Complete mitochondrial genome of the first deep-sea spongicolid shrimp Spongiocaris panglao (Decapoda: Stenopodidea): Novel gene arrangement and the phylogenetic position and origin of Stenopodidea.

Stenopodidea Claus, 1872 (Crustacea: Decapoda) is one of the major groups of decapods crustaceans. Hitherto, only one complete mitochondrial genome (mitogenome) from the family Stenopodidae is available for the infraorder Stenopodidea. Here, we determined the complete mitogenome of Spongiocaris panglao de Grave and Saito, 2016 using Illumina sequencing, representing the first species from the family Spongicolidae. The 15,909 bp genome is a circular molecule and consists of 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes and one control region. Although the overall genome organization is typical for metazoans, the mitogenome of S. panglao shows some derived characters. A + T content of 77.42% in S. pamglao mitogenome is second-highest among the dacapods described to date. The trnR gene exhibit modified secondary structure with the TψC loop completely missing, which might be a putative autapomorphy of S. pamglao mitogenome. Compared with the shallow-water stenopodidean species S. hispidus, the control region of S. pamglao exhibits three characteristics: larger size, higher A + T content, and more tandem repeat sequences. The gene order exhibited difference from the ancestral mitogenome pattern of the Pancrustacea, with 5 tRNA genes rearrangement. The result from BI was agreed with most morphological characters and molecular evidences, revealing that Stenopodidea and Reptantia had the closest relationship, as the sister group of Caridea. Still, the alternative hypothesis supported from ML topology cannot be completely rejected based on the current data. Estimated times revealed that the two stenopodideans families Stenopodidae and Spongicolidae diverged from each other around 122 Mya. The divergence time of spongicolid shrimp is in good agreement with the origin of their hexactinellid hosts (78-144 Mya).