripatopsis sedgwicki with 20 pairs of legs,^[9] which was long considered characteristic of this species,^[5] more recent studies find that velvet worms in the P. sedgwicki species complex can have as few as 19 or as many as 23 leg pairs.^[10] Leg number is diagnostic for the Fort Fordyce species P. margaritarius, which features 21 to 23 leg pairs, as only 19 or 20 leg pairs are recorded elsewhere in the rest of the species complex. For example, P. sedgwicki s.s. can have either 19 or 20 leg pairs in most localities. Although 20 leg pairs are usually observed in P. orientalis, some localities (four out of 17 localities sampled) yielded samples of this species with 19 pairs as well as 20 pairs. Finally, P. collarium is known from only a small sample in one locality, with 20 leg pairs recorded in four specimens (two males and two females).^[7]

All specimens of P. collarium feature a prominent white head collar that is absent in the other three species. The name P. collarium refers to this diagnostic trait.^[7] Color is otherwise highly variable in this species complex, even within a single clade, with the ventral surface varying from white to light pink and the dorsal colors ranging from dark blue, grey, or brown to bright orange or red.^[6][7][10] Thus, coloration proves to be generally unreliable as a basis for distinguishing among clades within this species complex.^[7]

Although gross morphology is of limited use in identifying individual species within this species complex, scanning electron microscopy reveals diagnostic differences beyond those noted above. For example, each species features a different number of scale ranks on the dorsal primary papillae, with seven in P. margaritarius, eight in P. sedgwicki s.s., nine in P. orientalis, and ten in P. collarium.^[7] In terms of gross morphology, however, the velvet worms in this species complex generally share the features associated with P. sedgwicki (sensu lato) as described below.

These velvet worms are relatively large:^[9] Females range in size from 12 mm to 68 mm in length, whereas males range from 10 mm to 46 mm in length.^[5] The outer blade of the jaw may have only one accessory tooth or no such tooth, and rarely may have two such teeth. The inner blade of the jaw features four to seven accessory teeth.^[11] The male genital opening is cruciform, and the female genital opening is a horizontal and small vertical slit.^[7]

The last leg pair (the genital pair) features claws,^[10] like those on the pregenital pairs, and is well developed compared to those in some other species in the genus Peripatopsis.^[9] The last leg pair, however, is smaller than the preceding leg pair and reduced more in the male than in the female.^[5][9] Each leg feature three or four spinous pads except for the last leg pair, which feature only one to three pads on each leg.^[5][11] The feet also feature three distal papillae (two anterior and one posterior).^[11]

These velvet worms share many traits with other species in the genus Peripatopsis. These shared traits include features considered characteristic for the genus, such as the reduced last (genital) leg pair, feet with three distal papillae (two anterior and one posterior), the cruciform genital opening in the male, and variable color.^[12] In 2009, a phylogenetic analysis of Peripatopsis species using molecular data found P. sedgwicki (sensu lato) to be most closely related to P. moseleyi,^[6] which has also since been found to be a species complex.^[12] Like the velvet worms in the P. moseleyi species complex, those in the P. sedgwicki species complex do not curl up into a spiral when initially exposed.^[5][12]

The velvet worms in the P. sedgwicki species complex can be distinguished from their close relatives in the P. moseleyi species complex based on marked differences in the last leg pair. This leg pair in the P. sedgwicki species complex is relatively well developed and features claws in both sexes,^[5] whereas this leg pair in the P. moseleyi species complex is rudimentary and reduced to mere tubercles. At most, this leg pair in the P. moseleyi species complex may feature a single claw (never two) on one or two of these legs in the female.^[12]

Like other velvet worms in the genus Peripatopsis, those in the P. sedgwicki species complex exhibit matrotrophic viviparity, that is, mothers in this genus retain eggs in their uteri and supply nourishment to their embryos, but without any placenta. Females in the P. sedgwicki species complex produce eggs with almost no yolk, and embryos develop large "trophic organs" or "trophic vesicles" that may function as means to absorb nourishment from the mother.^[13] The female gives birth to her first batch of young when she is about two years old. About a month before the birth of each batch, the next batch of eggs are fertilized. The young reach their maximum size when they are about three years old. These velvet worms have a life span of about six to seven years.^[5]