# The Presence of Ejaculatory Bulbs in Vasa Deferentia: A Well-Preserved Trait Among Alpheoid Shrimps (Crustacea, Caridea, Alpheoidea)

## TL;DR

This study finds that ejaculatory bulbs in the reproductive system are a unique and well-preserved trait among most Alpheoid shrimps, except for the Alpheidae family.

## Contribution

The study identifies ejaculatory bulbs as a synapomorphic trait in Alpheoidea, excluding Alpheidae, offering new insights into shrimp evolution.

## Key findings

- Ejaculatory bulbs are present in most Alpheoid families, suggesting they are a conserved trait.
- Alpheidae lacks ejaculatory bulbs, indicating a plesiomorphic condition within the superfamily.
- No other superfamily examined showed the presence of ejaculatory bulbs.

## Abstract

The superfamily Alpheoidea comprises eight families: Alpheidae, Barbouriidae, Bythocarididae, Hippolytidae, Lysmatidae, Merguiidae, Ogyrididae and Thoridae. Alpheoids are characterized by possessing two pairs of chelate pereopods, a multiarticulate carpus on pereopod 2, and a narrow strip as the last article on maxilliped 2. However, during the inspection of the reproductive system (RS) of several alpheoids, we consistently observed the presence of ejaculatory bulbs (EBs) in vasa deferentia (VDs) of these shrimps. To investigate whether the presence of EBs in the RS is a conserved trait among Alpheoidea representatives, we analyzed as many species as possible along the Brazilian coast: Alpheidae—5 genera, 19 spp., Hippolytidae—2 genera, 2 spp., Lysmatidae—2 genera, 10 spp., Merguiidae—1 genus, 1 sp., Ogyrididae—1 genus, 2 spp., and Thoridae—1 genus, 1 sp. In addition, we examined representatives of the superfamilies Atyoidea (1 family, 2 genera, 2 spp.), Nematocarcinoidea (1 family, 1 genus, 2 spp.), Palaemonoidea (2 families, 4 genera, 4 spp.) and Processoidea (1 family, 2 genera, 2 spp.) to determine whether EB are present in these groups. Among the groups analyzed, except for the family Alpheidae, most species of alpheoids exhibit an expansion on the ventral portion of the VD in continuity with the lumen of the vas deferens, i.e., the EB. This structure increases the surface area of the VD, consequently increasing the quantity of the seminal material to be ejaculated onto the female. We did not observe the presence of EB in any other of the analyzed superfamilies, suggesting that this structure is exclusive in Alpheoidea. In conclusion, the presence of EB in VD appears to be an exclusive trait in Alpheoidea, being considered a well-preserved synapomorphic trait in this group, except in the family Alpheidae that do not harbor EB, representing a plesiomorphic condition within this superfamily.